SE/30 recap – functional with checkered pattern

[apm]

Thanks for the great theory and reply apm. So following your advice I booted the mac up (interestingly the floppy does work intermittently, so that's a slight change from my original post). However, using the key command Shift-Command-3 to take the screenshot resulted in the system crashing (3 times). The cursor would display the watch icon, and the system (other than the mouse) became unresponsive indefinitely.

Does that fit with the UD8 theory? I don't have the hot air equipment or expertise to change out an IC (although I'm willing to learn). Would it be worth giving the board a good wash/toothbrush scrub with IPA and water in case its some hidden residue from the capacitor leakage shorting something out? Grasping at straws here haha.

Yeah, that does sound like a problem between the CPU and VRAM. Perhaps when it tries to read back the data in VRAM, it generates some kind of bus error because the address line is stuck in the wrong place. I'm not exactly sure of the mechanism there, but if the problem was on the video scan side, the CPU would be blissfully unaware of it and the screenshot would come out fine.

So I would check continuity on:

UD8 pin 4 to UK6 pin 10 and 68030 pin A2

UD8 pin 12 to UK6 pin 9 and 68030 pin C4

UD8 pin 7 to UC6 pin 17 and UC7 pin 17

UD8 pin 9 to UC6 pin 16 and UC6 pin 16

I also just noticed that the horizontal stripes in the video look to be 4 pixels high each. That's 4x512 bits = 2048 bits = 256 bytes per stripe. Probably not coincidentally, the address line that toggles every 256 bytes is A8, which also attaches to UD8. That makes a problem near/in UD8 even more likely.

So also check these:

Pin 14 should connect on UD8, UC8, UB8, UA8, connected to UE6 pin 13

Pin 2 should connect on UD8, UC8, UB8, UA8, connected to UE6 pin 8

[edit to add] Pin 1 and Pin 15 should connect to ground on UD8, UC8, UB8, UA8

It is possible, I think, to get the SMD chips off without hot air, if you patiently heat and pry up the legs one by one. Others here might have good advice on what works.

 

[techknight]

Now, I wonder if there was a known bad ROM that came from apple that was compiled wrong or something, or had bugs in it and they swapped it out with a newer version. I cant recall ever running into that though. 

 

[man4mac]

Man. I'm blown away you guys know this much about these machines. Incredible. I'm out of the country for a few days but illl post an update as soon as I'm able to check those pins.

@techknight, I don't have another se/30 to swap rom-sim but I do have a working SE. That wouldn't work would it?

 

[man4mac]

techknight and apm – I owe you both beers. She's working!!!!!!!!

apm, I'm blown away by the specificity of your diagnosis. You NAILED it. I pinned out the entire UD8 chip, and sure enough, UD8/4 had no continuity with UK6/10. I didn't have any really fine gauge wire, but I patched it with what I had, and holy crap – it works. It freaking works. That was a blast...

 

[apm]

Nice work! Great to see it working again!

 

[techknight]

I had a feeling it was bad traces. They stuck a cap literally right there, that leaks and kills them all.