Color Classic Flyback Replacement from LC5xx

[Garrett]

Yesterday I decided to open up a Color Classic I’ve had on the bench for a while. My Post-It note said that the analog board was inside, but the caps were removed… cool! I opened it up and got to replacing them. Strangely, I noticed some flux residue and fresh solder on the leads of the flyback (part 157-0146). Strange, not something I remember doing.

After the recap, I was delighted to have a crisp display with near-perfect geometry. But wait, was that a click I just heard? Oh yeah. Now I know what someone was trying to do with the reflow.

A few years back I bought a couple of spare analog boards for the 5xx series all-in-ones, and still hadn’t done anything with them. Decided to take the plunge and remove a flyback from that analog board (Part 157-0149) and solder it to the recapped CC analog board. Went in just fine, although the lead is much longer and the flyback is slightly taller than the stock part.

Upon doing a smoke test, I found that the picture was extremely dim, and the image size was reduced maybe 25%. Adjusting the pots got me a little closer to the correct image size, but obviously that’s not the right way to go about things. I don’t really understand how flybacks work. My thinking was that a flyback from a larger trinitron should have no problem with a smaller trinitron, but it seems I’m mistaken.

Just wanted to share these results in case anyone has thought of a similar thing but been afraid to try it. It works, kind of. Now you know.

 

[DatMac]

How is it since you did this? is it still working good? I have my CCII i recapped but it likes to arch and loose HV every now and then so I think the flyback is going. It did it before the recap and still doing it now. Im not sure if its also related to the pots because that is possible and seen it happen to other crts ive repaired. I have a lc575 board here that I can do the flyback swap with so its why I want to know if its worth while or just hunt for another cc flyback.

 

[Garrett]

I couldn’t live with the improper size and removed the 575 flyback right after I tested it. Based on what you’ve said, it does sound like your flyback is going out. Unfortunately a replacement would have to come from another Color Classic analog board.

 

[DatMac]

Was yours doing the same as mines? Mines would make a pop sound and the image would collapse and come right back after a split second then other times it would get bright and image would shake alittle for a bit then go back to normal about 20-30 seconds later or sometimes after power cycle. This is with also a almost brand new tube i swapped in with no dirt or anything around the HV wire and crt.

 

[Garrett]

Yup, that sort of behavior is almost certainly a failing flyback. Replacing capacitors and/or the CRT isn't going to help.

 

[ClassicHasClass]

I'd like to get my Mystic Color Classic's screen a little larger vertically (right now it's probably about 75%?) but the pots didn't seem to make much difference.

 

[Garrett]

I'd like to get my Mystic Color Classic's screen a little larger vertically (right now it's probably about 75%?) but the pots didn't seem to make much difference.

Are you using the High Res or VGA modded analog board? That may factor into the types of adjustments available. I've only ever done the 68V VGA mod myself and haven't run into this issue. Generally, people seem to have trouble setting the horizontal width as it should, so I'm surprised it's the vertical adjustment on yours!

 

[ClassicHasClass]

No, just the regular analogue board. It's perfectly useable but I'd like it to be a little taller.

 

[jonschultz]

I had pretty good success with an LC575 flyback in a Color Classic, though I found that the 86V B+ version of the VGA mod was necessary to get an adequate horizontal raster. I think I also probably had to adjust the G2 voltage and the RGB background pots relative to their optimal positions using the standard 157-0146 flyback. I also found there was a little bit of ringing in the horizontal deflection current at the beginning of each scanline, creating very subtle light and dark vertical bands, and adding some RC filtering on the HOT seemed to resolve that. I'm back to the original flyback on this particular machine, using 68V B+.

 

[Garrett]

Great observations - thanks for sharing. Good to know there are workarounds to make that flyback more usable. Sounds like AB/flyback longevity may be a concern if left to run like that though.

 

[JDW]

I found that the 86V B+ version of the VGA mod was necessary to get an adequate horizontal raster.
I'm back to the original flyback on this particular machine, using 68V B+.

So, it seems you tried the 84V 13" High Resolution mod but later switched to the 68.4V VGA mod, which would involve not only the change in the Horizontal Deflection Voltage (aka "B+") as shown below, but also changing the Sense Lines too (not shown below) in order to bump the resolution to VGA.

Changes to B+ and Sense Lines are most often done together, but there is nothing that prevents you from using one or the other. However, it is not practical to do only the SENSE LINE CHANGE (which changes resolution) because there would not be enough B+ voltage in that case for you to properly adjust the screen. But it is possible to perform only the B+ change without touching the sense lines (keeping your stock CC resolution). That would require you to use the POTs on back to adjust your screen width and height, but the increased B+ would give you more freedom to adjust the display area on your CRT to be taller or wider (in theory). Increasing B+ would put no more strain on your Analog Board than if you had also changed the sense lines.

If you are worried about "strain" on the Analog Board (or even if you're not), I recommend doing the BEEFY COMPONENT UPGRADE.

Do either of the B+ boost mods affect "Flyback longevity"? No one has definitively proven the increased B+ voltage has shortened the life of their flyback. My videos of both B+ mods merely show no increased heat in the flyback itself for either voltage mod.

 

[jonschultz]

I've often wondered if it would be a worthwhile project to try to adapt a more commonly available flyback to work with the Color Classic. I think it's definitely possible, but would likely require additional voltage regulators for the various odd semi-high voltages required by the analog board. It could be done with an adapter board that includes the necessary support electronics. The thing is, I'm not sure what counts as a "commonly available" flyback these days. I don't think there's really any modern alternative either for easily generating ~20kV. Has anyone looked into this? I'd be willing to take up the project if there's a flyback that's common/popular.