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54645D Power Supply Board (0950-2735)

Question asked by mccarthyda on Feb 1, 2010
Latest reply on Jun 28, 2013 by mattislind

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I have a 54645D scope that appears to have a dead power supply board (plug unit in, turn it on and nothing happens, the fan does not spin, and nothing appears on the screen). I don't know the history of the unit and I don't know when it stopped working and what happened to cause it to stop. The part number for the power supply is 0950-2735. I know this power supply board is used in the following products: 54615B, 54615T, 54616B, 54616C, 54645A, 54645AN, and 54645D. I am looking for a schematic for this supply board to try to troubleshoot it. I would also be interested in a source to purchase a new (or used) power supply board from. Also any tips you might have on troubleshooting this board would be much appreciated. Thanks in advance for any information you can provide.

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whitewing Feb 4, 2010 3:26 AM

A very common failure mode of switchmode PSUs is the electrolytic in the startup circuit going leaky - as it's typically fed via a high value resistor, leakage prevents the startup supply voltage getting high enough.
Look for any low voltage (<100v) electrolytics on the mains side of the PSU and replace it/them (use 105 deg types).

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mccarthyda Feb 14, 2010 3:16 PM

Well, I replaced all the electrolytic caps on the board. No luck. I called Agilent and they don't offer any support to this board any longer. Does anyone have other suggestions or test methods to debug the board? I don't have a schematic, so if anyone has a source for a schematic please let me know. Thanks.

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Jaa9 Apr 20, 2010 1:49 AM

We have the same oscilloscope in our lab . After taking the power in pieces I found that R27 (330k) was increased in value . I replaced it and now it works again

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Zetiq Aug 19, 2010 2:47 AM

Replacing R27 (330k ) on the main power supply board fixed two of our oscolloscopes.
Very good tip!

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MHEXROBOT Mar 6, 2011 2:42 PM

I'm glad I found this thread. I also had my '54645D die on me.

Symptoms:
No lights and dead silent - not even a suspicious chirp from the power supply.
No power to secondary side electronics.
No visible damage (charred components etc.).
All ominous looking switching diodes tested fine.
No blown fuse.

The culprit:
R27 next to the big rectifier cap on the mains side was open-circuit (measured >60k in situ).

Many thanks!

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MCDM Feb 20, 2012 1:12 AM

Hi I have just fixed the power supply in my HP 54645A Scope and as has been said in some of the replies I found resistor R27 330K was faulty it had not gone high in value, it was open circuit. Replacing this fixed the problem. If I had of had one I would have fitted a 1/2watt high voltage resistor with a 500 or 600v rating.

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mansfeldt Aug 16, 2012 2:51 AM

Hi,
Thanks for using this site. I too have a 54645D an with the same error. R27 Replaced an now the scope is working again, less than 30 min for google advise and repair.
Thanks guys

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PVSed Sep 21, 2012 12:17 AM

Unfortunately, the R27 of my broken power supply is still allright.

The power supply is pumping (intermittently going on-off).

Having the schematic diagram would enable me to have a further look. Where could I get this?

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PVSed @ PVSed on Sep 24, 2012 5:04 AM

I was able to repair the board: dual schottky diode CR6 was shorted. Replacing this made it work again. As a preventive measure, I will also replace some of the secondary side-elco's (as this is the same work as desoldering-testing-putting back).

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mattislind Jun 28, 2013 2:47 PM

Like PVsed my HP64616B had the CR6 shorted. Replacing that one and the capacitors to be on the safe side fixed the scope!

Thanks for the hints in this forum!

/Mattis

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10 Replies

whitewing Feb 4, 2010 3:26 AM
Mark Correct
Correct Answer
A very common failure mode of switchmode PSUs is the electrolytic in the startup circuit going leaky - as it's typically fed via a high value resistor, leakage prevents the startup supply voltage getting high enough.
Look for any low voltage (<100v) electrolytics on the mains side of the PSU and replace it/them (use 105 deg types).
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mccarthyda Feb 14, 2010 3:16 PM
Mark Correct
Correct Answer
Well, I replaced all the electrolytic caps on the board. No luck. I called Agilent and they don't offer any support to this board any longer. Does anyone have other suggestions or test methods to debug the board? I don't have a schematic, so if anyone has a source for a schematic please let me know. Thanks.
Like • Show 0 Likes0
Actions
Jaa9 Apr 20, 2010 1:49 AM
Mark Correct
Correct Answer
We have the same oscilloscope in our lab . After taking the power in pieces I found that R27 (330k) was increased in value . I replaced it and now it works again
Like • Show 0 Likes0
Actions
Zetiq Aug 19, 2010 2:47 AM
Mark Correct
Correct Answer
Replacing R27 (330k ) on the main power supply board fixed two of our oscolloscopes.
Very good tip!
Like • Show 0 Likes0
Actions
MHEXROBOT Mar 6, 2011 2:42 PM
Mark Correct
Correct Answer
I'm glad I found this thread. I also had my '54645D die on me.

Symptoms:
No lights and dead silent - not even a suspicious chirp from the power supply.
No power to secondary side electronics.
No visible damage (charred components etc.).
All ominous looking switching diodes tested fine.
No blown fuse.

The culprit:
R27 next to the big rectifier cap on the mains side was open-circuit (measured >60k in situ).

Many thanks!
Like • Show 0 Likes0
Actions
MCDM Feb 20, 2012 1:12 AM
Mark Correct
Correct Answer
Hi I have just fixed the power supply in my HP 54645A Scope and as has been said in some of the replies I found resistor R27 330K was faulty it had not gone high in value, it was open circuit. Replacing this fixed the problem. If I had of had one I would have fitted a 1/2watt high voltage resistor with a 500 or 600v rating.
Like • Show 0 Likes0
Actions
mansfeldt Aug 16, 2012 2:51 AM
Mark Correct
Correct Answer
Hi,
Thanks for using this site. I too have a 54645D an with the same error. R27 Replaced an now the scope is working again, less than 30 min for google advise and repair.
Thanks guys
Like • Show 0 Likes0
Actions
PVSed Sep 21, 2012 12:17 AM
Mark Correct
Correct Answer
Unfortunately, the R27 of my broken power supply is still allright.

The power supply is pumping (intermittently going on-off).

Having the schematic diagram would enable me to have a further look. Where could I get this?
Like • Show 0 Likes0
Actions
- PVSed @ PVSed on Sep 24, 2012 5:04 AM
  Mark Correct
  Correct Answer
  I was able to repair the board: dual schottky diode CR6 was shorted. Replacing this made it work again. As a preventive measure, I will also replace some of the secondary side-elco's (as this is the same work as desoldering-testing-putting back).
  Like • Show 0 Likes0
  Actions
mattislind Jun 28, 2013 2:47 PM
Mark Correct
Correct Answer
Like PVsed my HP64616B had the CR6 shorted. Replacing that one and the capacitors to be on the safe side fixed the scope!

Thanks for the hints in this forum!

/Mattis
Like • Show 0 Likes0
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54645D Power Supply Board (0950-2735)

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