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
toggle quoted message
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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Re: HP 141T Power Supply Help Needed
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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When is calibration data read off the internal bus on the HP 3478A
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?
?
Steve
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Re: 8566B Can't Calibrate
What are these O rings?
I have a spare attenuator if the installed one is blown. Not sure if it's compatible or not but it's an electronically-switchable type and does 10 through 70dB. Model number's 8495K. I was in the process of building a switching unit for it so it could be used as a stand-alone job for any of my other pieces of test equipment. If the faulty one in the 8566B is irreparable then I guess I'll just have to forget the stand-alone project and swap it out for the duff one. <shrug>
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Re: 8566B Can't Calibrate
The fact that 0 and 10 dB look different from 30 dB does point to a problem with the attenuator. In addition, there could be other problems as well. I would first confirm that the rest of the signal chain is good by connecting the cal signal to the place where the ouput of the attenuator normally goes. In other words, bypass the step attenuator for this test. Use a 10 dB fixed attenuator as a surrogate for the step attenuator. You should see something on the screen that is within the Ampl Cal adjustment range.
?
Once you confirm that the rest of the analyzer is working, it will be easier to know when you have fixed the step attenuator.
?
Vladan
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Re: HP 141T Power Supply Help Needed
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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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.
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Re: 8566B Can't Calibrate
Likely Attenuatoar O-Rings
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Re: WOT (Waay off topic): circular saw blade not cutting anymore (gets stuck on material)
I got a Grizzly G8689.? It's the mini-mill version, roughly a Sieg X3.? There are better ones out there, you might try looking at LittleMachineShop.com.? I've never had a problem with them and they have a good assortment.? If you do go for a mini-mill, you need to consider whether you want R8 tooling or MT3.? You also *really* want to get readouts on it.? I've used them in the past, and they make a real difference.? Be prepared to spend a substantial amount on tooling, of course.
If the mods consider this too far off topic, then we can go private with it, but to me, this tooling can help restore old equipment.....
Harvey
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On 9/1/2024 1:40 PM, Roy J. Tellason, Sr. wrote: On Sunday 01 September 2024 10:25:25 am Harvey White wrote:
If you want to trim connectors, then the mill might be a good idea.
Some of the Harbor Fright mills are good, I have a Grizzly, and can talk
to you about it. Which one did you get? I've been thinking about getting a mill for a good long time, but haven't pulled the trigger on one yet...
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Re: WOT (Waay off topic): circular saw blade not cutting anymore (gets stuck on material)
When I mentioned a shear, I did not mean shears.? You can get a PC board shear from Harbor Fright that will do about 12 inch wide material for not very much.? I would not try to use metal shears (as in hand variety) for that at all.
Harvey
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On 9/1/2024 1:11 PM, Radu Bogdan Dicher wrote: Wait, of?course!... (forehead slap audible west of the Rockies...) Quite a brain fart to say "occasionally cut PCB and wasn't aware there's an ominous aspect to it." I did/do, just tucked it away in obsolete sectors of the brain, as it's been many years since I stopped prototyping/fabbing my own boards (as opposed to designing and having them fabbed by some house), and so cutting PCB has not been a thing for me in a very long time.
Anyway, I very much like the idea of using shears (will need to figure their size and what would make them cut distinguishably straight - I'm unfortunately extremely anal with such things - as the boards I need to slice are about 6" long), and also I need to gear up on a shop vac, which I'd like to have HEPA-filtered.
Thanks a ton all.
Radu.
On Sun, Sep 1, 2024 at 8:34?AM John Griessen via groups.io <> <john@...> wrote:
On 9/1/24 06:56, Radu Bogdan Dicher wrote:
> PCB sawing dust? If yes, I'm not cutting PCB in this particular
step under examination here - but rather plastic (fiberglass?...)
> from the edge connector body - though I've occasionally cut PCB
and wasn't aware there's an ominous aspect to it. John - would you
> care to elaborate?
Sure.? Any dust with ceramic in it fills tiny sacs in lungs
leading to emphysema.? Also can be carcinogen.
Use a nice mask and ventilation when cutting.? ? ?Ventilation such
as a vacuum cleaner would do.
