MZ-80K where to start to repair

traindriver69
Posts: 17
Joined: Sun Apr 14, 2019 2:52 pm

Re: MZ-80K where to start to repair

Post by traindriver69 »

Hi
What about the other chips I need to replace are they available anywhere.
traindriver69
Posts: 17
Joined: Sun Apr 14, 2019 2:52 pm

Re: MZ-80K where to start to repair

Post by traindriver69 »

Hi All
Today I have replaced all the IC sockets not ram ones I have put in a new Z80 cpu and cleaned and replaced the broken legs on the rest turned it on and exactly the same as before just the lines moving side to side as in my original post any ideas where to go next with it.
Gortho
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Joined: Thu Mar 22, 2018 3:53 pm
Location: Poland

Re: MZ-80K where to start to repair

Post by Gortho »

Many things can be wrong. As S_U_C said, maybe ram buffers etc. It might be main ram, as 19V on 12V line is a bit too much for those chops.
It might be monitor-rom, and few more things ;)
Ok.What is done so far, maybe with a picture or two ;) Have you checked voltages that reaches chips already? +/- 5v, +12V...
Do you have way of checking the signals?
traindriver69
Posts: 17
Joined: Sun Apr 14, 2019 2:52 pm

Re: MZ-80K where to start to repair

Post by traindriver69 »

Hi
I have checked the voltages to the ram chips and they are correct I have a logic probe if that is any good I would love a oscilloscope but just to expensive unless the very cheap eBay ones would do the job.
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dat-alex
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Re: MZ-80K where to start to repair

Post by dat-alex »

Have you tried sound test:

Type SG (enter) to turn on key sound and test (don;t forget to check the volume in the rear)
if we have sound it is an indication of CPU working ... an maybe the problem is vram :idea:
member of retroclub.gr (Thessaloniki , Greece)
Gortho
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Joined: Thu Mar 22, 2018 3:53 pm
Location: Poland

Re: MZ-80K where to start to repair

Post by Gortho »

@traindriver69:

Any luck with the sat-alex's suggestion?

You can buy some cheap usb logic analyzers from ebay. It's 10ish eur for 8 channel one and 40ish for 16 channel one. They work quite nice with sigork/pulse view software, and can be really helpful.
traindriver69
Posts: 17
Joined: Sun Apr 14, 2019 2:52 pm

Re: MZ-80K where to start to repair

Post by traindriver69 »

Typing SG no sound but I have also discovered that banks 2 and 3 of the ram are faulty.
I have some more 4116 chips on the way but would this cause the fault I have got.
psmart
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Re: MZ-80K where to start to repair

Post by psmart »

A useful tool is this memory tester, I bought one a while back and is a great help https://www.ebay.co.uk/itm/124726020732 ... SwbldhCuZO. If you have an eprom programmer, write a small test program to write characters to VRAM without using Stack, ie.
ORG 0000H
LD HL,0D000H
LD A,'A'
LD B,0
LOOP: LD (HL), A
INC HL
DJNZ LOOP
STOP: JR STOP
You can get free Z80 assemblers for Linux/PC such as GLASS http://www.grauw.nl/projects/glass/ to assemble the code.

Basic test but will fill the first 256 screen locations with 'A'. If it doesnt work then the issue is potentially with your VRAM. A further check would be to initialise and load 8253 counter 0 and see if sound is output - verifies the CPU and the data/address paths.

I've had a few issues with monitors, repaired a few in the last months but if your not getting the sound from SG then probably not in this area.

Take a look at the service manual for any clues as well, ie: https://original.sharpmz.org/mz-80k/download/sm80k.pdf
Sharp MZ/X Series Projects and FPGA Emulator
engineers@work : https://eaw.app/sharpmz-series/
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