Electronics > Repair
(FIXED) Keithley 225 (current source) repair
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Vgkid:
Good job  :-+
motocoder:

--- Quote from: cncjerry on June 08, 2015, 03:56:26 am ---https://www.westfloridacomponents.

They had the mosfets I needed for my 228.  I only dealt with them that one time.

I'm thinking I'll just buy another 228 though Keithley made a lot of current and voltage sources.

Glad tee someone other than me stick with a difficult restoration.

--- End quote ---

They do have some interesting, older, parts, but I don't see any match for the challenging parts in that 225. I did find that Central Semiconductor has a part, 2N3585, which is pretty much an exact match for the output transistors. Mouser carries those if you need them, although I think the NTE parts I'm using are fine. It's really just Q104 that is a challenge. Even now that I have it working, it is the one part that heats up quite a bit under operation - up to 80C when I was watching it, and that was with the case open.

I don't think I'll be buying anything else from Keithley. This thing is a somewhat fragile design. Compared to the HP precision and Power Designs power supplies, it doesn't stack up very well.

motocoder:
I've scanned in the main schematic page with my annotations. I also added some notes and a list of replacement parts that I found to work. Hopefully this will save someone some time.

I have a higher res version in Photoshop format, with the annotations on separate layers. However, it is too big to upload here. PM me if you want a copy.



TiN:
I would be happy to rehost it on my site in Keithley section, if you may upload here.
 :-+
motocoder:

--- Quote from: TiN on June 09, 2015, 12:29:37 pm ---I would be happy to rehost it on my site in Keithley section, if you may upload here.
 :-+

--- End quote ---

Thanks. They are in a folder called Keithley_225.
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