Killed HP 6261B power supply - Can anyone have a look at my schematic?

[Ssybert]

Hi Everyone,

I have an older variable voltage / variable current HP power supply I was using to top balance some batteries. With the power supply off, I was removing the leads and dropped one to the chassis of my RV while the other was still attached. a 1200AH LiFePo4 pack drew current through the power supply and started arcing against the chassis. I quickly pulled the wire away from the ground but it was too late.

Now, when I turn on the power supply it goes in to a dead short immediately. The current is still controlled from the front panel and as I increase it, the power supply draws a larger AC load and reflects the current increase on the meter. The voltage however stays at zero.

I opened it up and tested final power transistors and believe they are OK. I'm not an electrical engineer and really don't know how to diagnose this. I did discover that by disconnecting the base of A4Q102, the power supply powered up without any output at all. Better than being in a dead-short state I suppose.

Can anyone with power supply knowledge have a look at the schematic on page 83 of this manual and maybe offer some direction? I can do a lot of things but I know when I'm out of my league. This is one of those times.

https://www3.nd.edu/~wzech/HP_6269B_Technical_Manual.pdf

Thanks for any help anyone can offer!

Scott

 

[pvdude]

I have one of those, great PS, worth trying to save.
I would be looking over the “short circuit protection” circuit.
W/ a bright light, look for burned, damaged or discolored components.
I have seen capacitors that shorted and expanded so as to bulge the metal case.
Also give it a smell test, when the RFI circuit in mine died, it smelled up the place.

here is a vintage HP forum that might have more help:

HP-Agilent-Keysight-equipment groups.io Group

This group is dedicated to the maintenance, repair, usage, and correct operation of HP, Agilent and Keysight test equipment and accessories. It concentrates on older equipment for which support from HP, Agilent or Keysight has been discontinued, but questions about current equipment may be...

groups.io

 

[Symbioquine]

Check out https://diysolarforum.com/threads/power-supply-reverse-shorted-it-might-not-be-toast.30312/

With some help from the folks at the eevblog.com forum, I was able to fix my power supply by replacing a diode...

 

[Ssybert]

Are you talking about the crowbar circuit? This was my first suspicion based on the theory of operation in the manual but the components didn't look like they were current carrying such to be able to handle a dead short. The crowbar circuit seems to manage the driver circuits It would seem power transistors are carrying this load as they're the only thing that can take this current. Maybe I'm wrong? I'll inspect later this morning for burnt components. Thank you!

Hi Everyone,

I have an older variable voltage / variable current HP power supply I was using to top balance some batteries. With the power supply off, I was removing the leads and dropped one to the chassis of my RV while the other was still attached. a 1200AH LiFePo4 pack drew current through the power supply and started arcing against the chassis. I quickly pulled the wire away from the ground but it was too late.

Now, when I turn on the power supply it goes in to a dead short immediately. The current is still controlled from the front panel and as I increase it, the power supply draws a larger AC load and reflects the current increase on the meter. The voltage however stays at zero.

I opened it up and tested final power transistors and believe they are OK. I'm not an electrical engineer and really don't know how to diagnose this. I did discover that by disconnecting the base of A4Q102, the power supply powered up without any output at all. Better than being in a dead-short state I suppose.

Can anyone with power supply knowledge have a look at the schematic on page 83 of this manual and maybe offer some direction? I can do a lot of things but I know when I'm out of my league. This is one of those times.

https://www3.nd.edu/~wzech/HP_6269B_Technical_Manual.pdf

Thanks for any help anyone can offer!

Scott

Thank you for the suggestion! I think I may have isolated the issue to the large capacitors in parallel with the output. I ran out of time to work on it today but will pick it up again tomorrow.

Fingers crossed its just simple (large) capacitors. Those are something I can handle.