Macintosh Classic no sound after recapping board

[blusk]

Hey guys,

I am repairing a macintosh classic and cannot get the sound to work.

Steps taken to resolve the issue:

1. recapped both the logic board and analog board. This fixed some display issues I was having. The Macintosh boots off of the rom just fine and all other functions appear to work. When recapping the logic board there was some corrosion of the pads but I was able to clean the dirty pads and revive them pretty well.

2. cleaned the logic board with 99% isopropyl alcohol

2. adjusted the voltage pot and have +12.1v on the 12v rail and +4.99v on the 5v rail

3. measured the resistance across the speaker and got 62.1 ohms which seems to indicate the speaker itself is working. (the speaker is rated at 63 ohms)

I have attached photos of the analog board and the logic board below. I am really scratching my head on this problem. I get no sound whatsoever. Maybe the sound chip itself is bad? Although, I have heard this rarely goes bad and if it does it usually causes other issues as it is tied in with the reset circuit. At this point, I am pretty sure I have read every other forum post on this issue and I still cannot seem to solve this problem. 

 

[rplacd]

This is not advice on fixing the board, but a headsup (that you might not need) – I think your board has riser socket for a Macintosh Classic accelerator upgrade! Do you have an accelerator card? If you call the folks at what used to be MicroMac (https://forums.macrumors.com/threads/old-mac-accelerators.1606496/), they might be able to sell you a '30 + FPU accelerator card without the socket

If you don't end up needing it, I'd love to buy it off ya.

 

[blusk]

I actually did not know that! I don't have an accelerator card. I am actually trying to fix this machine for a friend so unfortunately I can't sell it to ya. :-/

 

[bibilit]

Hard to say from the picture, but the sound chip is probably contaminated by fluid goo. 

Pins looked corroded. 

Chip is located near the reset switch

 

[blusk]

Yeah, I think I would agree with you. I think I am going to try and clean the board some more.

 

[bibilit]

Often the best option is to remove the chip, clean underneath and put it back. 

Best way to be sure traces are ok. 

 

[blusk]

up to this point I have only cleaned the board by using a q-tip with isopropyl alcohol. I was thinking about removing the capacitors (again) and then using some distilled water and submerging the board as well as scrubbing it with a toothbrush and letting it soak for some time? I am not sure that I can remove the sound chip without damaging it.

 

[rplacd]

I actually did not know that! I don't have an accelerator card. I am actually trying to fix this machine for a friend so unfortunately I can't sell it to ya. :-/

No worries, give them my compliments for having something cool!

Does listening through the audio-out port work?

 

[bibilit]

Hot air station is the only way to remove properly the chip. 

 

[IlikeTech]

As someone said, try plugging in headphones.  If the switch in the jack is stuck that might help, even though it's probably a corroded chip like bibilit says.  If the headphone sound does work, try spraying contact cleaner in it and unplug and replug the cable a few times.