Re: HP 141T Power Supply Help Needed
After a few second warmup I get 1v at q4 emitter
On Mon, Sep 2, 2024, 11:14?AM Bill Berzinskas via <bberzinskas= [email protected]> wrote: Yep all purple/white disconnected on the left.? Currently almost no voltage at output of q4 emitter, -0.02.? ? It's also getting hot.? ?Wonder if it's toast bc I lost my -2.5v since.? ??
Bill. ? You are making progress!? Now we have to find out where the -12.6 current is going.? Especially since the driver is getting hot.? It is funny that the current limiter is showing 0V.? I think some more ohm meter checks are? in order.? I assume the -12.6 to the A5 module is disconnected.? In fact I suggest pulling all of the white / violet wires from the A2 regulator board.? What voltage is there at the emitter of the pass device Q4?? Let me know¡ ? Mike ? ? Spent some time today checking through the rest of the line - basic checks on passives look ok. Transistors look ok.? Noticed the driver getting hot though.? ?Not making any progress, despite trying to figure it out.? ?
Current measurements:? B = 2.6v? (was 23.5v)
E = 1.9v (was -17v)
Q10..
C = 2.6v? (was 23.5v)
b = 0v again E = 0v
Q11..?
C=? ~2.2v (was 23.5v)
B = -0.2v, fluctuates? (was -.64)
E = -1v, fluctuates (was 0)
In other news, I believe I have located the short on the A5 board.? ?Stray lead clipping in a very tough to see location...? ?:\? ? ??
? On Sun, Sep 1, 2024 at 4:55?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: tiny update to the above, replaced?+100v driver and that helped immensely!
+100, -100,?+248 all work, adjust and appear happy!? ?
I gained .5v on my -12.6 line, but its still sitting at -3v.? ? ? Getting closer, seeing some signs of life finally.? ? Not all the way but progress is progress.??
I've found that CR16 and CR17 were not good, and the pass trans was also not happy anymore.? ?I've replaced all of that and am now getting a whopping -2.5v!? ?10 more to go.? :-).? Will check through resistors this evening.? ? ?I'm also seeing some off voltages in my other rails, will have to go back through the?+100 and -100 lines as well.? ? ?
Current status:?
+79
-82
+217
-2.5
The purple/white wire presenting the short was easy to find, its the one going to the board just in front of the power?supply. Looks like thats A5, so I'll start mulling over the schem?for that as well.? ?
? ? ? On Sat, Aug 31, 2024 at 5:00?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? It sounds like you are on the right track!? So find out were the .04Ohm wire goes¡ ? Mike ? ? Neat trick checking for shorts.?? As you expected probably, 0.04ohm.???? I have found one purple/white wire which when removed brings that up to 384 ohm.??? I'll be out of pocket for a day but will look at the supply one more time in isolated state and then trace that wire out.??? Thank you! ? On Sat, Aug 31, 2024, 12:11?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? So you replaced the pass transistor and Q9 then it popped the 3A fuse F4.? And at that point the regulator worked but there must be a short on the -12.6V buss.? Please run an Ohm meter check on the -12.6V buss which is / are the white / violet wires from the A2 assembly.? Check R42, CR16 and Q10.? ?From my calculations the current limiter Q10 should start taking drive away from the driver Q9 at about 2.8A.? ?I take it that no plugins are installed.? The only place in the 141T that the -12.6 goes is / the? plugin connectors, the flood gun filament, and the trace align control on the front panel.? If there is a short (<4 Ohms) then you have to find which wire has that low impedance.? Let me know what you find. ? Mike ? ? Those numbers just don't make any sense.??? I pulled all the transistors AGAIN, desoldered and cleaned.? Tested them all with a meter, repopulate.??? Back to 23.5v....??? ? On Fri, Aug 30, 2024, 6:22?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Replaced Q9, powered on and blew the fuse.? ?Replaced Fuse?+ Q9 again?+ pass transistor and no fuse pop.? ?
Not sure if better, worse or just different :-)? B = 54v?!? (was 23.5v)
E = -17v.?
Q10..
C = 54v..? (was 23.5v)
b = 0.58v (up from 0)? E = 0v
Q11..?
C= 54.7 (was 23.5v)
B = -.64
E = 0 ? On Fri, Aug 30, 2024 at 5:48?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK it seems that Q 9 has a base-emitter voltage of 38.5V which says that the base-emitter junction is open because a good NPN silicon transistor can only have a forward base-emitter voltage of 1V under extreme conditions.? Normally the Vbe is in the order of 0.7V. If the emitter or base connection of Q9 were open the emitter voltage will be dragged negative by R41.? That is not good for the pass transistor Q4 to see that much negative voltage because that will exceed the Vebo rating of the pass device which may degrade the Beta of the pass device.? Basically it will Zener the base emitter junction with that much reverse bias.? Typical Vebo is in the order of <10V which is in the absolute maximum ratings of the part.? A 2N3053 should work OK as the driver Q9.? Let me know how it goes. ? Mike ? ? That does make sense,?thank you for that explanation..? I do believe I've stated it backwards.? ? 22v appears on a 2n3053 that I've replaced at pin 3, which is actually the collector..? :facepalm:..? Remeasure / restate Q9..? ? On Fri, Aug 30, 2024 at 3:02?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? Lets back up a minute¡ If there is +22V at the emitter of the driver Q9 then there must be +22V at the base of the series regulator Q4 and you say that there is less than 1V ?at the emitter of the pass transistor Q4 and also no voltage at the top of R42 (the current sense resistor) then there is 22V across the base emitter junction of? Q4 and that can only be a failed device or some bad wiring or even a cracked runner on the board. A good NPN transistor has no more than 1V Vbe.? ??Does that make sense to you?? Or is the voltage at the emitter of the driver Q9 a negative 22V?? If the voltage at the emitter of Q9 is negative then what is the voltage at the base of Q9? ? Mike ? ? Ok..? I had a few bad transistors in the mix, but the one that was in the unit checks out ok.? ? ?I tossed a small handful to alleviate future issues.? ?
