Color Classic screen wavering.

[pizzigri]

OK, I got a sort of defect happening every now and then in the CRT of my CC. I always observed it, sicne I got it. The screen seems to waver every now and then, with the color washing out a bit. It happened before I recapped the AB, after I did it, and after I ddi the 640 mod. Flyback?
It is only just a bit annoying. Otherwise the CRT is fantastic.

 

[joshc]

Weak solder joint somewhere?

 

[pizzigri]

I looked at the solder side it seems ever ok, however since I wanted to replace the two zeners with a single, larger and better one, I’ll reflow all solder joints of the bord.

 

[Byrd]

Every CC I've come across has needed a reflow of anything video related to get a stable image. Colour loss was probably the main thing secondary to jumping/jittering display, make sure you check the yoke PCB and also the RGB wires running into the back of the CRT.

 

[armadillu]

Are your two zeners also extra toasty? What about the resistors that are near them? In my case they are extra extra toast, but they seem to read ok... Do you have specs for them? I don't really know what to buy to replace them.

 

[pizzigri]

OK, update. This is what happens to the screen, especially in the first 5 minutes. It stabilizes somewhat but it will do it occasionally throughout use, even 30minutes after power on.

 

[pizzigri]

What should I look for? I replaced the caps suggested by recapamac. Also replaced the zeners. Performed 640 mod (60hz) and added a 3nf cap to extend a bit the hor size of the screen. Past all this, it’s a bit blue, any way to adj color? forget that I went back to JDW excellent video and found out color balance.

 

[Chopsticks]

I had similar issues with my CC untill I added an extra 5v PSU. The analog board is woefully underpowered. After upgrading the logic board and adding a network card I was getting the same kinda problem on my screen. Once I added a second psu to power the 5v rail I’ve never had problems since.

 

[pizzigri]

That is quite interesting, con you detail how you do e that?

 

[chiptripper]

I think @Chopsticks is on the right track here, are you getting stable voltages?

Other ideas: if you're getting intermittent colour washout you might want to check the integrity and connection of the AB data cables. Swap out with another set to test, if you have spares. Also worth thoroughly cleaning the pots, focus and brightness in particular, but also the cluster found under that plastic cover on the back. They are dust traps.

 

[Chopsticks]

That is quite interesting, con you detail how you do e that?

i think the powerCC website has instructions to add an extra power supply.
basicually what i did was get a pcb mount psu that would fit where the hdd was ( as i use sd/compact flash devices these days rather then mechanical drives) and make a pcb with a relay on it and some connectors to attact to the system

what i did what solder to the back mains power sockets and ran those wire to the relay (switch side) then to the new power supply
basically depending on if you have a 5v or 12v relay you then wire the other side of the relay (the coil) that is used to energize (turn on the relay) to either the orginal analgue boards 5v or 12v rail (i used the wiring harness and attached to the red 5v wire.

so what happens is that when i turn on the back power switch it all works like normal. you click the soft power button on the keyboard and it turn on the both power supplys at the same time. and shutting down the computer turns them both on. i run all my 5v rails though the new internal psu, the 12v still comes from the original analog board but considering that most of what i have running uses 5v, theres not much load on the 12v rail so i wasnt worried about that.

since then ive gone and done a Takky mod and run 6400 board in there and have no issues.

one other thing to check is the solder on the crt neck board. remove the back metal plate of that board and reflow/resolder all the yoke connections.

 

[pizzigri]

Ok an update. this morning I turned the CC on and it started doing this. It’s also quite frequent, but more when I turn it on - does not matter if it was already on — meaning warmed up - for some time. Help!

 

[chiptripper]

Yeah that definitely looks like a classic bad flyback symptom.

 

[pizzigri]

Ok - so what do I do?

 

[chiptripper]

IMO the only long-term option is to replace it. It's a quick job, if you can source a good flyback.

 

[falen6]

have you tried GENTLY giving the mac a few nudges - as in hit it gently on the side to see if the display jumps - that would show dry connections- i have used a bit of wood to 'tap ' on the analog board of a mac , with the cover off and the mac running - - i have found similar problems on logic boards by carefully flexing the board as it is running to show bad connections

 

[pizzigri]

That is a great suggestion, will try it this WE when I get to the mac CC again!