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Hello eifeldude! No, I have not made additional progress on this board. I plan to work on it again over the next coming weeks. I'll keep you posted. Let me know if you make any progress as well. litriSE

I pull the last three remaining chips in the jellybean section - 74LS257 U2G, 74LS393 U1F, 74LS393 U1G. The 74LS257 in U2G was bad and the 74LS393 in U1G was bad. All the chips in the jellybean section have been replaced with tested known good. I still get the 02FFFF error, sad mac, and no...

I continue to struggle to clear the 02FFFF error. I've replaced all four 74F253s. I also pulled the 74LS257 at U2F — it tested clean on the T48 with no errors — but swapped in a new one anyway as a precaution. No change to the symptom. There's no smoking gun yet. I've begun checking traces and...

Update: Mac Plus 820-0174-A — pulsating vertical lines, no bong Located and replaced a faulty 74F253 mux (confirmed via DMM — polarity-dependent leak — and corroborated on a T48). Replaced all four 74F253s as a set, along with all nearby 0.1µF (C104) decoupling capacitors. Condition improved...

Mac Plus 820-0174-A: pulsating vertical-line pattern, no bong, good sync — TSM and LAG cleared via custom PAL exerciser. Where next? Hi all — long post, but I think it's worth the detail since I haven't found anyone documenting quite this deep on this specific symptom. Looking for ideas on where...

Update: it's fully working. Full writeup below with final measured values, in case it's useful to anyone else attempting this. Background: running a Macintosh Plus logic board (1MB RAM, booting off BlueSCSI) off a Macintosh SE's analog board, PSU, and CRT, in place of the Plus's own analog...

Update: found the actual mismatch, working on a fix. Scoped VSYNC directly at the connector on both boards for a real apples-to-apples (pun intended) comparison: - Macintosh Plus logic board VSYNC low (retrace) pulse: ~900µs - Macintosh SE's own logic board VSYNC low (retrace) pulse: ~200µs...

Update: got it working (mostly)! Connected a known-good Macintosh Plus logic board (1MB RAM, booting off BlueSCSI) to a known-good Macintosh SE analog board, PSU, and CRT, with power and video pins cross-referenced and wired. Direct connection, video out from the Plus straight into the SE's...

I'm looking at running a Macintosh Plus logic board off a Macintosh SE's analog board, CRT, and PSU, instead of the Plus's own analog board. I've cross-referenced and mapped the power and video pins between the two harness connectors. What I want to understand is the Plus's output video signal...

SOLVED: Checkerboard/noise turned out to be two separate faults — bad ROM LOW chip + a loaded reset line Wanted to close the loop on this thread with the full resolution, since it ended up being two independent problems stacked together, and the diagnostic path might help someone else down the...

Do we know what drives the 68000 Reset to high?

Update: RESET/HALT stuck low regardless of switch state — chasing what's actively driving it A fellow member, GreenBarOn, suggested checking whether the Reset and Programmer buttons on the logic board were operating correctly. That question ended up cracking this open. Step 1: Tested the...

Update: Macintosh SE checkerboard/noise — continuity testing complete, need advice on scope approach or component swapping Following up on my earlier post about a Macintosh SE 820-0176-B (1986, 630-4125) logic board showing a checkerboard pattern with random noise/static (speckled dashes) on...

I have a Macintosh SE 820-0176-B, 1986, 630-4125 logic board that shows a checkerboard pattern with random noise/static (speckled dashes) displayed on boot, with no audio boot chime — just a single speaker click. I've installed the suspect board into a known-good SE chassis (proven analog board...