archive.worldofdragon.org

Sometimes the smallest little glitches cause everything to break.
https://youtu.be/lQRipdxTPpg

I realized there *is* a diagnostics ROM! http://archive.worldofdragon.org/archive/index.php?dir=Roms/Dragon/ I have no idea what it does as there's no documentation, but I figured I would try it. I assume it goes in IC34 (left ROM, the one labeled 18). I popped it in, turn it on, the screen got garb...

Today I got the new SAM chip. I put it in and... nothing. Still the same. I decided to try the 74LS244 since a failure there could cause these symptoms and... nothing :-( Is there really no ROM for full computer diagnostics? Or at least a quick and dirty RAM-testing program that can be executed from...

robcfg wrote:That said, boot your machine and try typing EXEC and press return to see if something changes.

I didn't notice anything happening when I typed that.

What's the jumper labeled LK1 near the memory on the PCB? Just curious.

Have you visited IC25? 74LS244. It buffers RAM reads (Dout) to the CPU - testing by modifying XRoar suggests that if you could write but not read, you'd get a cleared screen with occasional glitches. That's very interesting! Especially those tables. The fact that when I pulled some chips I got some...

I tried piggybacking after you mentioned that, but I didn't have high hopes since the Dout on all the pins showed activity. In any case, it made no difference. So today I finished socketing the remaining 4 RAM ICs, and to nobody's surprise, I'm still getting the green screen with black border :-( An...

Progress update: I started removing RAM ICs, socketing them, and putting on good ones (I can go back later and put back the RAM ICs that were not defective). I did 4 of them and ran out of sockets (oops). So far no changes. One interesting bit that I suspect you're all aware of, is that with a RAM I...

A bad memory IC would seem to be the most likely cause at this point, though there could be other reasons. Next most likely is a poor soldered joint on one of the major ICs. I've seen quite a few of those. That makes sense. I don't imagine there's an easy way to narrow down which RAM IC it might be...

Two common failures I've found in Dragons are broken CPUs and some kind of weird crystalized deposits over a vertical variable resistance. Both usually causes garbage screens but that green with black border doesn't rings a bell... The CPU seems lively enough from what I can see from the scope. The...

Hello, I'm very new to Dragons, but I bought a Dragon 64 recently to continue exploring 8-bit computers. As I kind of expected, untested turned into "not working". The good news is I'm fairly experienced repairing other 8 bit computers (Amstrad CPCs, Spectrum). The bad news is, I don't know much abo...