Electronics > Repair

Keithley 225 - Transformer wanted (or replacement advice)

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705jas:
Hi All

I have a Keithley 225 that I think is otherwise in good condition but unfortunately, I get no voltages out of the transformer at all.  Looks to have been butchered at some time in the past??  I am looking for a replacement either new or second-hand.  If someone can advise on a suitable substitute that would be great.  Any help appreciated.

cheers...Allan

james_s:
Do you know the specs of the transformer? I assume from what you've said that the primary is open? Have you looked to see if there's a thermal fuse? I've repaired several transformers that had the thermal fuse blown by a power surge.

alm:
The transformer will very likely have a grounded shield between primary and secondary to reduce capacitance to ground (check the schematics). In that case replacing it with a generic transformer would probably degrade performance. I'd try to fix the existing transformer first.

wishboneash:
I had removed the transformer from my 225 when I thought I had destroyed it. It turned out to be fine. I measured the voltages on the windings while it was out. Attached a picture with some voltage details. I am not sure about the currents, but conservatively I would think it should be around 200mA on the high voltage windings and less than 100mA on the low voltage windings. I put up a video on Youtube (https://youtu.be/UovNGGD8vFE) on the work I did to make it functional again. Most of the problems were created by me due to carelessness or overstressing the instrument. Anyhow, it's working again although quite heavily modified from the original! I have a few more tweaks to do bring it up to original specs.

705jas:
HI guys

thanks for the replies.  i have donated the unit to Ian Johnston so he may end up posting a video about it.  All a bit beyond me, unfortunately.  Know your limits and stay well under them i say  :horse:

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