I spent a little time simulating this and from what I'm seeing this almost has to be a problem w/ the voltage divider / potentiometer.? ?I can do a lot of "shady" things in the sim and none of them give me issues like I'm seeing.? ?Removing R43 in the sim, or the pullup R45 seem to skew the voltages like I'm seeing.? ? ?The sim shows that the trimpot is kind of what "kicks things off", and the fact that I'm only getting about -1v here seems to further hint towards R43.? ? I don't have a 22.1k or even a 22k on hand, so I'll probably get creative to see what happens.? ?Resistance measurements on the pot itself look ok, i'm really hoping to not have to yank that thing.?? ? On Fri, Aug 30, 2024 at 11:58?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: I'll check these over lunch.? ?Interestingly, two of the original transistors in that spot cause the 3a fuse to blow.? ?Now sure if thats indicative of something else going on w/ a good transistor in the seat..? ? tbd.?? ? On Fri, Aug 30, 2024 at 11:43?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? 22V on the emitter of the driver is very strange.? It seems that the pass transistor Q2 has an open base ¨C emitter junction and a shorted collector base junction to come up with those voltages.? That would explain the ¡°on output¡± situation.?? An Ohm meter should be sufficient to check the status of Q2.? If your meter has a diode scale, that would give you a quick indication of the status of Q2.? ? I am thinking ?of designing an over voltage crowbar circuit to protect the -12.6 V supply from damaging sensitive circuits down stream of this supply if the regulator goes to an over voltage condition.? Some of the plugins appear to have a crowbar in just such a condition.? The filament of the flood gun is run from the -12.6V and in my case it went over voltage and it burned out the flood gun filament. ? ? Mike ? ? Thanks Michael,?
here's a recap what i'm seeing around the -12.6v line currently:?
?.65v at base of q11 sensor amp, .275v on collector.?? Driver has 22v on emitter, .27v on base and -.27v collector.????? Not much happening on the current limiter.?? 0v base.? ? On Fri, Aug 30, 2024 at 11:15?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK so you have the early version of the supply.? If you give me the voltages at the base of the driver transistors I can perhaps give you some more pointers. ? Mike ? ? correction, it did have the LAMP..? ?? ? My unit is 1615a prefix, it did have the zener and it was measuring closer to 100v instead of the expected 83 or whatever.? It has since been replaced by a pair of diodes that bring it to 89v but I have had to replace that string at least once in my travels so far, so I will eventually look for a more permanent?solution as I've read about.? ?I can check that again this evening!? ?I stopped thinking about it after I got the?+100v supply up! ? On Thu, Aug 29, 2024 at 4:50?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? There are 2 versions of this supply.? There is an early version that has a neon tube as the reference for the +100V supply and a later version that uses a 9V temp compensated Zener that is floating.? That is the reference Zener is connected from the +100V rail and the base of Q4.? It may help to know which version you have.? From my schematic the +100 V is the master and the other supplies are referenced from it.?? The one I have has a serial number prefix 2101A and it appears to be made in the late 1981 or early 1982 time frame. This one has the floating 9V Zener. ? Mike ? ? Finished that up.? ?On the -100 I can adjust up to 96v, a little low but it is adjustable so I think I should come back to that later.??
On 248v I'm currently seeing 290v, and -12v I'm seeing -1.5v.? ? ?I reckon I could go after either of them given the dependencies.? ? Will grab some measurements in between or after work today.? ? ? On Thu, Aug 29, 2024 at 10:52?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Well, this is awkward.? ? I had replaced both Diff Amp transistors with the same part number.??
I just found that this package is actually reverse from what i removed!? ?using a dorky little? heathkit transistor tester, i found the pinout to be CBE when looking at it from the flat side.??
The center leg was bent towards the rear of the part, while the original part was bent toward the front.??
I reversed both transistors, and got -106 which i was able to adjust appropriately!? ? ??
Strange, but makes sense.? ?I have a few more of these buggers in the supply, so it sounds like I'll be sorting through that today.? ? Will report back in a bit.??
Thanks for the help ya'll!? ? On Thu, Aug 29, 2024 at 10:45?AM Frank Mashockie via <fmashockie=[email protected]> wrote: Also, don't forget about Gianni's HP e-book.? If I remember correctly, he goes into great detail about the 141T.? Here's the link.? They can be slow to download and I forget which section includes the 141T. ?
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Re: HP 141T Power Supply Help Needed
Yep all purple/white disconnected on the left.? Currently almost no voltage at output of q4 emitter, -0.02.? ? It's also getting hot.? ?Wonder if it's toast bc I lost my -2.5v since.? ??
Bill. ? You are making progress!? Now we have to find out where the -12.6 current is going.? Especially since the driver is getting hot.? It is funny that the current limiter is showing 0V.? I think some more ohm meter checks are? in order.? I assume the -12.6 to the A5 module is disconnected.? In fact I suggest pulling all of the white / violet wires from the A2 regulator board.? What voltage is there at the emitter of the pass device Q4?? Let me know¡ ? Mike ? ? Spent some time today checking through the rest of the line - basic checks on passives look ok. Transistors look ok.? Noticed the driver getting hot though.? ?Not making any progress, despite trying to figure it out.? ?
Current measurements:? B = 2.6v? (was 23.5v)
E = 1.9v (was -17v)
Q10..
C = 2.6v? (was 23.5v)
b = 0v again E = 0v
Q11..?
C=? ~2.2v (was 23.5v)
B = -0.2v, fluctuates? (was -.64)
E = -1v, fluctuates (was 0)
In other news, I believe I have located the short on the A5 board.? ?Stray lead clipping in a very tough to see location...? ?:\? ? ??
? On Sun, Sep 1, 2024 at 4:55?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: tiny update to the above, replaced?+100v driver and that helped immensely!
+100, -100,?+248 all work, adjust and appear happy!? ?
I gained .5v on my -12.6 line, but its still sitting at -3v.? ? ? Getting closer, seeing some signs of life finally.? ? Not all the way but progress is progress.??
I've found that CR16 and CR17 were not good, and the pass trans was also not happy anymore.? ?I've replaced all of that and am now getting a whopping -2.5v!? ?10 more to go.? :-).? Will check through resistors this evening.? ? ?I'm also seeing some off voltages in my other rails, will have to go back through the?+100 and -100 lines as well.? ? ?
