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All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
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Hi Rich,
Considering that the power supply is a switcher, I suspect that some of the capacitors have gotten low enough in value that they don't allow the power supply to start.? Capacitors don't always fail in a destructive manner.
There are two supplies in the power supply "case."? A primary supply and a secondary supply.? The primary supply,? among other things, will generate a pulse, commonly referred To as a ticking.? This pulse charges a capacitor in the secondary supply.? once that capacitor is charged up enough to run the secondary supply the secondary supply will turn on.? I suspect that capacitor has lost the ability to charge up enough to allow the secondary supply to start.? At this point I'd recommend either shotgunning the power supply or replacing it.
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My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
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Hi Burt:
Luckily I have a replacement of both, but will start with the pre regulator (I think that is they call it). I was looking through the Service Manual last night. This part of the 8753E has a decent amount of information. I remember when I was troubleshooting a CPU Problem there was almost nothing of use to guide you. Of course no schematics so I may open the pre regulator (PSU) and see if it’s obvious.
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On Aug 27, 2022, at 1:34 AM, Burt K6OQK <biwa@...> wrote:
?Hi Rich,
Considering that the power supply is a switcher, I suspect that some of the capacitors have gotten low enough in value that they don't allow the power supply to start.? Capacitors don't always fail in a destructive manner.
There are two supplies in the power supply "case."? A primary supply and a secondary supply.? The primary supply,? among other things, will generate a pulse, commonly referred To as a ticking.? This pulse charges a capacitor in the secondary supply.? once that capacitor is charged up enough to run the secondary supply the secondary supply will turn on.? I suspect that capacitor has lost the ability to charge up enough to allow the secondary supply to start.? At this point I'd recommend either shotgunning the power supply or replacing it.
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Hi Peter:
I will start on this today, and post my results. As I stated elsewhere, to my surprise the service manual is pretty decent in regards to Power Supply diagnosis. I did look there first, because I did a repair about a year ago on the CPU board and recalled distinctly there was virtually no useful information in the service manual other than “replace board X’.
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On Aug 27, 2022, at 7:48 AM, peter bunge <bunge.pjp@...> wrote:
? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter. On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
Several possibilities I have run into in HP gear. If the power transformer goes through a molex connector to the mother board the contacts on the MB may have heated and poor connections. I have seen this a number of times and am sure thats?why the unit was dumped and now lives happily on my bench. If a switching supply there are small start up caps that if the switcher does not come up in a short period restarts the power control circuit. Lastly a bad memory?chip causing a restart IRQ can give this appearance. Those have been my experiences?good luck. Paul WB8TSL
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I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours?
My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich
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On Aug 27, 2022, at 12:53 PM, peter bunge <bunge.pjp@...> wrote:
? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
Rich; I think this is a case of "nothing works Thursday". It happens sometimes and maybe this only applied to 8753s. The electronics Gods work in mysterious ways. I read the manual and it says surging is the post regulator circuit sensing an overcurrent and shutting down the power supply repeatedly to protect it. Maybe a cap reforming after months of non use? I had disconnected the S-Param Test set and thought it may have been the culprit but reconnecting it made no difference. It still works. Peter
On Sat, Aug 27, 2022 at 2:02 PM Rich Miller via <av8torrich= [email protected]> wrote: LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich ? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
Hi Peter:
Have an update for you. The fault started again. If you follow the troubleshooting guide on Section 5-8 - Page 271 it would leave you to believe I have a post regulator problem (A8).? Swapped A8 out, and the problem precise. When I unplug A15W1 from the post regulator, the problem disappears. Being that I have a known good post regulator board to swap out, I think the problem is the A15 Pre Regulator (SMPS). Getting ready to swap that out and see what happens. ?
