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Yet another Sanyo MBC-55x thread?

generic486

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Mar 30, 2012
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Yes, first try cleaning the heads. You have to remove all the shielding from these TEAC drives unlike the later ones.
It would be bad if the floppy controller is failing as everything is intergrated. Usually it's the C9 cap at fault when something goes wrong with the floppy drives.
Also, although unlikely, your drives may be misaligned. However, I highly doubt this.
This is a guess but maybe you should reseat some of the DIP's on your mobo. I had a floppy problem in an XT because the Zilog FDC chip was not seated properly. However, I do not know if the floppy controller chip is socketed or soldered.
 

digress

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I desoldiered the c9 cap. I then swap the drives and changed their respective dip switches and now it's back alive. Thanks to everyone for the suggestions. The newly swapped to B: drive seems to not be functioning quite correctly anymore. Can get a directory but will not read the disk properly enough to execute a program... or boot apparently. I can live with one drive for now.

Now if only I could rig a hard drive or something.

Thanks again.

Oh by the way if the person who just discovered the cga video board needs it if have the sanyo video board boot disk and an opertional Sanyo with the CGA video board.

Gerry
 

generic486

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I have never seen a MBC-550 with the Winchester disk card. I think very few sold. Most people who wanted the 550 were people with a budget in mind. People who had lots of money to spend mostly got the MBC-775 (portable) or MBC-875. It's odd how you never hear about those computers. I think the 875 had the MFM hard drive as standard.
 

Old Computers

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I think that there were also 3rd party HDDs and controllers. I was looking through some of my Soft Sector issues a while ago, and there were several advertisments for them.
 

BradN

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Aug 27, 2006
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Just to clear up a little confusion on the CGA card and boot process (sorry for dragging up a months old thread):

The CGA cards contain a ROM but it is only a character ROM for text mode - no program code is ever executed from it, and it's not accessible at all from software. If you have MBC-55x hardware but no boot disk specific to it, the best you will get the machine to do is emit garbage to the screen on an attempted boot. There's no BIOS logo or anything other than a blank screen output (on the onboard video) and a persistent attempt to read the boot sector on drive A. Before the OS has loaded from floppy, the CGA is probably outputting a signal with bad sync as the CRTC chip hasn't been configured at all.

A missing motherboard ROM, as on the pictures in this thread, however is fatal. (It is possible though for an expansion card to override the system ROM but I'm not aware of this ever being done. The hard drive option could possibly use this mechanism to allow booting from hard drive.)

As far as I know, here is the compatibility list for different RAM-BIOS/DOS disks (the hardware compatibility is entirely determined by the boot disk):

Early onboard video version: Runs on motherboard graphics, might operate with CGA card present with no RAM expansion on the card (won't use the CGA for BIOS screen functions). Won't boot at all with RAM expansion on CGA card.

Later onboard video version: Runs using onboard video, can utilize expansion RAM on a CGA card or probably some other RAM expander board. Make sure to fill out the RAM sockets on the motherboard first if using RAM expansion.

Early CGA video version: Operates CGA but doesn't work with RAM expansion on CGA card (not all the CGA cards shipped with expansion RAM functionality).

Later CGA video version: Operates a CGA card with or without expansion RAM. Again make sure the M/B RAM sockets are filled to utilize expansion RAM on a CGA card.

Hard drive version: (???) I've never seen the hardware or boot disks for a hard drive option, if anyone has this it'd be quite a find.


CGA boot disk & onboard video note: Onboard video can still be used through direct hardware access when booted with a CGA disk but the BIOS makes no attempt to use it. The boot disk displays a badly worded message in the corner of the onboard output, and eventually when a program uses the memory area, the display gets garbled. Of note is that the 32KB of dedicated video RAM (@ addr F0000) is not used by anything and free for whatever purpose you can come up with. I'm actually a little surprised they didn't try to load the BIOS/DOS there, it would have provided a little more RAM on a system that can be sorely lacking without an expansion.

Onboard video places the 640x200 green plane within the upper 16KB of any 32KB block of the first 256KB of memory (so at 16-32KB, 48-64KB, 80-96KB, etc up to 240-256KB). I suspect that this arrangement is why the "early" disks can't operate with >256KB, perhaps the code that decides this video RAM mapping screws up and crashes.

The red and blue planes (or for monochrome output, dim intensity plane and blink plane if enabled via dip-switches) are fixed starting at address F0000 and ending at F7FFF. Maybe the only reason for those DIP switches is to allow loading other data into the video RAM without affecting monochrome display.



