Classic II occasional checkerboard, bad sound

[Ra226]

I have a Classic II with a couple of issues.  Before washing and recapping it, it would boot maybe 20% of the time, and otherwise would give a checkerboard pattern.  If it did boot, it'd run fine except for sound, which was intermittent, and terribly distorted.
 
Based on what I'd read on this forum, I washed the logic board gently (lots of hot water, using a q-tip dipped in alcohol where there was obvious buildup) and I replaced the caps.  I'm afraid I messed up C4 (a 47 uF electrolytic) and the pad separated from the track.  I tried to trace the contact back to another spot on the board, but no luck.  
 
Unfortunately, the problems haven't improved much.  Booting is quite a bit more reliable, but still not 100%, and sound is still completely messed up, though I'm pleased that C4 doesn't appear to be critical to the machine functioning.  So my remaining questions are:
 
- What does C4 do?  Is it sound related?  Is U1 an audio amp?  Any advice on getting this cap back into the circuit?
- I used MLCC caps where possible--I didn't see any reason why these wouldn't work, but are there any known issues?
- Was my washing maybe too gentle?  I've read about scrubbing and dishwashers but I was quite a bit more conservative than that
- What's my next step if I've already tried washing and recapping?
 
Thanks!

 

[360alaska]

1. Do you here good sound out of the jack?

2. I don't know of anyone having classic II wiring diagrams

3. It's near impossible to use surface mount caps for the 10uf caps on a classic II board, the pads are just to close together, it's relatively easy to use these caps for the 47 uf.

4. I think it would be best to uncap your motherboard if, figure out where that trace leads and go from there...

Also, check polarity... Good luck.. Josh

 

[Ra226]

It's distorted through the headphone jack as well.  The MLC caps I used don't have polarity, so at least I didn't need to worry about that. 

 

[360alaska]

I don't think you can't use non-polor caps where polarized caps are called for... Start over man...

 

[Ra226]

No, polarized caps can be replaced by non-polarized (though on googling, there seems to be a lot more confusion on the topic than I expected--and it's true that you generally can't go the other way around, replacing non-polarized with polarized).

The only reason polarized caps are ever used is because they're cheaper and smaller per uF than other technologies.  But recently, MLC Caps have come down so much in price that they make a viable replacement even for caps into the 47 uF range.  There's some good commentary in this thread .

I'm going to give it a more thorough washing, using soap this time, and try again to trace C4.  While it used to be checkerboard, now I get vertical stripes occasionally on boot.

 

[360alaska]

I guess you can use non-polar...

However, given that a bipolar capacitor will not have the ripple rejection properties that a polarized will I'm surprised there aren't any problems...

Maybe you got a bad new cap, it can happen...

Also: it's probably not out of the realm of possibilities that this could be an Analog board issue, maybe voltage is low, maybe a capacitor has gone bad one that guy...

 

[Ra226]

Well, now it's got the fish smell so it's probably time to look at the analog board caps...  Classic II--why you so high maintenence!??