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Nice detail. I think you have the right idea, but maybe need to take a simpler approach to prevent the rabbit hole effect. ;) You shouldn't have to do infinite tracing. The starting point is to figure out what data lines are on those 2 (or 3) devices, factoring out power, ground and clock (they...

If you are checking the board in a failed state, do the resistivity test again. If there is a bad trace or via, it may not be a full open. It could also be related to power, ground or maybe a bad cap. Check resistance on all the power/ground links. If it's a bad/intermittent device cell...

Stranded copper is good to use for trace repair as @zigzagjoe says. When flattened, you generally want something that is at least ~10 mils wide (standard trace width). Try to match the existing width whenever possible. But anyway -- not super-important at the moment, since it's working, which is...

You could probably also use a very small amount of fingernail polish to fasten and protect thing, but soldermask would be best.

Great job! You did it! (y) Very creative rework! And most importantly, it works! You were definitely losing the high order RGB bit. What a weird, kind of lucky hardware issue! If you want to try to hide the rework vs. running the wires over the edge, you could do the following (but it's a bit...

Yeah - it shouldn't be doing that. Must be a hardware issue. Clean the whole board with a brush and compressed air, eliminate any debris shorts and address the rusty SRAM. The SRAM devices are probably still available if it turns out to be the culprit and not just a pin connection/corrosion...

I looked more closely at that corroded SRAM. I guess you should pull it, clean it and resolder it. There could be a corroded connection. I think that SRAM is only being used by the accelerator. The main frame buffer on board is the zip RAM.

Great - that helps. Different Mac? Anything non-stock in your IIci? Just rule it out. I just messaged you about the fact that it looks like the RGB values on accelerated transfers are missing the high order bit. So, 0xffffff (white) is being seen as 0x7fffff (cyan). Given that you have seen...

OK - that fixed the ROM issue then. ;)

For reference, on the original Spectrum/24 PDQ (Codename: Shockwave): SMT01 is the custom graphics controller (became SMT02 in later SuperMac board designs) the 3 BSR02s are the custom bit-shift registers (became BSR03s in later SuperMac board designs), the Bt453s are the DACS (of course -- and...

Or, you could actually have a super-awesome cosmic ray detector. :unsure: Ultimate delayed feature creep!

Do you have a local Voodoo Shaman? Chicken blood might stain the ROM label slightly, but is otherwise washable.

I don't think the problem is with random noise artifacts. It sounds like an address translation issue -- and it only takes 1 upper-order bit to put a blit into hyperspace. Early-on, the Spec/24 III daughtercard did have an acceleration device/timing problem with thermal pixel drop-out, but that...

Great job! 👋 Really happy for you! Nice to have a fully working board, and it was worth saving! Yeah, the -ES2 DAC substitution was probably a stretch, but glad you were able to find a comparable Bt473 part. Also, it is helpful for others that you confirmed that the AD/Bt parts are a direct...

The v1.27 ROM should be backwards compatible with earlier Spectrum24 PDQ boards that were originally released as v1.11. The Xilinx parts were different on earlier boards. I think the later devices had slightly faster timing and there were some Xilinx code changes to accommodate them. SuperMac...

Pull-up or pull-down -- a 10k is fine - it doesn't matter in this case. The pins appear to be no-connects, so you don't really need to do this test. It's true that the chips face inward when the daughtercard is assembled. It's also true that the problem is near the center, which might be in an...

Bolle is (obviously :D ) correct about the internal pull-up. Here is what the datasheet says: "The input and I/O pins also have built-in active pull-ups. As a result, floating inputs will float to a TTL high (logic 1). However, Lattice Semiconductor recommends that all unused inputs and...

They are probably just no-connect inputs that were never tied low or high. So...what you could do is take those 2 pins and put a 10k axial pull-down on them to ground (put one end of the 10k resistor lead to nearby ground and j-bend the other end and solder it across those 2 pins). Then, if the...

In terms of no-connects, those pins might be unused inputs. According to the spec, unused inputs should be: 1. tied to adjacent inputs, 2. pulled up to Vcc or 3. pulled down to ground (maybe most likely). So, check continuity to adjacent/power/ground - if one of them is true, then they are...

It could be a device issue...maybe an intermittent wire bond. If you had no change in resistivity on the board connections during cold/hot cycles when depopulated, then it doesn't seem like the PCB. And, if the 2 pins are open whether cold or hot, they are probably no-connects and likely don't...