My MSX machine just died. Is it final, or can it be fixed?

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By misterspin

Resident (56)

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06-12-2011, 13:16

My favorite MSX Hitachi H2 just stopped working:
When I turn the computer on, power LED turns on, the monitor screen turns black, but then the OS is not booting, and nothing happens from there on.

What can be done to further diagnose it?

I'm thinking of getting an oscilloscope to check if the main clock is running, but that is the only idea that I have.
My questions are:
- Is it realistic to try to revive it?
- What other tests I can do?
- Are there any online resources that I could use? So far google didn't help much.

Though I am not a hardcore H/W engineer, I could've, if needs be, replace a chip or something like that...

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By Daemos

Paragon (1668)

Daemos's picture

06-12-2011, 14:21

Allright lets start with the obvious. Have you allready retraced the technical manual with all the schematics an such. Do that first so you know where your connections are.

Then Measure all the powerlines. See if the nescessary voltages are there. Usually +12V -12V and 5V

Report back at us and we will do our best.

By misterspin

Resident (56)

misterspin's picture

06-12-2011, 14:40

Daemos, I am afraid, I won't be able to find a tech manual / schematics. But I will check the power module and see if the proper voltage is there. Something tells me, it is, as the embedded cassette player if functioning (rewind, play, etc) and the power LED is turning on. Caps lock LED is not on / toggling.

Anyhow, I will check the power and report back with some pictures.

By RetroTechie

Paragon (1460)

RetroTechie's picture

06-12-2011, 15:06

Similar test as Caps Lock response: with audio output connected, type CTRL-G a few times - on a working machine that should give a short beep.

- Is it realistic to try to revive it?
- What other tests I can do?
- Are there any online resources that I could use?

Depends on what's broken, what means/knowledge you have available & value of the machine. Usually the difficult part is getting someone who knows a lot about MSX hardware internals, machine & equipment together. A forum like this is a way, but not optimal... Eek!

Dont know this MSX Hitachi H2 personally, is it an MSX1? MSX2? Maybe you could take a photo of its mainboard so that we know what's on it?

If power LED lights, but Caps Lock doesn't respond, it's likely a CPU / ROM / RAM / MSX-engine issue. If any of the IC's are in sockets, a simple thing to try is pull these out & re-insert in the IC socket. Of course with power off, and be careful that you place IC's back the same way! Also: do you have any external RAM cartridges?

By misterspin

Resident (56)

misterspin's picture

06-12-2011, 16:02

type CTRL-G a few times - on a working machine that should give a short beep.
Tried it, and there was no sound.
Depends on <...> what means/knowledge you have available
I could get (and I know how to use Smile ) most of the necessary tools: oscilloscope, multimeter, etc. As for me, being a programmer, I have an intermediate knowledge of electronics. And a collective power of knowledge of fine folks at this forum. Smile
value of the machine
Well, it's priceless for me, seriously. Being a hobbyist / fun of MSX and all that... But you know what I mean.
is it an MSX1?
Yes, it is MSX1
Maybe you could take a photo of its mainboard so that we know what's on it?
Here, someone has already posted exact same machine earlier, but I will make more pictures myself:
imageshack.us/f/268/cimg7513.jpg/
do you have any external RAM cartridges?
Yes, I do. I tried to insert them and re-boot the machine.

By Daemos

Paragon (1668)

Daemos's picture

06-12-2011, 18:27

Wait a minute... Haven't I seen that mainboard somewhere before?

Yes there was another guy not so long ago with a black screen problem and he got his MSX back to life. Not the same cause of error though. Eventually almost everything was fried. Memory, CPU, some glue logic ic's.

I may be mistaken though.

Anyway did you allready check the voltages. If absolutely nothing is happening you may be missing +5V.

By misterspin

Resident (56)

misterspin's picture

06-12-2011, 19:21

Wait a minute... Haven't I seen that mainboard somewhere before?
Some fella from Japan tried to sell his stuff, this was his photo. Smile he misteriously disappeared, though, you can see the thread here: www.msx.org/forumtopic13538.html , but I have nothing to do with him other than I tried to buy his Hitachi. :)

Anyways, here are some more (mine) photos:

https://picasaweb.google.com/111314133182937932580/MSXRepair?authuser=0&feat=directlink

If absolutely nothing is happening you may be missing +5V.
I will dig out my multimeter to check the voltage at the power supply and on the logic board and post the results here.

Brief symptoms, again:
- CTRL-G and Caps Lock doesn't work,
- power led is on,
- embedded cassette recorder works (rewind, play etc), and there is normal sound when the cassette is playing,
- monitor screen turns black when computer turns on.

By misterspin

Resident (56)

misterspin's picture

06-12-2011, 21:39

Just checked the voltage: +5v exists. Question

By Manuel

Ascended (14738)

Manuel's picture

06-12-2011, 22:19

sounds like a short-circuit somewhere.

That photo isn't very sharp. Can you post a higher resolution one, so I can have a look at the chips and read the texts on them?

By RetroTechie

Paragon (1460)

RetroTechie's picture

06-12-2011, 23:24

Just checked the voltage: +5v exists. Question
That's measured on the main board itself, not just @ the power supply?

I could get (and I know how to use Smile ) most of the necessary tools: oscilloscope, multimeter, etc.
With "get" I hope you mean "use/borrow", not "buy for this occasion" ? Wink

At this point it would be very helpful to know what's going on at various Z80 control signals. Especially the Z80 clock input, but also signals like /MREQ, /RD, /WR, chipselects at the ROMs (pins 20 / 22), and RAMs (/RAS, /CAS). I myself have a homebrew logic tester I'd use for that, which has a small piezo buzzer that gives an acoustic indication of frequency. If you're willing to dig something like that up, it would help. An oscilloscope is even better, but perhaps a bit overkill for simple diagnostics. Another thing you might do is switch machine on for a few minutes, and feel with a finger if any IC's on the main board become suspiciously hot. As for suspects:

PSG: probably would garble sound, but computer should still work.
RAM: could cause dead machine, but you tried with external RAM & that didn't help.
ROM: possible, but in this respect old EPROMs are more often problematic than factory-made ROMs. And if a few single bits fail, chances are the machine would still boot.
8255: not a very complex chip, doesn't get hot under normal operation, usually very reliable.
Z80: dead ones do happen, but it's quite rare (usually results from something inserted into cartridge connector while powered on).
glue logic (those little 74xx chips in between): possible, but normally very reliable.
IC socket contacts: no sockets used here AFAICT, so doesn't apply here.
Videochip: runs quite hot under normal operation, in most MSX1's I have they're half dead. Normally also supplies Z80 clock so when 'dead enough' that would also cause things like Caps Lock response to fail.

The latter normally has a cooling plate on top, which is not installed on this machine's VDP. So if I'd had to take a gamble, I'd put my money on the VDP @ this point. Should that turn out to be the culprit: do you have a replacement for that?

Btw: what's that 40-pin chip between Z80 (Sharp LH0080) and 8255?

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