Re: HP 8566B repair: -10V rail went down
"Harvey White" <madyn@...> writes: Thinking of fuses, a 1 amp fuse doesn't blow at 1.1 amps.
Certainly Chemical fuses (resettable) say may blow in 30 seconds at 2
amps, maybe 5 seconds at 4 amps, and almost immediately at 10 amps.
Since regular fuses may well behave similarly, that 5 amps may be an OMG
rating, (if it was the correct fuse in the first place). Interesting. Why wouldn't the designers use a fuse closer to the max current draw? FYI it is the right fuse, I'm just taking the value from the manual. With a current limited supply (highly recommended), I'd have started out
at, say 100ma, then gone up by increasing the current limit.? Note that
you can thoroughly confuse some of the circuitry by doing this, so it's
a bit iffy.
Otherwise, say setting it an an amp, then two amps, etc, may give you a
better idea of how the circuit is behaving.
All a bit dicey, though, depending on the equipment. Yeah, lesson learned I guess. Matt
|
Tom,
?
Thanks for pointing this out.? I was on the way out the door when I wrote the post and overlooked some details.
?
From what I can gather from the scatty information I have it appears that they are trying to match the diodes with a maximum delta Vf of 20 mV and a maximum delta Co of 0.2 pF.? It doesn¡¯t appear that there are actual hard values for both of those parameters but, instead simply trying to match the two diodes as close as possible to each other no matter where the values fall.
?
What bothers me a bit is that the probe schematic shows a quad set of diodes.? A pair would only serve to replace half of the quad.? HP did sell a matched quad set of this particular diode under part number 5082-2370.? Any thoughts on this one?
?
Greg
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[Troubleshoot] HP 08590-60352 / A-3202-53 narrow band IF card Option 130 with HP 8594E
Hi, following the other topic that I started but then closed, I am now facing what I think is the real issue.
Without the card, the CAL is successful.
However, when the card is installed, it fails at different tests depending if I run a second CAL right after a failure or not.
The failing error messages are when the card is installed are :
CAL : GAIN FAIL <-- This one is usually the first to appear
CAL : NBW gain failed
CAL : NBW 200hz notch failed (I see the notch, but the marker is not in it and I see the Freq drifting when stopped)
What would be the first steps to troubleshoot this ?
Thank you.
|
Or look for an avionics shop that might be interested in it, and then get something you might use more regularly.?
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On Jan 17, 2022, at 6:32 PM, Stevegibson@... wrote:
?Hi
Yep, got a sensor, although privacy not going to be measuring many pulse signals.
Probably need to experiment to see what uses I can find for it
Steve
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Re: HP 8566B repair: -10V rail went down
Yes, I understand, just be sure you look wherever you can see them. Can you get any sense of where the smell came from? Did you see any smoke? That would be a good place to look. Burned resistors are sometimes hard to spot because they don't "carbonize" they just get a little bit darker.
The comment about cards shifting in their sockets causing the problem is a possibility, but probably a lower probability event if everything was screwed down.
The obvious approach it to look at all cards that use the -10v supply.
Cheers!
Bruce
Quoting Matt Huszagh <huszaghmatt@...>:
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"Bruce" <bruce@...> writes:
Be sure to examine the motherboard for burned traces. I didn't notice any burned motherboard traces when viewing the bottom of
the unit. Unfortunately, viewing motherboard traces from the top is a
bit tricky.
Matt
|
Re: HP 8566B repair: -10V rail went down
Thinking of fuses, a 1 amp fuse doesn't blow at 1.1 amps.
Certainly Chemical fuses (resettable) say may blow in 30 seconds at 2 amps, maybe 5 seconds at 4 amps, and almost immediately at 10 amps.
Since regular fuses may well behave similarly, that 5 amps may be an OMG rating, (if it was the correct fuse in the first place).
With a current limited supply (highly recommended), I'd have started out at, say 100ma, then gone up by increasing the current limit.? Note that you can thoroughly confuse some of the circuitry by doing this, so it's a bit iffy.
Otherwise, say setting it an an amp, then two amps, etc, may give you a better idea of how the circuit is behaving.
