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Hello!

I´m new to the Dragon community. I recently got hold of two Dragon 32. One works perfectly, but optically it isn´t in good shape. The other one looks much nicer, but its video signal (I use a DIN-Cinch cable to get the Composite signal) flickers about every two seconds, resp. the colours disappear for a very short period of time - hard to explain. Is it very likely to be the PSU daughter board or is the Composite signal generated elsewhere? Thanks!

Edit: When I opened up the Dragon, I found that both RV1 and RV2 are covered with white powder/crystals?!?

Hello and welcome!

The white powder could be a build-up of tin oxide. This is known to happen on old components and is more likely to happen if the plating is rough instead of smooth and shiny. I would carefully brush it off while collecting the dust with a vacuum cleaner. Take no chances, don't breath the dust and wash hands afterwards! Lead (Pb) is also found in component plating so it's best to minimise exposure.

I had a Dragon that had no video display at all but was restored by moving a pot very slightly. There must have been a build up between the wiper and track that was cleared by the movement. If this doesn't improve things for your Dragon then I think you will first need to look at the power supply voltages to see if they're stable.

I see you have collected one or two items of sinclair equipment You did well to get hold of the calculator and pocket TV!

Thanks for the welcome and your advice. I will give the two components a clean. Forgot to mention that I used the same PSU for both Dragons and the other one showed a stable signal. However, the voltages get modified on the RF board, so this could also be the bad boy?

p.s. Yes, I do seem to have some liking for Sinclair and other British technology...

I'm a little hazy on this as it's been a long time since I've looked at it in detail but there are different versions of the main board and PSU/RF board and not all combinations work together. Someone else here may know better.

I think one of the pots adjusts the amount of colour present in the PAL signal so this seems like a reasonable starting point. After that I would suggest checking voltages on the connector between the two boards. Bad regulation on one of the lines may well cause instability in the video. If it's not the pot then it might be worth replacing the electrolytic caps on the PSU/RF board. It wouldn't be surprising if they've dried up after 30 years.

sorchard wrote:I'm a little hazy on this as it's been a long time since I've looked at it in detail but there are different versions of the main board and PSU/RF board and not all combinations work together. Someone else here may know better.

You can swap one Dragon external power transformer with any other, so long as it is the correct type for your electricity supply. You need to be careful swapping internal power boards around, you can swap like with like, others may need modification (see the service sheet for details), but you cannot swap Dragon 32 power boards with 64 boards (or vice versa).

You can also try to push a little bit all socket chips.

You´re stars! The Dragon is fixed. Removing the powder/crystals, especially from RV1 and turning it back and forth cured the flickering signal. Thanks a lot!

After working on many other vintage computers, I have to say the Dragon is one of the easiest ones to get access to and it´s very service-friendly. Clear layout, large screws, no brittle membrane, some parts like the keyboard clamp are even labelled etc. I´m impressed!