November 8, 2021 Test Equipment, Repair

Keithley 224 - Electrolytic capacitor replacement and EPROM backup

Ready to keep pumping electrons for the next 30 years

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.