HP 6200B dc power supply repair

[resistcircuitresist]

Hey guys. I have a HP 6200b that it not working properly. It will only output ~3v with any load connected in the 20v or 40v range, but outputs full amperage (1.5amp) Not sure where to start checking for problems.

[bd139]

Service manual is here: https://www.matsolutions.com/Portals/0/Product%20documents/Agilent%20Technologies/6200B/6200B%20User%27s%20Guide.pdf

Check section 5 in there - there's a whole section on low voltage output. The last two broken HP supplies I've had were fixed by following the diagnostics flow. Very well written manuals!

[resistcircuitresist]

Looking at the test procedures and it asks for voltage between +S and A6, would i be correct in assuming that the positive probe would go to +S since it isn't outlined in the guide.
 Response for this test  is (more negative than 0v) OR (0v-.8v) and i'm getting 54mV or -54mV

EDIT: Also noticed that this board is missing a resistor @ R19, unsure if was never install from factory or if removed.  Which is listed as fxd, comp Selected 5% 3w

[resistcircuitresist]

Think i may have found the culprit.  Q4 is a listed as a  " SS PNP si"
Part # (sJ203) from HLAB
Manufacturer code (56289)
stock # (1853-0040)


Part markings -------   S (symbol I assume this is Sprague)  3-063  7046
With my negative probe on Emmiter and positive on Collector, shorting base to collector i get no reading (infinite) on diode mode.  I would assume this indicate a faulty transistor. 
Also, i'm unable to find a replacement based on the data in the document other than used parts. How do i go about sourcing a new part ?

[wictor]

Hi,

HLAB 1853-0040 HP/Agilent 1853-0040 TRANSISTOR PNP SI TO-66 PD=25W FT=4MHZ https://4gte.com/products/hp-agilent-1853-0040-transistor-pnp-si-to-66-pd-25w-ft-4mhz/

Some data http://www.parttarget.com/5961-00-421-6234_5961004216234_1853-0040.html/-41456C60-A93F-4453-9496-41217B6E9450

[resistcircuitresist]

Thanks for the info, after making the post i realized that i was testing it incorrectly, i now believe the transistor is functioning properly. Still Stuck though on the rest.

[Ordinaryman1971]

See if you have the diode that's across the terminals shorted... it's right on the front... by two big shut resistors on the front of the power supply...

[resistcircuitresist]

Thanks for all the help. I must say i'm EXTREMELY embarrassed.  I didn't understand how the CC and CV controls worked even after reading the documentation too many times to count. I have learned a great deal in the process though. It appears to be working properly, but may be a little out of calibration. 

The voltage and current limiting feature are kicking in a hair under current and under voltage, and the meter is also outputting more than rated voltage and amperage with the knobs fully cranked. Will adjusting the pots take care of this, OR is this normal function?

[bd139]

HP power supplies usually deliver a little bit more voltage and current than advertised.  As long as the meter matches the measured output with a DMM or something you’re good.

[Ordinaryman1971]

Correct, those power supplies will output way more than they are rated for. Though regulation is guaranteed only in specified range.
So... yes, you can pull more voltage out of them but it may be noisy.
I can't stress enough how great are those power supplies. Cheap, always available on ebay for very reasonable price and in so many flavors. Name the voltage and current rating and there is one...
And, such a great project if you buy it broken.
Great learning curve and extremely forgiving to screw-ups.
Also... all through-hole components.
Did I mention small footprint.....
Highly recommended for everyone with limited budget.