MZ700 video problem

AndyR
Posts: 7
Joined: Tue Mar 17, 2020 2:40 pm

MZ700 video problem

Post by AndyR »

Hi All
First post on this great site!
I'm trying to resurrect an old MZ700. Have got the power supply working but the video output is scrambled - see photo.
Note that the picture is not entirely random, it's identical each time I switch the machine on.
I was thinking RAM maybe?
Any ideas?
Cheers
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MZ700.JPG
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Pacman
Posts: 132
Joined: Mon Feb 05, 2018 2:59 pm

Re: MZ700 video problem

Post by Pacman »

I had a similar problem with one of my MZ-700 and removing, cleaning the connectors and reconnecting the CG ROM re-worked.
AndyR
Posts: 7
Joined: Tue Mar 17, 2020 2:40 pm

Re: MZ700 video problem

Post by AndyR »

Hi Pacman, I'll give that a go and let you know how I get on.
hlide
Posts: 504
Joined: Thu Jan 25, 2018 9:31 pm

Re: MZ700 video problem

Post by hlide »

I have a similar issue with my fourth MZ-700 (bought as such). I tried to swap every IC (CPU, ROM, CGROM) to a working MZ-700 and they work. In the meantime, the PSU on the problematic MZ-700 broke. So I suspended my trials. Pacman, I'm surprised it was an issue with CGROM because you can see characters well, which means address decoding and output data seem good on the CGROM. I would think it might be an issue with VRAM which gave random attributes (apart from a periodical $FF or $00 to give that checkboard?) and characters.
Gortho
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Joined: Thu Mar 22, 2018 3:53 pm
Location: Poland

Re: MZ700 video problem

Post by Gortho »

Does it react to any input? key presses? Or it's completely dead?
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Pacman
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Re: MZ700 video problem

Post by Pacman »

hlide:
It is quite possible that it is VRAM. For my part, I juggle the CG and Monitor ROMs that I reprogram, and I only say what I see. Besides, we must add in my previous message the same thing for the ROM monitor this time.
AndyR
Posts: 7
Joined: Tue Mar 17, 2020 2:40 pm

Re: MZ700 video problem

Post by AndyR »

I haven't had chance to try anything out yet but in answer to Gortho's question there wasn't any response from the keyboard.
By the way, does the MZ700 beep on startup becuase this one doesn't - might be a clue if it's supposed to?
hlide
Posts: 504
Joined: Thu Jan 25, 2018 9:31 pm

Re: MZ700 video problem

Post by hlide »

There is a volume potentiometer behind, just set in the middle. Yes there is one beep when you power it.
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Pacman
Posts: 132
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Re: MZ700 video problem

Post by Pacman »

I made some tests, and those that reproduce a blow on the problem, it's a defect in the MONITOR ROM, i.e. when I remove the ROM and I restart the machine, it locks in exactly the same way on the random display of characters and colors on the screen without doing anything. I'm investigating a problem with the ROM MONITOR to be replaced by a freshly programmed ROM. (MONITOR 1Z-013A)
It makes sense since the MONITOR does not run, and the VRAM memory is not initialized.
Certainly the machine is working properly.
AndyR
Posts: 7
Joined: Tue Mar 17, 2020 2:40 pm

Re: MZ700 video problem

Post by AndyR »

Hi Pacman, you are correct. If I remove the ROM it's exactly the same.
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