All a bit dicey, though, depending on the equipment.
Harvey
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On 1/17/2022 6:15 PM, Matt Huszagh wrote: "Radu Bogdan Dicher" <vondicher@...> writes:
That said, I find an intermittent header contact - or any other contacts -
much more likely a source of intermittent behaviors of the circuit. I'd
typically clean up such things with 99.99% pure IPA, and then apply a
conservative amount of deoxit for contact conditioning (most contacts
benefit from this). But be careful near plastic, as it can affect it
negatively in time.
Radu. That's what I'm thinking too. It seems possible it's a failing cap, but
it's going to be really hard to track down unless it gives me a
consistent error to diagnose, especially since the -10V rail feeds so
much downstream circuitry, and a lot of it like the YTO loop and RF
module are hard to get at.
It also seems really possible (and maybe more likely, as you mention)
that some board wasn't properly seated, or a connector was loose, or
similar, especially since it demonstrated the error after spending some
time in the trunk of a car. I did pull out and reseat a number of cards
while troubleshooting, so it's possible I inadvertently fixed the
problem. Still, I don't totally understand why this would cause the -10V
rail to disappear.
If there was a failing cap on the -10V rail I think I'd see some
ripple. But I didn't measure any.
Since I'm not inclined to pull apart the entire instrument looking for a
problem that will be hard to recognize when I see it, I think I'll
probably put the instrument back and wait for the problem to reappear to
troubleshoot. If anyone thinks this is a bad idea, please let me know.
FWIW, my supply is current-limited but I set the limit to the current
rating of the -10V fuse (i.e., 5A). I did quadruple check that I got
polarity right, so I don't think that was the problem (and my supply is
floating). I probably should have set the limit lower, but I had trouble
finding how much current that regulator should supply under normal
conditions. I'm now measuring a current draw of about 1.5A.
Matt
|
Re: HP 8566B repair: -10V rail went down
"Bruce" <bruce@...> writes: Be sure to examine the motherboard for burned traces. I didn't notice any burned motherboard traces when viewing the bottom of the unit. Unfortunately, viewing motherboard traces from the top is a bit tricky. Matt
|
Re: HP 8566B repair: -10V rail went down
Be sure to examine the motherboard for burned traces.
Quoting Matt Huszagh <huszaghmatt@...>:
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Show quoted text
Update:
I plugged in the instrument and left it long enough for the oven to warm
up. I then powered it on. No error messages appeared and the instrument
sweeps fine. I provided a few test signals to the input and they all
look good. 5 GHz, 10 GHz and 15 GHz at 0 dBm all appear as they should.
There's obviously still a problem, but it no longer sounds like my
blunder caused serious damage. I'll keep searching downstream of the -10
and -5.2V rails.
Matt
|
Hi
Yep, got a sensor, although privacy not going to be measuring many pulse signals.
Probably need to experiment to see what uses I can find for it
Steve
|
Re: HP 8566B repair: -10V rail went down
"Radu Bogdan Dicher" <vondicher@...> writes: That said, I find an intermittent header contact - or any other contacts -
much more likely a source of intermittent behaviors of the circuit. I'd
typically clean up such things with 99.99% pure IPA, and then apply a
conservative amount of deoxit for contact conditioning (most contacts
benefit from this). But be careful near plastic, as it can affect it
negatively in time.
