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Colour Classic - Mystic - black screen


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HI! I’m new here!

 Well, I might have been a member 20-16 years ago - that was when I collected and played with old Macs. But as always wife, kids, work, life and divorce got in the way.
After cleaning the attic I found most of the old toys I had forgotten about. There among two Colour Classics. One is (was) pristine and in almost original condition, and one heavily modified.
After some work - primarily changing or kicking life into the old hard drives, I got them both up and running. "The good one" had a Mystic motherboard, shipped from the USA 17 years ago and use modified system 7.6. Only thing not working perfectly was the p-ram battery - the machine double-booted and forgot settings. The original motherboard was ok before putting into storage, but tough it still looked god (in my eyes) it now wouldn't boot. Having read a lot around here and other places of the Internet I realized a recap was long overdue. I did that with both the motherboards yesterday and to my surprise now both motherboards booted and turned on the screen as they should (I used to love Macs better than electronics and soldering)! Success! I kept the 575-motherboard in the machine and turned it off to check if it would remember the date next time

And here the happy story stops and this post get its title. The machine boots, but the screen stays black. There is only a faint purple 5 mm horizontal line two thirds up on the screen. It moves a little as the machine reaches the desktop (at least I can’t hear the little bong telling me the time and date is wrong :-). I hit the power button on the keyboard and turned it of the normal way.  

No smell or strange sounds.

There was one sound missing: earlier when the screen lit, there was a faint high-pitched sound. I think this was gone and I was afraid this used to come from the flyback.  I let it be for the night and went to bed.

 

Today I checked the analogboard: it still look very good and I saw no sign of leaking caps or bad solders. Then I put back the CC motherboard. This time it boots to a perfect screen again. Of course it can't use the modifies system 7.6 and asks for a diskette. But the analogboard and screen is obviously still good! Back with the 575 and the black screen with purple/blue line is also back. This time there is some crackles from the speaker as well. I’ve peeked underneath the motherboard to check that the grounding still is ok.

The 575-motherboard also used to produce some buzzing in the speaker when opening menus or windows (larger white areas), but I was hoping this could be fixed with the recap. 

Sorry, long story! Do you have any ideas?

 

I might be back with the not so good Takky later :-)

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How do the edge connectors look (both the pins on the boards and the slots on the IDC flex? I just fixed one that had crackly audio and occasional video and it ended up being mostly due to corrosion in the IDC receptacles. Granted, this machine had seen serious humidity, but a quick brush with a nail file and everything was good to go. 
 

On another one with strong audio but intermittent video I ended up doing a full recap to get it working. I first replaced just the “typical” weak points per this site but that wasn’t enough: https://recapamac.com.au/macintosh-cc-analog/

 

@elemenoh posted a digikey cart for the full recap that I can recommend, with the additions I note in that thread: 

 

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Thank you! No, the analogboard in this CC is completly stock, and looks very nice. The computer was very well kept when I bought it back in 2000-somthing. I used ResEdit on the systemfiles to make the 575 motherboard work in this CC because I didnt want to tamper with the hardware (I had backup of these files to make it work again now).

The 575- motherboard on the other hand, posibly led a harsher former life in America. I will check the edge-connectors tomorrow.

I was thinking I might also have a closer look around the soundchip, reseat the video-ram and try to figure out witch chip(s) generate the videosignals. I read another post reffering to the «RAM DAC» for video-problems with a Mystic - should I look around this IC?

Thanks again!

 

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Gee! Its back! :wub:

I reseated the v-ram and gave them a wash. The edge-connector looked good, but also recieved a polish.

No strange sounds and no whine :-)

Thanks!

As I told you, I might be back with my Takky. It has some issues.

But is this the right forum? Should the Mystic realy be in LC/Performas (and the Takky would belong i Powermacs)?

8B1CB174-3388-450A-8B9D-E81E6F6C2307.jpeg

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On 12/6/2020 at 8:40 PM, ttb said:

On another one with strong audio but intermittent video I ended up doing a full recap to get it working. I first replaced just the “typical” weak points per this site but that wasn’t enough: https://recapamac.com.au/macintosh-cc-analog/

 

@elemenoh posted a digikey cart for the full recap that I can recommend, with the additions I note in that thread: 

 

Thanks, I might need this!
I dug out my Takky again (6500, 300mhz motherboard), to see if I could fix its shortcomings: the blue channel was missing from the display.

After rinsing the display-adjustment pots and resoldering some dodgy looking connections on the analogboard, the blue channel was back. I think the rinsing would have been sufficient, though. 


But the display is still not stable. It flickers occasionally and the geometry is drifting from boot to boot. I think I will try a recap.
And I will order for my Mystic as well.

 

Greetings from Norway!

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4 hours ago, 8tto said:


But the display is still not stable. It flickers occasionally and the geometry is drifting from boot to boot. I think I will try a recap.
And I will order for my Mystic as well.

 

Greetings from Norway!

 

You should clean with DeOxit, and work all the adjustment potentiometers on the analog board first before diving into a recap. 

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  • 1 month later...

Ok, so I’ve tried a recap of the Takky analogboard. I did it halfway through with most of caps marked as important to change according to Branchus Creation here: https://recapamac.com.au/macintosh-cc-analog/ , plus most of the caps inside the video “cage” underneath the flyback. Had to take a brake and order more caps. Meanwhile I tested the board. The screen looked better than ever. Then I heard a “pop” - the Mac and screen was still running fine but I turned it of immediately using the keyboard.

Turned out I had the orientation wrong on the 2,2 uf 200V in the middle closest too the video-pots, and the sound was the alu-can popping.

At arrival of more caps I changed the rest and double checked the orientation of each cap. No pops this time, but the blue channel was gone again and the picture is jumping up an down. Argh!

I’m guessing the blue channel stil is a bad pot for the blue channel and that my rinse wasn’t enough. Ordering replacement pots.

 

But does any of you have an idea why the picture started jumping up an down?

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Update: changed both pots for Blue Gain and Blue Background. The blue channel was back for a while and then disappeared again.

Am I right assuming the videosignal comes from the analogboard edge connector, through the gray cabel into the white connector to the left in the picture in my last post and out to the CRT-board through the white connector to the left?

 

Ps. Also recapped my 6500- 300mhz motherboard. Forgot to connect the CPU-fan. Boot chime, HD-spinn, no screen and then the machine shut down. Could I have burned the CPU in that short time? My 5400-160mhz MB still works fine.

Edited by 8tto
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Hi! The machine shutting down probably was because G2 (voltage?) on the analog board was sett to high after recap.

But The 300mhz MB still won`t boot. There`s a nice chime, the HD-spins but doesn`t look for a system folder and the screen stays black. I can reboot the computer from the keyboard. I also tried to boot without RAM and cache - same result :-(

 

As said the 5400 MB still boots fine. I`ve changed all the pots in the Video section (Sub-contrast, Green-drive, Blue-drive, Red background, Green background and Blue background). First boot the blue channel was fine, but the green was missing instead :-). Took it apart again and tried to check all the traces/components from the yoke board to the edge connector for the green and blue channel and gave the yoke connector and edge connector a cleaning with IPA/cotton/toothpick.

Now it seems to be fine, but I`m not sure I trust it will stay that way. At least the picture is stable, bright and more sharp than when I bought the machine some 20 years ago. Not half bad for a total makeover :-) (with the 300mhz MB as an unfortunate casualty - but haven`t given up on it).

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