Sanyo MBC-200

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Sanyo MBC-200

Postby matsondawson on Sat May 14, 2011 10:49 am

I've finally picked this beast up and am furiously taking pictures atm.
It doesn't work right now, but I've confirmed PSU OK, and CRT is OK, with signs of life on the screen (garbage, no decernable text), also A drive runs continuosly.
On the back it says "TOKYO TRANSLATIONS LTD., CHRISTCHURCH".
It has:
16 x HM6116P-3 2K x 8 SRAM soldered onboard (so 32k ram)
4 x HM6116P-3 2K x 8 SRAM socketed (so 8k ram)
4 x mb83256 32K x 8 socketed (128k ram)
Dual 5.25" floppys.
And also.... dum dum dum... dual Z80's!
Which makes it look llike a MBC-1250
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Re: Sanyo MBC-200

Postby tezza on Sat May 14, 2011 10:59 am

matsondawson wrote:Which makes it look llike a MBC-1250


So that's what it is you think? I wonder why it was re-branded?

Still, wierd things go on sometimes. Like the Commodore PC-5 I have. Very similar to the PC-10 but practically unknown.
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Re: Sanyo MBC-200

Postby matsondawson on Sun May 15, 2011 12:23 pm

Ok, so I've looked at the CPU's using a logic analyser and note that what I think is the main one in the middle seems to be doing nothing but running DRAM refreshses.
So I replaced it, and also the main one just in case. No change it's still broken and doing the same thing.
So I think I'll have to work through each of the LS series chips surrounding the CPU to see if I can find a broken one.
Interesting thing is desoldering on this board is a complete pain.
For both CPUs there was one pin that didn't seem to de-solder, I had to put the soldering iron on full power just be able to wiggle the cpu's out, that means the solder won't even melt (just softens) at maximum temperature for those pins.
I suspect all chips may be this way, as in the RS232 section someone has had to replace a chip, but ripped off a bunch of vias and tracks doing it. So now it has some ugly hunks of wire soldered on the board.
Also the board is very brittle, the epoxy cracks just from looking at at.

BTW, isn't a Z80A and a D780C-1 compatable? I tried a known working Z80A replacement and it didn't work.
Last edited by matsondawson on Sun May 15, 2011 12:48 pm, edited 1 time in total.
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Re: Sanyo MBC-200

Postby tezza on Sun May 15, 2011 12:31 pm

Sounds like it's not going to be easy. If there is evidence of prior work (and clumsy prior work at that) then there is a possibility that repair/mod attempt zapped chips in the first place.
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Re: Sanyo MBC-200

Postby matsondawson on Mon May 16, 2011 6:59 pm

It appears I didn't notice 8 drams on the board, 4164 64k x 1's. That's another 64k of ram.
What a crazy mishmash, 232 KB so far
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Re: Sanyo MBC-200

Postby micko on Fri Oct 28, 2011 9:27 pm

Hi matsondawson,

I see you own this quite rare machine. Would you be kind of making ROM dumps from it, and if possible some
board images so chip markings could be read from it? I am asking since I am interested in emulating this machine in MESS.

Micko
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Re: Sanyo MBC-200

Postby matsondawson on Fri Oct 28, 2011 9:58 pm

I'll see what I can do about dumping the ROMs as it's in the garage at the moment, but luckily I took a lot of pictures before I started trying to fix it.
They are available here: http://www.mdawson.net/gallery/main.php?g2_itemId=1506
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Re: Sanyo MBC-200

Postby micko on Fri Oct 28, 2011 10:05 pm

Thanks for quick response. Good thing is that ROMs are socketed which makes things easier.

Thanks,
Micko
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Re: Sanyo MBC-200

Postby matsondawson on Mon Oct 31, 2011 6:25 pm

I just went to the garage, pulled the ROMs and stuck them in the programmer, then found out I'd already dumped them when I first got the machine.

They can be retrieved from here:

http://www.mdawson.net/files/mbc200

The 2732A has writing on it saying FJ9-1, and is in the center of the board (IPL i guess).
The 2764 is at the top right (CRT).
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Re: Sanyo MBC-200

Postby matsondawson on Mon Oct 31, 2011 6:26 pm

BTW do you have any boot disks for this machine, or similar as I have nothing to test it with.
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Re: Sanyo MBC-200

Postby micko on Mon Oct 31, 2011 9:18 pm

Thank you very much for rom dumps. I have start working on emulation, but probably disk image will be needed.
So far I have found http://www.gaby.de/sysdisk.htm that there was a person who had these disks but he died about 5
years ago, and no info of someone continuing his work. If I find something will publish.
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Re: Sanyo MBC-200

Postby matsondawson on Wed Nov 02, 2011 4:21 pm

I've been tracing some stuff on the board today and found the CRT CPU seems to be working fine, but the IPL is not.
It appears to be reading E9 AF constantly. The DRAM refresh is working fine, and RESET, NMI, INT, HALT etc are all fine.
There's an 8255 PI chip in the middle of the board which I think maybe the processors use to communicate with each other? or possibly for banking ram?
Anyway its RD pin (pin 5) floats up and down predictably from 1 to 2 volts every second, which seems rather un-digital.
I've tracked the trace to an LS32 Quad 2 input OR whose output doesn't seem to match its inputs, but I'm not sure if there is any other thing involved with keeping the line in the bad state.

Am I right about the 8255 micko?
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Re: Sanyo MBC-200

Postby matsondawson on Wed Nov 02, 2011 8:32 pm

BTW the 8225 is addressed by CRT CPU A0,A1 and chip select is A7.
I can't work out where any of its ports go though.

And the 6845 CS is connected to CRT CPU A6
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Re: Sanyo MBC-200

Postby matsondawson on Wed Nov 02, 2011 8:55 pm

Ah, I've found a route between the CPUs, CRT Data bus is connected to Port A on the 8255 port closest to the printer port.
The Data lines on that 8255 is connected through a LS245 to the IPL CPU.
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Re: Sanyo MBC-200

Postby micko on Wed Nov 02, 2011 9:45 pm

Hi,

Sorry did not have much spare time last few days. My idea was to try to disassemble full code of IPL and CRT roms.
So far IPL rom content looks strange. Most of roms start with DI and init of registers. This one start with counting.
Maybe someone played with machine and put notworking rom in it, but I hope I am not right :)

Micko
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