My new Colour Classic is tripping on acid

[BadGoldEagle]

Hey folks.

I remember reading about something similar to this some time ago. But I didn't pay that much attention to it as I wasn't really into CCs back then. Now I am though.

I recently picked up a nice looking original CC. The seller advertised it as non working/for parts only and as it turns out, it boots up just fine. (apparently he had completely forgotten about soft power...) So that's good. What isn't though is this:



NB: The flag in the top right section of the screen is supposed to be the French flag. Blue, White and Red. It's definitely not supposed to be green, white and blue. 

Interesting fact: when you give it a little whack on the side, the display becomes wavy for a couple of seconds then it goes back to the weird acid trip colours....

I know the last owner has been tinkering with its insides lately, so he could have messed things up a bit. But IIRC this problem can be caused by cold solder joints on the A/B or on the neck board PCB or simply by a completely shot CRT. That would suck. Or could it be just caps? I really doubt it though.

Any clues to what I should look into first?

Thanks in advance!

Cheers,

BGE

 

[techknight]

CRT Degaussing circuit is bad, or the CRT has been jarred too hard knocking the aperture grille out of place. 

If you have a pull trigger soldering gun, you can use that to degauss the CRT to rule out physical damage. 

Otherwise, the thermistor is likely bad or broken solder on the analog board. 

 

[BadGoldEagle]

You mean one of these?

I think I have one somewhere. How do I degauss the CRT?

 

[techknight]

No, not one of those... 

Youtube/Google is your friend here. Lots of different ideas and methods. 

But the ultimate goal is to inspect and fix the analog board. Its possible the coil is even unplugged. 

 

[snuci]

This is what I use.  It's a TV degausser and I have used it on two Mac Color Classics but it was blotchy and wasn't similar to yours.  Might work still but I don't have experience with what you are seeing. 

 

[BadGoldEagle]

Well, I had a look at this video here

And this guy managed to bring his CRT back. I followed the same method but it didn't do much to my CC. It's reacting all right and the french flag gets its colours back (until I release the trigger that is...). So I think the CRT itself is okay but something isn't on the A/B. (that was my first guess anyway, but it's good to know the tube's all right.) As suggested here, I left it plugged in for the night. I'm gonna fire it back up in a couple of minutes and see if it made a difference.

I think that CRT degausser does more or less the same job as the soldering iron (albeit better). I wish I had one of those though.

So next step today is to take the damn thing apart and re-do all the connections.

 

[BadGoldEagle]

Sit rep. Reflowing every single thing on the AB and on the neck board didn't change anything. I'm starting to think something is wrong with the degaussing circuit and the CRT's frame. 

I've played around with the pots at the back. Didn't change anything either.

I know absolutely nothing about color CRTs, but aren't there magnets I can fiddle with?

Edit: Just for kicks I left the degauss cable unplugged, and it doesn't change a thing. So apparently the problem is coming from there.

 

[techknight]

Yea, I can tell.... but before you irreparably damage the unit if it hasn't been already, 

You need to take a look at the degaussing thermistor, you MAY have to replace it with another one. its a black square boxy thing near where the coil plugs into. the coil is a black thing wrapped around the face of the CRT and has 2 wires coming off of it. You could also unsolder the 3 pin black box thermistor and test it with an ohm meter when cold. only should be a few ohms. If its open thats your problem, if its good then the CRT is likely your problem. 

IF you had a variac, you could plug the coil into that and start it up hard, and slowly wind it down.

if you cant degauss the CRT then its entirely possible that the CRT is damaged from shipping and will need replaced. 

No amount of adjustments anywhere in the unit will fix this problem unless the deflection yoke has completely slipped away from the CRT and then put back in place, that will affect the purity. 

 

[BadGoldEagle]

Next week-end I'll bring it to a TV repair shop and ask them to degauss it with proper tools. I hope they still have the CRT hardware. 

I'll have a look at that themistor before I do so though. But even if the circuitry is damaged, it should still be possible to degauss it using an external source, right? Unless the tube is gone that is...

But from what I've heard, the Mac had been sitting in a basement since the late 90s (it was working back then) and the previous owner had just unearthed it before he put it for sale. I picked it up myself, drove about 10 miles very slowly as I always do when I carry old macs with me and plugged it the day after. I don't think it has suffered much damage since the 90s. And the case is in perfect condition too.

 

[techknight]

So if it hasnt been shipped then the CRT is likely fine unless it took a huge jarring. 

So time to inspect the degaussing circuitry. Need to test the thermistor. 

When cold, if you flip the switch in the back, youll hear a small "thump". Its more noticeable with much larger CRT setups and thats because of the degaussing kicking in. 

As far as a TV repair shop, your lucky you still have them. The last one left in Los angeles just closed so its only a matter of time. 

 

[BadGoldEagle]

Well as I said before, the guy had it opened before I bought it so he could have done some damage trying to bring it back to life. 

I can definitely hear the "thump" when I flip the switch after a few hours unplugged. Is that good or bad? The degaussing clearly kicks in but is it effective? Hum...

There was actually a really good Philips repair shop literally 3 blocks from my place. This guy fixed my Beocenter 2200's amp in a matter of a few days but unfortunately the shop's gone now. There's still about half a dozen around but you're right, they won't last that much longer. New sets can't really be repaired nowadays and people just prefer buying a new TV instead. Sad but true.

Now unfortunately I won't be able to check on that themistor until next Saturday. But I'll definitely report back once that's done.

 

[just.in.time]

I think the Color Classic that you saw a while back was mine.

In my case, it was the aperture grill had shifted inside the CRT. This is a non-reparable problem.

GOOD NEWS! Mine looked slightly different than yours. My messed up colors were uniform across the display. Yours, as you mentioned, are acid-trip in nature. That said, I don’t think the issue is inside the CRT tube. Hopefully it is just the degaussing circuit

Best of luck!

 

[beachycove]

I have seen odd things happen on a screen when a vram SIMM goes bad — garbled images and varied colour distortions. You might try simply replacing your Vram before spending real money.

Just saying....

 

[Daniël]

I have seen odd things happen on a screen when a vram SIMM goes bad — garbled images and varied colour distortions. You might try simply replacing your Vram before spending real money.

Just saying....

No way that bad VRAM is going to create color distortion that looks that distinctively as a magnetized CRT monitor. Especially his mention of the French flag regaining its colors temporarily when degaussing debunks that.