Need some help getting an old Mac Plus working

[Morgan]

Hello, I'm trying to get an old Mac Plus working but I've hit a point where I don't know what to do next. The problem I'm having with the system is that it does nothing when I plug it in and turn it on.

I have been following along with The Dead Mac Scrolls until I got to page 22. I tested CR21 with my multimeter in diode mode and I got current going both ways so I assumed it was bad and replaced it, however my replacement also has the same thing going on so either I'm testing it wrong or there is something else going on that I don't know about. When I tested the old one outside of the system the current only goes one way so it looks like there is something else wrong on the board that I don't know about. Does anyone know what could be causing this or if its normal?

Other than that if there is a better way to figure out what is wrong I am all for using it, I've just been going along with this because it was all I had to go off of. 

Other than CR21, I just replaced the Rifa caps because they exploded when I first turned the computer on.

Thanks a ton for any help you can give!

 

[superjer2000]

Fuse is good?

 

[bibilit]

Analog Boards are an issue on those, pretty tricky to troubleshoot.

First thing to be done is to have a look at the Analog board for broken solder joints, common issue.

 

[Morgan]

Fuse is good?

Fuse tests ok.

Analog Boards are an issue on those, pretty tricky to troubleshoot.

First thing to be done is to have a look at the Analog board for broken solder joints, common issue.

I found some joints that didn't look to great so I fixed them up, unfortunately nothing changed when I plugged it in.

 

[omgmonsters]

On my Plus it was a few broken joints in this row near the center of the analog board - I've heard they're really common to break.

 

[Morgan]

I redid all of those joints and unfortunately nothing has changed.

 

[krishnadraws]

Can you test the voltage levels of the PSU separately? If you are getting the proper voltage levels there, check the voltage levels from the fan to ground on the analog board. Next, measure the voltages coming from the analog board to the logic board. Let us know what you find. Good luck!