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Good thoughts, thanks. I think the HOT and its driver (TEA2037) are okay: there's a sensible signal at the HOT gate (not itself diagnostic), and a reasonable voltage appears on the one flyback secondary I felt comfortable to test with a 10x probe. When I retrieve my 100x probe from the office I...

DP5 is on the primary side of power supply. Why it shorted I'm not sure. See attached reverse-engineered schematic. (Apologies for low-quality photo; no time to format this properly right now.) A few components I couldn't read the value, especially the SMT caps.  In any case, I believe RP13...

I've worked out a schematic for quite a bit of this monitor by now. It has some similarities for the later Classic analog board, though with considerably more complexiy in the video circuit for various types of geometry correction. The CRT neck board looks like a pretty good design on which to...

The main challenge with VGA on the internal monitor is that the horizontal scan rate is different, and this requires substantial modification to the existing analog board. There's a secondary challenge around grayscale vs. black and white, which needs a different CRT neck board, but that's an...

I was thinking the same. Is this an internal card or an ADB device? snuci do you have pictures of the board(s)?

The internal monitor will work fine with the Radius card. The black screen will be due to a fault with either the logic board or the analog board. If it's an SE/30, start by recapping the logic board. The Compact Mac forum has a number of threads that might be useful for how to diagnose having...

I'm working on repairing a non-functioning Macintosh 12" Monochrome Display. The proximate cause seems to be that resistor RP13 is missing -- completely gone, nowhere to be found, nothing but a blackened set of pads left behind. The underlying fault appears to be that DP5 has shorted, but...

The checkerboard is from caps on the logic board, but the unstable image is almost certainly the analog board. It will also need a full recap. I've come across all sorts of unstable screen issues from bad caps in the Classic analog boards. For whatever reason they are often in much worse shape...

For what it's worth, with a Classic II the stuff I was trying to do on the "Compact Mac retina display" thread might actually be possible. The flyback used in all the compacts up through the early Classic basically can't be run much above 22kHz -- there's so much internal capacitance in the...

It's definitely a vertical sweep problem, so as @techknight says, nothing to do with the flyback. What you don't know is whether the problem is on the analog board (vertical drive circuitry) or the logic board (no vertical sync signal). A scope is the right way to test that, but if you have a...

Never mind, you're right. I had remembered that the SE had a faster video circuit compared to the Plus, but they both use main memory. It's hard to debug this without a schematic, but the closest I can find is Figure 12-1 (p. 251) in Designing Cards and Drivers for the Macintosh Family. Video...

If it was a RAM issue you'd have a Sad Mac, or at least other crashes. I'm pretty sure that the SE, like the SE/30 but unlike the Plus, has separate video memory that doesn't use main RAM. Unfortunately, I can't find any schematics of the SE video circuits. The logic board schematics online are...

Here's a weird idea, maybe not a good one but probably not harmful (@techknight?). Try shorting out R29, a 22-ohm SMD resistor on the bottom side of the board, just under UI6 (I think). R29 is in series with the CLK16M signal (i.e. the main system clock), which is generated by UI6. If there's...

Interesting! The question then is whether UE8 is faulty, or if it's just sitting on the very edge of spec because of the other load on the PDS slot. I wouldn't bother heatsinking UE8: try replacing it and see if the problems still persist.

It looks like the horizontal drive is switching on and off. That would be why you see the bright squiggly line, which would be the horizontal sweep collapsing (same thing the Lisa does sometimes when powered down, I think). It's also why you hear the noise. The flyback is also powering up and...

I've seen something similar twice before, and as far as I know there's no verified cause yet: The second one is also related to the presence of a PDS card, which makes me think this has something to do with loading on one or more signals. If I had to guess, I'd say it would be the 16MHz...

It could be the magnets around the yoke, or maybe even the yoke itself. It's interesting that the horizontal yoke coils contain a diode and other components inside the case. See the thread below. I don't know exactly what the diode is for, or what the effect might be if it failed, but almost all...

I have one of these, with the cable (no FPD though sadly). I'll try to beep it out in the next few days and post the results back here.

Pin 1 and pin 8 are generally NC on most common single op-amps, and if they were used it would be for minor offset adjustment. I think you can safely ignore the missing pads. From memory, sound issues can come from UB10 and UB11 (Sony sound chips) as their location makes them prone to being...

Sounds like it could be a video card for an external mono (TTL) monitor. Many of them used a 9-pin connector, and the SE can't address more than 4MB of memory anyway so there wouldn't be any obvious reason to make a memory board for it. Post a photo?