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Daniël Oosterhuis

Macintosh SE/30 - Broken trace related to video?

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So now that I've gotten my hands on a Macintosh SE/30 to fix up, I went and checked the seller's conclusion on what was wrong it. According to him, the CRT wouldn't come on, and he suspected the analog board. To put that theory to the test, I swapped boards between my working SE, and the SE/30. The SE in the SE/30 chassis booted, and was happily driving the CRT. Thus, the issue was not with the SE/30 analog board or CRT. And to be expected, the SE/30 totally failed to boot in the SE chassis. The seller thought the SE/30 didn't chime because the speaker cable wasn't plugged in, but his memory failed him because it was firmly plugged in.

 

So, now that the SE/30 board is definitely the culprit, I decided to give the board a good look over. And would you believe it, there was a broken trace (open the image for the full resolution):

post-6509-0-75938800-1509235566_thumb.jpg

 

The jumper might obscure it a bit, but it connects from a pin from the UI6 to a pad that continues to a trace that is completely dug out just below the UG7 chip. On the underneath of the board, the pad doesn't have any connections to any other part of the board. What I can't figure out however is what the jumper cable is supposed to do. The schematic I was looking at made it seem that that pin on UI6, which is the PAL HSync chip from what I can find, isn't used for anything and not connected to anything. So why is it jumpered, and how does it influence the way to system works? I can't quite find out where the trace goes to, it goes underneath the GLUE chip and from there on out it's anyone's guess if it connects to the GLUE or goes elsewhere. 

 

Now, I knew the caps were highely likely bad, and some pins of chips near the electrolytic capacitors looked a little dull, so I gave it a bath of warm soapy water followed up by some 96% cleaning alcohol, then I left it to dry. After drying, it managed to display a bunch of dots across the upper section of the screen for a while, which started to disappear one by one, to now just showing a very, very faint grey image with lines going across it horizontally. So the question is, is this the result of bad capacitors, or that bad trace? And if it is the trace, where does it go?

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I would recap it before doing anything else. I believe that wire is normal for an early revision SE/30 with the soldered PALs. Here’s a picture of another board with the same wire.

post-9242-0-25868300-1509253708_thumb.jpeg

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The cut trace is also normal. If you habe the wire that trace will have to stay cut.

Your problem is most likely related to caps.

If HSync would be non existent you would still get a bright horizontal line. Also take a look at UE8 and its neighbors as they are prone to failure.

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Good to know the cut trace is normal. It just looked like either something ate the trace away, or someone clumsily carved out the trace, weird that that's how they came out of the factory. Does anyone know why that is? Just curious, but it just seems weird to me that a pin of that chip that according to schematics doesn't do anything, and doesn't go anywhere on the board, has a jumper attached to a trace that ends up just getting severed. Wouldn't not putting that jumper there not have done the trick? It might actually have a reason to be like that, so I guess asking wouldn't hurt.

 

Anyways, I'm going to order the caps and replace those first. If UE8 and co end up being bad, what P/N should I look for, for their replacements?

Edited by Daniël Oosterhuis

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