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On Aug 27, 2022, at 2:44 PM, peter bunge <bunge.pjp@...> wrote:
? Rich; I think this is a case of "nothing works Thursday". It happens sometimes and maybe this only applied to 8753s. The electronics Gods work in mysterious ways. I read the manual and it says surging is the post regulator circuit sensing an overcurrent and shutting down the power supply repeatedly to protect it. Maybe a cap reforming after months of non use? I had disconnected the S-Param Test set and thought it may have been the culprit but reconnecting it made no difference. It still works. Peter On Sat, Aug 27, 2022 at 2:02 PM Rich Miller via <av8torrich= [email protected]> wrote: LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich ? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
Peter:
I have it back and running. It was the A8 board, despite the service manual pointing to the post regulator board. I replaced the SMPS, and I am back in business. I opened the SMPS, and did not find anything out of the ordinary. I may plug this in, leave it sit for a few hours, and then begin probing the output.?
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On Aug 27, 2022, at 3:30 PM, Richard Miller <av8torrich@...> wrote:
? Hi Peter:
Have an update for you. The fault started again. If you follow the troubleshooting guide on Section 5-8 - Page 271 it would leave you to believe I have a post regulator problem (A8).? Swapped A8 out, and the problem precise. When I unplug A15W1 from the post regulator, the problem disappears. Being that I have a known good post regulator board to swap out, I think the problem is the A15 Pre Regulator (SMPS). Getting ready to swap that out and see what happens. ? On Aug 27, 2022, at 2:44 PM, peter bunge <bunge.pjp@...> wrote:
? Rich; I think this is a case of "nothing works Thursday". It happens sometimes and maybe this only applied to 8753s. The electronics Gods work in mysterious ways. I read the manual and it says surging is the post regulator circuit sensing an overcurrent and shutting down the power supply repeatedly to protect it. Maybe a cap reforming after months of non use? I had disconnected the S-Param Test set and thought it may have been the culprit but reconnecting it made no difference. It still works. Peter On Sat, Aug 27, 2022 at 2:02 PM Rich Miller via <av8torrich= [email protected]> wrote: LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich ? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
Rich; I would be interested?in what you find. I plan on putting my 8753 on a variac to run with lower voltage. If it was a failing reservoir?capacitor in the pre-regulator this should show it up. The other thing to check is to 'scope the ripple on the pre-regulator. Keep me informed. Peter.
On Sat, Aug 27, 2022 at 7:16 PM Rich Miller via <av8torrich= [email protected]> wrote: Peter:
I have it back and running. It was the A8 board, despite the service manual pointing to the post regulator board. I replaced the SMPS, and I am back in business. I opened the SMPS, and did not find anything out of the ordinary. I may plug this in, leave it sit for a few hours, and then begin probing the output.? ?Hi Peter:
Have an update for you. The fault started again. If you follow the troubleshooting guide on Section 5-8 - Page 271 it would leave you to believe I have a post regulator problem (A8).? Swapped A8 out, and the problem precise. When I unplug A15W1 from the post regulator, the problem disappears. Being that I have a known good post regulator board to swap out, I think the problem is the A15 Pre Regulator (SMPS). Getting ready to swap that out and see what happens. ? ? Rich; I think this is a case of "nothing works Thursday". It happens sometimes and maybe this only applied to 8753s. The electronics Gods work in mysterious ways. I read the manual and it says surging is the post regulator circuit sensing an overcurrent and shutting down the power supply repeatedly to protect it. Maybe a cap reforming after months of non use? I had disconnected the S-Param Test set and thought it may have been the culprit but reconnecting it made no difference. It still works. Peter On Sat, Aug 27, 2022 at 2:02 PM Rich Miller via <av8torrich= [email protected]> wrote: LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich ? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
Hi Peter:
When I get a few moments to take a look with a scope I will. This problem seems very much temperature related. My plan is to let it run for a good couple of hours, and then probe the A15W1 Feedthrough points on the SMPS.?
My only concern is, I may not see a lot of ripple with the SMPS unloaded. I have had two cases in various instruments where the switcher fooled me like this. It was not until I loaded it down did I begin to see a lot of ripple.?
