I got an Amiga 4000 to do the short fix for a ZZ9000 and some audio problems.
Can we call it audio?
Lets see what the problem is with the audio area..
I use a 500Hz test frequency, and that doesn’t look good.. missing bottom..
hmm.. lets see..
Both +12V & -12V on the opamp are good, so that’s not the problem. Replaced both 220uF caps (they were placed in wrong polarity, silkscreen is not good on the A4000 rev D). By replacing those two caps the problem still existed, so removed the next thing to go.. C403.. Ahhh… that’s the problem..
It came from the board like this.. time to replace that one.
Lets see.. audio good or not?
Yes audio is good again!
After I did the ZZ9000 & audio fix, I inspected the board..
This is a picture taken under one of the SIMM sockets.. THAT DOESN’T LOOK GOOD.. LOOKS LIKE BATTERY (Alkaline) LEAKAGE ..
I took my blacklight to see if there are more traces affected by the acid..
As you can clearly see there are some trace that are more black then other ones, that indicates they are affected by the acid..
I have to do some cleaning I guess..
When removing U177 one trace came loose..
So added a small wire to fix that.
Fixed the bad traces and covered them with nail polish.
All or nothing..
I agreed with the owner of the board to replace all SIMM sockets, so they are all equal and better quality (non plastic clips), so I removed all the sockets.
New sockets, a new U311 (7404) and a new U177 (HCT174).
Hmmm.. that’s not good.. That should be 16MB of FASTRAM.. Let’s see..
No connection between Bank 3 (U851) & Bank 2 (U850) signal D27.