Vertical bars on an SE

[roz303]

I just picked up an SE today, and it works... Kind of. There are 16 fat and evenly spaced vertical bars across the screen - other than that it's ready for a disk. I can drag the cursor anywhere on the screen just fine; it's as if the screen is behind white jail bars. 

I tried reseating RAM and battery, and reseating any connectors that I could get to. 

My money is that it's a bad SIMM and I'd have to get a new set. But I'd like to get a second opinion before I drop more money on it! 

 

[BadGoldEagle]

Congrats on your new dual floppy FDHD. Those are somehow rare I think.

Yeah, it looks to me some SIMMs and/or sockets are bad. Although it should have crashed and not passed the tests like it seems it did. You should be able to boot your SE with only 512k installed. It's not recommended but it works. What you can do to be sure is swap them out with the ones you already have and see if it partly resolves the problem. I know SEs can boot with only 512k of RAM because one of my SEs came to me with only 2 256k SIMMs. That was never a factory option. I guess the original owner sold two to make some profit on his newly acquired SE...

But anyway, try with only 2 SIMMs first. The rows form banks, so there's two of them... Populate one bank with two SIMMs, test, rinse and repeat with the other. If it doesn't work with your two SIMMs, try with the other two. See if it makes a difference and report back. You should be able to identify if the socket is bad or if some SIMM is bad. 

Good luck!

 

[MOS8_030]

Howdy!

Yes, it's likely a memory issue. Loose SIMM perhaps.

Head over here: http://maccaps.com/MacCaps/Repair_books.html

and check out the repair books for more info.

 

[roz303]

So, I tried every possible placement of Simms in both 2 and 4 stick configurations. Just out of curiosity I also tried 3 SIMMS, with simm 1 empty. No matter what I did, I get the jailbar Mac.

This then makes me think it's either the PLA or maybe the video board. Either way, I don't know if I want to put more money into it. 

 

[maceffects]

If you decide not to invest more into it and want to sell it to someone who has plenty of parts to fix it, let me know.

 

[roz303]

I'd like to at least know what the problem is, first. Because I was *really* looking forward to having a cute ol' Mac on my desk and using it for useful things. I know I can. Just need to fix the stripes. 

 

[apm]

If it was a RAM issue you'd have a Sad Mac, or at least other crashes. I'm pretty sure that the SE, like the SE/30 but unlike the Plus, has separate video memory that doesn't use main RAM.

Unfortunately, I can't find any schematics of the SE video circuits. The logic board schematics online are missing that page. Anyone around here have them?

The problem will be somewhere in the video circuit. An interesting test can be to take a screen shot (Cmd-Shift-3) and look at the result. If the screen shot shows the jail bars, then the problem is getting the data into the video memory -- probably a broken trace on the address lines somewhere. If the screen shot is clean, the problem is between video memory and the screen.

 

[techknight]

Pretty sure the SE uses main memory for video. 

 

[apm]

Pretty sure the SE uses main memory for video. 

Never mind, you're right. I had remembered that the SE had a faster video circuit compared to the Plus, but they both use main memory.

It's hard to debug this without a schematic, but the closest I can find is Figure 12-1 (p. 251) in Designing Cards and Drivers for the Macintosh Family. Video on the SE is generated by the BBU, the big square custom chip on the logic board. It grabs 16 bits of video at a time out of main RAM which seems significant in light of the 16-pixel-wide bars.

A broken trace between RAM and the BBU is one possible culprit, more likely an address trace than a data one, though I'd think that would produce a duplicated image rather than white stripes. Or the BBU itself could be faulty. It's socketed so a swap could test that quickly. Or there could be something else entirely going on that's preventing the BBU from accessing RAM in time.

 

[MOS8_030]

Check out The Dead Mac Scrolls pg. 206. It specifically describes this problem with an SE as 1mb simms being the wrong row based on the logic board rev.