HP 6038A DOA, troubleshooting, FIXED

[valley001]

Hi all,

Just a quick update.

My 6038A seems to be working.  C20 on the HPIB board was a dead short and I replaced the X cap on the main board.  I also replaced all of the other electrolytics on the daughter boards as well as C20 and 21 on the main board.  All of the other caps I removed tested perfectly, I had expected one or two others to be at least marginal but they all showed very good capacity and low ESR.  Go figure. 

I have not run it up to 10 amps yet but I put a lead acid on it limited to 5 amps and it happily obliges (charging a smaller batt in the pic below).

Thank you all for your help with this. Cheers everyone. 

[alm]

Congratulations on the repair! Maybe you already know this, but it's recommended to use protection, like a series diode rated for the current, when charging batteries using a bench supply. If the power supply loses power, for example because of a power outage or a breaker tripping, the battery will force power into the power supply, and reverse-bias some junctions.

Also, if you'd turn down the voltage with the battery connected, the active downprogrammer, which I believe this power supply have, will try to discharge the battery. The over voltage crowbar may short the battery when tripped. Depending on the size and impedance of the battery, this can produce some fireworks.

[Jay_Diddy_B]

Hi group,
I just finished working on a very similar power supply. I was working on the HP 6033A, this is a 20V 30A 200W unit.

These pictures will look very familiar to valley001. You almost have to remove every screw in the unit to get the main board out.




and




I replaced the Rifa Y capacitors and while I was there I replaced the 1000uF 50V axial electrolytic capacitors.

These parts should be common between the 6033A and the 6038A.

Parts used

Code: [Select]

HP 6033A Capacitors



Description QTY MFG Part No. Digikey

CAP FILM 2200PF 20% 1.5KVDC RAD 2 B32021A3222M289 495-5035-1-ND

CAP FILM 4700PF 20% 1.5KVDC RAD 2 PHE850EA4470MA03R17 399-5417-ND

CAP FILM 10000PF 1.25KVDC RAD 2 PHE850EB5100MB04R17 399-5419-ND
CAP FILM 10000PF 20% 1.5KVDC RAD or 2 B32022A3103M289 495-4916-1-ND

CAP ALUM 1000UF 20% 63V AXIAL 2 MAL213818102E3 4249PHBK-ND



Regards,
Jay_Diddy_B

[valley001]

I left the original Y caps in mine for now, didn't want to spend the money until I was sure I had a working unit but boy is it a pain to get that main board out!  Also, those transformers weigh a ton so some care is needed when handling the PCB to avoid damage from the unsupported weight.  Ill probably do the Y caps when I find a suitable quiet replacement for the fan.  I also missed an electrolytic cap on the power mesh board.   

I did NOT know about the use of a diode but that makes sense.  Ill scrape through the parts bin and see if I can muster up something appropriate.