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Yep, and then replace the optocoupler again. Voltages will probably be back to normal - for a while. Cleaning the analog board in hot soapy water does seem like a good idea, if you’ve had that much gunk floating around that a diode leg was corroded off.

Good stuff. One thing to think about - when you replace the optocoupler - I think they are possible to damage with soldering temperature, and I think that’s why they are socketed in the original Mac/Mac Plus analog board. So, the last optocoupler I fitted to a Classic, I took a row of pin...

So you heard a bang, but you’ve still got some voltage produced? Check the two 0.1uF capacitors that are wired across the AC input - they are near the metal frame. They often split/explode. If anything else has gone bang, it seems impossible that it would turn on at all. To fix the low voltage...

It feels like if there was one cracked via (corroded via from capacitor leakage perhaps), then there’s probably another, this time from the SWIM? I really appreciate your thorough report of the sound and boot problems and their cause, I feel I may be facing something similar one day.

I’ve now replaced the 6522 - which has changed the display to that below (please disregard the 512K Mac case/analog board used for testing - this is a Plus logic board producing this display) It’s now bars alternated with slightly-shorter bars below - I don’t know what it means, does anyone...

Luckily no-one commented on the filthy condition of the Mac 512K that I was working on - it’s finished now :) I treated the case with water+peroxide+sunlight, but then I also gave it a light spray-painting of a carefully-matched beige colour, so with a bit of luck, it should stay this way...

It’s been a while but I think it’s the edge closest to the display that pops free first. I recall they are robust (the white plastic stabiliser is not brittle). Use something like a blunt knife to pry the edge of the keycap upwards.

Best of luck! I eventually reached a situation that I was happy with. Several further learnings; 1 - I recommend arranging a longer cable, for example an external drive cable, to avoid the EMI interference problem (from the Mac’s screen) while making adjustments with the drive’s top cover...

I’ve learned a few things today, but the most stark was the truth in the above. I learned that if I click Format Disk in the test program, it should immediately start formatting - if it returns to track 0 and throws an error, then starts formatting on a second click of Format Disk, that means...

Funny; we’ve both been dealing with Powerbook 500-series at the same time, and now, we’re both dealing with 400K drives on the same day… :) State of play with mine is that, after much adjustment of the track-0 sensor, I can get it to display a Happy Mac (when a boot disk is inserted) but then a...

Nice work :) With regard to the video loss (I had that recently too), it really is often caused by the pins of the analog board connector (for the logic board cable) as people say - one of the pins stands separate from the others, is often missed in resoldering, and that’s the video signal. I...

Yes - I’ve noticed the same on the two Mac Plus machines I have on the bench at the moment. We’re only talking a small shift of a few millimetres to the left, and I think it happens within about 20 minutes. The solution is to adjust the display position after it’s warmed up, which has always...

Thanks biblit - I appreciate your inspection - unfortunately my photo was not clear and I agree, it looked like the resistor wasn’t connected when, in fact, it is. Sorry about that… it does look like I should clean up those solder joints!

Ah - thanks - that isn’t the Reddit thread I’d found - the one I found didn’t go anywhere :) Great to see a solution, and interesting that it was the 6522 as I’ve previously replaced that in a different board to correct a fault with a mouse not working. My guess is that the 6522 is used for...

Thanks - I’ve seen that one :) In that case, it was the ROMs and the RAM that were faulty. That isn’t the case with this Plus, unfortunately, since the ROMs and the RAM both work ok in another logic board.

This logic board is clean and tidy (unlike some others I deal with that have had battery leakage or damp storage…) and yet unfortunately, it displays the vertical bars typical of a ROM fault. I’ve swapped the ROMs and the RAM with a working logic board, to determine that they are OK. Could you...

It’s amazing that this exact same problem crops up again and again - I’m trying to deal with a Classic analog board doing exactly this at the moment. Blowing air on the optocoupler (an idea I got from someone else) produces low voltage (4.5V) and a wobbly screen, then it quickly recovers (5.0V)...

I’m sorry I haven’t been any help - thank you for tagging me, jmacz - I’ve started the year away on holiday for a month. I have four EMM boards that don’t respond (EMMPathy waits for the EMM to come online and it doesn’t) - so I have a way to go yet, but I do have one working battery which...

Some of mine have it and some don’t, I think it was a mod applied at the same time as the resistors? The resistors seem to have been either applied directly to the ICs with insulation tape and white blobs of glue; or there is that board you pictured with all the coloured wires. Both...

Interesting because I had a 1300 1FFA error code which I think was caused by the interrupt line being stuck as though the button was pushed. I reckon it’s right where those two small capacitors leak behind the buttons, it sets up some kind of via-corrosion problem. I eventually managed to cut...