Okay, I guess, then I will start looking for a RAM cart, and postpone further tinkering with the scope, unless someone else has some other ideas.
Just a thought: Is there anyone who would be willing ( and able ) to fix it at a sane price?
@RetroTechie et all
Someone is sending me a RAM cart, might take a week or two during holiday season.
Meanwhile I have calibrated the scope and re-checked the pins:
Pin 6 (clock) is on the first shot, for comparison.
Scale is 2 volts per square.
All shots are in the same scale (volts and timing).
Pin 16 has just 5 volts, nothing else.
Does that mean the VDP is dead?
Pins 19 and 20 have some garbage.
Shall I replace the VDP first?
That looks fine as clock signal, so leave VDP alone for the moment...
Pin 16 is /INT, this should be high most of the time with very short low pulses, unlikely you'll see that on a scope easily.
Pin 19 is /MREQ, and shows regular memory request + refresh cycles (no garbage! ). Same for pin 21 (/RD).
Pin 20 is /IORQ, it's normal if that's high >99% of the time (most program code involves very few I/O instructions).
And since it's probably just hanging in a loop or something, it's likely not writing anything either. So pin 22 (/WR) is also what you would expect.
It's too early to say for sure, but (if this machine comes back to life) I think you'll find that Z80 is working fine (have you pulled it out & re-socketed yet ). Looks like it's just reading & executing instructions, as normal. @ This point I'd suspect the RAM, and thus wait for that RAM cartridge to arrive. RAM failure is common for old machines like this, and if just 1 RAM chip is dead, the MSX will get stuck very early in the boot process. Other things you could check:
oops. my bad, sorry. I meant to say - 20 and 22 had strange shape... And - yes, I have reinserted the z80, as you've suggested.
BTW: In case I will need to replace the Z80, does it have to be by the same manufacturer, or any will do?
Any Z80 will go. Clones will go as long as they are the compatible ones. I believe that it is even possible to use another clock graded Z80. The zilogs are very cheap though on ebay.
Please, post here, a full resolution pic of the mainboard, but the soldering side.... FULL FULL resolution... take pictures fron at 45º left side point of view & 45º right side point of view.
That way, a technician's eye can examine the solders.
you already tried to push in its sockets the ROMs chips (if any socketed)?
Dunno if you tried already, but does inserting a game cartridge have any effect?
if it does boot a game cartridge it is most likely a ROM problem.
check any socketed IC that starts with the number 27..... (like 27C512 or alike).
You might have luck just removing+reinserting them once or twice. (that usually solves small oxidation problems on IC pins in sockets)
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