Random MBC-55x trivia: RAM refresh is ensured by the onboard video hardware. If you set a very short output frame - say, only outputting a few bytes of video memory per frame, and execute a tight delay loop, after some seconds memory corruption will set in. Upon exiting the delay loop, chaos awaits. The video hardware must read at least 256 bytes per frame to avoid this - each memory read refreshes that corresponding byte within each 256 bytes of RAM. Anyone feel like coding up a true hardware random number generator?
 
Last edited:

BradN

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Aug 27, 2006
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MBC-55x ROMs

MBC-55x ROMs

Here's a copy of the MBC-55x ROM in attachment. Use an 8 or 16KB ROM. If you use a 16KB one, duplicate the ROM to both halves for best results.

I presume the CGA ROM could be replaced with an IBM PC CGA ROM, or you could even cook up your own font, or maybe even copy the one inside the MBC-55x ROM (it contains its own character font at offset 0x1000 to 0x17FF for use with the onboard video, though I don't think the BIOS actually uses it in normal conditions!)

View attachment mbc-555.rom.zip
 

digress

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Cool,

I have the IBM video board boot disk for the Sanyo 550 if anyone needs it. I also have a 550 with the CGA video board operational. Can actually run some IBm games. I even got Sierras Mixed Up Mother Goose to run. kind of. It had the full 16 colour graphics working too.

No sound support though, not even the pc speaker.

I do have a few video board friendly games & programs. Notable I have Microsoft flight simulator 1 with a special patch disk for the sanyo with the video board.



Here's a copy of the MBC-55x ROM in attachment. Use an 8 or 16KB ROM. If you use a 16KB one, duplicate the ROM to both halves for best results.

I presume the CGA ROM could be replaced with an IBM PC CGA ROM, or you could even cook up your own font, or maybe even copy the one inside the MBC-55x ROM (it contains its own character font at offset 0x1000 to 0x17FF for use with the onboard video, though I don't think the BIOS actually uses it in normal conditions!)

View attachment 12369
 

mikey99

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I have never seen a MBC-550 with the Winchester disk card. I think very few sold. Most people who wanted the 550 were people with a budget in mind. People who had lots of money to spend mostly got the MBC-775 (portable) or MBC-875. It's odd how you never hear about those computers. I think the 875 had the MFM hard drive as standard.

I have a Sanyo MBC-885, there are some pictures of this and also the 775 at the following link :

http://www.vintage-computer.com/vcforum/showthread.php?11284-Sanyo-MBC-885

The MBC-885 is basically an XT clone, with a switchable 4.77->8 MHZ processor. Seems to be fully IBM compatible
as far as I can tell.
 

digress

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I personally used a Sanyo MBC 885 back in the 80's at my cousins house. It was definitely more IBM compatible than the 550. We could run IBM cga games on it with no trouible. Sierra boxing, Jet, Bushido , pool some others.

Would have loved to own one back then. Got a tandy 1000tl a few years later( 1989) and still have it and use it to this day.

I have a couple of sanyo mbc 885 original disks here if you are looking for something. Only 2 though.Wordstar & Correct star
 

tonata

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Hi,

Can somebody please upload and post the technical manuals for Sanyo MBC 55x?.
 

JohnElliott

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I've scanned the user manual, which has some technical info, but I don't think I've ever seen a full-on technical manual for the Sanyo.
 

krebizfan

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The SAMS schematics for the Sanyo are out there which might provide some additional information. However, the schematics only cover 22 pages of the 56 from the SAMS booklet so the troubleshooting charts are not available.
 

tonata

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Sep 11, 2019
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Hi,

I am sorry but I can not find anything downloadable on Internet(without asking me for credit card).
Can you please be so kind to post links or upload it somewhere free? I could host it after that.
I am still nowhere with my problem with my Sanyo MBC 555.
 

tonata

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Sep 11, 2019
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Hi.

What kind of ROM chip is compatible?
Mine says:
SANYO 55x - NO - 1
M5M2364-171P

It is an 8 KB Mask Programmable ROM, but what is the equivalent? I can not find one on ebay.

Here's a copy of the MBC-55x ROM in attachment. Use an 8 or 16KB ROM. If you use a 16KB one, duplicate the ROM to both halves for best results.

I presume the CGA ROM could be replaced with an IBM PC CGA ROM, or you could even cook up your own font, or maybe even copy the one inside the MBC-55x ROM (it contains its own character font at offset 0x1000 to 0x17FF for use with the onboard video, though I don't think the BIOS actually uses it in normal conditions!)

View attachment 12369
 

Chuck(G)

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Pinout (28 pin) says that it's compatible with the 2764 EPROM, so should be pretty easy.

Cited datasheet says " The M5M2364-XXXP...is interchageable with the M5L2764K an Intel 2764 in read mode."

The 68764/65/66 are 24 pin DIP, so not compatible.
 
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