MZ700 video problem

Hansona
Posts: 1
Joined: Sun Oct 31, 2021 10:44 am

Re: MZ700 video problem

Post by Hansona »

Hi all, I appear to have a similar issue with my MZ700, the checkerboard pattern on boot up along with no beep. Only difference for me is that the pattern changes everytime I switch on. Did you manage to resolve your issues? Was it related to Monitor ROM? I've taken out both Monitor ROM and CG ROM and cleaned + replaced but no joy, same issues. Are replacement ROMs available??
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Pacman
Posts: 172
Joined: Mon Feb 05, 2018 2:59 pm

Re: MZ700 video problem

Post by Pacman »

I haven't seen any for sale, but it's possible. A 2732 and an EPROM programmer should suffice. The images are on the site in the download section. Maybe one of the forum members living in the same area as you could do it for you.
S_U_C
Posts: 69
Joined: Sun Feb 17, 2019 6:41 pm

Re: MZ700 video problem

Post by S_U_C »

The screen full of random characters on power up that is different each time you power up is the norm and suggests that the CPU is not running as the screen is cleared by code. A faulty M-ROM or no M-ROM normally produces a repeating pattern or vertical lines.
The CPU needs a automatic power up reset pulse (low) to reset its PC counter to 0.
Have you tried the reset button on back of the machine.
Also the reset signal must be high for the CPU to run, it also needs a clock signal.

PS
I have written a new EPROM for the MZ80K/A that tests the VRAM, RAM, unused M-ROM address lines, the 8255, 8253 and the flash timer 555(6) that is out for tested at the moment. It comes with a 19 page PDF with its development and instructions.
Will post it shortly after tests.
hlide
Posts: 681
Joined: Thu Jan 25, 2018 9:31 pm

Re: MZ700 video problem

Post by hlide »

S_U_C wrote: Mon Nov 01, 2021 11:33 pm I have written a new EPROM for the MZ80K/A that tests the VRAM, RAM, unused M-ROM address lines, the 8255, 8253 and the flash timer 555(6) that is out for tested at the moment. It comes with a 19 page PDF with its development and instructions.
Will post it shortly after tests.
Does it use keyboard? I seem to get repeated failures on a real (Japanese) MZ-80K with my KBD routine (stack starts at the bottom of VRAM) for unknown reason.
S_U_C
Posts: 69
Joined: Sun Feb 17, 2019 6:41 pm

Re: MZ700 video problem

Post by S_U_C »

Yes and no.
It only scans the keyboard and displays a symbol on the screen if a key is pressed.
Normally a space is displayed, if there is a stuck key(s) then a symbol is displayed but the symbol changes when another key is pressed.
I am not using any stack area, no CALLs or PUSHes used, the SP reg, is used as the loop counter for the RAM test.
psmart
Posts: 138
Joined: Thu Nov 21, 2019 10:12 am
Location: Leeds
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Re: MZ700 video problem

Post by psmart »

Hi John,

I keep seeing quite a few posts coming up about MZ-80K/MZ-700's not booting/video problems. Would it be an idea to post your binary in a sticky so that enthusiasts with a prom programmer can blow your test program? I (and no doubt others) could also offer an at cost (prom+postage) aid so at least people could see if their machine functions via use of your program in an eprom or if it shows that they require more experienced repairs.

Would be interesting to see the actual reasons behind failures overall, EPROM decay I'd put at number 1 but could quite easily be the RAM/buffers and your program would easily identify this.
Sharp MZ/X Series Projects and FPGA Emulator
engineers@work : https://eaw.app/sharpmz-series/
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