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Date Posted: 03:00:58 10/27/01 Sat
Author: Adam
Subject: Failed VGA mod - I think I killed my CC !!!!

Today I attempted the VGA mod as provided by Chris Lawson at http://www.colourclassicfaq.com/general/vga.html.

Throughout the thing I took care to ensure that all isolation was correct and that nothing was shorted out with solder etc. After finishing up, I stuck in my 575 logic board, powered 'er up...

Nothing.

Well, not quite nothing. The machine chimes, the fan spins, but the screen doesn't switch on. It tries to, and this is where the problem starts. As it makes that faint "doomph" sounds CRTs make when they fire up, the fan spins down. Moments later it (the fan) spins right up again (The fan loses power only momentarily, not long enought to come to an actual stop). The screen remains dark, though everything else seems to continue normally.

Given that this seems to be an electrical issue, I immediately suspected the power isolation/voltage conversion part of the mod. I checked the integrity of the pin 8 isolation, which seemed to be fine, though to make sure, I went back over it with the dremel. I didn't test the integrity of the pin 8 -> pin 12 jumpering at this time, but did so as I was doing it, so I believe this to be fine.
Just to be thorough, I went back over the sense-wire mods, which also seem to have been successful.

My guesses would be:

I. Pin 8 was not isolated correctly and has now fatally wounded the analog board
II. Pin 8 is a little too isolated. i.e. I dremeled to much of the trace away, and the voltage path is now too narrow.
III. Crappy solder joint on either pin 8 or 12. Will check tomorrow
IV. Bad wire between pin 8 and 12. I used a wire stolen out of a PC power wiring loom, which while designed for probably 12 volts is quite thick. (made from aluminium)

Tomorrow when I'm feeling a little less exhausted, I'll look over the board more thouroghly. If none of the above work, I'll break out the solder-sucker and conductive pen, revert it back to its original status and see whether I've buggered the thing. If it's OK, then I'll reattempt the mod. If it isn't, then I'll have the most exquisitely designed (not to mention expensive) paperweight in the office.

If anybody can offer _any_ help, It would be very (very) much appreciated.

Cheers,
Adam

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