Large problem, MSX computer not displaying anything

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بواسطة RetroTechie

Paragon (1563)

صورة RetroTechie

06-10-2009, 00:54

If the CAPS LOCK doesn't respond, that means the Z80 doesn't get to a point where it waits for user input. Often because something else failed (a ROM, EPROM, circuit track broken, short circuit, clock signal from VDP gone etc). Z80's themselves don't die very often.

You could try to pop out any IC's that are in a socket, and put them back in their socket once or twice. The socket contacts may have corroded, and some flexing of the circuit board (during transplant operation) may be just enough to 'push a contact over the edge'. Small chance that is the cause, but easy to try. Or do a very thorough inspection of the board to see if you can find cracks / shorts in circuit board traces. Oh and: whatever position that service switch is in: try the reverse setting. If no effect, reset to original state.

Some other things to try: you did try pushing the reset button, after powering up, did you (just in case)? And perhaps try with original powersupply, not the Xbox one. And did you check those supply voltages on both MSX boards (main + analog) themselves, for example across supply pins of some IC's on those boards (any 74LSxxx logic IC: bottom left pin = GND, upper right pin = +5V)? As opposed to checking at the power supply connector?

Which chip is it? Is it dumped? Can I just burn a new one?
Nope, it's a videoprocessor, not a memory chip. Only common source for an MSX2 videochip is another MSX2. Or you could replace with a V9958, but difficult unsoldering job and needs some re-wiring too. Only worth the trouble & expense if you're 100% sure that is what's broken (and only that).

بواسطة Adam

Rookie (18)

صورة Adam

06-10-2009, 02:05

The power supply I was using is the original. I tried resetting a few times, and noticed the back of the computer clicks only when the switch is pressed. I will try pressing the IC's back into place. There was one place where a trace was lifted near a controller port, but I wired it by hand to where it needed to go. Maybe thats the problem? A couple of traces look abrased, but definitely not cut all the way through the track. I will test out some things.

بواسطة RetroTechie

Paragon (1563)

صورة RetroTechie

06-10-2009, 04:55

If you have one: try connecting an external memory mapper (or plain 16~64K RAM cart), just to exclude the possibility of a dead RAM chip. And when you have external RAM plugged in, that would be a good time to repeat that CAPS LOCK response test.

بواسطة Jipe

Paragon (1594)

صورة Jipe

06-10-2009, 13:33

if the "maintenance" switch is broken the msx don't start just click in k7 relay

بواسطة Jipe

Paragon (1594)

صورة Jipe

06-10-2009, 16:02

try the C-INCH composite signal and the C-INCH sound signal present on video board

بواسطة flyguille

Prophet (3031)

صورة flyguille

06-10-2009, 19:58

mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

wait guys, he is saying that before to transplating all was ok.......

maybe, .,...... what about CARTRIDGE POWER switches? are all ok?.....Normal Open, right?....

maybe you needs just to push chips in sockets..... (or extract, clean, re-insert) the movement may cause fakes-contact.

others things, that can be, verify if all is well grounded, on original cases there is not a interference shield screwed in several points to MB?

try to ckeck if those points are well grounded anyway...

بواسطة Adam

Rookie (18)

صورة Adam

07-10-2009, 00:07

Could it be the grounding!!?!

The original case is 100% metal, and the one it's in now is all plastic. I took off all of the metal casing around the video board and stuff too. Could the be it? How can I fix it?

بواسطة RetroTechie

Paragon (1563)

صورة RetroTechie

07-10-2009, 00:58

maybe, .,...... what about CARTRIDGE POWER switches? are all ok?.....Normal Open, right?....
The NMS8250 doesn't have any (few MSX models do, btw), and works fine without cartridge slots connected.

verify if all is well grounded, on original cases there is not a interference shield screwed in several points to MB?
NMS8250 has metal case which doubles as ground/shielding, but is mostly for mechanical strength (for example, because shape invites people to place heavy monitor on top). Some metal plates inside, but again: for keeping things together, regulate airflow/cooling, not shielding.

I'm pretty sure a plain NMS8250 mainboard lying loose on the table, with analog board & power supply connected, will work normal. Remember the metal case isn't grounded (as: in connected to ground pin on wall outlet) anyway. The power supply will have some coupling to AC lines, with or without case, and it's like that for most electronic equipment.

So forget all that - I'm still guessing it was something Adam did during the transplant operation, we just don't know what. Question

بواسطة Adam

Rookie (18)

صورة Adam

07-10-2009, 02:18

I think it just may be the trace...

I will photograph it or something. One trace was lifted removed a controller port, so I just used an actual wire to connect the two points.

بواسطة Jipe

Paragon (1594)

صورة Jipe

07-10-2009, 13:18

the 8250 work outside metal case
then i modify to 2+ i'am testing and no problem

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