Current status:?
+79
-82
+217
-2.5
The purple/white wire presenting the short was easy to find, its the one going to the board just in front of the power?supply. Looks like thats A5, so I'll start mulling over the schem?for that as well.? ?
? ? ? On Sat, Aug 31, 2024 at 5:00?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? It sounds like you are on the right track!? So find out were the .04Ohm wire goes¡ ? Mike ? ? Neat trick checking for shorts.?? As you expected probably, 0.04ohm.???? I have found one purple/white wire which when removed brings that up to 384 ohm.??? I'll be out of pocket for a day but will look at the supply one more time in isolated state and then trace that wire out.??? Thank you! ? On Sat, Aug 31, 2024, 12:11?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? So you replaced the pass transistor and Q9 then it popped the 3A fuse F4.? And at that point the regulator worked but there must be a short on the -12.6V buss.? Please run an Ohm meter check on the -12.6V buss which is / are the white / violet wires from the A2 assembly.? Check R42, CR16 and Q10.? ?From my calculations the current limiter Q10 should start taking drive away from the driver Q9 at about 2.8A.? ?I take it that no plugins are installed.? The only place in the 141T that the -12.6 goes is / the? plugin connectors, the flood gun filament, and the trace align control on the front panel.? If there is a short (<4 Ohms) then you have to find which wire has that low impedance.? Let me know what you find. ? Mike ? ? Those numbers just don't make any sense.??? I pulled all the transistors AGAIN, desoldered and cleaned.? Tested them all with a meter, repopulate.??? Back to 23.5v....??? ? On Fri, Aug 30, 2024, 6:22?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Replaced Q9, powered on and blew the fuse.? ?Replaced Fuse?+ Q9 again?+ pass transistor and no fuse pop.? ?
Not sure if better, worse or just different :-)? B = 54v?!? (was 23.5v)
E = -17v.?
Q10..
C = 54v..? (was 23.5v)
b = 0.58v (up from 0)? E = 0v
Q11..?
C= 54.7 (was 23.5v)
B = -.64
E = 0 ? On Fri, Aug 30, 2024 at 5:48?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK it seems that Q 9 has a base-emitter voltage of 38.5V which says that the base-emitter junction is open because a good NPN silicon transistor can only have a forward base-emitter voltage of 1V under extreme conditions.? Normally the Vbe is in the order of 0.7V. If the emitter or base connection of Q9 were open the emitter voltage will be dragged negative by R41.? That is not good for the pass transistor Q4 to see that much negative voltage because that will exceed the Vebo rating of the pass device which may degrade the Beta of the pass device.? Basically it will Zener the base emitter junction with that much reverse bias.? Typical Vebo is in the order of <10V which is in the absolute maximum ratings of the part.? A 2N3053 should work OK as the driver Q9.? Let me know how it goes. ? Mike ? ? That does make sense,?thank you for that explanation..? I do believe I've stated it backwards.? ? 22v appears on a 2n3053 that I've replaced at pin 3, which is actually the collector..? :facepalm:..? Remeasure / restate Q9..? ? On Fri, Aug 30, 2024 at 3:02?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? Lets back up a minute¡ If there is +22V at the emitter of the driver Q9 then there must be +22V at the base of the series regulator Q4 and you say that there is less than 1V ?at the emitter of the pass transistor Q4 and also no voltage at the top of R42 (the current sense resistor) then there is 22V across the base emitter junction of? Q4 and that can only be a failed device or some bad wiring or even a cracked runner on the board. A good NPN transistor has no more than 1V Vbe.? ??Does that make sense to you?? Or is the voltage at the emitter of the driver Q9 a negative 22V?? If the voltage at the emitter of Q9 is negative then what is the voltage at the base of Q9? ? Mike ? ? Ok..? I had a few bad transistors in the mix, but the one that was in the unit checks out ok.? ? ?I tossed a small handful to alleviate future issues.? ?
I spent a little time simulating this and from what I'm seeing this almost has to be a problem w/ the voltage divider / potentiometer.? ?I can do a lot of "shady" things in the sim and none of them give me issues like I'm seeing.? ?Removing R43 in the sim, or the pullup R45 seem to skew the voltages like I'm seeing.? ? ?The sim shows that the trimpot is kind of what "kicks things off", and the fact that I'm only getting about -1v here seems to further hint towards R43.? ? I don't have a 22.1k or even a 22k on hand, so I'll probably get creative to see what happens.? ?Resistance measurements on the pot itself look ok, i'm really hoping to not have to yank that thing.?? ? On Fri, Aug 30, 2024 at 11:58?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: I'll check these over lunch.? ?Interestingly, two of the original transistors in that spot cause the 3a fuse to blow.? ?Now sure if thats indicative of something else going on w/ a good transistor in the seat..? ? tbd.?? ? On Fri, Aug 30, 2024 at 11:43?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? 22V on the emitter of the driver is very strange.? It seems that the pass transistor Q2 has an open base ¨C emitter junction and a shorted collector base junction to come up with those voltages.? That would explain the ¡°on output¡± situation.?? An Ohm meter should be sufficient to check the status of Q2.? If your meter has a diode scale, that would give you a quick indication of the status of Q2.? ? I am thinking ?of designing an over voltage crowbar circuit to protect the -12.6 V supply from damaging sensitive circuits down stream of this supply if the regulator goes to an over voltage condition.? Some of the plugins appear to have a crowbar in just such a condition.? The filament of the flood gun is run from the -12.6V and in my case it went over voltage and it burned out the flood gun filament. ? ? Mike ? ? Thanks Michael,?
here's a recap what i'm seeing around the -12.6v line currently:?
