HP 3611A - wrong current set pot and raised cap

[JustSquareEnough]

Hello,

I picked up an HP 3611A off ebay. when testing the voltage control was within spec but found that the current would only adjust to about half of spec for both the .85A and 1.5A ranges.  upon further investigation it looks like r19, which should be a 10k 5 turn pot, was replaced with a single turn pot, I did not check its value! So, I'll be ordering a new pot for this unit and that should clear that up, very strange.

my question though, I also see a capacitor with a raised vent, should I go ahead and replace it or should I replace the pot only and see if measurements are in spec under load?

Thanks!

[singapol]

The cap should be replaced as it's not normal...something changed.

[JustSquareEnough]

I finally got around to repairing this. Turns out the pot was the right value, 10k but was not a 10 turn as it should be. So the raised and by repair time leaking capacitor was causing the issues with not getting the upper limit on the current limit control.  I recorded a video and put a few pictures on my blog if any one cares to watch 

although it was pretty easy diagnostic it was still a fun repair, and it was my first 





website: http://justsquareenough.com/Electronics/HPE3611ARepair

[anotherlin]

Hey, I just watch the video, nice !

As for your question about the 35V vs. 50V rated capacitors on the schematic vs. the actual device.
My guess is that when the schematic was drawn, the 470uF wasn't available at 35V or rather, they've just made a mistake, drawing 470uF instead of 330uF. For the design at hand, 330uF is probably more than sufficient, not much current is to be drawn from the +/-12 rails. Also, the AC voltage shouldn't be higher than 20VAC, so a 35V is perfectly adequate with much than enough safety margin.

As for testing the current limiting, why don't you just short your DMM in ampmeter "mode" ?

[bitseeker]

Congrats on your first repair, JustSquareEnough. Warning, it can be addictive.