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The PSU should be a Sony unit, most of them have bad output capacitors

I think so, all plus roms should work

Yes, but unless you change the floppy drive (and its cage) too, I don't see a reason. Also, 512ks are a lot harder to find than 512kes, I suggest keeping you 512k in its original configuration.

I think increasing R45 is going to make the circuit even less stable. I also tried changing R44 and R48 (which should make a voltage divider) to no avail. No matter what I do, it becomes less stable or the display starts wobbling

Here are a few measurements: Unfortunately my digital scope is not isolated and the Idea I had in mind (hooking it up to a UPS) only lasted for a few minutes. So I had to use an old 15Mhz Philips with a million hours on the CRT This what I get on the Gate of Q10 This is test point 6...

So far I've gone from bad to worse: by decreasing R45 to 200Ohms and increasing R44 and R48 to 1K, I've only gained about 7 volts or so, but now the screen is wobbling (or should I say twerking?)

You could always ground the negative rail if not needed

Yes, the ROMs are standard (but each pack has a different size). The board itself just contains the two memory chips (one ROM for the tests, one EEPROM for the logs), a resistor and the connector for interfacing to the TechStep, so it should be possibile to recreate said board to house a modern...

Great! It looks like those video issues are getting more and more common, probably because those ICs don't like capacitor goo around them. Out of the three boards I have, two of them had the same issue as yours, and the third one had a broken Data line on the SCSI IC.

The Apple II was one of the first computers to use a SMPS, and the Classic also uses an IC that was probably around when the Mac was first made, but I guess they thought "why bother improving a thing that already works?"

Tomorrow (actually, later today) I'll swap the resistors with trimmers (I usually put 2x the original value to have some room both ways) and see what happens. Also, where is R60? I cannot find it on my schematic (probably because I'm way too tired)

I'm not an EE (I study telecommunications), but I think I should increase the resistance on the gate (by adding a resistor) to limit the current and lower R45 to bypass some current around the gate cathode junction, to make it less sensitive

Here's a picture of the carnage: This leads me to believe that the original SCR might not be a E0102. The front is blown, so I thought it was an E0102 by reading this post: https://68kmla.org/forums/index.php?/topic/20838-macintosh-128k-240v-analog-board-component-identification/?p=211733 I...

Thanks for the datasheet. comparing the characteristics between the two, I don't see that big of a difference that would cause such problems I've also tried a P0102 and it still behaves exactly the same way, and those are pretty much identical...

Sad news: nothing changed. with the 1K resistor it still reaches 63Vac and then starts flubbing. maybe tomorrow I'll rig up an isolated oscilloscope and I'll probe the output. (I don't have an isolation transformer, but I could power the scope with a UPS detached from the mains) I think it...

I'll try right now (it's 00:30 in the morning here, and I'm half asleep), Hopefully I won't fry it

Really? so essentially I was using the noise in the pulses to drive the main transistor?

If a datasheet is available, I cannot find it. And if there is one around in the inernet, it would probably a low res scan taken fron an 80's book or magazine with diagrams drawn by hand and waveforms acquiried with film cameras. I have older books about semiconductor replacements, but they...

This is the third time that I found a board with this kind of issue, the same fix also works with board that produce low voltages at startup and ramp up as they heat up. The Board in question is a 630-0560-240V. This is a 240V international board, but the same fix should work on the US ones...

Actually yes, I was able to fix a RAM issue on my SE/30, it didn't like mismatched pairs. It also fails serial handshake on the same machine, probably another broken trace (the board is not in great shape)