?.65v at base of q11 sensor amp, .275v on collector.?? Driver has 22v on emitter, .27v on base and -.27v collector.????? Not much happening on the current limiter.?? 0v base.? ? On Fri, Aug 30, 2024 at 11:15?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK so you have the early version of the supply.? If you give me the voltages at the base of the driver transistors I can perhaps give you some more pointers. ? Mike ? ? correction, it did have the LAMP..? ?? ? My unit is 1615a prefix, it did have the zener and it was measuring closer to 100v instead of the expected 83 or whatever.? It has since been replaced by a pair of diodes that bring it to 89v but I have had to replace that string at least once in my travels so far, so I will eventually look for a more permanent?solution as I've read about.? ?I can check that again this evening!? ?I stopped thinking about it after I got the?+100v supply up! ? On Thu, Aug 29, 2024 at 4:50?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? There are 2 versions of this supply.? There is an early version that has a neon tube as the reference for the +100V supply and a later version that uses a 9V temp compensated Zener that is floating.? That is the reference Zener is connected from the +100V rail and the base of Q4.? It may help to know which version you have.? From my schematic the +100 V is the master and the other supplies are referenced from it.?? The one I have has a serial number prefix 2101A and it appears to be made in the late 1981 or early 1982 time frame. This one has the floating 9V Zener. ? Mike ? ? Finished that up.? ?On the -100 I can adjust up to 96v, a little low but it is adjustable so I think I should come back to that later.??
On 248v I'm currently seeing 290v, and -12v I'm seeing -1.5v.? ? ?I reckon I could go after either of them given the dependencies.? ? Will grab some measurements in between or after work today.? ? ? On Thu, Aug 29, 2024 at 10:52?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Well, this is awkward.? ? I had replaced both Diff Amp transistors with the same part number.??
I just found that this package is actually reverse from what i removed!? ?using a dorky little? heathkit transistor tester, i found the pinout to be CBE when looking at it from the flat side.??
The center leg was bent towards the rear of the part, while the original part was bent toward the front.??
I reversed both transistors, and got -106 which i was able to adjust appropriately!? ? ??
Strange, but makes sense.? ?I have a few more of these buggers in the supply, so it sounds like I'll be sorting through that today.? ? Will report back in a bit.??
Thanks for the help ya'll!? ? On Thu, Aug 29, 2024 at 10:45?AM Frank Mashockie via <fmashockie=[email protected]> wrote: Also, don't forget about Gianni's HP e-book.? If I remember correctly, he goes into great detail about the 141T.? Here's the link.? They can be slow to download and I forget which section includes the 141T. ?
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Re: HP 141T Power Supply Help Needed
Bill. ? You are making progress!? Now we have to find out where the -12.6 current is going.? Especially since the driver is getting hot.? It is funny that the current limiter is showing 0V.? I think some more ohm meter checks are? in order.? I assume the -12.6 to the A5 module is disconnected.? In fact I suggest pulling all of the white / violet wires from the A2 regulator board.? What voltage is there at the emitter of the pass device Q4?? Let me know¡ ? Mike ?
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Show quoted text
From: [email protected] < [email protected]> On Behalf Of Bill Berzinskas Sent: Sunday, September 1, 2024 6:45 PM To: [email protected]Subject: Re: [HP-Agilent-Keysight-equipment] HP 141T Power Supply Help Needed ? Spent some time today checking through the rest of the line - basic checks on passives look ok. Transistors look ok.? Noticed the driver getting hot though.? ?Not making any progress, despite trying to figure it out.? ?
Current measurements:? B = 2.6v? (was 23.5v)
E = 1.9v (was -17v)
Q10..
C = 2.6v? (was 23.5v)
b = 0v again E = 0v
Q11..?
C=? ~2.2v (was 23.5v)
B = -0.2v, fluctuates? (was -.64)
E = -1v, fluctuates (was 0)
In other news, I believe I have located the short on the A5 board.? ?Stray lead clipping in a very tough to see location...? ?:\? ? ??
? On Sun, Sep 1, 2024 at 4:55?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: tiny update to the above, replaced?+100v driver and that helped immensely!
+100, -100,?+248 all work, adjust and appear happy!? ?
I gained .5v on my -12.6 line, but its still sitting at -3v.? ? ? Getting closer, seeing some signs of life finally.? ? Not all the way but progress is progress.??
I've found that CR16 and CR17 were not good, and the pass trans was also not happy anymore.? ?I've replaced all of that and am now getting a whopping -2.5v!? ?10 more to go.? :-).? Will check through resistors this evening.? ? ?I'm also seeing some off voltages in my other rails, will have to go back through the?+100 and -100 lines as well.? ? ?
Current status:?
+79
-82
+217
-2.5
The purple/white wire presenting the short was easy to find, its the one going to the board just in front of the power?supply. Looks like thats A5, so I'll start mulling over the schem?for that as well.? ?
? ? ? On Sat, Aug 31, 2024 at 5:00?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? It sounds like you are on the right track!? So find out were the .04Ohm wire goes¡ ? Mike ? ? Neat trick checking for shorts.?? As you expected probably, 0.04ohm.???? I have found one purple/white wire which when removed brings that up to 384 ohm.??? I'll be out of pocket for a day but will look at the supply one more time in isolated state and then trace that wire out.??? Thank you! ? On Sat, Aug 31, 2024, 12:11?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? So you replaced the pass transistor and Q9 then it popped the 3A fuse F4.? And at that point the regulator worked but there must be a short on the -12.6V buss.? Please run an Ohm meter check on the -12.6V buss which is / are the white / violet wires from the A2 assembly.? Check R42, CR16 and Q10.? ?From my calculations the current limiter Q10 should start taking drive away from the driver Q9 at about 2.8A.? ?I take it that no plugins are installed.? The only place in the 141T that the -12.6 goes is / the? plugin connectors, the flood gun filament, and the trace align control on the front panel.? If there is a short (<4 Ohms) then you have to find which wire has that low impedance.? Let me know what you find. ? Mike ? ? Those numbers just don't make any sense.??? I pulled all the transistors AGAIN, desoldered and cleaned.? Tested them all with a meter, repopulate.??? Back to 23.5v....??? ? On Fri, Aug 30, 2024, 6:22?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Replaced Q9, powered on and blew the fuse.? ?Replaced Fuse?+ Q9 again?+ pass transistor and no fuse pop.? ?
Not sure if better, worse or just different :-)? B = 54v?!? (was 23.5v)
E = -17v.?
Q10..
C = 54v..? (was 23.5v)
b = 0.58v (up from 0)? E = 0v
Q11..?
