Color Classic (almost) Mystic video issue.

[camateg]

Hello -

I have performed, with a tiny degree of success, the following mod on my new Color Classic which has a 575 motherboard:

http://www.colourclassicfaq.com/general/vga.html

The problem that I'm having is that the screen takes about 5 or so minutes to "heat up" and display a usable picture of the Mac Desktop. However, he picture that it displays then gets larger and brighter until it more than fills the screen and the screen eventually shuts itself down.

My question, I guess, is could this be caused by a failing capacitor or did I perhaps not convey the video signal properly, based on the above? Can I provide any other details that I might have missed to my description which may help?

Thanks for any insight!

Matt

 

[tomlee59]

Obvious things first: Carefully double-check everything that you did. Watch out for solder bridges (either fat ones or hard-to-see whiskers). Make sure that you disconnected what should be disconnected, and connected only that which should be. It's easy to miscount pins, for example, and be off by one or two. Count up from the first pin, and also count backwards from the last pin, just to make sure you get the same answer both ways. This simple trick has helped me out many times (it's hard to doublecheck your own work, because you know what you intended, so that's what you tend to see; counting backwards and similar tricks forces you to use different neural pathways).

Next, a 5-minute interval is very long for anything purely electronic, and is suggestive of a thermal problem (possibly induced by miswiring). The fact that it ultimately shuts down is itself serious. The additional fact that you get simultaneous brightening and enlargement is extremely worrisome, because these two symptoms together imply a gross increase in beam current, and a diminution in high voltage (probably caused by the excessive beam current loading down the HV supply). I wouldn't be surprised if you noticed degraded focus at the same time.

If you can't find a wiring error, then you have a complicated troubleshooting session ahead of you, I'm afraid. Someone here can walk you through the next steps after you report back.

 

[Mac128]

I second the advice. I have done this procedure myself and had no problems whatsoever. While not proof positive, most likely it is a misconnected pin. But if I had to hazard a guess, I would bet you did not isolate pin 1 well enough as this is the power transformer pin section. You have to really cut into the board to ensure you got the entire trace. Solder on pin 12 bridging the circuit could be a problem too. I doubt it has to do with sense mod in step 3, but you never know.

 

[camateg]

I did some basic continuity testing and the connections seem ok so far.

- a/b pin 8 is isolated and connected to 12

- sense wiring seems ok - 25 is isolated and 24 is connected to 20 on the analog board connector

I believe I mis-spoke regarding the "shutting off." It seems that the signal generated degrades to such an extent that the monitor simply "gives up." Sorry for the ambiguity.

I am able to confirm a resolution of 640x480@60Hz in the Monitors and Sounds control panel, if that helps (while I can see it...)

Thanks for the quick response!

Matt