| Electronics > Repair |
| (FIXED) Keithley 225 (current source) repair |
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| cncjerry:
Are you not able to get the actual parts? For my keithley parts I found a place called something like westfloridasupply. They shipped the old transistors I needed pretty quickly. |
| motocoder:
--- Quote from: cncjerry on June 07, 2015, 03:03:31 pm ---Are you not able to get the actual parts? For my keithley parts I found a place called something like westfloridasupply. They shipped the old transistors I needed pretty quickly. --- End quote --- I emailed Keithley before I started the repair - still no reply from them. If you know of a place that stocks the parts, can you give me a link or phone number? I searched for "westfloridasupply", but all I found was some company selling trash bags. BTW - every thing is working now, except for the power supply ripple and some oscillation. Swapping the big yellow caps out for some Nichicon 220uF helped some, but there's still what I would describe as a ridiculous amount of 60/120Hz noise, and a lower level oscillation. |
| motocoder:
There is more noise on the output then I would like, but it's not the dire situation I posted earlier. A lot of that was noise I was picking up on my differential probe. |
| motocoder:
After the clean and De-Oxit on the switch contacts, it's pretty well. Output noise is still around 60mV. I'll poke around with it and see if I can figure out the source there, but in general I am pretty happy with it. I'll prepare some notes and get a scan of my annotated schematic, so that hopefully someone else that buys one of these turkeys doesn't have to go through as much effort on the repair. (Late breaking update on noise) I soldered a 1uF film cap on the underside of the board on the +/- 130V transformer secondary. That dropped the mains noise way down. Measuring on my scope, into a 50 ohm terminator (not the one inside the scope - too scary) the peak-to-peak noise is around 14mV. RMS is 240uV. Spec in the manual says to measure it using a meter into a 10 ohm load. I can't even measure anything using that method. |
| cncjerry:
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. |
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