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UE8 may be worth a replacement, but it could also be the inputs to the PALs: garbage in, garbage out. In that other thread, whether or not there was a card in the PDS slot caused the problem to come and go. That would seem to suggest that at least one signal connected to the PDS is somehow...

Interesting thought. A similar problem with UF8 was responsible for that bizarre "hidden menu bar" situation that came up on a different thread here last year. UG8 is clocked from C2M (2MHz) so it's counting bytes. I think it's used for generating the HSYNC and TWOLINE signals among other...

I'm really interested in this one since it's come up twice, and defies the usual explanations. Some things we know: * Probably not an addressing problem, since it affects single bits and not whole bytes of data. * It must come from the serial data side of the circuit (VRAM/UE8/PALs) since the...

It's probably not the caps themselves, nor the pads they connect to directly. More likely, the cap goo has rotted out a nearby trace or via which is now intermittent. You'll need to test all the traces near the caps for continuity. It won't be easy since it only happens when the board is flexed.

I'm not sure you need anything beyond a stock system (so yes, I suspect Disk Tools would be fine if there's enough free space for the image). Cmd-Shift-3, and then you get a PICT file.

Ah, here's the thread with the similar problem. That one only showed up when an ethernet card was in the PDS slot. There never was any solution. Can you see if the problem turns up in a screen shot (to see what's actually in VRAM)? Might be worth looking at the D31 line on UC6 too, maybe even...

Absolutely no idea! But I've seen this pattern before so there must be some way for it to happen. It should absolutely be 1 bit per pixel, 1 pixel per clock cycle. It might be some kind of timing problem with loading the data into the shift register. Maybe some clock or signal arrives too...

For every pixel in the stripe, think of it like an AND gate. If the pixel should be white AND the pixel to its right should be white, you get a white pixel. Any other combination (should be black, or should be white, with its right neighbour black), you get black. The floppy isn't striped...

Another reason to suspect the scanning circuit after all: the bars used to jump around. I don't think the checkerboard gets rewritten all the time, though I could be wrong. If the bars were jumping around even within a single frame, it's probably coming from reading back the contents, since a...

Maybe it could be a scanning circuit issue after all. Two observations: 1. The last column, right edge of screen, is a full 8 pixels wide. No missing column. 2. That abnormality on the floppy icon. It looks like there's a clear pattern with the stripes: pixel should be black --> pixel is...

When you say the picture and lines were jumping around, was the whole raster moving back and forth, or just the lines on top of it? Were the lines in any random vertical slot, or always on the same 8-pixel boundaries?

Even so, the fact that the temperature of UG7 ever made a different suggests there's something borderline on the board. The SC line seems like a place to start since it goes from UG7 to the VRAM (by way of a 22 ohm resistor). Does the resistance check out? Any unusual impedance to ground, power...

With the caveat that you've got a lot more experience and so have probably been over all this: it sure sounds like a VRAM write issue. I might check the traces between the PALs and VRAM, especially the ones other than the address or data lines: UC6/UC7 pin 1 (SC), pin 4 (DT/-OE/), pin 7...

It's probably at least as likely to be a (nearly) broken trace or via as a failed solder joint. The most likely cause of that is leftover cap goo continuing to slowly corrode the traces, so look for your culprit around the caps. Given that you see bad screen pixels appear consistently, it...

You won't see anything from the CRT without a video signal from the logic board. For that matter, the high voltage circuitry won't even power up without a horizontal sync signal from the logic board. So if +5V and +12V are fine, and there's no chime and no video, I'd say caps are by far the most...

It's probably caps, but before doing anything with the logic board, check the voltages (+5V especially, and also +12V). The fan is powered from +12V, but +5V could be missing and you'd see the same result. You can find them on the floppy port on the back -- there's a thread here about it somewhere.

I don't know anything about Snooper, but usually the serial tests need a loopback cable installed (i.e. routing the transmit signal back to the receive). If you don't have anything like that attached, then I would expect it to fail.

@techknight so is it only the neck PCB and perhaps the yoke that changed? From the Compact Mac CRT Guide thread I had always assumed the CRT itself had changed pinout or socket from early compact Macs to later Classics, but reading it again I guess it might only be the connectors on the analog...

Are you talking about the connector to the analog board or the connector on the CRT itself? I think the late model Classics and all Classic II CRTs have a different pinout to the earlier compact Macs. Perhaps you could swap the entire CRT neck board and splice the wires to the analog board, but...

Having seen this strange beast in person, I was curious how the 640x400 video board works. Disassembling the "640 x 400" INIT from haplain's archive revealed a few tidbits: Hardware   The DynaMac is based on a Plus logic board with stock ROMs. It appears that the VRAM for the DynaMac 640x400...