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Hi all, I have looked through other threads and can't quite find one similar, so hopefully someone can help.

Finally got a D32, but sold as untested, so took the risk.

Plugged into aerial socket, and switched on, and heard the click and TV screen went into life (using channel 36). Could see the start up screen and OK, but very faint and wavy. Remembered the MOTORON, MOTOROFF (amazing what you remember after over 30 years), and this was fine. So lid off, and tried the pots on the modulator. Seemed to get a tiny bit better, but still very wavy and mainly black and white.

Decided to get a monitor lead, and tried this alternative instead. A bit more success. The full screen is displayed, but alternates between the normal green and black, and grey and black. Seems to stay green and black for under a second, and remains B&W for about double the amount of time.

So my question is what should I test? I am more of a software person, but don't mind getting out a DMM to test voltages. I did build a few Maplin projects back in the day, but never really went under the hood on my old machine, so will need a bit of help.

Cheers

Hi AndyP, welcome to the forum!

Hard to think of anything specific but going for easy things:

Depending on your main board version there should be one or two pots; RV1 & RV2. These can go bad and mess up the video so it's worth adjusting these slightly to see if it has any effect. Make a note of the positions before moving them.

Look for stable supply voltages on the main board connector. Starting from the right you should have +12V, +5V, -5V, 0V. If the -5V line is fluctuating then this could affect the video with the rest of the system working OK.

The tantalum bead capacitors have a limited life and can fail short circuit so it's worth replacing these if you feel confident enough to do so. (I've had two Dragon's stop working for this reason.) Aluminium electrolytics dry up over time as well and may need replacing though I've not had to do this yet.

Dragon's also seem to suffer from bad solder joints and applying light pressure to the main board in various places can provoke faults to appear and disappear.

Maybe someone else has seen this before but failing that it's probably a case of looking at the schematic and poking around with a scope to see if the bad signal can be traced to source.

Good luck!

Welcome to the Archive Andy!

Could you tell us if the screen appears to be rectangular or square? There's a chance that your machine is a NTSC one instead of PAL.

Also, which is the motherboard model?

A picture of it may be helpful too.

Cheers,
Rob

Cheers for the help guys. I have it working (of sorts). Opened the hood up (attached is a photo of the motherboard), and switched on. The image still flashing on the screen, plugged in via the monitor cable.

Started applying slight pressure across the board, and no effect.
Next I applied slight pressure to RV2, some slight flicker on the screen
Next I applied slight pressure to RV1, and BINGO screen went green.

The regular aerial cable still not getting a picture, but I'm going to get an old CRT TV to test this out more.

Now just waiting to get hold of an old tape deck so that I can start writing some programs old school on the machine directly

Ok, it seems that your board is one of the first production batches, with 8x64 KB chips.

You can take a look at the different board revisions here.

A version with an addon to make the video output better (Part number 48200) was released with MKII Issue 6 boards, later included in the Dragon 64 boards.