C= 54.7 (was 23.5v)
B = -.64
E = 0 ? On Fri, Aug 30, 2024 at 5:48?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK it seems that Q 9 has a base-emitter voltage of 38.5V which says that the base-emitter junction is open because a good NPN silicon transistor can only have a forward base-emitter voltage of 1V under extreme conditions.? Normally the Vbe is in the order of 0.7V. If the emitter or base connection of Q9 were open the emitter voltage will be dragged negative by R41.? That is not good for the pass transistor Q4 to see that much negative voltage because that will exceed the Vebo rating of the pass device which may degrade the Beta of the pass device.? Basically it will Zener the base emitter junction with that much reverse bias.? Typical Vebo is in the order of <10V which is in the absolute maximum ratings of the part.? A 2N3053 should work OK as the driver Q9.? Let me know how it goes. ? Mike ? ? That does make sense,?thank you for that explanation..? I do believe I've stated it backwards.? ? 22v appears on a 2n3053 that I've replaced at pin 3, which is actually the collector..? :facepalm:..? Remeasure / restate Q9..? ? On Fri, Aug 30, 2024 at 3:02?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? Lets back up a minute¡ If there is +22V at the emitter of the driver Q9 then there must be +22V at the base of the series regulator Q4 and you say that there is less than 1V ?at the emitter of the pass transistor Q4 and also no voltage at the top of R42 (the current sense resistor) then there is 22V across the base emitter junction of? Q4 and that can only be a failed device or some bad wiring or even a cracked runner on the board. A good NPN transistor has no more than 1V Vbe.? ??Does that make sense to you?? Or is the voltage at the emitter of the driver Q9 a negative 22V?? If the voltage at the emitter of Q9 is negative then what is the voltage at the base of Q9? ? Mike ? ? Ok..? I had a few bad transistors in the mix, but the one that was in the unit checks out ok.? ? ?I tossed a small handful to alleviate future issues.? ?
I spent a little time simulating this and from what I'm seeing this almost has to be a problem w/ the voltage divider / potentiometer.? ?I can do a lot of "shady" things in the sim and none of them give me issues like I'm seeing.? ?Removing R43 in the sim, or the pullup R45 seem to skew the voltages like I'm seeing.? ? ?The sim shows that the trimpot is kind of what "kicks things off", and the fact that I'm only getting about -1v here seems to further hint towards R43.? ? I don't have a 22.1k or even a 22k on hand, so I'll probably get creative to see what happens.? ?Resistance measurements on the pot itself look ok, i'm really hoping to not have to yank that thing.?? ? On Fri, Aug 30, 2024 at 11:58?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: I'll check these over lunch.? ?Interestingly, two of the original transistors in that spot cause the 3a fuse to blow.? ?Now sure if thats indicative of something else going on w/ a good transistor in the seat..? ? tbd.?? ? On Fri, Aug 30, 2024 at 11:43?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? 22V on the emitter of the driver is very strange.? It seems that the pass transistor Q2 has an open base ¨C emitter junction and a shorted collector base junction to come up with those voltages.? That would explain the ¡°on output¡± situation.?? An Ohm meter should be sufficient to check the status of Q2.? If your meter has a diode scale, that would give you a quick indication of the status of Q2.? ? I am thinking ?of designing an over voltage crowbar circuit to protect the -12.6 V supply from damaging sensitive circuits down stream of this supply if the regulator goes to an over voltage condition.? Some of the plugins appear to have a crowbar in just such a condition.? The filament of the flood gun is run from the -12.6V and in my case it went over voltage and it burned out the flood gun filament. ? ? Mike ? ? Thanks Michael,?
here's a recap what i'm seeing around the -12.6v line currently:?
?.65v at base of q11 sensor amp, .275v on collector.?? Driver has 22v on emitter, .27v on base and -.27v collector.????? Not much happening on the current limiter.?? 0v base.? ? On Fri, Aug 30, 2024 at 11:15?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK so you have the early version of the supply.? If you give me the voltages at the base of the driver transistors I can perhaps give you some more pointers. ? Mike ? ? correction, it did have the LAMP..? ?? ? My unit is 1615a prefix, it did have the zener and it was measuring closer to 100v instead of the expected 83 or whatever.? It has since been replaced by a pair of diodes that bring it to 89v but I have had to replace that string at least once in my travels so far, so I will eventually look for a more permanent?solution as I've read about.? ?I can check that again this evening!? ?I stopped thinking about it after I got the?+100v supply up! ? On Thu, Aug 29, 2024 at 4:50?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? There are 2 versions of this supply.? There is an early version that has a neon tube as the reference for the +100V supply and a later version that uses a 9V temp compensated Zener that is floating.? That is the reference Zener is connected from the +100V rail and the base of Q4.? It may help to know which version you have.? From my schematic the +100 V is the master and the other supplies are referenced from it.?? The one I have has a serial number prefix 2101A and it appears to be made in the late 1981 or early 1982 time frame. This one has the floating 9V Zener. ? Mike ? ? Finished that up.? ?On the -100 I can adjust up to 96v, a little low but it is adjustable so I think I should come back to that later.??
On 248v I'm currently seeing 290v, and -12v I'm seeing -1.5v.? ? ?I reckon I could go after either of them given the dependencies.? ? Will grab some measurements in between or after work today.? ? ? On Thu, Aug 29, 2024 at 10:52?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Well, this is awkward.? ? I had replaced both Diff Amp transistors with the same part number.??
I just found that this package is actually reverse from what i removed!? ?using a dorky little? heathkit transistor tester, i found the pinout to be CBE when looking at it from the flat side.??
The center leg was bent towards the rear of the part, while the original part was bent toward the front.??
I reversed both transistors, and got -106 which i was able to adjust appropriately!? ? ??
Strange, but makes sense.? ?I have a few more of these buggers in the supply, so it sounds like I'll be sorting through that today.? ? Will report back in a bit.??
Thanks for the help ya'll!? ? On Thu, Aug 29, 2024 at 10:45?AM Frank Mashockie via <fmashockie=[email protected]> wrote: Also, don't forget about Gianni's HP e-book.? If I remember correctly, he goes into great detail about the 141T.? Here's the link.? They can be slow to download and I forget which section includes the 141T. ?
