Dead Dragon repair - black and white vert.bars on screen

[mikek]

Hello,
at first I must mention I am just a beginner in 8-bit repairs. I collected few experiences in repairs like changing the capacitors, voltage regulators and building kits like Minstrel 2,3, etc.

I want to play with my Dragon 32 after couple of months again. It was working previously, but now it developed some fatal failure.

I had to power it on and off couple of time to boot in into working state, but after few other tries it died completely. Now I can see only white and black vertical bars on screen.

The processor seems to be live - with scope I see some activity on address and data lines. Couple of time during the probing and restarting the pattern on screen changes, but most of the time I see the vertical bars.

I already removed all the socketed chips and cleaned them with contact cleaner. I am able to remove only memory chips from the daughter board. With removed memory chips the behavior did not changed.

Does anybody has a clue what could the culprit? Where should I start?

M.

[robcfg]

Welcome to the Dragon Archive!

I had a similar problem with a CoCo2, and turn out to be a bad MC6847 video chip.

Other culprits could be the roms. If they have given up their ghost and become corrupted, you could get a bad video initialization.

If you type CLOAD and press Enter, do you hear the relay click?

Do you have any spares, and can we get a picture of your board?

Cheers,
Rob