I bought a OSI Challenger C1P, and it arrived today.

I hooked it up to a projector (only display I have that accepts composite input) and it was dead. Hooked up a logic probe, probed all the 6502 pins, and they were all stuck high or low.

I then checked the clock and it was definitely stuck. From what I can tell, the clock is generated with a 74LS00 (at U58) and a crystal, and pin 8 of the the 74LS00 is open - neither high nor low.

I can't find my desoldering tool, so I'll have to wait till Monday and get one down at Jameco. The plan is to desolder U58 and solder in a socket.

Toshi

One of my favorites, and my 2nd computer was a Super Board II. The heart of a C1P. Hope you get it working!

_________________
Bill

I "stacked" another 74LS00 on top of the suspicious one, and now I'm getting a clock! It looks like the address and data lines are toggling now, so it's closer to running.

Toshi

After:

o 15 hours of debugging with a logic probe
o Fixing about a dozen cut traces
(Looks like previous owner attempted a modification to the video because most of cut traces were in the video section, and never completed it)
o Desoldering three chips for testing
o Replacing two 74LS123s (dual retriggerable one-shots were...."shot")

I now see it displaying "D/C/W/M ?" on the screen.

As it turns out, the projector I had been using for testing wouldn't display anything after I couldn't find anything else to fix. So on a whim, I took it over to another projector, and I could faintly see the D/C/W/M ? prompt.

From what I can tell, the Superboard II has a horizonal scan frequency of 15 khz, and the first projector I was using couldn't handle it.

So now the next problem is: at the D/C/W/M prompt, I press C, but nothing happens. My guess is something wrong with the hardware involved in keyboard scanning.

Toshi

(I forgot to mention a bad solder joint I had to fix in the power supply - the output voltage was 3.85 volts because the electrolytics were not properly soldered...)

It looks like the keyboard is never being read because the address decoder for the keyboard uses the phase 2 out (pin 39) from the 6502. However, I don't see a pulse train on pin 39? I don't think I used phase 2 out on the 6502 SBC I built...?

Toshi

I forgot to press BREAK before testing to see if the keyboard was being polled...the Superboard does not have power-on reset, and the 6502 is basically wedged on powerup until you hit BREAK. Doh.

Also, the screen flashed every time I hit a key, so I figured it was reading the keyboard properly. Just on a whim, I hit CAPS LOCK, then hit the C key. It then asked me for memory size and terminal width, and dropped into BASIC. Doh! then Yay!

The system only detects 276 bytes of RAM, so apparently some of the RAM is bad...

Toshi

I fiddled around with the RAM, and figured out if you have 1K of good RAM installed, it would say 255 BYTES FREE.

So basically I pulled all the 2114x out of the machine, and paired each suspect 2114 with a known good 2114 to see if it would say 255 BYTES FREE when booted - basically using the Superboard itself as a RAM tester.

So out of 16 2114s which came installed on the machine, fully 6 of them were bad. Wow.

I plugged the good 5k of RAM back into the machine, and it reports 4351 BYTES FREE when it drops into BASIC.

So took about 20 hours total to fix the board.

Toshi

Great story! I'm surprised(*) it's happy to boot with as little as 1k ram, but it's helpful that it is. (I have a UK101 which is basically a copy with some tweaks to the video. I think it was withdrawn after some legal challenge.)

(*) The memory map shows that I shouldn't be surprised

Looks like excellent troubleshooting skills! Almost like you've done it before on the OSI?...

No, never fixed an OSI Challenger before.

I did fix a dead SYM-1 about ten years ago, though. The address decoding was bad, and the culprit was a bad 74LS138 3-to-8 demultiplexer.

Toshi

Hopefully these links work:

http://www.flickr.com/photos/tm314159/6 ... /lightbox/
http://www.flickr.com/photos/tm314159/6 ... /lightbox/

I've bought another OSI (Superboard II). Should arrive in a week or two. This one is in worse shape, and the board has corroded traces and missing chips. Hopefully fixable.

Toshi

Awesome! They are addictive, right? It would be great if you join the forums at OSI forums and post there about your repairs, as well as your pictures (pictures can be posted directly on the forums.)

Good luck!

Dave