Electronics > Repair
Bench PSU not much current limit adj range after pots replaced
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Circlotron:
I've got one of these cheapo noisy bench power supplies that I use for rough-enough-is-good-enough purposes. A while back the voltage setting was becoming unstable, jumping up and down several volts. I read somewhere that they have dodgy pots. As luck would have it, I had a big bag full of exactly suitable 10K pots that work threw out, so I replaced all four and things were back to normal, or so I thought. I was so pleased with myself... Some time later I found that the adjustment range on the current limit setting is not what it should be. Should go from zero to 5 amps, but it only goes from about 4 to 5 amps.

Now I'm *fairly* sure all four original pots were 10K but maybe they weren't. Does anyone have one of these that they could have a look? Or maybe a schematic. Haven't found a schematic on the interwebz. Seems like the same case is used with any number of different internals.
FIXITNOW2003:
only circuit i can find on this not all 10K!
Circlotron:
In the meantime I found the info that put me onto the bad pots, but it seems I didn't look too carefully. The fine adjustment pots are both meant to be 1K. It's weird that the volts setting works okay with one wrong pot but not the current setting.

Circlotron:

--- Quote from: Circlotron on October 01, 2024, 07:50:20 am ---It's weird that the volts setting works okay with one wrong pot but not the current setting.

--- End quote ---
Just now I set the coarse voltage pot to 20.0V and with the fine pot I could wind it up to 22.9V Could someone try that with their same PSU and see what the figure is?
Circlotron:

--- Quote from: FIXITNOW2003 on October 01, 2024, 06:23:27 am ---only circuit i can find on this not all 10K!

--- End quote ---
That one is a bit different to mine.
https://www.eevblog.com/forum/testgear/mch-k305d-cheap-switching-lab-power-supply/
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