Simasimac Help Please!

[epalama1]

Background:
Skill Level: Hobbyist - I have restored a number of vintage Macs before, but beyond reading a schematic to check for continuity between parts and basic/sub-par soldering skills, I have no knowledge.

Hello everyone! I bought this SE/30 off of eBay a few weeks ago and was very happy to see that it wasn't battery bombed. However, it did still have the typical simasimac symptoms (no chime, pattern on screen)..

I got to work with recapping the board, which went semi-smoothly minus one pad and three traces, all of which I repaired. After the recap, I got the normal SE/30 chime, but the same pattern on the screen.

I kept going and replaced UE8; however, after I did, the chime stopped and the screen went blank..

Keep in mind, I originally put in a few wires between this chip and its connection points as I was having a hard time soldering to those small pins. However, one of these was incorrectly placed. I corrected it and confirmed continuity between UE8 and all of its connections. I also reflowed UD8 and UF8 and confirmed all pins were connecting where they were supposed to.

I had removed the neck board from the CRT, but did it very carefully and checked the tube for any cracks. Didn't see any...

Here are some pictures of the board:

Thanks for reading, everyone!

 

[epalama1]

Here's a video of how it's acting now...

 

[Nixontheknight]

SE/30's are picky about their RAM, but also make sure there are good connections between the CPU, ROM, and RAM

 

[epalama1]

Thanks for the reply! Yeah i've heard that about the RAM, but I did get a normal chime before I replaced UE8 (even tried putting the original back and nothing). I'll definitely be checking all of those connections next...

 

[epalama1]

Update: still have the simasimac pattern. Screen comes on to the pattern if left on for a few minutes.. so it might have an analog board problem as well. Bought new VRAM chips and will put those in to see what happens. Also looking for PAL chips if anyone has...

 

[Elemenoh]

Screen comes on to the pattern if left on for a few minutes

Can you explain that a bit more? What specifically is happening at cold boot and how does it change after warmup?

Bought new VRAM chips

The lined pattern you're seeing is the default state of the VRAM and it looks consistent. So the VRAM is almost certainly okay. You more likely have a continuity or contention issue on the address/data lines or an issue with a component on that path. If it's a failed component, it'll likely be one or more of the video or RAM muxes. UE8 was a good start but one of its neighbors might have a problem.

I'd suggest:
— If you have a working board, swap test the socketed components since that's quick and easy to do
— If you have an oscilloscope, check for stuck (a straight line) or contented (floating 0-5V) signals on the address lines. A stuck signal would indicate an open somewhere (more likely) and a contention would indicate a short (caused by a solder bridge, stray solder ball or electrolytic fluid that hasn't been cleaned up).
— Check continuity along the address/data line path which includes the video muxes, RAM muxes, RAM, ROM, VROM, CPU, VIAs, etc. You can skip the CPU on the first pass since it's a pain to check and usually continuity to it is OK.

 

[epalama1]

Hey thanks for the help! I'll try out your suggestions soon and will report back. Although, I don't have an oscilloscope. By "screen comes on to the pattern," I meant that when you turn on the power, the speaker makes a crackling noise and the screen stays black. Once left on for a few minutes though, the screen flickers a bit only to come back on fully and display the simasimac pattern. The only thing I'm hung up on was the fact that I got a chime before replacing UE8, but even when I put the original back (and I confirmed that there was continuity with all endpoints and no bridged pins) it didn't work.

 

[Elemenoh]

From that description it sounds to me like you have a continuity issue that clears up after warmup. Something needs cleaning and/or reflowing IMO.

 

[croissantking]

I’d try reflowing the Glue chip.

 

[epalama1]

Thanks for the suggestion @CroissantKing! I took a break from it for a few weeks, but I’ll get back to it. I did need to put in a bodge wire from pin 70 on the GLUE to K3 on the processor. Now I’m getting a fairly consistent death chime. Maybe other pins aren’t making good contact/their traces are worn as well.

 

[epalama1]

Haven’t gotten around to reflowing the GLUE yet, but I did replace all of the F258s as well as UA8-UG8. Didn't' help much, although I did notice I was getting a faster death chime. Also noticed this..

When you put pressure on one of the PAL ICs, the pattern changed. I added a bit of solder to each of the pins on the underside of that socket. Now I just get a black screen. So maybe it's just dead PALs? Otherwise, I also have some new PurpleROM module on order and will get some new RAM to rule out any issues there. After that I think it's just going through the schematics and testing all of the traces, which I really don't feel like doing honestly haha.

 

[croissantking]

When you put pressure on one of the PAL ICs, the pattern changed. I added a bit of solder to each of the pins on the underside of that socket. Now I just get a black screen. So maybe it's just dead PALs?

That shouldn’t happen, I’d try to find out what’s causing this before going further. The correct pattern is the one that appears at the end of the video.

I’d suggest inspecting the VRAM chips that are adjacent as they might not be making a good connection. Putting pressure on the PAL could actually be flexing a marginal joint on one of the 41264s.

If it is the PAL chip you’re pressing on then the obvious thing to try would be to swap in a known-good replacement. Perhaps you could try desoldering it and socketing it, it’s way easier to troubleshoot.

Otherwise, I also have some new PurpleROM module on order and will get some new RAM to rule out any issues there. After that I think it's just going through the schematics and testing all of the traces, which I really don't feel like doing honestly haha.

Try to sort out the PAL issue first.

I’m not surprised you don’t feel like it as this is a ball-ache, lol. I would start with the Glue chip. Also, I’d firstly check to make sure none of the adjacent pins on any chip are bridged together, this will be easier and faster to check than checking individual pins for continuity.

As an example of how things can go wrong, I found a micro bridge between two pins on a 68882 and it wasn’t possible to correct this by reflowing. I had to desolder the whole chip and start again. I guess the bridge was under the chip.

 

[croissantking]

Sorry, reading your posts again I realise you’re not working on a new build board. Some of my advice is probably not relevant (the micro bridge thing in particular).