Mac SE (M5011) died after a week of working: chaotic lines on screen, no chime, HALT/RESET stuck at ~0 V, battery leak damage

[MacHack]

Hi all,

I have a Macintosh SE (M5011) with battery leak damage that stopped booting. Does anyone know what this is and how to fix it?

HISTORY

- Bought used. It worked normally for about a week, then one day it simply wouldn't start anymore. It had been left plugged in with the power switch off.

- I recapped the logic board and the PSU after it died, so the recap isn't the cause.

- The PRAM battery had leaked. The pad around the battery's + contact is completely eaten away: there is just a hole through the board there. So far I've only cleaned with isopropyl.

SYMPTOM

- The screen shows a raster with chaotic lines. No chime, no beep at all.

- 68000 pins 17 (HALT) and 18 (RESET) sit at about 0.01 V right from power-on.

- When I applied +5 V through a 1 kOhm resistor directly to the RESET pin of the 68000, it still stayed at 0.

WHAT I'VE CHECKED (multimeter)

- +5 V and GND at the CPU are fine.

- No short to ground on the RESET net with power off.

- R13 (1k pull-up) is good and properly connected.

- SND (343-0045-B): pins 5 and 6 are not shorted. Pin 6 reads about 45 Ohm to +5 V, which matches R4 = R3 (47 Ohm) on the Bomarc schematic. The reset button itself works.

- VIA pin 34, /BERR and BBU pin 38: no shorts.

- Address and data bus continuity between the CPU and both ROM sockets is good. /DTACK, /AS, /UDS, /LDS, r/W and /CE are good too.

Has anyone seen this before? Any idea what it is and how to fix it?

Thanks! Photos of the screen pattern attached (sorry for the quality)

 

[nilobject]

the bots are pretty good at electronic stuff, just don't blindly follow their instructions.

Mac SE port pinouts

The important clue is that RESET and HALT are both being actively held low, despite there being no hard short to ground. On the SE, /RESET and /HALT are directly tied together, so the CPU cannot do anything until that line is released.

The bots will find threads with similar problems:

https://tinkerdifferent.com/threads/macintosh-se-checkerboard-pattern-with-random-speckled-dashes-no-boot-chime.5457/

I found a very relevant SE repair case from this year with essentially the same symptom. The eventual fault was the Sony/Apple SND 343-0045-B reset circuit being loaded through its pin-6/reset-switch branch, rather than a simple short to ground.

Macintosh SE/30 Troubleshooting

Fault-finding for the Macintosh SE/30. Apple's symptom charts in the Macintosh SE/30 Service Source work down to the module (logic board, analogue board, power supply...

wiki.retrotechcollection.com

1. SND 343-0045-B / its reset circuitry
2. Corrosion/leakage around the reset network or a damaged via
3. VIA actively loading /RESET
4. Less likely at this point: ROM/RAM/GLU etc.

The chaotic raster isn't particularly useful for distinguishing these — the video circuitry can produce a raster even while the 68000 is permanently held in reset. That's why you can have video but absolutely no chime or CPU activity.