archive.worldofdragon.org

Hi all,

Has anyone else had a problem with the Dragon 64 overheating after about 15 minutes ?

Symptoms are that the video becomes corroupt and starts to lose sync. However the machine itself still runs fine in that any running program continues to run.
I have tried changing the SAM and CPU with known good ones however the problem remains.

I have also desoldered the LM1889 colour encoder (and fitted a socket). Running without the LM1889 fitted the machine is absolutely ok, and I get a normal display
no matter how long the machine has been on, though obviously only in monochrome. Fitting an LM1889 from another Dragon restores the colour however it starts to
corrupt again after a few minutes as before.

The above sugests to me that the fault lays somewhere in the colour encoder circuit.

So is this a known problem with a known solution I don't think my othr 64 does this, and none of my 32s do either.

Cheers.

Phill.

Hi Phill,

I use my d64 quite a lot and I haven't experienced such symptoms.

Just to be sure, does it have to be 15 min in a color mode like pmode 3?

I'll be glad to test it.

robcfg wrote:Hi Phill,

I use my d64 quite a lot and I haven't experienced such symptoms.

Just to be sure, does it have to be 15 min in a color mode like pmode 3?

Nope just sitting at the signon screen, not actually tried in a graphics mode, though I could do so I guess.

I'll turn i on later and try and take some piccies.

Cheers.

Phill.

Mine has been more than half an hour at more than 30 degrees celsius, and works well.

I've been displaying images in several modes and everything seems ok.

You should open it, let it go into the unstable state, and with your fingers (taking care, of course) test which chip is much warmer than the rest, that one should be the culprit.

Applied to D32 - but possibly of use:
C. Faulty Colour

1. Adjust RV1 (and RV2 if fitted).

2. Alter value of C7.

3. To obtain full green screen or to cure 'rainbow effect', fit a 2-22 pf capacitor trimmer instead of C7.

4. If colour fault on 22" or 27" SONY sets, then fit 15K resistor across Pin 4 of IC9 to Pin 4 of IC10.

5. Change IC9.

6. Change IC16.

7. Change IC12.

D. Garbage on Screen

1. If RESET switch cures fault, then change IC17.

2. Change IC15.

3. Change IC17.

4. Change IC18.