Macintosh Plus burnt analog board.

[dragonpunchu]

I've recapped (240v analog board) a Macintosh Plus a year ago and everything was fine. Recently when I tried to boot it it blew its fuse. On further inspection I can see burned off pcb in C33.
I've attached photos of the carnage. Can I recover this? or is this analog board now dead?

 

[bibilit]

Can you have a look at the bridge rectifier set (CR22 to CR25) for any shorted diode ? can see anything else that can blow the fuse and burn that capacitor on the neighborhood.

 

[dragonpunchu]

Can you have a look at the bridge rectifier set (CR22 to CR25) for any shorted diode ? can see anything else that can blow the fuse and burn that capacitor on the neighborhood.

CR24 is shorted, the other ones are fine. Good call!
What diode do I need to replace this one? Kind hard to read them.

 

[bibilit]

AFAIK probably a standard unit 1N4001 or 1N4007, but the best way is to remove the bad one a have a look at the reference.

 

[dragonpunchu]

AFAIK probably a standard unit 1N4001 or 1N4007, but the best way is to remove the bad one a have a look at the reference.

I've removed it and it is a 1N4007, ordered some and will be replacing and checking if that fixes it. Thanks

 

[techknight]

I've recapped (240v analog board) a Macintosh Plus a year ago and everything was fine. Recently when I tried to boot it it blew its fuse. On further inspection I can see burned off pcb in C33.
I've attached photos of the carnage. Can I recover this? or is this analog board now dead?

View attachment 49441

View attachment 49440

You should grab a dremel tool and clean out that carbon tracking below the capacitor. This will always remain conductive to some degree and start causing you problems.

 

[dragonpunchu]

You should grab a dremel tool and clean out that carbon tracking below the capacitor. This will always remain conductive to some degree and start causing you problems.

Well spotted!

 

[dragonpunchu]

I've replaced the CR24 and the mac cameback to life with no problems! Thanks for the tips

 

[marcelv]

You could possibly also replace CR22,CR23 and CR25 as they are the same age and wear.

 

[dragonpunchu]

You could possibly also replace CR22,CR23 and CR25 as they are the same age and wear.

It's on my todo list!