Unstable Mac SE

[displaced]

My SE SuperDrive’s inching closer to being restored, but hopefully someone can help me track down an elusive issue…

The machine will boot fine and appear to work well. I can copy files around, launch apps, play a bit of SimCity etc.

But, it will go through patches of being very crashy and freezy. Here’s what I’ve found so far:

• Booting from a bare 6.0.8 System Folder is fine.
• Leaving the machine at the desktop for a few minutes, then moving the mouse will usually immediately trigger a hang, with a white rectangular dialog that contains no text, but sometimes a flickering border.
• Sometimes I get as far as clicking the Apple menu before the same thing happens.
• Formatting a floppy *always* hangs with a blank dialog just after the format has completed but before verification starts.
• If I leave it in a hung state, I’ll eventually sometimes hear a burst of noise from the speaker, or see video ‘sparklies’.
• Sometimes when left, it’ll beep repeatedly and spontaneously reboot. Or just reboot without the beeps.
• Sometimes it will fail to redraw part of a Finder window and hang.
• Strangely, it’s most stable when playing games (?!)
• It’ll go through phases of crashiness, but after a few power off/ons, it’ll run fine for a bit.
• This all happens no matter where it boots from — SCSI or floppy.
  
  
• I’ve run Snooper 2 repeatedly and all tests have passed. However, I did get repeated System Error (ID=02) messages until it randomly decided to work.
• I eventually got MacTest Pro’s 68K Emergency disk to boot. It too failed repeatedly with Address Errors at program launch, but then

Now, MacTest appears to exercise memory much more thoroughly, including the video area. I just ran a video memory test and was happily watching the various patterns. At the ‘chessboard’ screen, the machine let out an almighty warble then shriek from its speaker which scared the crap out of me. The system spontaneously rebooted after about 15 seconds.

So, firstly - thanks for reading all that! Secondly, I get the feeling that the address errors are genuine, but beyond that I’m at a bit of a loss.

I’m currently repeatedly loading MacTest again so I can repeat that VRAM test, but currently it’s throwing address errors just as the MTP window appears. If I keep trying, it’ll work eventually.

The machine has had both its analog and PSU boards recapped. Voltages look fine even under load. The logic board is clean and the original battery was intact before being replaced.

The system has been upgraded with 4MB, but the symptoms persist between different sets of SIMMs, including the original 4x256KB modules. The SIMM slot pins have been carefully cleaned with IPA and the SIMMs themselves have had their contacts cleaned.

I’m currently a bit suspicious of the ‘filter’ ICs or the bus transceivers (which I’ve seen cause oddness on other systems), but I don’t know enough to be sure.

Any help or advice gratefully received!

 

[displaced]

Ok - the chessboard VRAM test does seem to reliably trigger the problem. It displays for a few seconds, then there’s a ‘wobble’ of noise vertically in the picture at which point the speaker emits a low-pitched rumble. About 1/2sec later the screen goes entirely corrupt and a single loud high-pitched tone is blasted out.

It could be whatever’s meant to happen immediately after the chessboard test that’s the trigger, as it’s on-screen for a while without issue, but I can’t be sure. Seems odd that so much of the VRAM test succeeds beforehand.

 

[Patrick]

I don't know. But you might need to do what i will have to do with my unstable mac plus .. bust out the multimeter and logic probe and check circuits. check for hot chips. or something.

Maybe for both of our computers a chip is overheating or something.

 

[Kai Robinson]

@Branchus had an issue that turned out to be faulty ADB - that might cover some of the symptoms you're experiencing.

 

[displaced]

Thanks both!

I received my ATX extension cable today, so I’ve been able to fiddle with the logic board outside of the case (great idea in @JDW ‘s recent video!)

I misremembered in my first post. I swapped back in the original 4x256K SIMMS and the machine is much more stable. Can’t say for sure as I can’t run the MacTest Pro VRAM test due to it using System 7. I did make a MacTest SE disk, but it complains about needing to run from an 800K floppy, which I can’t create.

The two 4MB SIMM sets I have are 3-chip parity modules. They both test fine in my Atari STE, but perhaps the SE has some stricter requirements?

Or maybe it’s not the modules themselves, rather some PCB line, driver, multiplexer or whatever that’s only used when 4MB is installed?

Oh, and just to triple check: the RAM Size jumper’s “2/4MB” setting is in fact a little mislabelled isn’t it? That setting (jumper on pins 1+2) is for 2MB, no jumper at all is 4MB.

 

[fehervaria]

If you are planning to check the logic board outside from the houseing, you could use hairdryer to warm up the board without overheating it. (I had a Plus - probably thousands of working hours in it - with similar freezing effects. I used hairdryer to partially heat the logic board. Finally, I had to resolder moslty all ICs on the logicboard, and it works now. But the Plus has passive ventilation, it easily cooks itself, the SE has the ventilator to pull cold(er) air through the logic board.
Bbased on @Kai Robinson 's idea about the ADB, try to test with mouse only or without any ADB device.
Let's hope!

 

[displaced]

Thanks! I shall give warming it up a try.