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Re: Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?
They almost certainly did specify a Schottky with an appropriate leakage spec. The problem wasn't the spec -- it was that the leakage increased beyond spec over time. More things can go wrong with the metal-to-semiconductor interface of a Schottky than for a regular diode, where there is continuity of crystalline order in going from P to N.? Likely HP had low confidence that they could find Schottkys with trustworthy aging behavior, so went the easy route and chose standard PN junction diodes as a replacement. Even the 1N914/4148 (quite leaky compared to other junction diodes) has much lower leakage than a Schottky with an equivalent forward current rating. Time-related reverse current increases in a junction diode are rarer and more moderate (unless the diode is abused or fabbed in an unclean environment).
-- Cheers
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
420 Via Palou Mall
Stanford University
Stanford, CA 94305-4070
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Show quoted text
On 9/2/2024 3:32 AM, Edward Prest wrote: That's what they say - but why go to? a 'regular' diode?? And go from 0.3 to 0.7 fwd drop. A better replacement would be a schottky with a low leakage spec.
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Re: Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?
That's what they say - but why go to? a 'regular' diode?? And go from 0.3 to 0.7 fwd drop. A better replacement would be a schottky with a low leakage spec. However, some power down circuits do get complex so to notify the software of empending mains loss , maybe a complicating factor.
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Thanks, Bruce. I'll have some time free later today to try this suggestion of yours. We'll see if it reveals anything in due course...
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Re: 8566B Can't Calibrate
On Sun, Sep 1, 2024 at 09:36 PM, pianovt wrote:
Vladan, that does make good sense and would certainly be worth trying. I just want to try any other possibilities first, as I don't have the time to take this thing to bits again right now.
?
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Re: Instrument Sram ( non Dallas ) Battery replacement: Original 3.0V Li+ >> To 3.6V Li+ & Schottky Diodes ?
CR123 are available in 3.0V and 3.6V
The 3.0V version is common in camera shops.
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8497K attenuator overhaul
I need to do an o-ring replacement of an 8497K attenuator with N connectors and a Viking control cable.
I have done this on an attenuator with SMA connectors and an IDC ribbon socket. Disassembly on that was fairly straight forward.
The SMA socket had nuts that when removed allows the cover plate to come off revealing the bolts to disassemble the attenuator bank but still retaining the SMA sockets.
With this one, it seems, I have to remove both N connectors before I can get to the cover plate. Is that right? Can someone with experience confirm that?
I also presume that the Viking connector is removed by taking off the circlip and pushing it through the side plate; is this correct?
?
The last one I did had three sections (12 o-rings) and that was a cow ... this one has four section (16 o-rings)!
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Michael 
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You should probably do the following:?
0) Connect CAL OUTPUT signal to RF input.
1) Press GREEN BUTTON, then RECALL followed by 8.? Adjust the amplitude to -10db using AMPLITUDE ADJUST next to the RF input.
2) Press GREEN BUTTON followed by RECALL 9.? Adjust for the highest amplitude line using FREQUENCY ZERO pot on 85662 front panel next to the CRT and just below the INTENSITY control.
3) with the CAL signal still connected to the RF input press GREEN BUTTON, then FREQUENCY SPAN.
?
The 8566 will run a calibration test of the gain and filters.? If it stalls with AMPL ADJ, there is a problem.? The attenuator is a possible cause, and there are others.
?
Note: Test results are invalid unless 0 - 2 are done properly and the results are as expected.
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If the test completes, press BLANK on the 85662, and BLUE BUTTON followed by LINE for a list of deviation from perfect for a number of gain and BW settings.? You may need to press HOLD to remove any overwritten messages.
?
This procedure is covered in the section discussing front panel diagnostics.? It gives a reasonable overview of the instruments state of calibration.? The data is stored internally and can be used to correct measurements.
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NOW you are getting to the fun part !!
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Cheers!
?
Bruce
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Re: When is calibration data read off the internal bus on the HP 3478A
?
AWolf provides a pretty nice description, (with cautions) about what is going on on the 3474a Bus.
?
??? A goofy short can render the Sram loss and ... demise.
?
?He describes an Fram mod, deleting the need for the old Sram back-up battery:
?
"modify my 3478A meters to use FRAM (ferreromagnetic RAM) instead of the original battery-backed up SRAM solution. FRAM acts like normal SRAM, with the big difference that FRAM does not loose the data when it is powered down. "
?
See:
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rick
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Re: When is calibration data read off the internal bus on the HP 3478A
?
Also See:
?
?
using Matlab by Jeff & Dick Benson
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rick
?
?
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Re: When is calibration data read off the internal bus on the HP 3478A
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Steve,
?
See:
?
?
?
?
?
?
rick
?
?
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Re: Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?
?
?
Negative.
?
It is indeed directly due to Schottky diode degradation,
? as stated in the Hp Service Bulletin 4274a-12?? ,? referenced above:
?
" Improvement for Memory Backup Battery"
? ...
" Symptom and Cause:
The characteristics of the Schottky didoes used for CR3 and CR4 in the level detector circuit on the A9 MPU board gradually deteriorate.? This causes increased reverse bias current which significantly shortens the life of the memory back-up battery.
?
Implementation:
To prolong battery life, the Schottky diodes ( 1901-0518 ) should be replaced with general purpose diodes.? The part number of the recomended replacement diode is : Hp? P/N: 1901-0025? "
?
-- My question is:
? What? other Hp instruments? *might* ? this modification for Schottky diode replacement
????? in Sram Battery ( non Dallas )? back-up circuits, ? apply ?
?
rick
?
?
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Re: When is calibration data read off the internal bus on the HP 3478A
You're pointing out a problem "we" all will have.
The people who are experts in the equipment we *can* repair are vanishing, as is their knowledge.? I think that the answer is going to be an individual responsibility for each person.? When you repair something, then document it.? Equally important, if you DO NOT repair something, then document that as well.
It is equally important to know what does not work as what does. Once you solve the problem, you stop learning.
How do we solve this one?
