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Macintosh Plus issues with analogue board

M

Maccollector

6502
I have recently obtained Macintosh plus in a poor state . After cleaning corrosion from the analogue board , board ran fine but now it seems to be power cycling when it get hot, Some diodes are getting very hot and resistors. Are these meant to get hot or not. I have some thermal images and normal images . Here are the pictures of components getting hot. Also there is a video of what mac is doing

I read somewhere this issue with the voltages but unsure as to how to fix them
 

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I will check voltages, you are getting a clear chime, so not bad, most AB are dead and not delivering any.

Can be a bad solder joint, don’t see any hot spot either.

But those two RIFA caps should go.
 
bibilit said:
I will check voltages, you are getting a clear chime, so not bad, most AB are dead and not delivering any.

Can be a bad solder joint, don’t see any hot spot either.
Click to expand...
So those thermal images do not seem out of ordinary .. Only asking as I don't know what is getting hot. If a leave it off for a while it will boot and stay at floppy drive with question mark logo for few minutes before starts power cycling

Where and how to check voltage if you can tell me please
 
Last edited:
And for the record, 5v rail at floppy connector sits @ 4.5 but does not fluctuate during power cycle. 12v rail sits @12.01 at wholes 7 & 8
 
5 volt rail is a bit low…try to crank it up to 4,8

There is a potentiometer on the side of the AB.

Try reflowing the solder joints at the usual places.
 
bibilit said:
5 volt rail is a bit low…try to crank it up to 4,8

There is a potentiometer on the side of the AB.

Try reflowing the solder joints at the usual places.
Click to expand...
I did adjust it and it seems stable I did it without proper tools.. and it goes like this. Turn the screw, start the mac, check voltage . One thing is that my 12v rails now sits at 12,7. Does this point out to capacitor issue?
 
Give the analogue board a tap at startup, I think you've some good old dry solder joints here too. Yes, replacing the capacitors will help you here - notably the low voltage big ones (eg. the 1 x 16V 4700uF and 4 x 16V 2200uF I think it is).
 
Byrd said:
Give the analogue board a tap at startup, I think you've some good old dry solder joints here too. Yes, replacing the capacitors will help you here - notably the low voltage big ones (eg. the 1 x 16V 4700uF and 4 x 16V 2200uF I think it is).
Click to expand...
I am ordering all electrolytic capacitors, but was curios ( i did not check) what are riffa capacitors values; This is 240v board
 
Earlier boards have a huge sized 0.47uF X2 RIFA capacitor, later boards have 2 x 4700pF X2 capacitor (much smaller), both rated 250V or higher. I'm restoring several Mac Pluses at the moment and yet to find a dud 200V 100uF capacitor (the four big ones usually purple colour. There is also a large 35V 3.9uF yet to touch (and hard to source much near the same uF).
 
Byrd said:
Earlier boards have a huge sized 0.47uF X2 RIFA capacitor, later boards have 2 x 4700pF X2 capacitor (much smaller), both rated 250V or higher. I'm restoring several Mac Pluses at the moment and yet to find a dud 200V 100uF capacitor (the four big ones usually purple colour. There is also a large 35V 3.9uF yet to touch (and hard to source much near the same uF).
Click to expand...
I have some Y2 riffa caps. Will they be sufficient enough considering this machine will be turned on periodically
 
CR1 is in the flyback circuit, so mains voltage doesn't matter.
The book says 3A diodes were originally used, they should be replaced with at least 5A rated diodes.
 
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