You are correct in calling it a “anode cap”.
It is not a suction cup. It’s there to keep the 10,000 volts in.
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- Thread starter PotatoFi
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It is not a suction cup. It’s there to keep the 10,000 volts in.
Sadly, replacing the optoisolator/optocoupler did not fix the problem.
Ok, that is all of the ideas that I had. Other than find a replacement Analog board, which would be a shame as this is a 128k board and almost all of the caps are new.
Is this the glass tube fuse very near the power plug and filter? If so, yes it is good, I tested it for continuity.
Ok, that is all of the ideas that I had. Other than find a replacement Analog board, which would be a shame as this is a 128k board and almost all of the caps are new.
I don't have much experience as my Plus only needed a ram replace, but my 128k came from a guy who replaced the analog board due to a bad flyback transformer. Now, I know that these flyback transformers are known to go bad so I wouldn't be surprised if that was causing your issue. If this is the case, then the flup noise could be the flyback repeatedly arcing internally.
Page 24 of the Dead Mac Scrolls also says to replace component CR20 on the board, right next to CR21. This component is an MBR1045 Schottky Rectifier Diode. In fact, pages 20 through 29 deal with this issue entirely. You didn't mention these steps so I thought I should point them out. Also, if you deduce that the flyback is the issue I could possibly send you one.
Thanks for chiming in here @MacAttack, I'm feeling pretty stuck on this and appreciate the help.
The Dead Mac Scrolls has been my #1 resource for this Macintosh Plus project, but I think there's a big gap in my knowledge around how to test for in-circuit resistance. I did test CR20, but I didn't really understand what setting to use on my multimeter (200, 2000, 20k, 200k, or 2000k), and I didn't understand what 31 Ohms/30 Ohms meant. Is that a range of resistance, is that a 31 or 30 statement? Just not sure.
If I remember correctly, resistance was at about 100, but steadily dropped to 35 or so during a few minutes (it took some time to fall to the "correct" amount). So yeah, NOT confident that I did troubleshooting properly.
In addition, I'm not finding the MBR1045 in the correct axial formfactor. If anyone has advice on locating the correct part I would appreciate it - I've been using Arrow.com for components because they have free 2-day shipping.
Many thanks for the hand-holding on this... I want to see this Macintosh Plus live, and I'd really like to preserve the analog board.
Do you have details? I have an SE here that is the same. Resoldering J1 did no good. Where was the filter?
For my Macintosh SE FDHD, it ended up being a broken filter near J1. It was the dumbest thing! The filter is susceptible to being broken off when removing/installing the analog board (it basically touches the CRT). Details here:
Keen to discuss your SE more, let's pick up the conversation in the SE No Video No Raster thread!
Hrm... I don't see any fuses on that cable? There a big magnet that I think acts as a filter, but not fuse. Not on two Pluses that I have right now.
Ok, I know it's been awhile, but here's where I am at:
Loom Fuse Investigation
I've checked for continuity on all wires. They're fine, including the blue one.
CR20 Rectifier Replacement
I replaced CR20 with an MBR1045, connecting the dot side (anode) to positive, and the non-dot side (cathode) to negative. Sadly, no fix: the Mac still does the exact same thing.
At this point, I think it's time to find a replacement analog board or replacement flyback. Sadly, a flyback is worth more than the Mac Plus itself, so I guess this one is going to go on-hold for awhile.
Loom Fuse Investigation
I've checked for continuity on all wires. They're fine, including the blue one.
CR20 Rectifier Replacement
I replaced CR20 with an MBR1045, connecting the dot side (anode) to positive, and the non-dot side (cathode) to negative. Sadly, no fix: the Mac still does the exact same thing.
At this point, I think it's time to find a replacement analog board or replacement flyback. Sadly, a flyback is worth more than the Mac Plus itself, so I guess this one is going to go on-hold for awhile.
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