I have decided to sell one of my Keithley 225 Current Sources.
http://www.ebay.com/itm/-/171854956041?I purchased one of these very nice Keithley 225 current sources off of eBay some months ago. The unit I purchased (not this one), had been virtually destroyed by the university that previously owned it. Because the electronics portion of the restoration was going to be so challenging, I purchased a second unit (this one) to use as a known working reference while troubleshooting. I ended up restoring the first Keithley 225 that I purchased without needing to resort to using this one as a reference. So I cleaned it up, replaced some old caps, and am now selling it. The unit I am selling is 99% original parts, and is NOT the one that required extensive repairs. I've decided to keep the one I put all the repair work into, even though it's not in cosmetically good a shape, because I am quite proud of the fact that I got that one working
Here is a list of what I've done to this unit:
- Replaced an old crumbling / cracked power cord.
- Replaced the two main DC filter capacitors, which were still the original leaky paper ones.
- Replaced a polyester film capacitor that was buzzing.
- Added an AC filter cap across the secondary winding that powers the output (this is a small enhancement that lowers output ripple and improves performance above the original specs).
- Cleaned all switch contacts with De-Oxit red and re-lubricated with De-Oxit gold. Switch bearings were lubricated with grease.
- Calibrated, tested, and verified all functions.
- Cleaned case and PCB, polished chrome on handles, replaced outside case screws, repainted top cover.
This is a great current source, and is featured in several of Dave's videos. The repair thread on the other unit (not the one for sale), including links to the manual and my annotated schematic, can be found here:
https://www.eevblog.com/forum/repair/keithley-225-(current-source)-repair/