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On Aug 27, 2022, at 7:22 PM, peter bunge <bunge.pjp@...> wrote:
? Rich; I would be interested?in what you find. I plan on putting my 8753 on a variac to run with lower voltage. If it was a failing reservoir?capacitor in the pre-regulator this should show it up. The other thing to check is to 'scope the ripple on the pre-regulator. Keep me informed. Peter. On Sat, Aug 27, 2022 at 7:16 PM Rich Miller via <av8torrich= [email protected]> wrote: Peter:
I have it back and running. It was the A8 board, despite the service manual pointing to the post regulator board. I replaced the SMPS, and I am back in business. I opened the SMPS, and did not find anything out of the ordinary. I may plug this in, leave it sit for a few hours, and then begin probing the output.? ?Hi Peter:
Have an update for you. The fault started again. If you follow the troubleshooting guide on Section 5-8 - Page 271 it would leave you to believe I have a post regulator problem (A8).? Swapped A8 out, and the problem precise. When I unplug A15W1 from the post regulator, the problem disappears. Being that I have a known good post regulator board to swap out, I think the problem is the A15 Pre Regulator (SMPS). Getting ready to swap that out and see what happens. ? ? Rich; I think this is a case of "nothing works Thursday". It happens sometimes and maybe this only applied to 8753s. The electronics Gods work in mysterious ways. I read the manual and it says surging is the post regulator circuit sensing an overcurrent and shutting down the power supply repeatedly to protect it. Maybe a cap reforming after months of non use? I had disconnected the S-Param Test set and thought it may have been the culprit but reconnecting it made no difference. It still works. Peter On Sat, Aug 27, 2022 at 2:02 PM Rich Miller via <av8torrich= [email protected]> wrote: LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich ? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
I am sending my repair log private. This same thing happened in Sept 2019. For those interested this is a summary ·????????
At
turn on all the front panel displays flash on and off continuously.
·????????
On
the rear of the instrument the top red LED flashes in time to the fan surges
and the bottom green LED stays on. The A15 pre-regulator is probably OK.
·????????
All
green LEDs on A8 are flashing. There is probably something loading one of the
power supplies.
·????????
?Pull A9, A10, A11, A12 and the power supplies
are OK. Start putting them back one at a time.
·????????
OK
until A9 is replaced and the problem returns. A9 capacitors all seem OK but A9
drives the display. Pulling the connector on the display driver board (molex
connector) removes the problem. Everything pointed to the Newscope LCD but various tests running it on a separate power supply were inconclusive. Conclusion:
It is
unlikely that the LCD display was the actual problem. There may have been a
marginal overload somewhere in the 8753B and the LCD current pushed the total
past the trip point.
The
problem could also have been that the trip point setting had shifted for some
reason to a level that tripped when the LCD was finally connected. The LCD only draws current from the +5v power
supply so this is where to look if the problem returns. A test
load was made to replace the Newscope9 if the problem re-appears.
It will
draw 100mA more than the Newscope 9 from both the +5v and +15v supplies and can
be easily modified.
I will report back here when I find the problem. Peter
On Sat, Aug 27, 2022 at 7:38 PM Rich Miller via <av8torrich= [email protected]> wrote: Hi Peter:
When I get a few moments to take a look with a scope I will. This problem seems very much temperature related. My plan is to let it run for a good couple of hours, and then probe the A15W1 Feedthrough points on the SMPS.?
