HP 3610a power supply issues

[dorkshoei]

HP3610a had been working well but is now having issues

- With voltage dial turned completely counter clockwise, reading on 3610a display is negative  0.20v.  If i connect Fluke DMM it shows 17mV.

- If I turn voltage on 3610A one turn clockwise Fluke DMM quickly shows 2.0v but the display on the 3610a slowly climbs to 1.8v over 60 seconds. Takes 30 seconds to go from 1.75v to final 1.8v    Fluke shows 2.0v all this time.

I checked Fluke DMM against seperate voltage reference and its accurate.

Anyone seen similar?

[Grandchuck]

Perhaps it is oscillating.  If you search EEVblog there are some discussions about this power supply becoming unstable.

[dorkshoei]

Perhaps it is oscillating.  If you search EEVblog there are some discussions about this power supply becoming unstable.

I've seen this thread in regard to oscillation with a capacitive load: https://www.eevblog.com/forum/testgear/hp-agilent-e3610a/

But I don't think my issue is related.  Mine is acting bizarrely with no load.

This is how it's supposed to behave.  https://youtu.be/-04CQ0Mug1o?t=240

You can see Dave increases voltage from 1.98v to 8.46v.   

On mine (no load also) if you did the above:
- the display would take a minute to reach 8.46v,  slowly climbing once you stopped turning.   
- the actual output voltage would be 8.26v almost immediately after you stopped turning but the display lags
- the voltage measured by a DMM is always 0.2v less than what is displayed

[pqass]

- If I turn voltage on 3610A one turn clockwise Fluke DMM quickly shows 2.0v but the display on the 3610a slowly climbs to 1.8v over 60 seconds. Takes 30 seconds to go from 1.75v to final 1.8v    Fluke shows 2.0v all this time.

This can be the result of poor bipolar power supply regulation.
It is common for C7 and C13 caps to leak.  Look for the caps and their residue just in-front of the transformer.
See attached partial schematic and the youtube video below.

But before you clean up the area and replace the caps first check the test points for proper voltages:   
    TP1 (pos) with TP6 (neg) should be +12VDC
    TP5 (pos) with TP6 (neg) should be +5VDC
    TP8 (pos) with TP6 (neg) should be -12VDC

While you're at it, check the display power supply too:
    TP9 (pos) with TP10 (neg) should be +5VDC

When I fixed my E3611A I also had to desolder the small bridge rectifiers and pot in the area to make sure all the residue was cleaned up.  I then reflowed solder over the naked traces and broken pads.

- With voltage dial turned completely counter clockwise, reading on 3610a display is negative  0.20v.  If i connect Fluke DMM it shows 17mV.

My meter also shows a zero with negative sign when dialed all the way down CCW.
But just a fraction of millimeter clockwise shows a positive zero.
I'm not sure it's anything to be worried about; just a meter quirk.


FYI:
The full service manual is here: https://neurophysics.ucsd.edu/Manuals/Hewlett Packard/Hewlett Packard Operating and Service Manuals for HP361XA 30W Bench Series DC Power Supplies.pdf

Cap replacement howto:

[dorkshoei]

pqass  thank you, I'll do some testing and reply back

[dorkshoei]

So I took it apart ready to take some measurements.

Powered it on to start,  noticed it's now working fine.

Reattached case.  Still working fine.  Reads 0.01V at full CCW.   DMM and 3610 display are within 0.01v of each other.

~shrug~