stepleton
Well-known member
I've had a Mac Classic (actually my first-ever computer) that's been ill for a while. Here's a report from a long time ago --- although it's a lot sicker now. I'd love to get it working again (since it was my first-ever computer ).
The symptoms today are these:
The fact that the reset button behaviour only works after a few moments makes me think that there's a chip that's sensitive to heat. I have a thermal camera, but nothing's getting too hot. Still, I try spraying the chips one-by-one with an upside-down air-duster can. For most of the chips it doesn't change anything, but if I chill the VIA chip --- that's UB5 over on the left-hand side of the board --- then the reset button stops working. After the VIA warms up again, then the partial-bong-on-reset behaviour is restored.
(Ruling out some other possibilities: the board has been recapped, there's little damage from the leaky old caps, and the power rails all look good.)
Does this sound familiar to anyone? What do you think --- bad VIA? Does that older post I mentioned seem consistent with that problem? Is there any resource online that describes a kind of theory of operation for the Classic or similar machines (so that I can try to diagnose what's going on)? A block diagram of the Classic logic board would be really helpful as a start.
The symptoms today are these:
- Switch it on after a long time switched off, and you get horizontal black and white bars. No bong.
- It doesn't do anything at first, but if you wait long enough, the reset button starts "working". Pressing it gets you as far as a partial bong and the dark grey screen you see before a normal boot would take you to the usual 50% grey, a happy Mac, and so on.
- You can keep pressing the reset button as often as you like, and most of the time, you get a partial bong. The dark grey screen never changes.
The fact that the reset button behaviour only works after a few moments makes me think that there's a chip that's sensitive to heat. I have a thermal camera, but nothing's getting too hot. Still, I try spraying the chips one-by-one with an upside-down air-duster can. For most of the chips it doesn't change anything, but if I chill the VIA chip --- that's UB5 over on the left-hand side of the board --- then the reset button stops working. After the VIA warms up again, then the partial-bong-on-reset behaviour is restored.
(Ruling out some other possibilities: the board has been recapped, there's little damage from the leaky old caps, and the power rails all look good.)
Does this sound familiar to anyone? What do you think --- bad VIA? Does that older post I mentioned seem consistent with that problem? Is there any resource online that describes a kind of theory of operation for the Classic or similar machines (so that I can try to diagnose what's going on)? A block diagram of the Classic logic board would be really helpful as a start.