SE/30 with Checkerboard Pattern but Boots normally

[nvdeynde]

Hi,

My SE/30 suddenly has the checkerboard pattern. However the machine boots normally and has startup bong too.
The pattern does not go away after boot and makes the machine unuseable.
I have reseated and cleaned the contacts of the Rom sim and all Memory modules without result. Pulled and reseated the Video Rom too, no result.

I'm sure the problem is on the Logic Board as the SE/30 works perfect with my spare board.
So the Analog board, PSU and Video board can all be excluded too.
Same for the Rom Simm, Memory modules, Video Rom as I have tried these from my spare working board to no avail.

All capacitors on the logic board have already been replaced about 1 year ago: ESR values are good so they aren't the problem either.
The machine is used several times weekly for years without problem until this one. I have never seen it before with a board that still boots into Mac OS.
It's the kind of thing you see when the board has SimasiMac and needs capacitor replacement but then you don't have the startup bong and no boot into Mac OS anymore while my board still has both.

Below photos of the screen and the logic board.








What can be the problem and is this board still repairable ?


Nico

[tt]

Bad VRAM or video controller? The desktop and menubar are definitely there. Cool pattern by the way.

[mcdermd]

I have something similar with a different patter on one of my SE/30s. I haven't figured it out either.

[TheoryBoy]

I had a problem very like yours, Display problem with complete booting. My problem was related to a faulty memory chip keeping certain lines low. I replaced them by taking them from an old mac II card.



Dont mind the crash, it was just a bad System install. Important thing is I got video.

[nvdeynde]

My problem was related to a faulty memory chip keeping certain lines low. I replaced them by taking them from an old mac II card.

There are so many different IC's in the video circuit...
Here are the schematics of the video circuit for an SE/30 logic board. I'm surprised that it is this complicated for B&W machine.



I'm going to replace the 2 video memory chips. I doubt it will solve the problem since the checkerboard pattern is static and identical every time. I would expect a random pattern with a bad video chip.
However it's worth a try: I'm going to dig in my old Mac II video cards


Thanks,


Nico

[nvdeynde]

I've replaced the 2x Vrams yesterday and checked all the traces in the video circuit to no avail: still the checkerboard pattern.
I guess the board is beyond repair

[techknight]

one of the 74 series chips is bad, or one of the PALs is bad.

[nvdeynde]

one of the 74 series chips is bad, or one of the PALs is bad

Probably but I don't have a hot air or SMD rework station to remove these from the PCB.

[techknight]

What you need is an oscilloscope and a working board to compare it to. You'll find the culprit real quick, as the waveforms compared against one to another will be wrong on the bad chip. If you were closer, i would volunteer to take a look at the board for you, as I have a working SE/30 here i can go off of.