My only concern is, I may not see a lot of ripple with the SMPS unloaded. I have had two cases in various instruments where the switcher fooled me like this. It was not until I loaded it down did I begin to see a lot of ripple.? ? Rich; I would be interested?in what you find. I plan on putting my 8753 on a variac to run with lower voltage. If it was a failing reservoir?capacitor in the pre-regulator this should show it up. The other thing to check is to 'scope the ripple on the pre-regulator. Keep me informed. Peter. On Sat, Aug 27, 2022 at 7:16 PM Rich Miller via <av8torrich= [email protected]> wrote: Peter:
I have it back and running. It was the A8 board, despite the service manual pointing to the post regulator board. I replaced the SMPS, and I am back in business. I opened the SMPS, and did not find anything out of the ordinary. I may plug this in, leave it sit for a few hours, and then begin probing the output.? ?Hi Peter:
Have an update for you. The fault started again. If you follow the troubleshooting guide on Section 5-8 - Page 271 it would leave you to believe I have a post regulator problem (A8).? Swapped A8 out, and the problem precise. When I unplug A15W1 from the post regulator, the problem disappears. Being that I have a known good post regulator board to swap out, I think the problem is the A15 Pre Regulator (SMPS). Getting ready to swap that out and see what happens. ? ? Rich; I think this is a case of "nothing works Thursday". It happens sometimes and maybe this only applied to 8753s. The electronics Gods work in mysterious ways. I read the manual and it says surging is the post regulator circuit sensing an overcurrent and shutting down the power supply repeatedly to protect it. Maybe a cap reforming after months of non use? I had disconnected the S-Param Test set and thought it may have been the culprit but reconnecting it made no difference. It still works. Peter On Sat, Aug 27, 2022 at 2:02 PM Rich Miller via <av8torrich= [email protected]> wrote: LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich ? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
Hi Peter:
There was one thing I negated to mention. I am not sure if it was from a temperature DELTA caused from opening the enclosure/chassis or not, but I did reseat the molex connector which attaches to the Motherboard. While this allowed me to get through the boot sequence but, all kinds of strange errors started to appear. The one most seen was related to the source not being found (forget the exact text).?
I have seen a very similar problem in a Tektronix 2400 (2440) series scope PSU. The problem was on the secondary side of the SMPS, and was caused by a high precision current sense resistor drifting out of tolerance. This caused the scope to recycle much in the same manner as I described with my 8753E. These resistors were there to sense an overcurrent condition, and shutdown the scope in order to save it. That one took me forever to figure out, because I did not realize the tolerances needed to be so tight, and with a normal hand held DMM everything looked OK. I needed to see another decimal or two, if memory serves me.
I looked briefly in the Post Regulator assembly, and I did not see any such resistors. The caps looked ok (physically speaking), as in they had not spewed their guts, or swelled based on my physical inspection of them.?
As I stated, I am going to look for ripple, as that would tell me a lot.?
toggle quoted message
Show quoted text
On Aug 27, 2022, at 8:06 PM, peter bunge <bunge.pjp@...> wrote:
? I am sending my repair log private. This same thing happened in Sept 2019. For those interested this is a summary ·????????
At
turn on all the front panel displays flash on and off continuously.
·????????
On
the rear of the instrument the top red LED flashes in time to the fan surges
and the bottom green LED stays on. The A15 pre-regulator is probably OK.
·????????
All
green LEDs on A8 are flashing. There is probably something loading one of the
power supplies.
·????????
?Pull A9, A10, A11, A12 and the power supplies
are OK. Start putting them back one at a time.
·????????
OK
until A9 is replaced and the problem returns. A9 capacitors all seem OK but A9
drives the display. Pulling the connector on the display driver board (molex
connector) removes the problem. Everything pointed to the Newscope LCD but various tests running it on a separate power supply were inconclusive. Conclusion:
It is
unlikely that the LCD display was the actual problem. There may have been a
marginal overload somewhere in the 8753B and the LCD current pushed the total
past the trip point.
The
problem could also have been that the trip point setting had shifted for some
reason to a level that tripped when the LCD was finally connected. The LCD only draws current from the +5v power
supply so this is where to look if the problem returns. A test
load was made to replace the Newscope9 if the problem re-appears.
It will
draw 100mA more than the Newscope 9 from both the +5v and +15v supplies and can
be easily modified.
I will report back here when I find the problem. Peter
On Sat, Aug 27, 2022 at 7:38 PM Rich Miller via <av8torrich= [email protected]> wrote: Hi Peter:
When I get a few moments to take a look with a scope I will. This problem seems very much temperature related. My plan is to let it run for a good couple of hours, and then probe the A15W1 Feedthrough points on the SMPS.?
