Well I'm stumped on this one...

[ral-clan]

As some of you might have read, a few months ago I was having problems with my MPS-801 printer:

http://sleepingelephant.com/ipw-web/bul ... ght=mps801

...I got it working for a while, but now it has started doing the same thing again (only printing partial listings, then simply stopping).

I was sure it was a printer problem (as my VIC-1525 and Canon Inkjet with interface worked find on the VIC). But the 1525 is impossible to find ribbons for and the Canon is non-Commodore gear so not my first choice.

So I bought another MPS-801 off of Ebay and found out it does the exact same thing.

Here are the things I've tried:

• opening the printer and reseating the ROM
  replacing all serial cables.
  hooking the printer directly to the VIC-20 (instead of daisy chaining)
  moving the serial cable away from power lines
  trying a different VIC-20 (just stops in a different place).

I just CANNOT figure out what would be causing such a strange error and ONLY with MPS-801 printers.

I suppose I could just have two MPS-801 printers with identical problems, but I'm thinking it's more likely a problem somewhere else.

The confounding thing is that it was working reliably for about a month, and now, every once in a while, everything will work just fine for a 'session' (until I turn it off for a while).

Argh!

I thought it was some sort of problem with buffering chips in the printer....but who knows now....

If anyone has a clue I would appreciate it.

[carlsson]

Is the VIC and the printer connected to the same mains outlet? I don't know, but perhaps a difference in voltage potential could make a difference over the serial cable.

[ral-clan]

Is the VIC and the printer connected to the same mains outlet? I don't know, but perhaps a difference in voltage potential could make a difference over the serial cable.

Okay, UPDATE: I just tried a third (very yellow, later model) VIC-20 on the MPS-801 and was able to get a full print-out without any stopping. (crosses fingers that this will last).

So my latest theory is that there was something wrong with the first two VIC-20s I tried. What chip controls the commodore serial port, and is it known to go bad? Is it easy to replace (If it is indeed a serial port problem I'd like to fix my problem VICs as one was my original one from 1982).

[ral-clan]

Okay, third UPDATE: after a quick internet search, I found out it is the 6522 chip(s) that control the serial port. I opened up my first VIC-20 (that was giving me problems with the MPS-801) and swapped the two 6522 chips in their sockets. So far, it is working with the printer (I really, really hope this is the solution). Maybe one is bad, or they both just needed re-seating. (cross fingers).

As an added observation: It's amazing how quickly I can go from feeling crabby because a VIC item isn't working to feeling great when solving it....and then crabby again when it malfunctions again. Any of you guys go through "VIC-20 mood swings" like that?

[Boray]

As an added observation: It's amazing how quickly I can go from feeling crabby because a VIC item isn't working to feeling great when solving it....and then crabby again when it malfunctions again. Any of you guys go through "VIC-20 mood swings" like that?

Oh yes! Not right now, but I sure have...

[carlsson]

I believe one 6522 handles userport, serial bus, most of the joystick and part of the cassette. The other 6522 then handles keyboard, rest of cassette and one joystick line.