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Re: Caps a poppin!
Charlie Springer wrote:
> On Sat, 6 Jan 2007 19:09:22 -0800, Tristan Mumford wrote
>> I watched the hatch pattern for a while and noticed it changes a little.
>> Every so often one of the irregular blocks disappears.
>> My guess is it's either corrupt RAM changing states, or the CPU doing a
>> turing machine through the mangled memory map.
>
> Check the bottom (and top) of the board for any evaporated traces.
> Whatever blew up the caps could probably have blown up a trace as well. I
> find a great majority of problems on all types of boards by inspection
> under a stereo microscope.
Nice piece of gear to have. I use a magnifying glass. That's a good idea
though. Odds are it'd be on the underside.
I started pulling chips in a semi random manner, with power off of course.
Just taking one at a time and putting the other back.
I tied taking RAM chips, ROMS, character ROM etc. All it ever did was alter
the pattern a little. I even pulled the 6502. Didn't even affect it. So I
guess the occasional pattern change wasn't due to the CPU.
Then there was one chip that does make a difference. The '153 at E-11.
Closest to the RAMs. Unless I've missed the mark, would that be for
selecting that row of RAM?
When I pulled it the result was a nice white screen.
I may be totally wrong but I can't help thinking that the top of memory is
bad.
Also I had another look at my dead z80 card. Finally solved the mystery I
hope. There's a transistor that looks like the top had some severe heat
damage. I'll try replacing that.
>
> I got my first big ARM4 board that duplicates everything that a PC has
> from VLSI when they could not figure out what was wrong with it. Since it
> was free, I took it home. Close inspection showed a bent under pin on a
> ROM, in a socket yet! Fixed it and everything worked great.
You did really well! Bet you had fun with that. I know I would.
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