Radu. That's what I'm thinking too. It seems possible it's a failing cap, but it's going to be really hard to track down unless it gives me a consistent error to diagnose, especially since the -10V rail feeds so much downstream circuitry, and a lot of it like the YTO loop and RF module are hard to get at. It also seems really possible (and maybe more likely, as you mention) that some board wasn't properly seated, or a connector was loose, or similar, especially since it demonstrated the error after spending some time in the trunk of a car. I did pull out and reseat a number of cards while troubleshooting, so it's possible I inadvertently fixed the problem. Still, I don't totally understand why this would cause the -10V rail to disappear. If there was a failing cap on the -10V rail I think I'd see some ripple. But I didn't measure any. Since I'm not inclined to pull apart the entire instrument looking for a problem that will be hard to recognize when I see it, I think I'll probably put the instrument back and wait for the problem to reappear to troubleshoot. If anyone thinks this is a bad idea, please let me know. FWIW, my supply is current-limited but I set the limit to the current rating of the -10V fuse (i.e., 5A). I did quadruple check that I got polarity right, so I don't think that was the problem (and my supply is floating). I probably should have set the limit lower, but I had trouble finding how much current that regulator should supply under normal conditions. I'm now measuring a current draw of about 1.5A. Matt
|
Re: HP 8566B repair: -10V rail went down
That said, I find an intermittent?header contact - or any other contacts - much more likely a source of intermittent behaviors of the circuit. I'd typically clean up such things with 99.99% pure IPA, and then apply a conservative amount of deoxit for contact conditioning (most contacts benefit from this). But be careful near plastic, as it can affect it negatively in time. Radu.?
On Mon, Jan 17, 2022 at 2:40 PM Radu Dicher < vondicher@...> wrote: Matt, I think I've seen intermittent failures with "not quite shorted" tantalum caps (maybe driven by heat?). Generally speaking, tantalums seem to either fail spectacularly - lots of smoke, sparkles, and smell - or very inconspicuously, such as this cap I recently honed into, that was bringing the entire switching supply?of a Tektornix scope I was working on into "ticking mode," and all that was visible was a tiny silver bob on its side. I saw it with a large self-lighted magnifier, as it was not visible to the naked eye. At least not mine.?
But if you got smoke during the "un-overcurrent-protected" -10V external?supplying (are you sure it was 10V lower than whatever ground you supplied it with into the circuit, externally?) I suggest a good look at the source of the smoke and see the effect on the stressed component. Hopefully, it's a solid ground from PCB to a stanoff, or something similar that may be able to take it, but it may be a component that may now fail shortly, and the bonus is it may give you information on the underlying problem.?
My bench power supply - as most of them are - is both voltage and current adjustable, so it'd never exceed a certain current into a faulty circuit.?
Good luck! Radu.?
Hey Matt,
Here's a problem I found in my IF unit:? /g/HP-Agilent-Keysight-equipment/message/89319. Apparently this is somewhat endemic there, though I only have a sample of one. I've never been into my RF unit in anger, but maybe the connector from the transformer is worth looking at critically?
Siggi
"Bruce" <bruce@...> writes:
> I agree that providing an uncurrent limited -10v was a mistake.
>
> Some suggestions:
> 1) A loose part (screw, nut, washer) that found itself a place
> shorting the -10v seems likely
> 2) A cap failure - how long was the 8566 off - long enough for the cap
> to depolarize.
I hadn't considered that first possibility. Thanks for the hint! I did
at some point measure a short across the -10V rail, but I wasn't able to
reproduce the measurement. Maybe that could be a screw sometimes
shorting the rail. Will keep an eye out.
Do failing caps ever intermittently present shorts? I've read that most
8566 failures are from electrolytics, so I'm on the lookout for
that. But I'm a bit surprised that this rail is sometimes up and
sometimes not.
> Thoughts on how to proceed:
> Isolate sections of the power distribution on the PCB -pull cards,
> pull connectors, etc.
> If something smoked, it will be either a component on a PCB or the
> motherboard (There are a few).? Or it could be a PCB trace (bad news
> if it is in a relatively inaccessible place.
>
> Hardest but most through is to remove all cards, test for appropriate
> voltages and then plug in a selection of cards.? I usually start with
> the control section (CPU, etc), then RF, then M/N, then 20/30.? Don't
> forget the front pannel, but it is easy to isolate (don't remember if
> -10v is used on FP - think it is not).
