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mdanh2002

troubleshooting SE/30 motherboard

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Hi,

 

I recapped 2 SE/30 around 2 months ago. One of them still works fine, while the other has developed some weird problems. First, I notice that during operation, the PAL and video chips above the 8 SIMM memory slots are very hot, to the point of burning my hands. Secondly, the machine works fine with the original Apple ROM but not with the Macintosh Rominator II ROM (by BMOW) - it would show various stripe patterns or play the chime of death upon boot up. Finally, if left running for a while (30-60 mins) then the machine would no longer boot up with either ROM (chime of death is played). If this happens I will need to wait for a few hours before it will work again.

 

I have washed the board again the second time but the symptom does not change. The other SE/30 which was recapped around the same time still works well. This is the list of what I have done to this SE/30, in case they are related:

 

1. Install 128MB of RAM (purchased from OWC)

2. Install the Mac Rominator Kit II from BMOW. The custom ROM worked fine at first, and only started to show the above problem yesterday.

3. Adjust the trimmer on the analog board for the CRT vertical width to better fit the screen as the original display is a bit small.

 

I am well aware of the overscan design of the original Mac, to make the screen WYSIWYG with 72 dpi printout, hence I still leave some black borders at the top and the bottom. With this, the new CRT image did not fit the screen entirely, just that it was bigger compared with the original display. 

 

Any ideas what is the problem and how should I debug it? I suspect there is a short somewhere on the board which results in the ICs getting hot and failing as the temperature increases. Are those PAL and video chips also hot on your SE/30 board?

 

If it helps, a few days before this happened and after I adjusted the CRT trimmer, I started to observe that the CRT would sometimes shrink slightly or shake shortly after power on, but it would stop doing so once the machine had warmed up. I attributed this to the old analog board, but after checking the voltage rails all look good (12.57V, 5.02V) with only 60-70mV ripple, which are acceptable.

 

Let me know what you think.

 

PS: I accidentally broke the CRT neck tube this afternoon when trying to adjust the trimmers on the analog board. The CRT is now trashed and I had to test the logic board using another Mac SE CRT, but that's a different story. :(

Edited by mdanh2002

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The shrinking display is a different story - I will check the analog board on another day.

 

The 6 or 7 socketed chips above the 8 RAM slots get hot together, so the shorts must be something common to all of them. I have tried to power the on with each individual chip connected and others removed, and yes, each chip individually will get hot. 

 

I do not think that the traces on the logic board are broken because if they are, the machine would not work at all. I did manage to install a full System 7.1 with tons on software on this machine before this happens. In my case the ICs get very hot and the machine would only stop working once the ICs get 'hot' enough. So maybe some short circuits somewhere. 

 

I also checked the my soldering work on this board and it seems OK. Interestingly, the problem only started to happen yesterday.

 

If all fails, I will borrow a Flir thermal camera and use it with the logic board powered on and the socketed chips removed, to see where the short might be.

Edited by mdanh2002

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The SE/30 works fine again with the stock ROM after a second wash of the logic board. I leave it running for the whole day today with no weird behaviour observed. Strangely it still doesn't work with BMOW Mac-rominator II (chime of death upon power on). I will have to investigate this on another day, after I get another SE/30 and see whether the new machine will work with the custom ROM. Maybe some marginal voltage or logic levels that are within the tolerance of the stock ROM, but not with the Rominator II.

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Check your RAM. The IIsi and the rominator II ROM SIMMs have a little bit less tolerance for weird ram combos.

 

EDIT: nevermind, noticed you got a matching 128MB kit.

Edited by Themk

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Check your RAM. The IIsi and the rominator II have a little bit less tolerance for weird ram combos.

 

EDIT: nevermind, noticed you got a matching 128MB kit.

 

I still think it's got to do with the RAM modules, or the circuits surrounding them. I did run a thorough test on all of the 16MB SIMMs using the SIMCHECK II RAM tester, and all tested good, which is expected since they are new. I suspect one or more of the 74F253 multiplexers are dying and producing marginal outputs not tolerated by the Rominator II. When I am free I will use my oscilloscope to examine the voltage levels at their output pins to see what's going on.

 

Unfortunately the SE/30 motherboard and its CRT are not convenient to mess with. The logic board cable is very short, making it impossible to lay the board flat on the table and far away from the CRT with deadly voltages for easy troubleshooting. If it's an LC, or perhaps a Commodore or something, I will be more comfortable to play with it and see what is wrong. I just do not want to trash the CRT a second time. :(

Edited by mdanh2002

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I would think that if the mux had failed, it wouldn't work at all, now, that isn't to say that there isn't a RAM related problem.

 

You should try to shim it as joe suggested, lot of people have to do that.

 

 

If you are trying to troubleshoot an SE/30 board, and it has to be powered, yeah it is quite a pain. If you are going to be doing a lot of these, you could build an extension cable for the main connector. Thankfully many times like when searching for rotten traces, it can be done without the board installed in the machine. Also, breaking the CRT is not fun at all... :(

Edited by Themk

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I tried shimming with no effects. I realize that if it's going to work, just a standard socket insertion would do and no additional press/shimming is required on the module. If it's not going to work, shimming isn't going to help either.

 

Anyway the board failed on me again today (horizontal stripes on the screen with chime of death). This happened for both the stock and the BMOW ROMs. My suspicion now falls on the power supply. I just ordered another fully working Macintosh SE from eBay today. When it arrives in a few weeks' time, I will swap the motherboards and see if it's indeed a motherboard issues.

 

On a side note, what do you do with your 68k Macs once you have repaired them? For me, the most excitement (and also the most time spent) happens during the repair/setup phase. Once I've managed to do that, it'll be like "oh, cool", and that's it :) The same machine will only be turned on again once in a while for testing. I don't feel like opening a working Mac to tinker around, for there is always a risk that I would mess something up. But if I don't play with them, it will be sitting there doing nothing.

 

Over the past 2 years since I started to play with vintage Macintosh, I have acquired quite a few machines (2 SEs, 2 SE/30, 2 512k, 1 Plus, 3 color Powerbooks and 7 B&W Powerbooks). I am thinking to resell some of them to get back some of the money spent. Here in Singapore a compact B&W Mac, with keyboard and mouse, in working condition, can fetch around US $300 if sold locally. A working vintage Powerbook can get you around US$150. But if I do this, I will feel somewhat bad since I no longer have machines to play with. :(

Edited by mdanh2002

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