Original Mac Video Issue

[khannonnd]

I am sure this has been posted about before, but my lack of technical expertise doesn't even know what to search for.

I have an original mac - Last week it worked fine. This week, when I turned it on, I got nothing on the screen. The boot chime sounded as normal, and when a disk is inserted I can hear the disk drive reading it as normal.

I opened the machine and messed around with the brightness dial on the board itself. If both it and the "normal" brightness dial are turned all the way up, I see diagonal white lines. If I kind of touch the "Voltage" dial on the board (the small screw adjustment), I catch glimpses of the blinking question mark through the diagonal white lines.

Any ideas what has given up the ghost here and is it fixable short of a complete replacement?

 

[volvo242gt]

I'm assuming we're talking about a Mac 128K, right? Sounds like the analog board has some problems. If you thump the side of the case, do you get video, even for a second or so?

 

[khannonnd]

Haven‘t tried thumping it, haha. But as mentioned, if I touch the “voltage” screw adjustment on the analog board, I get a glimpse of an image (with the brightness turned all the way up). Definitely sounds like an analog board issue, but not sure what part (or if it is as simple as the capacitors are dying)

 

[volvo242gt]

It might be worth getting in touch with @CC_333 and seeing if he has a known good AB. If he does, get it, then swap it into your 128K. Send the original out to someone for replacement of the flyback and the caps, that way, you can have it as a spare.

 

[khannonnd]

That is a good idea! @CC_333, Do you by chance have a known good AB?

 

[robin-fo]

Did you check the relevant solder connections on the analog board? This is a very common issue and rather easy to fix. The cracks in the solder are sometimes hard to see, though…

 

[khannonnd]

I did not, mostly because I would not know what I was even looking at - I thought I had heard of others having similar issues in the past but couldn't remember what they said it was. Cracked solder connections was what I was trying to remember. Thanks!

I posted in the Trading Post to see if someone on the board from the SF area could help me with this.

 

[Byrd]

Definitely a dry solder joint, usually look where the cable from the yoke goes to the analog board - one or two solder joints will be dry/cracked with tell tale signs of scorch marks/arcing around the join. From there of course you might note the yoke connector pins look in poor condition, and then while there the inevitable recap of the analog board will be in order.