My only concern is, I may not see a lot of ripple with the SMPS unloaded. I have had two cases in various instruments where the switcher fooled me like this. It was not until I loaded it down did I begin to see a lot of ripple.? ? Rich; I would be interested?in what you find. I plan on putting my 8753 on a variac to run with lower voltage. If it was a failing reservoir?capacitor in the pre-regulator this should show it up. The other thing to check is to 'scope the ripple on the pre-regulator. Keep me informed. Peter. On Sat, Aug 27, 2022 at 7:16 PM Rich Miller via <av8torrich= [email protected]> wrote: Peter:
I have it back and running. It was the A8 board, despite the service manual pointing to the post regulator board. I replaced the SMPS, and I am back in business. I opened the SMPS, and did not find anything out of the ordinary. I may plug this in, leave it sit for a few hours, and then begin probing the output.? ?Hi Peter:
Have an update for you. The fault started again. If you follow the troubleshooting guide on Section 5-8 - Page 271 it would leave you to believe I have a post regulator problem (A8).? Swapped A8 out, and the problem precise. When I unplug A15W1 from the post regulator, the problem disappears. Being that I have a known good post regulator board to swap out, I think the problem is the A15 Pre Regulator (SMPS). Getting ready to swap that out and see what happens. ? ? Rich; I think this is a case of "nothing works Thursday". It happens sometimes and maybe this only applied to 8753s. The electronics Gods work in mysterious ways. I read the manual and it says surging is the post regulator circuit sensing an overcurrent and shutting down the power supply repeatedly to protect it. Maybe a cap reforming after months of non use? I had disconnected the S-Param Test set and thought it may have been the culprit but reconnecting it made no difference. It still works. Peter On Sat, Aug 27, 2022 at 2:02 PM Rich Miller via <av8torrich= [email protected]> wrote: LOL - I just got to my office with a replacement PSU, and Post Regulator Board. This was an hour drive.?
?Turned on the VNA, and its fine now. This maybe temp related, so I am going to run some more measurements and wait for the fault to manifest once again. A little annoyed, but such is life I suppose.
I was in the middle of an important measurement when this happened yesterday, so I am going to take it while I can. I will keep you updated, as I learn more. Rich ? I took the cover off and everything works. I have no idea what the problem was. This unit had a manufacturer's fault on it for 30+ years. The problem showed up once and fixed itself after re-seating?boards but I could not confirm what fixed it. Two years later the fault re-appeared and it was these two bad solder joints. It is not the problem this time because they were re-soldered and the symptoms are different anyway. So the fan was surging and it would not start up. I will 'scope the filter caps before putting the cover back on. How are you making out with yours? My HP8753B suddenly started doing this surging with all the front lights on (I will have to re-check that statement but it is what I remember). This was several weeks ago and I have not had time to check it. If you start on yours take the top lid off and look at the row of lights on the power supply board. They should be green if OK and red to indicate a bad power supply (I'm going from memory so anyone correct me if I am wrong). Check the?power supplies with a good digital meter BUT DO NOT ADJUST ANY, especially if they are marginally off,?you do not want an additional fault of your own doing. Check each one with a 'scope and I would not be surprised if you find high ripple on one or more in which case replace the bad capacitor.? The manual will tell you what they should look like. Also there is?a start up sequence for the?CPU row of red lights. Check the manual. The fans are special on these?and are?controlled by a circuit. The VNA will not turn on if the?fan is bad and it?must be replaced by the correct one. I will be starting on mine next week, possibly Monday. I have family visiting right now. Peter.
On Fri, Aug 26, 2022 at 7:35 PM Rich Miller via <av8torrich= [email protected]> wrote: All:
My HP-8753E started demonstrating what I believe is a PSU related fault. When I switch the VNA on, it attempts to boot up, but before it can, I hear the fan stop, and then turn back on, and the VNA attempts a start again. This cycle goes on forever at this point.
