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Diagnosing a Plus that won't turn on

EvieSigma

Young ThinkPad Apprentice
I have a Plus (that was converted from a 128k) that doesn't power on at all. Where can I probe with my multimeter to see if the power supply is putting out any voltage?

 

IlikeTech

Well-known member
The connector that connects to the logic board on the analog board side.

Attached is the pinout of that connector.

IlikeTech

Screen Shot 2019-03-02 at 7.15.48 PM.png

 

EvieSigma

Young ThinkPad Apprentice
Thank you, that is exactly what I was looking for! I'm thinking something in the power circuitry is toast as literally nothing happens when you flip the power switch. The CRT heater doesn't even come on.

 

EvieSigma

Young ThinkPad Apprentice
Took almost a month to get back to this but sure enough, I have basically no voltage on the +5, -12, and +12 lines, literally less than a volt. Bad power supply?

 

Ildefonso

Member
I solved a similar problem in my mac plus changing the R46 resistor (look at Larry Pinas “The Dead Mac Scrolls”, page 23)

 
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