I’ve been doing some RAM experiments this afternoon.

100% stable with the stock 4x256.

Tried 2x1MB and 4x1MB with both sets of modules I have - the odd behaviour returns.

These are 3-chip parity modules rather than the 8-chip non-parity 256K sticks. So I whim I desoldered the parity chip. Still the same unstable result.

I saw some listings for Mac memory on eBay. One listing from a company called MacMemory was for 3-chip SIMMs of the same design as my upgrade ones. The listing mentioned that they’re not recommended for the SE due to instability. So perhaps there’s something about them other than their parity-ness that’s causing a problem?

I do need a set for one of my Ataris, so it won’t hurt to try to find some more 1MB modules that more closely resemble my SE’s stock RAM.

Could it still be an ADB issue or heat-related issue if the machine’s fine with its stock RAM?

 

[fehervaria]

Could it still be an ADB issue or heat-related issue if the machine’s fine with its stock RAM?

In my opinion, if it works with the stock RAM, then probably no issue on the ADB nor with hidden connection breaks (warming up could cause problems).
Try with a known good 1MB RAM modules.
...and stress test it with the stock RAM sticks... I would build it back to the "normal" state (back in the housing, connect all devices what you normaly use) and execute the test program and let it work "longer" to reach a constat but warmed up temperature... if it is stable, then the non-compatibe RAM modules are/were the problem.

 

[displaced]

Good plan!

I re-fitted the stock 4x256 SIMMs, buttoned the whole thing up and have left it running MacTest Pro’s tests on loop. Absolutely rock-solid.

(I suddenly realised I could run MTP from floppy after booting into System 6. So therefore could run the tests that I wouldn’t have been able to by booting from the System 7 floppy.)

My two sets of 4x1MB SIMMs test perfectly on my Atari STE, so I don’t think they’re necessarily bad, just incompatible. And there’s nothing about their specs that would immediately raise a warning flag.

But anyway, I’ve ordered another set which looks physically much more like the SE’s stock memory (i.e., 8-chip modules, not 3 and the same DRAM manufacturer as that on the stock modules). Should be here Friday.

I’m cautiously optimistic they’ll be the answer, particularly after seeing the machine run so well on its stock RAM.

 

[fehervaria]

Don't we have somebody here, maybe @Kai Robinson, who know the exact SE memory specifications?

 

[Kai Robinson]

Thinking about it, the BBU does have issues wth two chip 1MB SIMM's - i seem to recall i knew why, but i can't place the reason why...

 

[max1zzz]

Thinking about it, the BBU does have issues wth two chip 1MB SIMM's - i seem to recall i knew why, but i can't place the reason why...

I have seen that said about a few macs (notably the SE/30) and would be really curious to know the exact reason, I personally have 2 chip simms in both my SE and SE/30 and have no issues with them

 

[displaced]

Hmmm -- just realised I've ordered more SIMMs from the same place that sent me the 3-chip modules, which were actually listed as 9-chip modules. So I'll probably get yet another 3-chip set on Friday. Boo!

It suddenly hit me that, of course, "1MBx9" means "9-bit" not "9-chip", so 3-chip RAM still meets the description.

I'll stick a post in the appropriate forum asking for recommendations for RAM sellers who are amenable to requests like "can you send me 9-chip RAM please?"

(EDIT: Actually, the seller’s been great and has found me the correct 9-chip SIMMs. Brilliant!)

 

[ScutBoy]

I'm also aware of random problems with 2-chip and 3-chip SIMMs, but don't have any hard references handy. I've been lucky that I can generally scrounge up other SIMMs until I find something that works reliably.

 

[polpo]

Apple's own spec pages for the SE and Classic (still hosted on support.apple.com!) both state that 2-chip SIMMs are not supported (and by extension, probably 3-chip SIMMs also, as the 3rd chip is used for parity which is ignored): "This system cannot use two-chip 1MB SIMMs."

Macintosh SE: Technical Specifications - Apple Support

support.apple.com

Macintosh Classic: Technical Specifications - Apple Support

support.apple.com

However, there's no such warning on the SE/30's spec page: https://support.apple.com/kb/sp195?locale=en_US

Personally, I've seen older SE boards with resistor-based RAM size selection not work work with 2-chip SIMMs that happily work in newer SE boards with jumper-based RAM size selection.

 

[Patrick]

Would it follow that Mac Plus's could also have problems with 2 (or 3) chip RAM SIMMSs ?

 

[polpo]

Would it follow that Mac Plus's could also have problems with 2 (or 3) chip RAM SIMMSs ?

Looks like it – the note is also on the Mac Plus's page: https://support.apple.com/kb/sp190?locale=en_US

 

[displaced]

Great finds -- didn't occur to me that I might be able to, y'know, just check Apple's website!

Still rather curious about why this is the case... Not that it matters -- just interested to know what the SE does differently to, say, an Atari STE.

 

[displaced]

Ok, quick update: got four 9-chip 1MB SIMMs in the post today, installed them, and the SE’s running absolutely perfectly!

Time to button this one up and call it done!