Harvey
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Show quoted text
On 9/1/2024 7:11 PM, Dave McGuire wrote: On 9/1/24 16:54, Steve Holland via groups.io wrote:
This question is for a future project. The HP 3478A has an internal bus that is used to read data from an internal memory with battery backup. I'm interested in knowing when calibration data is read off the internal memory on startup. Are all banks read at startup or is calibration data read just when the instrument is switched to a particular mode and range? ? Damn, if only we hadn't lost George Hnatiuk not long ago. :-( He could've answered that question right off the top of his head.
? One approach to make this determination is to put a chip clip on the NVRAM and watch its accesses with a logic analyzer.
???????????? -Dave
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Re: HP 141T Power Supply Help Needed
Spent some time today checking through the rest of the line - basic checks on passives look ok. Transistors look ok.? Noticed the driver getting hot though.? ?Not making any progress, despite trying to figure it out.? ? Current measurements:? Q9..? C = 16.27v (was 22v) B = 2.6v? (was 23.5v)
E = 1.9v (was -17v)
Q10..
C = 2.6v? (was 23.5v)
b = 0v again E = 0v
Q11..?
C=? ~2.2v (was 23.5v)
B = -0.2v, fluctuates? (was -.64)
E = -1v, fluctuates (was 0) In other news, I believe I have located the short on the A5 board.? ?Stray lead clipping in a very tough to see location...? ?:\? ? ??
On Sun, Sep 1, 2024 at 4:55?PM Bill Berzinskas via <bberzinskas= [email protected]> wrote: tiny update to the above, replaced?+100v driver and that helped immensely!
+100, -100,?+248 all work, adjust and appear happy!? ?
I gained .5v on my -12.6 line, but its still sitting at -3v.? ?
Getting closer, seeing some signs of life finally.? ? Not all the way but progress is progress.??
I've found that CR16 and CR17 were not good, and the pass trans was also not happy anymore.? ?I've replaced all of that and am now getting a whopping -2.5v!? ?10 more to go.? :-).? Will check through resistors this evening.? ? ?I'm also seeing some off voltages in my other rails, will have to go back through the?+100 and -100 lines as well.? ? ?
Current status:?
+79
-82
+217
-2.5
The purple/white wire presenting the short was easy to find, its the one going to the board just in front of the power?supply. Looks like thats A5, so I'll start mulling over the schem?for that as well.? ?
? ?
On Sat, Aug 31, 2024 at 5:00?PM Michael Bafaro via <m.bafaro= [email protected]> wrote: Bill, ? It sounds like you are on the right track!? So find out were the .04Ohm wire goes¡ ? Mike ? ? Neat trick checking for shorts.?? As you expected probably, 0.04ohm.???? I have found one purple/white wire which when removed brings that up to 384 ohm.??? I'll be out of pocket for a day but will look at the supply one more time in isolated state and then trace that wire out.??? Thank you! ? On Sat, Aug 31, 2024, 12:11?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? So you replaced the pass transistor and Q9 then it popped the 3A fuse F4.? And at that point the regulator worked but there must be a short on the -12.6V buss.? Please run an Ohm meter check on the -12.6V buss which is / are the white / violet wires from the A2 assembly.? Check R42, CR16 and Q10.? ?From my calculations the current limiter Q10 should start taking drive away from the driver Q9 at about 2.8A.? ?I take it that no plugins are installed.? The only place in the 141T that the -12.6 goes is / the? plugin connectors, the flood gun filament, and the trace align control on the front panel.? If there is a short (<4 Ohms) then you have to find which wire has that low impedance.? Let me know what you find. ? Mike ? ? Those numbers just don't make any sense.??? I pulled all the transistors AGAIN, desoldered and cleaned.? Tested them all with a meter, repopulate.??? Back to 23.5v....??? ? On Fri, Aug 30, 2024, 6:22?PM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Replaced Q9, powered on and blew the fuse.? ?Replaced Fuse?+ Q9 again?+ pass transistor and no fuse pop.? ?
Not sure if better, worse or just different :-)? B = 54v?!? (was 23.5v)
E = -17v.?
Q10..
C = 54v..? (was 23.5v)
b = 0.58v (up from 0)? E = 0v
Q11..?
C= 54.7 (was 23.5v)
B = -.64
E = 0 ? On Fri, Aug 30, 2024 at 5:48?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK it seems that Q 9 has a base-emitter voltage of 38.5V which says that the base-emitter junction is open because a good NPN silicon transistor can only have a forward base-emitter voltage of 1V under extreme conditions.? Normally the Vbe is in the order of 0.7V. If the emitter or base connection of Q9 were open the emitter voltage will be dragged negative by R41.? That is not good for the pass transistor Q4 to see that much negative voltage because that will exceed the Vebo rating of the pass device which may degrade the Beta of the pass device.? Basically it will Zener the base emitter junction with that much reverse bias.? Typical Vebo is in the order of <10V which is in the absolute maximum ratings of the part.? A 2N3053 should work OK as the driver Q9.? Let me know how it goes. ? Mike ? ? That does make sense,?thank you for that explanation..? I do believe I've stated it backwards.? ? 22v appears on a 2n3053 that I've replaced at pin 3, which is actually the collector..? :facepalm:..? Remeasure / restate Q9..? ? On Fri, Aug 30, 2024 at 3:02?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? Lets back up a minute¡ If there is +22V at the emitter of the driver Q9 then there must be +22V at the base of the series regulator Q4 and you say that there is less than 1V ?at the emitter of the pass transistor Q4 and also no voltage at the top of R42 (the current sense resistor) then there is 22V across the base emitter junction of? Q4 and that can only be a failed device or some bad wiring or even a cracked runner on the board. A good NPN transistor has no more than 1V Vbe.? ??Does that make sense to you?? Or is the voltage at the emitter of the driver Q9 a negative 22V?? If the voltage at the emitter of Q9 is negative then what is the voltage at the base of Q9? ? Mike ? ? Ok..? I had a few bad transistors in the mix, but the one that was in the unit checks out ok.? ? ?I tossed a small handful to alleviate future issues.? ?
