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Marginal Power Supplies -- What are the symptoms?

beachycove

Well-known member
I have one SE/30 that is giving me a bit of trouble. Its logic board has been recapped, but its analog board and ps have not been recapped. I'll probably run the logic board through the dishwasher over the Christmas break just to be sure it isn't any residual goo, too, but have a question about those non-capped items.

At present, the screen seems fine, with no distortion, so that is not the symptom I am thinking about. Instead, I get occasional crashes including bus errors and other less common weirdness, like Finder errors. Bus errors can be software related, I know, but I have seen the behaviour on minimal Systems, and as bus errors can also have to do with memory and the hardware side things, I am wondering if there are times when those electrons are just not reaching the places they need to reach....

Meantime, the machine passes all tests in Apple Personal Diagnostics, so nothing obvious is being identified as problematic.

Any advice from the more technologically enlightened on here would be warmly received.

 

just.in.time

Well-known member
Despite passing hardware diagnostics, I wouldn’t rule out faulty RAM too soon. If you have enough (such as 8 sticks), try running with just 4 sticks. If one batch happens to be 256k then you will be knocked back to system 6 with that 1MB of RAM but just for testing purposes. Try different configurations for a couple days.

That said, it could very well be a voltage dip causing your issues. The external floppy drive port is the easiest place to measure voltages. Get a voltmeter and rig it up to the appropriate pins (pin out available on google) to measure each of 12v and 5v (iirc I think you can see both + and - there, so 4 measurements). Careful to not cause a short! That would make for a bad day. Once you have a safe and reliable connection measuring voltage, make sure it is within a good tolerance of range (again, been 3 years since I did mine but +/- 0.05 v is okay I believe double check to be sure). While measuring, turn the brightness up, pop in a floppy, use the keyboard, etc. to help put more electrical load on the system. Continue to monitor voltage and verify it doesn’t dip significantly while under load.

Last but not least, that board washing. If the dishwasher has worked for you in the past then do what you have had success with. My personal method is to wet board with distilled water, spray down with original Simple Green, and use a soft bristle toothbrush to gently scrub the board. Then, I rinse all Simple Green off with distilled water. Finally, I rinse with rubbing alcohol to displace water. Compressed air can to remove any remaining liquid. I follow this up with a drying session of 1 hour to make sure everything is really dry. I avoid the dishwasher because of the high mineral content of the tap water in my city.

 

beachycove

Well-known member
It was, it seems, one or all of three things:

ROM slot: On another thread, I posted about a bent pin in the ROM slot of the logic board originally used in this machine. I replaced the logic board, and am waiting for a chance to repair the slot of the spare board (to go in the other SE/30 I have waiting for some TLC).

RAM: The machine had, first of all, 32mb of 3-chip RAM installed (8x4mb). I learned on searching here that SE/30s and Compact Macs in general can be picky about 3-chip SIMMs, which is not something I had ever heard of before, so I had to forage to find a set of low density SIMMs. I then came up with another 32mb from my stash, and installed these with the faster (60ns) RAM in Slot A, and the slower (80ns) in Slot B. Still the machine did not run very well, so I swapped them so that the slower were in Slot A and the faster in Slot B. The machine then ran much more stably.

There was still a less severe problem, however, and I got less frequent but continuing random crashes. These occurred in 7.5 in particular, some in 7.1, and a few in 7.5.3 (e.g., Finder errors using Appleshare, like a divide by zero error or some such thing).

So I decided to try a fresh System installation, post ROM slot and RAM solutions, and went with 7.5.3, as, in terms of stability, it had been the best of the triumvirate of Systems installed to date. And now the SE/30 is humming along contentedly, with Mode32 under 7.5.3. There are no more random crashes, woohoo! I am actually a little taken aback by how well it runs 7.5.3. I have long thought that a little 16mhz 68030 would choke on anything higher than 7.5, an opinion based on my experience years ago with a Performa 600 (crap machine), but in fact the SE/30 runs 7.5.3 like a champ (with the System cut down somewhat so that the demands place on the machine are not too great -- e.g., no QDGX or voices). Switching networking to Open Transport also made a dramatic difference in networking speed with a Faralon ethernet card.

I am delighted to get this little thing running well again.

My working hypothesis is that the hardware problems were problems in themselves, which further caused corruption in the System software installed while those hardware problems stood in the way, and that the System corruption was resolvable only after those hardware problems had been circumvented. But what a runaround! The whole process started with a logic board recap (I haven't done the analog board or PS yet), and the machine must have been taken apart ten or twelve times over the Christmas break to get this far. An SE/30 is not exactly, you know, easy to work on.

 
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