Diagnosing a Plus that won't turn on

[EvieSigma]

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]

The connector that connects to the logic board on the analog board side.

Attached is the pinout of that connector.

IlikeTech

 

[EvieSigma]

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]

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?

 

[dochilli]

Perhaps this may help:

http://www.ccadams.org/se/classicmac2.pdf

Search for Larry Pina: Macintosh Repair & Upgrades Secrets. There you will find a lot of information about the Macintosh Plus.

I think, you need a recap of the analog board.

 

[Ildefonso]

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

 

[EvieSigma]

Where can I find schematics of the 128k analog board?