Sometimes the smallest little glitches cause everything to break.
https://youtu.be/lQRipdxTPpg
Search found 10 matches
- Thu Sep 23, 2021 5:15 pm
- Forum: Dragon Hardware
- Topic: Video: Fixing the color on a Dragon 64
- Replies: 2
- Views: 4037
- Fri Sep 21, 2018 2:39 pm
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Re: Help repairing Dragon 64
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...
- Thu Sep 20, 2018 10:42 pm
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Re: Help repairing Dragon 64
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...
- Mon Aug 20, 2018 6:51 pm
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Re: Help repairing Dragon 64
I didn't notice anything happening when I typed that.robcfg wrote:That said, boot your machine and try typing EXEC and press return to see if something changes.
What's the jumper labeled LK1 near the memory on the PCB? Just curious.
- Sun Aug 19, 2018 10:59 am
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Re: Help repairing Dragon 64
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...
- Sat Aug 18, 2018 11:15 pm
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Re: Help repairing Dragon 64
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...
- Tue Aug 14, 2018 10:05 pm
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Re: Help repairing Dragon 64
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...
- Tue Aug 14, 2018 5:27 pm
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Re: Help repairing Dragon 64
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...
- Mon Aug 13, 2018 10:53 pm
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Re: Help repairing Dragon 64
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...
- Sun Aug 12, 2018 11:25 pm
- Forum: Dragon General
- Topic: Help repairing Dragon 64
- Replies: 19
- Views: 15825
Help repairing Dragon 64
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...