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Yet another Sanyo MBC-55x thread?

I

iulianv

Experienced Member
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Romania
A couple of days ago a fellow collector gave me two bags full of various parts he did not need anymore after clearing his vintage inventory. Among them, the following two cards:

https://sites.google.com/site/iulianvshw/other/fs559.jpg
https://sites.google.com/site/iulianvshw/other/fs580b.jpg

At first I was going to toss them (since I thought there was no chance I could test this "unusual PC XT clone"), but I was curious to know what system they came from, so I did a bit of searching and now I find myself wanting to know more... so here goes :):

- do the cards come from a Sanyo MBC-550/555 computer?
- is there any way to easily modify a "modern" AT or XT switching PSU to get the required voltages to power up the boards?
- I do have an AMD P8088 CPU but it seems that the ROM chip is missing from the mainboard (the central socket labeled 2764); will it display anything without that?
- I see some sockets for 41256 RAM chips on the CGA card; do they have to be populated in order for the card to work?
- connector CN4 on the CGA card has 4 pins on the other side - what are those for? connector CN3 has no pins - was it originally meant for anything?
- there is an empty DIP-28 socket on the CGA card - what is it for?

More questions may follow, depending on the answers I get for these ones :)... many thanks in advance.
 
I'm NOT an expert on these by any means (want to be clear about that) but for the sake of a quick response:

I believe it is.
The layout and default connectors appears to be perfect for the MBC-55x case.

Printer -> Video Out DIN -> Video Out Composite -> Keyboard with an expansion card just above.

It wont display anything without the ROM.
I would guesstimate you do not need the CGA card to boot if you used the motherboard video signals
I also guesstimate that those 41256 sockets would've been a memory expansion, because you don't need 256 or 512K of RAM for CGA. This would make sense because it looks like that motherboard only has 128KB of RAM so a previous owner likely would've wanted a tiny bit more (would've taken them to 384KB)

Since the voltages are labelled, hooking it up to a desktop PSU would be quite easy and I'm sure other owners could help you identify any missing chips to replace but keep in mind it may not be worth the time (personally I'd keep it as an 'untested spare'). Of course if you just really enjoy the idea of making it work - then go for it - I'm always hesitant on parts with removed chips because often the chips were removed because the board failed ( but not always ).

Edit: the 4 pins by CN4 are probably for a light pen
 
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I can verify, these cards are infact from a MBC-55x.
The CGA card might be needed if you only have a standard CGA monitor but you can hook it up to the TV using the composite video connector on the mainboard.
About the ROM, it is an offical Sanyo chip. I would kindly dump the contents of my ROM but I do not have the correct hardware to do so.


If you are thinking selling the CGA card, I might be interested.

I find it interesting that a few months ago, there was very little interest in the Sanyo MBC-55x series. I remember trying to get info but little was available. However, recently, the Sanyo MBC-55x has to be one of the most talked about machines in this sub-genre. I don't know if I started something but at least it is much easier to get the machine up and running now.
 
The connector closest to the parallel printer connector is an RGB output for a monitor. I do not know the specific output of that connector.
The connector below that is a composite video connector.
The final connector is the keyboard connector. A normal keyboard will not work; you will need a Sanyo specific keyboard.

As for the missing chips the rows A, B, and C are for RAM chips. The missing RAM chips should be okay because the RAM was user expandable.
You are also missing the processor. That is right below the socket labeled 8087 (the 8087 was also a user installed option).
The socket labeled CN8 is for a joystick, not a chip.

If you want to get this board working you will also need the proper floppy drives. I have read somewhere that a certain signal is different on the drives, but I am not totally sure about the specifics.

Also when you get a ROM for the system, the system will not display anything until a boot disk is inserted. So do not be alarmed if nothing appears on the screen when you first turn the computer on. The disk images for the Sanyo can be found on the internet.
 
As indicated in one of the other threads about the Sanyo MBC-550 series, should you decide to sell off these boards at any point I am also very interested in the CGA board.

In the mean time if I have any information that can help you with these parts, I will gladly do so.
 