I have taken a close look at the spare PSU, and there are no fuses externally. I also note there is a Voltage Regulator Board. I am wondering if anyone has had this issue, and was it the PSU itself or the Regulator Board?
My thinking is if this was a hard fault in the PSU something would have self destructed, or blown a component/fuse internal to the PSU. That being said, I have never seen the inside of the PSU to know if there is some sort of soft restart, or a fuse which should blow.
I would also be curious if there is some other protection feature in the 8753E which would cause it to power cycle like I describe above?
Thanks in advance!
Rich
|
Rich,
I have cured a lot of weird problems by fixing the obvious things first.? I suspect that if you were to re-cap the power supply module you would be pleased.? That's been my experience in 90% of the symptoms you describe.
Burt, K6OQK
|
Rich,
I will second Paul's suggestion. I had an HP3586B that developed strange problems.? The big Molex connector between the power transformer and the mother board looked fine... until I turned it over.? The bottom side was black.? I replaced the connector by hard wiring directly from the transformer to the motherboard.? In my case I put about a foot of service loop in a coil tucked between the transformer and the motherboard.? My 3586B has been working flawlessly since doing that; about 10 years ago.
Burt, K6OQK
|
Burt:
Probably will end up doing that. I had a spare SMPS for the rig, and that is doing the job for now. I have the A15 open and on my desk. When I get back to the office on Monday, I will start looking at the filter capacitors.?
toggle quoted message
Show quoted text
On Aug 28, 2022, at 12:54 AM, Burt K6OQK <biwa@...> wrote:
?Rich,
I have cured a lot of weird problems by fixing the obvious things first.? I suspect that if you were to re-cap the power supply module you would be pleased.? That's been my experience in 90% of the symptoms you describe.
Burt, K6OQK
|
In message < [email protected]>, Burt K6OQK <biwa@...> writes Rich,
I have cured a lot of weird problems by fixing the obvious things
first.? I suspect that if you were to re-cap the power supply
module you would be pleased.? That's been my experience in 90% of
the symptoms you describe. FWIW - Mine too!...
Burt, K6OQK
-- Tony Sayer Bancom Communications U.K.
|
Not so easy to recap. Do you have a list of suitable replacements from DigiKey or Mouser? How do you get the boards out? Do I have to unsolder anything? Is the power switch mounted?to the PCB? I have the PreReg supply split open. I also do not think this is the problem because the manual troubleshooting points to the +5v supply which is where my troubleshooting pointed?from a different?direction. If the?caps are easy to get at with the boards out I can check them for value and resistance. I prefer to identify a?definite fault rather than randomly replace components.? I put the?8753B on a?variac and dropped?the?voltage to 100VAC but could?not?trigger the fault. This probably eliminates the rear half of the PreReg with the two big capacitors,?but not the front board with the six big?caps.? It worked fine for?a?few hours but the next time I turned it on the?fault returned. I took?the?Pr-Regulator out and split the?module and turned it on and it?is back to working perfectly. I wiggled all?connectors?and cannot?get?it to quit again. I don't think it is a bad connection. I checked the current in all wires to the display when the fault was happening and there was nothing obvious (disconnecting the display cured the fault repeatedly but it was only because it dropped the drain on the +5v. It is an LCD display). It seems more like a marginal?trip point setting which is why I have the supply open.?
On Sun, Aug 28, 2022 at 4:42 PM tony sayer < tony@...> wrote: In message <[email protected]>, Burt K6OQK
<biwa@...> writes
>? ? Rich,
>
>? ? I have cured a lot of weird problems by fixing the obvious things
>? ? first.? I suspect that if you were to re-cap the power supply
>? ? module you would be pleased.? That's been my experience in 90% of
>? ? the symptoms you describe.
FWIW - Mine too!...
>
>? ? Burt, K6OQK
>? ?
--
Tony Sayer
Bancom Communications? ?U.K.
|
Burt K6OQK