A500+ battery damage repair questions on U12 chip

[Groppo91]

I am in the middle of checking continuity around the battery damage on an a500+ and have a question around chip U12.

I thought things had been going well found two bad traces so far from testing the U12 chip. I found a potential 3rd but I am not sure if it is a problem.

PCB explorer when you select U12 pin 19 shows a line to U12 pin 1 and effectively everything that pin 1 goes to. However when I put the prongs on for continuity I get no beeps between U12 pin 19 and any of the points including pin 1.

Does anyone know if I should be getting continuity or forgive me if this is a noob question could this be some kind of data line with no continuity until data is flowing?

I'm getting mixed results from sources online and do not have a known working board to check against.

[rubber_jonnie]

Looking at the schematic it does look like pin 1 connects to pin 19. I'm assuming at this point you've removed the IC from the board, if not then you probably should as there may be corrosion underneath the IC.

I would suggest cutting the legs high up on U12 and removing each leg individually, as the IC may be compromised so worth replacing anyway. That's the safest removal method as the traces may be fragile due to corrosion.

It's very possible that there is corrosion damage internally to one or both of the vias at those pins due to battery goop. Once neutralised with white vinegar and cleaned up with IPA you can install a socket and just use a bodge wire on the underside to restore the connection between the pins. They are output enable pins on the IC so quite necessary.

I'd also check connectivity to R113 as that also connects to pin 1 across the underside of the board.

[Groppo91]

Looking at the schematic it does look like pin 1 connects to pin 19. I'm assuming at this point you've removed the IC from the board, if not then you probably should as there may be corrosion underneath the IC.

I would suggest cutting the legs high up on U12 and removing each leg individually, as the IC may be compromised so worth replacing anyway. That's the safest removal method as the traces may be fragile due to corrosion.

It's very possible that there is corrosion damage internally to one or both of the vias at those pins due to battery goop. Once neutralised with white vinegar and cleaned up with IPA you can install a socket and just use a bodge wire on the underside to restore the connection between the pins. They are output enable pins on the IC so quite necessary.

I'd also check connectivity to R113 as that also connects to pin 1 across the underside of the board.

Thankyou, I did notice the connection to R113 I know pin 1 tests fine to it but 19 had no connection.

I am going to take everyone's advice and remove. I did order new IC and sockets as was expecting this to be the case after reading around online. Just good to know that there should be connection from pin 19.

I have done two vinegar scrubs on the board and water green didn't shift I have bought replacement components for such as resistors, caps and diodes.

Overall the board visually isn't bad and I am determined to get this back to life 😅

[rubber_jonnie]

Looking at the schematic it does look like pin 1 connects to pin 19. I'm assuming at this point you've removed the IC from the board, if not then you probably should as there may be corrosion underneath the IC.

I would suggest cutting the legs high up on U12 and removing each leg individually, as the IC may be compromised so worth replacing anyway. That's the safest removal method as the traces may be fragile due to corrosion.

It's very possible that there is corrosion damage internally to one or both of the vias at those pins due to battery goop. Once neutralised with white vinegar and cleaned up with IPA you can install a socket and just use a bodge wire on the underside to restore the connection between the pins. They are output enable pins on the IC so quite necessary.

I'd also check connectivity to R113 as that also connects to pin 1 across the underside of the board.

Thankyou, I did notice the connection to R113 I know pin 1 tests fine to it but 19 had no connection.

I am going to take everyone's advice and remove. I did order new IC and sockets as was expecting this to be the case after reading around online. Just good to know that there should be connection from pin 19.

I have done two vinegar scrubs on the board and water green didn't shift I have bought replacement components for such as resistors, caps and diodes.

Overall the board visually isn't bad and I am determined to get this back to life 😅

All I'd say is that sometimes you need to leave the vinegar in place a little while before it breaks down the battery goop. You should see it fizzing. Fingers crossed you've got away with it, but do be careful, I have an Archimedes A5000 and I missed some battery goop that caused it to fail a 2nd time, so do be thorough.

[Groppo91]

Oh cool good to know I didn't really leave it on for too long.

[Steve_w]

I have repaired many A500+ boards, 100% pin 19 needs continuity to pin1 on U12, and pin 19 and 1 should have continuity to R113.

1. Is there battery damage around the group of resistors and cap between Gary and the Battery?
2. Is there any battery damage on the traces between U12 and the battery as these often get the full force of the leaked battery and are corroded through.
3. if above is yes and you see dark spots/marks on the traces scratch off the solder mask with fibreglass pen or small screwdriver, clean the dark spots with vinegar and a fibreglass pen, test continuity and if ok apply solder mask (leave board in the sunlight outside for about 5 minutes for it to totally harden). If the trace is broken then either fix inline with wire and cover with solder mask or put a fix wire underneath.
4. To test U12 I normally use Amiga PCB explorer, To test the data traces, test continuity from one end of the trace to the other, in the case of U12, D15 to D8 on the CPU (pins 54 to 61) with one probe and the other probe on U8 (even CIA) on pins D15 to D8 (pins 26 to 33). Next test the DRD traces between the DRD15 to DRD 8 on U4 (Denise) (pins 40 - 47) and the pins on U12. The only other pins on U12 now to test are 19 and 1, as already discussed, pin 10 ground and pin 20 VCC.
5. I would test the other chips in the data path (u10,u11,u13) in the same way. Then test every pin from Gary and all the traces around the battery (again Amiga PCB explorer is your friend here)

Good luck.