MZ-700 Blank Key.

psmart
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Re: MZ-700 Blank Key.

Post by psmart »

Np, just let me know.

Re: CGROM, look at original.sharpmz.org - go to Download, MZ-700, ROMS and you will see the image there, ie. https://original.sharpmz.org/download/MZ7CGint.zip

Probably best thing to do is to just read your rom contents and compare with the above image, that will direct you in terms of reprogramming. If the contents differ then just erase the chip, blank check it and reprogram with verify. Your better equipped than me :) - I used to have two UV erasers but goodness knows where they went! Maybe time to visit ebay and order one up!
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Doz
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Re: MZ-700 Blank Key.

Post by Doz »

Thanks, sadly the link returns PHP error, bad file/directory permissions or invalid site software configuration

:(

I was going to attach the bin of my rom, but that's not allowed either.

So it's here: https://1drv.ms/u/s!Aq35rJMV1i5Fgu8vCWd ... w?e=DXmzYO



Have you thought about a UV LED? May take a little longer... I've successfully exposed PCB's that way.
psmart
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Re: MZ-700 Blank Key.

Post by psmart »

Wild goose chase I'm afraid, your rom is fine.

Do you see some kind of flashing on the screen, reminiscent of a cursor and if you press keys does the screen change? This is what I was getting on the 80A hence the CGROM being the culprit. If your just getting random characters up then like hlide points out, could be DRAM and the monitor isnt starting up and clearing the screen, albeit in saying that, on the MZ-700's I have, if you remove the CPU you get multicoloured and multi character output not a blue pattern like you have (blue is the value written into the attribute ram). This in itself is a good pointer as the monitor rom, in order to fill the attribute with blue background/white foreground makes a call so the stack appears to work and by association the DRAM.

The only other culprit would be the 2016 static RAM chips used for the video (check by pressing many keys and seeing if the screen changes but to random values) or IC 8D (74S245) which reads/writes to the video ram but given you have a blue background it is less likely to be this IC.The rasterisation of the character is done by the gate array driving the lower CGROM address lines so a possibility.

Simple quick test, remove the Z80 and power on, what do you get on the screen, if multicolour and multi character (clearly visible characters) then it shouldnt be the video output circuit. If a mush of pixels then I'd say potentially the gate array Q1-Q3 lines as the CGROM isnt faulty. Try some of these checks and we can analyse further from there.
Last edited by psmart on Wed Jun 09, 2021 9:40 pm, edited 1 time in total.
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psmart
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Re: MZ-700 Blank Key.

Post by psmart »

Re UV, it is the wavelength that is important, I have a 50W UV unit which I shone onto an eprom and it didnt erase it and when I checked the wavelength against a UV eraser spec it was different. Good idea though just need to source a UV led of the right wavelength.
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psmart
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Re: MZ-700 Blank Key.

Post by psmart »

Also the original.sharpmz.org website, all the file download links look broken, I wonder if it needs restarting or something has expired?
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psmart
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Re: MZ-700 Blank Key.

Post by psmart »

Just rechecked the circuit and the attribute ram is driven by IC AD (74LS245) and the video by IC8D so this could be a potential candidate. Your screen output is white on blue so the attribute ram must be getting written to under software control.
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psmart
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Re: MZ-700 Blank Key.

Post by psmart »

Doz wrote: Wed Jun 09, 2021 8:57 pm Thanks, sadly the link returns PHP error, bad file/directory permissions or invalid site software configuration
Just made some analysis on the original.sharpmz.org website. Seems there is an incorrect setup or transfer to a case sensitive filesystem.

Most of the files are stored as lower case yet the links capitalise them, ie https://original.sharpmz.org/download/MZ7CGint.zip - if you try https://original.sharpmz.org/download/mz7cgint.zip it will work, same for many of the others that come up with an error message.
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Doz
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Re: MZ-700 Blank Key.

Post by Doz »

Thanks again. I can see the characters changing as I type, and there appears to be some sort of cursor.

Thanks for checking the ROM. The 74S157 multiplexer should be here today. I've got a dirty great Luxman amplifier to finish and get off the bench, so hopefully I should get to it again at the weekend.
Doz
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Re: MZ-700 Blank Key.

Post by Doz »

psmart wrote: Wed Jun 09, 2021 9:30 pm Re UV, it is the wavelength that is important, I have a 50W UV unit which I shone onto an eprom and it didnt erase it and when I checked the wavelength against a UV eraser spec it was different. Good idea though just need to source a UV led of the right wavelength.
Valid point. I hadn't considered wavelength. I use my PCB exposure box, which is an RS thing of much vintage. It's managed to erase many eproms with it, although it does take about an hour.
Doz
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Re: MZ-700 Blank Key.

Post by Doz »

Well, that took a little (a lot) longer to get done, but I'm back. I've fitted the new 74S157, and the display is still corrupted, but it never changes now on reset or power up, so that's something...

No I need to know where to start looking next .. We know the CG ROM is good, so where do I need to investigate next ?
IMG_20210704_205946.jpg
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