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Old 30th July 2020
Lives for gear
acreil's Avatar

Originally Posted by Marshall Karr View Post
I used an infrared probe to scan KLM661 and located elevated temperatures in ICs 49-55. These ICs ma be associated with the RAM. No info in the service manual but what little I could find for free indicates they are RAM chips. Note all the chips heating up are identical. Texas Instruments SN74S189.
Those store the oscillator frequency and phase information. They get hot but it's no big deal, and a failure there wouldn't cause the problems you're noticing anyway.

I'd look for activity on various CPU bus lines. See if it's scanning the buttons, etc.