For anyone else that sees this, the A8 rectifier assembly provides a
nice list of the assemblies fed by the various power rails. For the -10V
rail, I believe all the downstream modules are:
- A19 DAC
- A20 main coil driver
- A21 FM coil driver
- A11A4 YTO phase detector
? - C3
- A11A5 sampler
? - C3
- A6 RF module
- A7A5 reference
- A16 scan generator
- A10A5 PLL2 VCO
- A10A1 PLL1 VCO
- A10A6 PLL2 phase detector
- A10A3 PLL1 IF
- A10A7 PLL2 divider
- A10A4 PLL3 up converter
- A10A8 PLL2 discriminator
and for the -5.2V rail:
- A17 positive regulator
- A11 YTO loop
- A7A5 reference
- A15 controller
- A16 scan generator
Matt
|
Re: HP 8566B repair: -10V rail went down
Matt, I think I've seen intermittent failures with "not quite shorted" tantalum caps (maybe driven by heat?). Generally speaking, tantalums seem to either fail spectacularly - lots of smoke, sparkles, and smell - or very inconspicuously, such as this cap I recently honed into, that was bringing the entire switching supply?of a Tektornix scope I was working on into "ticking mode," and all that was visible was a tiny silver bob on its side. I saw it with a large self-lighted magnifier, as it was not visible to the naked eye. At least not mine.?
But if you got smoke during the "un-overcurrent-protected" -10V external?supplying (are you sure it was 10V lower than whatever ground you supplied it with into the circuit, externally?) I suggest a good look at the source of the smoke and see the effect on the stressed component. Hopefully, it's a solid ground from PCB to a stanoff, or something similar that may be able to take it, but it may be a component that may now fail shortly, and the bonus is it may give you information on the underlying problem.?
My bench power supply - as most of them are - is both voltage and current adjustable, so it'd never exceed a certain current into a faulty circuit.?
Good luck! Radu.?
Hey Matt,
Here's a problem I found in my IF unit:? /g/HP-Agilent-Keysight-equipment/message/89319. Apparently this is somewhat endemic there, though I only have a sample of one. I've never been into my RF unit in anger, but maybe the connector from the transformer is worth looking at critically?
Siggi
"Bruce" <bruce@...> writes:
> I agree that providing an uncurrent limited -10v was a mistake.
>
> Some suggestions:
> 1) A loose part (screw, nut, washer) that found itself a place
> shorting the -10v seems likely
> 2) A cap failure - how long was the 8566 off - long enough for the cap
> to depolarize.
I hadn't considered that first possibility. Thanks for the hint! I did
at some point measure a short across the -10V rail, but I wasn't able to
reproduce the measurement. Maybe that could be a screw sometimes
shorting the rail. Will keep an eye out.
Do failing caps ever intermittently present shorts? I've read that most
8566 failures are from electrolytics, so I'm on the lookout for
that. But I'm a bit surprised that this rail is sometimes up and
sometimes not.
> Thoughts on how to proceed:
> Isolate sections of the power distribution on the PCB -pull cards,
> pull connectors, etc.
> If something smoked, it will be either a component on a PCB or the
> motherboard (There are a few).? Or it could be a PCB trace (bad news
> if it is in a relatively inaccessible place.
>
> Hardest but most through is to remove all cards, test for appropriate
> voltages and then plug in a selection of cards.? I usually start with
> the control section (CPU, etc), then RF, then M/N, then 20/30.? Don't
> forget the front pannel, but it is easy to isolate (don't remember if
> -10v is used on FP - think it is not).
For anyone else that sees this, the A8 rectifier assembly provides a
nice list of the assemblies fed by the various power rails. For the -10V
rail, I believe all the downstream modules are:
- A19 DAC
- A20 main coil driver
- A21 FM coil driver
- A11A4 YTO phase detector
? - C3
- A11A5 sampler
? - C3
- A6 RF module
- A7A5 reference
- A16 scan generator
- A10A5 PLL2 VCO
- A10A1 PLL1 VCO
- A10A6 PLL2 phase detector
- A10A3 PLL1 IF
- A10A7 PLL2 divider
- A10A4 PLL3 up converter
- A10A8 PLL2 discriminator
and for the -5.2V rail:
- A17 positive regulator
- A11 YTO loop
- A7A5 reference
- A15 controller
- A16 scan generator
Matt
|
Re: HP 8566B repair: -10V rail went down
"Siggi via groups.io" <siggi@...> writes: Here's a problem I found in my IF unit:
/g/HP-Agilent-Keysight-equipment/message/89319. Apparently
this is somewhat endemic there, though I only have a sample of one. I've
never been into my RF unit in anger, but maybe the connector from the
transformer is worth looking at critically? Interesting, thanks for the heads up Siggi. The unregulated ~18V input to the negative regulator always appeared consistent to me, and the -40V from that same assembly was never intermittent. But, I'll keep an eye on that. Matt
|
Re: HP 8566B repair: -10V rail went down
Hey Matt,
Here's a problem I found in my IF unit:? /g/HP-Agilent-Keysight-equipment/message/89319. Apparently this is somewhat endemic there, though I only have a sample of one. I've never been into my RF unit in anger, but maybe the connector from the transformer is worth looking at critically?
