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New Sanyo MBC-550

I would like Dos 2.11 if an image is available for download from somewhere, as i currently only have dos 1.25.

Cheers.

Phill.
 
An update regarding the floppy drive delays I am experiencing. I looked at the datasheet and the schematics, and it does appear that C9 is incorrectly installed. I am going to do some voltage measurements and possibly look at the waveforms coming from the chips before I fix it. I am going to go ahead and just reverse the existing capacitor. That way the machine stays as original as possible, and I won't need to source the new part. Since the problem only manifests itself after the computer has been active for a long time, I think that the capacitor might still be viable.
 
C9 is incorrectly installed

C9 is incorrectly installed

this seems to be dicussed here:

http://www.vintage-computer.com/vcf...-Flaw-identified-in-Sanyo-MBC-55x-motherboard




Old Computers said:
An update regarding the floppy drive delays I am experiencing. I looked at the datasheet and the schematics, and it does appear that C9 is incorrectly installed. I am going to do some voltage measurements and possibly look at the waveforms coming from the chips before I fix it. I am going to go ahead and just reverse the existing capacitor. That way the machine stays as original as possible, and I won't need to source the new part. Since the problem only manifests itself after the computer has been active for a long time, I think that the capacitor might still be viable.
Click to expand...
 
That's the thread that I was pointed to about this problem.

I just thought I would give an update here since I mentioned the problem here in an earlier post.
 
I just did the repair. I checked the capacitor by connecting the multimeter probes to its leads. The poliarity did not coorespond to the markings on the board, so I reversed the capacitor. I am letting the computer run for a while now to see how it will do. I hope that it works.
 
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Congrats on your new acquisition!

Aside from that capacitor issue, these things are beasts when it comes to reliability. The only way I've found to damage one is quick repeated turn-on/turn-off which can blow a fuse *inside* the transformer. It's possible but not particularly easy to bypass the fuse if this happens - one has to drill into a plastic part on the transformer and solder a wire on after the fuse, about a centimeter underneath the plastic. It's not fun, so don't play with the power switch like a maniac.

One other glitch I saw once is the power supply failed to start up correctly and seemed to output a too low voltage, perhaps latchup inside the error amplifier IC, but this seems exceedingly rare. But if you ever turn it on and see the keyboard LEDs glowing weird with nothing happening, just power it off and back on and it should be ok.
 
Yes it does. The hardest part about cleaning my 550-2 was the power supply. It is not kept in a nice little box so you have to unscrew everything and put it all back. However, the 55x series are really nice machines.
 
No, the 55x PSU is only linear for the 12V rail - the 5V rail is a bonified switching supply. But, it is a buck converter using an inductor, not a transformer like modern PC supplies. Isolation is done using an enormous step-down transformer at the input.

The 55x PSU will actually run from battery if a battery pack is connected in place of the transformer, but -12V will be unavailable unless you also supply a negative voltage to the other AC pin (the transformer and input to the PSU board is center tapped so this is possible). On 12xNIMH batteries, the PSU & motherboard together consume about 18 watts.

I'd like to eventually build a microcontroller operated battery backup + power supply with ~100W inverter capability (output using the handy AC receptacle on the back) but this is a big undertaking and I have another paid project that needs to get finished first. Another possibility is a microcontroller based memory expansion card (16MB 30 pin SIMMs + SD storage). There are interesting possibilities for that because it should be possible to override the boot ROM and trap I/O and memory accesses with the expansion interface, as well as having a page table. The memory scheme used gives one memory cycle to the CPU and then one to the video system, which means a microcontroller would be able to manipulate its own expansion memory (to perform refresh or DMA with SD card, etc) on the cycle that the MBC is reading its video RAM. Looking at using PIC18F46K22 for both of these ideas. I hate to hype it up because I know it will be a long time until I get anywhere with it though.
 
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I stress tested the repair last night for about an hour (that's how long it took the problem to manifest itself before the repair) and it appears to work just fine. I am really glad about knowing that fix because the delay for the drives was really annoying. I was also glad that I was able to just reverse the capacitor. I think that that cap wasn't probably badly damaged because the problem wasn't present at startup, so maybe the cap will self heal any problems that it might have.

BradN: I will be sure to look out for that problem if it ever arises.

The PSU for this computer sounds very interesting. Probably nowhere near as complicated as my PDP-11/44's PSU. That thing is extremely complicated (I am in the process of restoring it right now).
 
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