help for a MZ-700

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emilen
Posts: 4
Joined: Fri Mar 13, 2020 2:08 pm

help for a MZ-700

Post by emilen »

Hi to all,
I get this machine as faulty, as blank screen.
Power it up, led ok, no beep and blank screen, no sync on TV.
I test the PSU, the Z80, the two ROM, the two VRAM, all are OK
I see that the LSI output a strange CPU clock so I reflow it and... I get right CPU clock and a strange video output, garbage, 4 bit pattern and no top-bottom margin, it lack of Vsync and Vblack at all.
Now for what I can read in the Service Manual, the LSI generate all the video sync internally without any help of other signal than main clock 17,73Mhz. Right?
If so the LSI are broken? Other signal is missing from LSI, from P2 to P10... only P0 and P1 have train of bit on it...

LSI DEAD?

Any chance to find a working LSI?
hlide
Posts: 576
Joined: Thu Jan 25, 2018 9:31 pm

Re: help for a MZ-700

Post by hlide »

You took a big risk with the LSI the only component that you cannot replace. Let us be optimist. Have a micro-look at each pins to check there no blob connecting two neighboring pins or traces as they are very tight.
emilen
Posts: 4
Joined: Fri Mar 13, 2020 2:08 pm

Re: help for a MZ-700

Post by emilen »

Hi Hilde, thanks for reply
I test every pin and no short at all or any solder joint, I have magnify glass and very fine solder tip and hot gun.
So the LSI is ever missing in some signal out of it.
I have replaced the IC in the Vsync line too but still no change.

I think that LSI is semi-dead :-( and seems to be very impossible to find one as spare.

An idea to no trash the mz-700 it is to fit an hardware emulator in it... a bare metal not exist by my knowledge, i know the mz80rpi emulator (you have a fork of it rigth? I know too your sd2cmt work and help on lepsd posted on systemcfg forum) but can be possible use the real mz-700 keyboard with it?
hlide
Posts: 576
Joined: Thu Jan 25, 2018 9:31 pm

Re: help for a MZ-700

Post by hlide »

If LSI is dead, there are some people who design a replacement chip using FPGA (GDG1500). @Martin8bity, someone seems to have a bad LSI chip. Do you think a solution is possible?
emilen
Posts: 4
Joined: Fri Mar 13, 2020 2:08 pm

Re: help for a MZ-700

Post by emilen »

I see the photo oh mz-1500... great job and working at first run !!!
Do you know if he sell fpga or share the project?
hlide
Posts: 576
Joined: Thu Jan 25, 2018 9:31 pm

Re: help for a MZ-700

Post by hlide »

I have an answer. That's just a prototype only done for NTSC MZ-1500. No PAL version. No complete PCB and maybe no available PCB at all. So consider it as a difficult job. Supposedly you can program a FPGA, you would need to modify the source to make it work in PAL version.

https://www.nobomi.cz/8bit/GDG1500/
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