Siggi
"Bruce" <bruce@...> writes:
> I agree that providing an uncurrent limited -10v was a mistake.
>
> Some suggestions:
> 1) A loose part (screw, nut, washer) that found itself a place
> shorting the -10v seems likely
> 2) A cap failure - how long was the 8566 off - long enough for the cap
> to depolarize.
I hadn't considered that first possibility. Thanks for the hint! I did
at some point measure a short across the -10V rail, but I wasn't able to
reproduce the measurement. Maybe that could be a screw sometimes
shorting the rail. Will keep an eye out.
Do failing caps ever intermittently present shorts? I've read that most
8566 failures are from electrolytics, so I'm on the lookout for
that. But I'm a bit surprised that this rail is sometimes up and
sometimes not.
> Thoughts on how to proceed:
> Isolate sections of the power distribution on the PCB -pull cards,
> pull connectors, etc.
> If something smoked, it will be either a component on a PCB or the
> motherboard (There are a few).? Or it could be a PCB trace (bad news
> if it is in a relatively inaccessible place.
>
> Hardest but most through is to remove all cards, test for appropriate
> voltages and then plug in a selection of cards.? I usually start with
> the control section (CPU, etc), then RF, then M/N, then 20/30.? Don't
> forget the front pannel, but it is easy to isolate (don't remember if
> -10v is used on FP - think it is not).
For anyone else that sees this, the A8 rectifier assembly provides a
nice list of the assemblies fed by the various power rails. For the -10V
rail, I believe all the downstream modules are:
- A19 DAC
- A20 main coil driver
- A21 FM coil driver
- A11A4 YTO phase detector
? - C3
- A11A5 sampler
? - C3
- A6 RF module
- A7A5 reference
- A16 scan generator
- A10A5 PLL2 VCO
- A10A1 PLL1 VCO
- A10A6 PLL2 phase detector
- A10A3 PLL1 IF
- A10A7 PLL2 divider
- A10A4 PLL3 up converter
- A10A8 PLL2 discriminator
and for the -5.2V rail:
- A17 positive regulator
- A11 YTO loop
- A7A5 reference
- A15 controller
- A16 scan generator
Matt
|
Re: HP 8566B repair: -10V rail went down
Matt, FWIW my Wavetek 166 function generator had a flaky -5.2 V rail that dropped out after about 5 minutes after power up.? I assumed it was a cap and replaced several.? Didn't help. And after poking around a bit, I found the -5.2 V was fine on the power supply board but dropped out on the destination board.? Turns out it was a poor contact on the power supply connector.? I bent the male pin just a tad so it made better contact, and the problem has never returned.? Could be something similar in your 8566 (also got one of those myself).? HTH.? ? ? ? Jim Ford?
