I recently started looking at my emulator 2 again, having got a debug eprom. Trying to use the eprom, and surprise surprise it won't work. It loads and says static ram okay, but trying to do any tests, and it would hang. Okay, so there must be a fault somewhere on the main board, decided to go back to basics, the finger test. I discovered that there was a flip flop getting incredibly hot, so hot it burns. The flip flop that controls the RAS and CAS strobes to the RAM, which makes sense, since the memory test could not even access the RAM to give a pass or fail. Replacing that, and horay the debug memory test works! Also the HxC is now deciding to read floppy images, but! It still won't work.
I ran the memory test on the eprom, and it passes all memory until it reaches bank 8, the piggy back memory board. That then immediately fails, it cant access any bank on the piggy back board, so its not just some bad ram, theres a fault with the ram addressing somewhere, could be buffers, could be latches, could be decoders, theres a lot going on with the ram in this machine.
Trying to load an image with the HxC, when it reads the tracks, it skips tracks 3-10, which I think I read somewhere are the tracks that contain the OS. It continues to read tracks all the way up to 78, then it stops. The display shows the patch name, but none of the buttons respond or do anything. Makes sense if its skipping loading the OS. Trying with a real drive and disk and it stops after 3 clicks and gives disk read error, consistent with stopping at track 3 on the HxC
Also, when I run the Disk test, it gives me this error message
CRC: CR1: WT: WT1: XFR:
0000 807F 0000 0000 4C18
I'm not sure exactly what it means, other than the CRC (cyclic redundancy check) is coming back as failing. So it cannot read the disk properly, or it cannot store the memory on the disk properly. Which also makes sense, as it cannot load the OS. XFR is data transfer error, which I guess makes sense too as it cannot transfer the data on tracks 3-10 to the memory to compare it at the end.
So I'm currently stuck trying to work out, A why the piggyback memory is failing constantly, and B why it won't load the images properly. Possibly the same fault but the OS isn't loaded into the piggyback board, so maybe not. I'd like to point out that this has a new mean well T60 PSU, so I'd like to think that the PSU is not the problem.
Its quite specific, but does anyone have any idea/clue as to how I track down this problem? The whole thing is covered with 74S244 buffers, so most likely one of them down, but I don't have one of those fancy chip testers or a logic analyser, so I feel I may be stuck
I really don't want to order loads of chips and start randomly blanket replacing, but I'm not sure what else to do
Author