by matsondawson on Sun May 15, 2011 12:23 pm
Ok, so I've looked at the CPU's using a logic analyser and note that what I think is the main one in the middle seems to be doing nothing but running DRAM refreshses.
So I replaced it, and also the main one just in case. No change it's still broken and doing the same thing.
So I think I'll have to work through each of the LS series chips surrounding the CPU to see if I can find a broken one.
Interesting thing is desoldering on this board is a complete pain.
For both CPUs there was one pin that didn't seem to de-solder, I had to put the soldering iron on full power just be able to wiggle the cpu's out, that means the solder won't even melt (just softens) at maximum temperature for those pins.
I suspect all chips may be this way, as in the RS232 section someone has had to replace a chip, but ripped off a bunch of vias and tracks doing it. So now it has some ugly hunks of wire soldered on the board.
Also the board is very brittle, the epoxy cracks just from looking at at.
BTW, isn't a Z80A and a D780C-1 compatable? I tried a known working Z80A replacement and it didn't work.
Last edited by
matsondawson on Sun May 15, 2011 12:48 pm, edited 1 time in total.