Sent from my T-Mobile 4G LTE Device
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-------- Original message -------- From: Matt Huszagh <huszaghmatt@...> Date: 1/17/22 1:23 PM (GMT-08:00) Subject: Re: [HP-Agilent-Keysight-equipment] HP 8566B repair: -10V rail went down
"Bruce" <bruce@...> writes: > I agree that providing an uncurrent limited -10v was a mistake. > > Some suggestions: > 1) A loose part (screw, nut, washer) that found itself a place > shorting the -10v seems likely > 2) A cap failure - how long was the 8566 off - long enough for the cap > to depolarize. I hadn't considered that first possibility. Thanks for the hint! I did at some point measure a short across the -10V rail, but I wasn't able to reproduce the measurement. Maybe that could be a screw sometimes shorting the rail. Will keep an eye out. Do failing caps ever intermittently present shorts? I've read that most 8566 failures are from electrolytics, so I'm on the lookout for that. But I'm a bit surprised that this rail is sometimes up and sometimes not. > Thoughts on how to proceed: > Isolate sections of the power distribution on the PCB -pull cards, > pull connectors, etc. > If something smoked, it will be either a component on a PCB or the > motherboard (There are a few).? Or it could be a PCB trace (bad news > if it is in a relatively inaccessible place. > > Hardest but most through is to remove all cards, test for appropriate > voltages and then plug in a selection of cards.? I usually start with > the control section (CPU, etc), then RF, then M/N, then 20/30.? Don't > forget the front pannel, but it is easy to isolate (don't remember if > -10v is used on FP - think it is not). For anyone else that sees this, the A8 rectifier assembly provides a nice list of the assemblies fed by the various power rails. For the -10V rail, I believe all the downstream modules are: - A19 DAC - A20 main coil driver - A21 FM coil driver - A11A4 YTO phase detector ? - C3 - A11A5 sampler ? - C3 - A6 RF module - A7A5 reference - A16 scan generator - A10A5 PLL2 VCO - A10A1 PLL1 VCO - A10A6 PLL2 phase detector - A10A3 PLL1 IF - A10A7 PLL2 divider - A10A4 PLL3 up converter - A10A8 PLL2 discriminator and for the -5.2V rail: - A17 positive regulator - A11 YTO loop - A7A5 reference - A15 controller - A16 scan generator Matt
|
Re: HP 8566B repair: -10V rail went down
"Bruce" <bruce@...> writes: I agree that providing an uncurrent limited -10v was a mistake.
Some suggestions:
1) A loose part (screw, nut, washer) that found itself a place
shorting the -10v seems likely
2) A cap failure - how long was the 8566 off - long enough for the cap
to depolarize. I hadn't considered that first possibility. Thanks for the hint! I did at some point measure a short across the -10V rail, but I wasn't able to reproduce the measurement. Maybe that could be a screw sometimes shorting the rail. Will keep an eye out. Do failing caps ever intermittently present shorts? I've read that most 8566 failures are from electrolytics, so I'm on the lookout for that. But I'm a bit surprised that this rail is sometimes up and sometimes not. Thoughts on how to proceed:
Isolate sections of the power distribution on the PCB -pull cards,
pull connectors, etc.
If something smoked, it will be either a component on a PCB or the
motherboard (There are a few). Or it could be a PCB trace (bad news
if it is in a relatively inaccessible place.
Hardest but most through is to remove all cards, test for appropriate
voltages and then plug in a selection of cards. I usually start with
the control section (CPU, etc), then RF, then M/N, then 20/30. Don't
forget the front pannel, but it is easy to isolate (don't remember if
-10v is used on FP - think it is not). For anyone else that sees this, the A8 rectifier assembly provides a nice list of the assemblies fed by the various power rails. For the -10V rail, I believe all the downstream modules are: - A19 DAC - A20 main coil driver - A21 FM coil driver - A11A4 YTO phase detector - C3 - A11A5 sampler - C3 - A6 RF module - A7A5 reference - A16 scan generator - A10A5 PLL2 VCO - A10A1 PLL1 VCO - A10A6 PLL2 phase detector - A10A3 PLL1 IF - A10A7 PLL2 divider - A10A4 PLL3 up converter - A10A8 PLL2 discriminator and for the -5.2V rail: - A17 positive regulator - A11 YTO loop - A7A5 reference - A15 controller - A16 scan generator Matt
|
New to the group, troubleshooting HP4261A
Hi from Canada?
I have a recently acquired LCR meter, the relatively compact 4261A.
It seems to have a very quirky problem. When left overnight powered off then powered up next day it runs normally for a while. Then the display starts flickering with all manner of random digits, the sound of relays clicking is heard.
