Color Classic screen is waaaay too bright. Analog board?

[iphillips77]

Hey there, everyone! Long time reader, first time poster.. These forums have been a great help to me in bringing some dead Macs back from the brink. I've recently added a Color Classic to my collection. Of course it was completely dead when it entered my possession, but I've managed to coax it partially back to life. I've re-capped and thoroughly cleaned the logic board, and now she fires right up.

I'm having display issues, though. Of course. The screen is crazy bright. The contrast controls on the front work, and do a fine job of making the image look washed out. I can't reduce the brightness at all -- the brightness control panel refuses to work. I was going to pull the analog board tonight and give it a more thorough inspection, but I thought I'd reinstall System 7.1 from scratch in case it was a software issue. No dice. Now I'm leaving it sit for a day or two to discharge before I tinker with it again. Figured I'd pick some brains here in the meantime.

The analog board looks okay after a cursory inspection. No bulging caps that I can see. I imagine I'll replace them regardless eventually. Haven't checked for bad solder joints yet. I'll be doing that once I crack it open again. But at this point I'm not really sure what I should be looking for. Info on the CC is tricky to find.. Does this problem I'm having sound familiar to anyone?

Here's a pic of the screen I've got. You can see at the top of the display where the extra-bright raster is extra-noticeable above the menu bar. Thanks in advance for any advice!

 

[bigmessowires]

I can't explain what might cause super-brightness, but I don't think it's necessary to leave the CC sitting for a day in order to safely dicharge the CRT. Every compact Mac from about the SE/30 onward has a bleeder resistor that quickly discharges the high voltage stuff when it's turned off. If you're paranoid, you can be double-safe if you also use the "screwdriver under the suction cup" technique that's standard for the Mac Plus and earlier compacts. I was very nervous about this the first time I did it, but it's quite simple and I've now done it dozens of times without electrocuting myself.

 

[Brooklyn]

This should help:

http://tim.id.au/laptops/apple/legacy/color_classic.pdf

 

[sadmanonatrain]

iphillips77,

Welcome to the 68kMLA!

One of the adjustments on the analog board should be a 'brightness cutoff' which dictates the maximum brightness that can be set via software.

I am not too sure about the Colour Classic but I know that this applies to B&W Compact Macs.

I hope this helps!

 

[iphillips77]

Thanks for the welcome and the advice!

Oh hey, bigmessowires -- I remember stumbling across your website quite some time ago.. Was quite impressed with your FPGA Mac Plus. I've read about this bleeder resistor, though old habits die hard.. With my luck, I'd start messing around in there and find out that they'd forgotten to install it. I cut my teeth recapping dangerous old Electrohome G07 arcade monitors, so I'm quite familiar with the screwdriver-under-the-suction-cup technique. Though after frustrating myself with piles of corrupt floppies getting a fresh system installed, I didn't have the nerve to start shorting things out.

Brooklyn.. Thanks for the link. That'll be a big help in getting the analog board out, though it doesn't seem to delve into any kind of board-level diagnostic..

Sadmanonatrain.. I'll fiddle with that setting and see if it helps things at all. I have a feeling there's something else wrong here, though. The fact that the Mac is telling me that the Brightness control panel can't even be used on this model suggests something's amiss.

How does this computer-controlled brightness work? Is there a special monitor sense line that tells the mac that it is in fact connected to an internal monitor and that is should be controlling the brightness? Should I pop over to the LC forums and see if this problem ever occurs with 500-series machines? (That last question is rhetorical, I'm doing that as soon as I submit this post.)

Thanks everyone!