I've read that the CGA card is rare... so rare that it would be quite difficult to establish a reference price for it :).

I've also read here - http://www.old-computers.com/museum/computer.asp?c=473 - that the CGA card may add system memory; is this what the 41256 sockets are for? Would it be enough to solder the second row of sockets and capacitors for a total of 512KB on the card? I also have some Sanyo LM33256G-12 chips, would they fit this purpose?
 
Could somebody who has one of these Sanyos and a video camera please post a YouTube video demonstrating it? So far, no one has. These are very quirky and unique computers and I'd love to get a more in-depth look at one in operation.
 
Old Computers said:
The connector closest to the parallel printer connector is an RGB output for a monitor. I do not know the specific output of that connector.
Click to expand...
I'm curious too; does that connector do anything without the CGA card, i.e. just the basic motherboard? If so, is the pinout available anywhere?
 
The RGB connector will output video without the CGA card. The CGA card, from what I understand, re-maps the video memory and adds a BIOS extension for CGA. The Sanyo supports color graphics natively, just not CGA. I will check my manual and see if it gives a pinout for the video.

Edit: I just checked the manual and it does not give the pinout for the RGB connector. It does have extensive technical information though. If you want to know something the manual probably will have it.
 
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vwestlife said:
Could somebody who has one of these Sanyos and a video camera please post a YouTube video demonstrating it? So far, no one has. These are very quirky and unique computers and I'd love to get a more in-depth look at one in operation.
Click to expand...

Certainly. I'll see if I can make a video.
 
Nice video. The Sanyo monitor is really nice. My monitor is a small third party amber monitor. In my opinion green is much nicer to look at.

What program was run at the very end of the video?
 
I was demonstating that it isn't IBM compatible. I was demostrating it running MS-DOS 5, however, it is incompatible and gives you a weird screen.
 
Yeah, it is a Fujitsu Leaf Spring keyboard, linear action, full stroke. Quite like your Zenith Green Alps keyboard. HP used Leaf Spring action on their keyboards but they have a small tactile bump at the end which make it kind of clicky.
 
my sanyo just died! help!

when i turn it on the drive light comes on before i put a disk in but now it won't boot. drive light never turns off.

was working 2 days ago.
 
It might be related to the C9 capacitor. According to BradN, there is no loss in cutting it and not replacing. Maybe try that. Also maybe try cleaning the heads.
Or maybe try swapping Drive B with Drive A and change the DS settings accordingly and see if it is the drive or the disk that is at fault.
 
I am not too sure about this idea, but try swapping the first drive with the second one. It could be a much worse problem, but maybe the sensor that indicates that a disk is in the drive is bad, and it activates. Does the drive spin up?

Another thing that would be good to do would be to check the voltages the power supply is generating.

Edit: It appears I posted this at the same time as generic486. Sorry about that.
 
hi, i have swaped the power and data cables to the second drive but no luck. the drive is spinning.

right before this happened i had just finisyed soldering a wire onto a volume control for the speaker. This is based on a technique from soft sector mag and had previously already been installed and just the solder joint had come free. I completed this and booted dos with no problem,, then I booted demon seed to test the volume control in the game and it worked. After completing a round about 10 minutes. I was in dos but was getting a disk read error on a disk I know not to be corrupted. And then when rebooting it never did.

Drive light stays on. disks spining but never booting.

I have removed the speaker and tried both drives on the . I have dettached and reattached all power connections. I removed the mother board and checked for any thing and even pulled the cpu and tried a v20 with the same result.

thanks for the suggestions and any help. I'll try to check the voltages the power supply is generating.
 
Another thing you might want to do is see if there are any shorts on the mother board. Maybe a piece of wire fell on the board when the solder joint broke free.

If you can find a service manual (there might be one on Ebay) and you have an oscilliscope you could check the signals on the board. The service manual would probably also have a troubleshooting section which might describe the problem. If you say that the computer gave read errors on a known good disk, there might be a problem with the floppy controller.

Did you try cleaning the drive heads like generic486 suggested?
 
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