Keithley 224 - Electrolytic capacitor replacement and EPROM backup
Judging from the date codes on the chips my 224 current source is a 1986 model. That makes it 35 years old. And although the Richey capacitors did not fail yet it is high time for a replacement.
Here is the list of capacitors to be replaced:
| Designator | Description | Digi-Key part no. |
|---|---|---|
| Display Board | ||
| C201 | 10μF, 25V | 493-12467-ND |
| Mother Board | ||
| C101 | 10000μF, 25V | 493-7297-ND |
| C103, C119, C120 | 10μF, 25V | 493-13463-1-ND |
| C117 | 330μF, 160V | 493-14440-ND |
| C121, C122 | 1000μF, 35V | 493-1322-ND |
| Analog Board | ||
| C312, C315, C316, C324, C325, C327 | 10μF, 25V | 493-13463-1-ND |
| C317, C323 | 4.7μF, 350V | 493-1437-ND |
| C330 | 1.5μF, 25V | 493-11328-1-ND |
The lead spacing of some capacitors are not a perfect fit so if you want to be a stickler for neatness you may need to check each type.
EPROM backup
The two EPROMs are easy to spot. They are socketed and have a sticker with the firmware version on them. Try to extract them gently.
To read the contents I used my TL866II. The chip is the following. If you need the files send me a message. My firmware version is B1.