MZ-80B Power Supply Repair

hlide
Posts: 576
Joined: Thu Jan 25, 2018 9:31 pm

Re: MZ-80B Power Supply Repair

Post by hlide »

gregctaylor wrote: Tue Jun 12, 2018 8:57 am I am beginning to wonder if it might be the monitor ROM (EPROM?) at fault.
It looks like VRAM is fine as the display is perfect. I just cannot understand what else might stop the monitor program completing its loading as I assume the memory test is in ROM?
ROM needs a small RAM space (0x1000-0x11FF) to store its system variables and its stack. So the ROM may not be faulty but acts as faulty due to the small RAM place corruption.
hlide
Posts: 576
Joined: Thu Jan 25, 2018 9:31 pm

Re: MZ-80B Power Supply Repair

Post by hlide »

I would love to have both MZ-80A and B but I guess the prices won't be cheap. And damn I start lacking places to put my retro-computers :/.
gregctaylor
Posts: 27
Joined: Tue May 29, 2018 5:38 pm

Re: MZ-80B Power Supply Repair

Post by gregctaylor »

I unplugged all the main RAM than placed the III bank chips into bank I with no change. Unless a lot of the RAM is faulty (which must be extremely unlikely) then it must be something else. Shame the VRAM is not socketed as I could have tried that. I don't think it is the VRAM though as the screen is so regular. There is some slight screen flicker.

Have repaired the 80A. I think those Japanese must have smaller fingers than me - some of the screws were a real pain to replace. The one capacitor had really blown. It was about three times its original size!

Greg
parc
Posts: 17
Joined: Wed Mar 20, 2019 8:29 am

Re: MZ-80B Power Supply Repair

Post by parc »

gregctaylor wrote: Fri Jun 08, 2018 3:19 pm Normally, it is the two mains voltage capacitors which fry (0.047 mfd, 250V) and these are on a small board between the on/off switch and the transformer. I found it easier to slide out a bit by unscrewing the power switch. Now just waiting for the new capacitors to arrive.....
This problem hits my "B" yesterday :-)
parc
Posts: 17
Joined: Wed Mar 20, 2019 8:29 am

Re: MZ-80B Power Supply Repair

Post by parc »

parc wrote: Sun Jul 04, 2021 7:43 pm
gregctaylor wrote: Fri Jun 08, 2018 3:19 pm Normally, it is the two mains voltage capacitors which fry (0.047 mfd, 250V) and these are on a small board between the on/off switch and the transformer. I found it easier to slide out a bit by unscrewing the power switch. Now just waiting for the new capacitors to arrive.....
This problem hits my "B" yesterday :-)
I ordered https://www.reichelt.de/de/de/funkentst ... tml?&nbc=1 one and replaced both capacitors in the Power suppley.
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