Thinking it was simply due for a recap (and one of the PSU caps did show a bulge) I ordered replacement caps from Digi-Key and replaced all electrolytic caps.
The problem seemed to go away for a short time only to return.
+12, -12 and +5 Volt rails show correct DC levels with no ripple.
I¡¯ve tried to chill this device by leaving it outside for a little while to see if temperature is a trigger. It is not.
Help?
geo
|
Re: HP 8566B repair: -10V rail went down
Update:
I plugged in the instrument and left it long enough for the oven to warm
up. I then powered it on. No error messages appeared and the instrument
sweeps fine. I provided a few test signals to the input and they all
look good. 5 GHz, 10 GHz and 15 GHz at 0 dBm all appear as they should.
There's obviously still a problem, but it no longer sounds like my
blunder caused serious damage. I'll keep searching downstream of the -10
and -5.2V rails.
Matt
|
Re: HP 8566B repair: -10V rail went down
I agree that providing an uncurrent limited -10v was a mistake.
Some suggestions:
1) A loose part (screw, nut, washer) that found itself a place shorting the -10v seems likely
2) A cap failure - how long was the 8566 off - long enough for the cap to depolarize.
Thoughts on how to proceed:
Isolate sections of the power distribution on the PCB -pull cards, pull connectors, etc.
If something smoked, it will be either a component on a PCB or the motherboard (There are a few). Or it could be a PCB trace (bad news if it is in a relatively inaccessible place.
Hardest but most through is to remove all cards, test for appropriate voltages and then plug in a selection of cards. I usually start with the control section (CPU, etc), then RF, then M/N, then 20/30. Don't forget the front pannel, but it is easy to isolate (don't remember if -10v is used on FP - think it is not).
Fun times are afoot :-)
Cheers!
Bruce
Quoting Matt Huszagh <huszaghmatt@...>:
toggle quoted message
Show quoted text
Hello,
I've got an HP 8566B that was functioning correctly. However, after
moving to a new apartment, it stopped working.
The first thing I did was to check the power rails. Sure enough, the
-10V rail showed 0V across it. I probed different points on the negative
regulator. This seemed to be functioning correctly: the opamp had a
diode forward voltage drop across it's inputs and was driving the output
to about 17V. The voltages at A23Q1 (the darlington that provides
current for this rail) were C=17V, B=1.6V and E=250mV. However, the
voltage across the current sensing resistors was only about 250mV (so
the current through them was about 600mA). I believed this meant A23Q1
wasn't able to source enough current and was therefore the faulty
component.
My next move, in retrospect, I believe was stupid. Thinking this
transistor was at fault, I attempted to supply the -10V externally. The
unit began to smoke and smell burnt and I pulled the power.
Now if I turn on the unit, the -10V rail sometimes comes on and other
times does not. Unfortunately this makes it a bit tricky to diagnose
since I can't just pull assemblies until the supply comes back up.
Thoughts on how to proceed? I'm concerned I did some serious damage
supplying external power.
Thanks
Matt
|
Thank you, Greg. I transposed the 3 and 8, so I gave info for -2803
diodes. Similar enough for most cases, probably, but ain't the same.
Greatly appreciate the correction!
As to the mismatch criteria, do you happen to have those values? You
list the test conditions (thanks!), but not the allowed limits.
--Cheers,
Tom
--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
On 1/17/2022 10:08, Greg Muir via
groups.io wrote:
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Just some additional information
The individual diodes for this pair are found under part number
5082-2303.
HP
crosses that diode directly to a 1N5167.
?
5082-2303
diode specifications:
??????????? Minimum
breakdown voltage VBR (V): 20
??????????? Minimum
forward voltage VF (mV): 400
??????????? VF
= 1V Max at forward current IF (mA): 35
??????????? Maximum
reverse leakage current : IR (nA): 500 at VR
(V): 15
??????????? Maximum
capacitance CT (pF): 1.0
??????????? ???????????
5082-2308
diode pair matching test conditions:
¦¤³Õf
at If = 0.75V at 20 mA
¦¤°äo
at f = 1.0 MHz
Greg
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