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Classic II Logic board issue

MegaImg

Active member
I have in my hand 2 logic board of Classic II with the blue wire on them, I alredy recap both of them and clean them....but when I try to test them on my working unit, black screen, no bomb but costan energizing of the speaker. Example Some Kind of sound........silent.....sound....


Any ideas of what is the issue with this logic boards....maybe someone had the same behavior before.....

Thanks
 

joshc

Well-known member
Has the DFAC/ASC (Apple sound chip) been cleaned and traces checked?

Can you post some photos of the boards?
 

MegaImg

Active member
Has the DFAC/ASC (Apple sound chip) been cleaned and traces checked?

Can you post some photos of the boards?
Added the photos... no damage traces that I can tell.... Customer don’t know if the boards work neither....so trying to figure it out was wrong with them.
 

jajan547

Well-known member
Two things the RAM and Sound Chip areas can be greatly affected by leaking caps even on a clean board a trace can be bad. You say both boards have the same black screen issue? Also you're positive this 100% works with a good board but only experience this with these two boards?
 

MegaImg

Active member
Two things the RAM and Sound Chip areas can be greatly affected by leaking caps even on a clean board a trace can be bad. You say both boards have the same black screen issue? Also you're positive this 100% works with a good board but only experience this with these two boards?
The tested the memory of my working board in both logic board. So again, my board with memory work great...this 2 logicboard, same behavior....
 

joshc

Well-known member
Those boards do indeed look very clean. Let's not make assumptions about what might or might not be good or bad, you'll need to do some actual diagnosis using the schematics.

The only obvious thing I noticed on the second pic, two legs of the 68030 could be touching - check that isn't the case.

1655792042019.png

What happens if you press the reset button with these logic boards? Does it interrupt the sound from the speaker?

Also, what hapens if you plug in headphones, can you hear anything different from that?

Classic II schematics attached. Page 8 has the pinout for the DFAC (Apple sound chip) - things there have to check out because the DFAC is part of the startup circuit.

Check if the RESET line is stuck low, if it is, you won't get any video at all.

The other important part to check is U10 (Egret) - a Motorola microcontroller with Apple code that is responsible for some housekeeping startup/shutdown routines on these machines. It is shown on page 1 of the schematics.

The issue has been covered before, see here:


They had to pull and resolder the Egret before the RESET line would come unstuck. I've had to do this before on Classic II boards as well.

The other thing I'd suggest, using the schematics, is lots and lots of checking of traces and vias - if any are bad, it could lead to the problem.
 

Attachments

  • Macintosh Classic II Schematic (bomarc).pdf
    4.5 MB · Views: 5

imactheknife

Well-known member
If you have any luck, please let me know. I have same board. I have lines on screen which are better after recap, static in speakers. Dim screen though..
 

bibilit

Well-known member
Classic II boards... often the Egret is contaminated (i agree with joshc) and won't work without a thorough removal and cleaning.
 

jajan547

Well-known member
Those boards do indeed look very clean. Let's not make assumptions about what might or might not be good or bad, you'll need to do some actual diagnosis using the schematics.

The only obvious thing I noticed on the second pic, two legs of the 68030 could be touching - check that isn't the case.

View attachment 42989

What happens if you press the reset button with these logic boards? Does it interrupt the sound from the speaker?

Also, what hapens if you plug in headphones, can you hear anything different from that?

Classic II schematics attached. Page 8 has the pinout for the DFAC (Apple sound chip) - things there have to check out because the DFAC is part of the startup circuit.

Check if the RESET line is stuck low, if it is, you won't get any video at all.

The other important part to check is U10 (Egret) - a Motorola microcontroller with Apple code that is responsible for some housekeeping startup/shutdown routines on these machines. It is shown on page 1 of the schematics.

The issue has been covered before, see here:


They had to pull and resolder the Egret before the RESET line would come unstuck. I've had to do this before on Classic II boards as well.

The other thing I'd suggest, using the schematics, is lots and lots of checking of traces and vias - if any are bad, it could lead to the problem.
I agree with this I didn’t mean the on board RAM or DFAC were necessarily bad but more so that cap goo could’ve gotten under them as they are closest to that cluster. Absolutely agree that the EGRET can cause issues I had a similar situation in an LC520 board, the computer would give similar results so even after recap I removed the EGRET, removed old solder with some wick, applied new solder and the EGRET. I’ve had no issues since.
 

MegaImg

Active member
Check the CPU pin, none are touching, maybe artifac of the photo....One of the board Re-Solder the EGRET because it was contamidated but I test continuity before and for me it was working....but just in case. Remove the reset and interrupt push siwtches and deoxit them, one of them look like it was stock in close mode....so will test soon, will let you know!
 

imactheknife

Well-known member
Check the CPU pin, none are touching, maybe artifac of the photo....One of the board Re-Solder the EGRET because it was contamidated but I test continuity before and for me it was working....but just in case. Remove the reset and interrupt push siwtches and deoxit them, one of them look like it was stock in close mode....so will test soon, will let you know!
How do you check continuity of egret etc. I have multimeter, just dont know the process of that and check capacitors continuity.. thanks in advance, mark
 
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