Mac Classic - will it ever run again!!

[rubber_jonnie]

Wobbling screens are quite often video cables going too close to a mains cable or somesuch. You may get away with just rearranging the cable routing inside the machine.

I'd already tried that, but it's made no difference. All the cables, bar the HV cable from the flyback are tucked well down in the chassis. The mains cable is nowhere near the monitor.

Trouble is I just went to power it on and the old problem is back again!!! So low 5v, slowly rising until the HDD starts to spin up.

This is driving me insane!!! How did it work first thing, then not now. Well, I did say I like a challenge!!

[Tomswork]

Fingers crossed

Tom

[rubber_jonnie]

Fingers crossed

Tom

Well, it actually at least runs now, thanks to your board, which is more than it was doing before :)

[Tomswork]

I have had trouble with opto couplers in psu before those and the power mosfets can be hard to find and i do not like sticking my oscilloscope on the oscillator


Tom

[rubber_jonnie]

I have had trouble with opto couplers in psu before those and the power mosfets can be hard to find and i do not like sticking my oscilloscope on the oscillator


Tom

I know that uncomfortable feeling putting anything near the analog board!!

I have managed to get a read off the TDA at pin 5 and it is reading correctly though. I have a power Mosfet on the way (QP2) in case that is dying. I am running out of things to change though!

[rubber_jonnie]

No major progress, have replaced the last 2 electrolytics in the video circuit, and here's how it looks:

IMG_20220106_155910.jpg

I was going to reassemble it, but have instead decided to wait until QP2 arrives and just replace that too. In for a penny....

The main problem is that it is both the PSU and the video/high voltage sections, divided about 50/50 across the middle, left to right.

Aside from my Amstrad Alt-386, it's probably the worst board I've had to deal with, you have to disassemble each time, and confirm all the HV has dissipated, especially the big cap, CP1, as although it does drain, it holds a charge for quite a while, enough for a BIG spark if you short it.

Hopefully more over the weekend.

[rubber_jonnie]

Ok, so the power Mosfet, Q2, arrived in the actual post that actually came today!! I fitted it at lunchtime, so I need to allow some standing time now, see if that finally fixes the PSU.

If it does, then that just leaves 2 remaining problems:

1. The screen wobble is seemingly fixed, but I have some keystoning. It's more like reverse keystoning actually, as the narrow part is at the top of the screen. None of the pots seem to adjust that, so I need to look into that.
2. The RAM expansion doesn't work. i need to convert the Sad Mac error code into something that tells me where the fault is.

I'll take that for now though, at least it runs, which is far from what it was doing before.

It's a warning to Mac lovers out there, re-cap your Classic logic and analog boards before it's too late, and make sure the battery is out too!!

[rubber_jonnie]

And I think the keystoning is fixed!!

There are 8 magnets mounted around the deflection yoke, one of them has been knocked slightly during all the removal/refits of the analog board.

I may have to check the others, but adjusting this one loose magnet has pretty much fixed it bar some minor tweaking. :)

Just the RAM to deal with next.

[stephen_usher]

:yay: :yay2: :cheer:

[rubber_jonnie]

:yay: :yay2: :cheer:

Thank you sir :)