Tick Tick Tick (power supply issues)

[bradholland]

Hey Guys, 

So, my neighbour had a garage sale a week or so back, and sitting there was a mac classic II with a box of stuff to go with it. 

He only wanted $10 for it, and so of course I had to drag it home, just because.. 

Upon plugging it in in just made a ticking sound, eventually flashing the screen to the rhythm and then eventually coming up to a checker pattern. 

Reading around I have seen about the cap replacement, having a huge

stock of pretty much everything in my garage I replaced all the caps on the logic board. although this did not sort the problem out.  the checkerboard has now turned into 3 thick bars

I gave the board a good clean beforehand in the ultraosnic bath and she looks like new. 

at the hard drive power port I'm measuring 13.2v for the 12v rail and 4.5v on the 5v rail. 

If i connect the hard drive it will just tick and  flash the screen, never going solid. 

I suspect caps on the analog board, but there are quite a few.. Of course it makes sense just to change them all, but would anyone know those I might want to start with to see if i can get some life, or indeed if It might not be the caps at all?

cheers!!

Brad

 

[bibilit]

here is the information from maccaps:

http://www.maccaps.com/MacCaps/Capacitor_Reference/Entries/1990/10/15_Macintosh_Classic_Analog_Board.html

I will replace also one Optocoupler in the Analog board (CNY17 or 75) don't remember clearly but quite usual (as you are getting a voltage above expected)

 

[Ferrix97]

If replacing the caps does not solve the issue, try heating p the are where the switching IC and optocoupler are located. sometimes a bad switching IC causes this problem

 

[bradholland]

woke up this morning and recapped the psu board.. now i have life, but as it's a lot different, I'll start a new topic..

 

[mraroid]

Hey Guys, 

I gave the board a good clean beforehand in the ultraosnic bath and she looks like new. 

Brad...

I have a smaller ultrasonic cleaning machine I bought at Harbor Freight.  Not large enought for a analog or logic board.  What cleaning machine did you use?  Also, did you use just water, or a chemical as well?

Thanks

mraroid

 

[bradholland]

i have a prosonix heated bath. 

I use distilled water from the store and a rather nasty (burns your skin) electronics cleaner I can't remember what its called now as i siphoned it off from a large can on an old job. 

It smells kinda like amonia and is quite thick, a few capfuls in the water is more than enough.