dragon 32 not displaying anything on screen

[robcfg]

Then, if you could post some pictures of your Dragon 32 PCB, specially near where the video connectors are, we may spot a blown capacitor or any other problem.

[starfrog]

happy to do that I'll take some shots of the boards tonight but I have looked at every CAP and they all look good but then again I'm no technician so the more that can see it the better.

[tormod]

Check also the voltages coming from the power board. See http://www.grempc.demon.co.uk/dragon/info/psu.html

I thought my VDG (6847) was broken, but it turned out to be a bad capacitor on the power board. It shorted the -5V needed for the video circuitry. (C5, the one being cooked between all the diodes and the R5 energy waster).

[Alastair]

A word of warning. Do not swap power boards between Dragon 32s and 64s, should you be thinking of swapping them around for testing purposes, because their outputs differ (+12V, 0V, & -5V on a Dragon 32, and +12V, 0V, & -12V on a Dragon 64).

[starfrog]

Check also the voltages coming from the power board. See http://www.grempc.demon.co.uk/dragon/info/psu.html

I thought my VDG (6847) was broken, but it turned out to be a bad capacitor on the power board. It shorted the -5V needed for the video circuitry. (C5, the one being cooked between all the diodes and the R5 energy waster).

Thank you for the info but I think I would need someone to literally draw each component that I needed to check and then tell me what I use to actually check it ! sorry Im not that technically advanced but I assume a multimeter is needed

[starfrog]

A word of warning. Do not swap power boards between Dragon 32s and 64s, should you be thinking of swapping them around for testing purposes, because their outputs differ (+12V, 0V, & -5V on a Dragon 32, and +12V, 0V, & -12V on a Dragon 64).

Thank you Thank you Thank you I was about to try swapping out my 64 power board to see if that made the 32's work. I assume that I'm okay to use the 32 power brick to power the 64 ? just not the actual board inside for my 32 ?

[starfrog]

dragon image 2

IMG_0201.jpg (5.95 MiB) Viewed 5246 times

dragon image 1

IMG_0200.jpg (6.05 MiB) Viewed 5246 times

hopefully this lets you see what I'm working with but there doenst appear to be any obvious issues ?

[jltursan]

RV2 (the 10K vertical black variable resistor) in the upper center of the second pic looks like it has some crystalization or dirt over it. If so, deeply clean it using isopropyl and a cotton swab.

I've found several times that it's covered by that "salt" and always has been responsible of weird boot faults: screen garbage, empty green screen ,etc.

[Alastair]

I assume that I'm okay to use the 32 power brick to power the 64 ? just not the actual board inside for my 32 ?

The external power bricks are fine, it's the internal power boards that cannot be swapped between 32s and 64s.

Regarding the Dragon 64 producing monochrome output. You state that you obtained it in 1988, if it is second-hand it could be that the previous owner modified it to produce a clearer video signal. It's a relatively simple procedure that was mentioned in an issue of Dragon User (though I cannot remember which issue) but it comes at the cost of losing colour output.

[starfrog]

Regarding the Dragon 64 producing monochrome output. You state that you obtained it in 1988, if it is second-hand it could be that the previous owner modified it to produce a clearer video signal. It's a relatively simple procedure that was mentioned in an issue of Dragon User (though I cannot remember which issue) but it comes at the cost of losing colour output.

Sounds like a possible lead just need the info to make it less clear ! I have all the early dragon user mags so i'll take a look.