I like the recommendations to use an abrasive diamond wheel, and
also use it at low speed if possible, not on an angle grinder.
for instance, for floor and countertop polishing, diamond embedded
in rubber discs is used at low speed with a spigot for water
flowing through the motor shaft, out the abrasive wheel center.?
Keeps it safe.? (If the GFI works!)
--
John
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Re: Hp Schottky diode HP QSCH 1691 ( or HPQSCH-1691 ?) ... Data Sheet wanted
The Q indicates it was a custom part and data sheets are not available (unless someone leaked one).
?
Can't find any info on this Hp QSCH 1691 ( Schottky ) diode.
?
It does not seem to be mentioned in either of the 1972, 1980, nor 1984
? Hp Diode & Transistor Designer's Handbooks.
?
Anyone have a .pdf Data Sheet for this small glass diode (HP package 15) ?
?
thank you,
?
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Re: Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?
I believe it's because schotty's leak more so at low currents it matters? I doubt it's a diode degrading issue. I have some hw with 45 year old schottky diodes that work just fine (mixers).?
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Schottky Diode degradation / Replacement in instrument Sram Battery backup circuits ?
?
Notes & possible concern: ?Schottky Diodes in these Sram circuits.
?
Some instruments having a Battery backed up ( non Dallas ) Sram seem to have a ?"Ram Shutdown" circuit that provides for seamless transition of the Mains PS to the battery standby on Pwr Off / On ;
?? ( possibly a Zener ?(say 3.3V) , & 3 transistors + a P-ch Fet ?+ 2 to ?3 other diodes, ? ...sometimes Schottky Diodes are used. ).
?
Recently, I found an Hp Service Note that ? **recommends removing the Schottky diodes** ? and replacing them with ?regular Si diodes ?in the Sram battery backup circuit ?of an Hp LCR meter Hp 4274a , because the Schottky diodes? degrade over time,
???? .... sapping the Sram Battery and decreasing its lifetime.
?
HP Service Note: Hp 4274a LCR Sram Battery life:
" To prolong battery life the Schottky diodes should be replaced with general purpose diodes "
http://www.doe.carleton.ca/~nagui/labequip/lcr/4274A_Service%20Manual.pdf
? ? -- Has anyone noticed this for other instruments
??????????????? & replaced their Schottky diodes ?
?
rick
?
? other Refs:
Hp 3476a:
/g/HP-Agilent-Keysight-equipment/topic/24805436#msg31826
Hp 8662a:
?
?
?
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Instrument Sram ( non Dallas ) Battery replacement: Original 3.0V Li+ >> To 3.6V Li+ & Schottky Diodes ?
??
?Anyone done this with a? *suitable*? 3.6V Li+? Battery replacement,?
?????? for? a BR-2/3a? 3.0V Li+ cell ?
?
Some older instruments have an Sram ( non Dallas ) Battery such as the BR-2/3a? 3.0V Li+ 1200mAh , soldered ( tabs ) to the motherboard,? ( Hp 3457a,? etc. ).?
?
After 20 years, and a lowered cell voltage( 2.7V), it is time to replace the BR-2/3a to preserve the Cal Data in a GR Digibridge 1693 LCR meter.?? Doing so, with the precautions of a temporary new Battery + Diode in parallel ( or PS + diode ) & non-grounded soldering iron, are obvious.
?
Shipping issues make obtaining a new, bonafide, ( non Counterfeit ) BR-2/3a cell almost impossible here.
?
It was easier to get an SAFT LSH-14 ? long life? low leakage? 3.6V Li+? cell with solder tabs, locally.
-- Why not use the 3.6V Li+ cell instead ?
?
Many of these instrument? Sram circuits seem to use a +5V Vcc Sram, with the Li+ cell wired via a diode
( or diode +? small limiting resistor ),? to the Sram Vcc.
?
? So, it might Not seem to be an issue to use a *suitable*? 3.6V Li+ ,? to replace the old? 3.0V cell ... ?
??
? Or,? perhaps with an (additional)? Diode drop ( Schottky or an Si 1N4148 ) in Series with the 3.6V Li+ ,
????? to bring the Voltage down to ~3V? ?
?
--? Thoughts from anyone who has done or contemplated? ?
?
rick
?
OT? Refs:
Hp 3457a:
?
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Precaud
Dave McGuire
Jinxie
Steve Holland