I spent a little time simulating this and from what I'm seeing this almost has to be a problem w/ the voltage divider / potentiometer.? ?I can do a lot of "shady" things in the sim and none of them give me issues like I'm seeing.? ?Removing R43 in the sim, or the pullup R45 seem to skew the voltages like I'm seeing.? ? ?The sim shows that the trimpot is kind of what "kicks things off", and the fact that I'm only getting about -1v here seems to further hint towards R43.? ? I don't have a 22.1k or even a 22k on hand, so I'll probably get creative to see what happens.? ?Resistance measurements on the pot itself look ok, i'm really hoping to not have to yank that thing.?? ? On Fri, Aug 30, 2024 at 11:58?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: I'll check these over lunch.? ?Interestingly, two of the original transistors in that spot cause the 3a fuse to blow.? ?Now sure if thats indicative of something else going on w/ a good transistor in the seat..? ? tbd.?? ? On Fri, Aug 30, 2024 at 11:43?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? 22V on the emitter of the driver is very strange.? It seems that the pass transistor Q2 has an open base ¨C emitter junction and a shorted collector base junction to come up with those voltages.? That would explain the ¡°on output¡± situation.?? An Ohm meter should be sufficient to check the status of Q2.? If your meter has a diode scale, that would give you a quick indication of the status of Q2.? ? I am thinking ?of designing an over voltage crowbar circuit to protect the -12.6 V supply from damaging sensitive circuits down stream of this supply if the regulator goes to an over voltage condition.? Some of the plugins appear to have a crowbar in just such a condition.? The filament of the flood gun is run from the -12.6V and in my case it went over voltage and it burned out the flood gun filament. ? ? Mike ? ? Thanks Michael,?
here's a recap what i'm seeing around the -12.6v line currently:?
?.65v at base of q11 sensor amp, .275v on collector.?? Driver has 22v on emitter, .27v on base and -.27v collector.????? Not much happening on the current limiter.?? 0v base.? ? On Fri, Aug 30, 2024 at 11:15?AM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? OK so you have the early version of the supply.? If you give me the voltages at the base of the driver transistors I can perhaps give you some more pointers. ? Mike ? ? correction, it did have the LAMP..? ?? ? My unit is 1615a prefix, it did have the zener and it was measuring closer to 100v instead of the expected 83 or whatever.? It has since been replaced by a pair of diodes that bring it to 89v but I have had to replace that string at least once in my travels so far, so I will eventually look for a more permanent?solution as I've read about.? ?I can check that again this evening!? ?I stopped thinking about it after I got the?+100v supply up! ? On Thu, Aug 29, 2024 at 4:50?PM Michael Bafaro via <m.bafaro=[email protected]> wrote: Bill, ? There are 2 versions of this supply.? There is an early version that has a neon tube as the reference for the +100V supply and a later version that uses a 9V temp compensated Zener that is floating.? That is the reference Zener is connected from the +100V rail and the base of Q4.? It may help to know which version you have.? From my schematic the +100 V is the master and the other supplies are referenced from it.?? The one I have has a serial number prefix 2101A and it appears to be made in the late 1981 or early 1982 time frame. This one has the floating 9V Zener. ? Mike ? ? Finished that up.? ?On the -100 I can adjust up to 96v, a little low but it is adjustable so I think I should come back to that later.??
On 248v I'm currently seeing 290v, and -12v I'm seeing -1.5v.? ? ?I reckon I could go after either of them given the dependencies.? ? Will grab some measurements in between or after work today.? ? ? On Thu, Aug 29, 2024 at 10:52?AM Bill Berzinskas via <bberzinskas=[email protected]> wrote: Well, this is awkward.? ? I had replaced both Diff Amp transistors with the same part number.??
I just found that this package is actually reverse from what i removed!? ?using a dorky little? heathkit transistor tester, i found the pinout to be CBE when looking at it from the flat side.??
The center leg was bent towards the rear of the part, while the original part was bent toward the front.??
I reversed both transistors, and got -106 which i was able to adjust appropriately!? ? ??
Strange, but makes sense.? ?I have a few more of these buggers in the supply, so it sounds like I'll be sorting through that today.? ? Will report back in a bit.??
Thanks for the help ya'll!? ? On Thu, Aug 29, 2024 at 10:45?AM Frank Mashockie via <fmashockie=[email protected]> wrote: Also, don't forget about Gianni's HP e-book.? If I remember correctly, he goes into great detail about the 141T.? Here's the link.? They can be slow to download and I forget which section includes the 141T. ?
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Re: Almost free to good home, HP 3570A/3330B system + manuals and spares
The 3570A system is spoken for.
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Re: When is calibration data read off the internal bus on the HP 3478A
On 9/1/24 16:54, Steve Holland via groups.io wrote: This question is for a future project. The HP 3478A has an internal bus that is used to read data from an internal memory with battery backup. I'm interested in knowing when calibration data is read off the internal memory on startup. Are all banks read at startup or is calibration data read just when the instrument is switched to a particular mode and range? Damn, if only we hadn't lost George Hnatiuk not long ago. :-( He could've answered that question right off the top of his head. One approach to make this determination is to put a chip clip on the NVRAM and watch its accesses with a logic analyzer. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
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That's what happened with a Marconi signal generator I have. It was quite a high-end one for its day and still fetches quite a tidy sum on Ebay, so I really wanted to get it fully working if at all possible. The power level output was all over the place when it stepped through its attenuators. I could hear them clunking in and out as the attenuation was incremented. However, I just left it cycling through repeated sweeps from -144dBm to +10dBm over and over and eventually all came good again with no disassembly required. Perhaps the same might happen with this 8566 with a bit of luck...
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"My last 2 used SA's puchases both had blown 10 and 20dB attenuator wafers. Never risk DC damage for a half dB. There is no repair possible, just used scrap parts. Lucky for me the mixer diodes were still Ok."
Well, thats not really true. Myself and others have "made one from two". Hard but do-able, especially when you cant find the type you need but have a weird "junker" around (bad connector, weird voltage or something similar).
Asd to the othe comment: Tons of details about the internal sticky O rings and how to replace them, here on the group. Common problem, even in a replacement (40 years old!).
You may not have blown pads, just sticky O rings not allowing the plungers to set the contact fingers fully! Have fun! Jeff Kruth
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Jinxie
vk2bea
Precaud
Dave McGuire