Help Understanding ACC

[TinCanAlley]

Okay, latest update.....

I decided to watch a few shows on the set last night and a couple of new issues came up that is pointing me towards the Chroma module.

Upon turn on the set, the tint was still not working as it should. The it was almost all the way counter clockwise in order to get decent skin tones. Anything more than a quarter turn and it went way into the green. Then after around 30 minutes the color flashed a couple times and it went B&W. I had to change channels and then back to get color again. This one is either the AFT or the Chroma module and possibly with the burst signal. A little while later, the color flashed again and this time it went full color saturation as if I turned up the color control to full. It stayed this way for about a minute or so, then went back down, but still higher than initially set.

So I know that the tone control is connected to the Subcarrier module and it manipulates the burst signal sent to the Chroma module. The color control is connected to the Chroma module directly. So if the tint setting is changing, and the color setting is changing, it seems the Chroma module is the culprit. The color disappearing might also be the fault of this module as well and changing channels resets the burst signal, or so I believe it does.

I will do what I can with the module as I can test all the caps, resistors and reseat the IC, but I don't know about the coils. Those coils are for Chroma Bandbass and Chroma Take-off. Not sure what those do and if it's even possible to test them in circuit or how to readjust one of them if I do something that changes its adjustment.

Might be time to look for a replacement module just in case.

[old_tv_nut]

The coils should not need adjustment unless you replace associated tuning capacitors.
Abrupt intermittent changes imply intermittent contact, solder, or potentiometer problems.
Color disappearing and coming back could be intermittent problems in the tuner.

Do not adjust coils until you have searched for the much more likely causes of intermittent behavior.

[TinCanAlley]

Originally Posted by old_tv_nut

The coils should not need adjustment unless you replace associated tuning capacitors.
Abrupt intermittent changes imply intermittent contact, solder, or potentiometer problems.
Color disappearing and coming back could be intermittent problems in the tuner.

Do not adjust coils until you have searched for the much more likely causes of intermittent behavior.

Only one coil is adjustable and I wasn't about to touch it as I believe it would require a sweep generator. I will focus on all the capacitors and resistors. When I inspected the board visually, I found no cracked solder joints or other abnormalities.

Question.... The SM has a resistance chart and IC903 on the Chroma board is there with readings for all legs. However, it doesn't state how to go about getting those readings. Do I leave the module plugged in and probe from chassis ground to each pin? Remove the board and probe from ground point on module to each leg? Do I remove the IC and problem from ground leg to all other legs?

I have a Hickok 246 arriving Friday. It does the keyed (gated) rainbow as well as a few others my Leader doesn't. It should allow me to verify correct APC adjustment via waveforms.

[old_tv_nut]

Unless the manual says otherwise, resistance readings should be with everything connected normally (and the power off and power cord disconnected, of course).

[TinCanAlley]

Originally Posted by old_tv_nut

Unless the manual says otherwise, resistance readings should be with everything connected normally (and the power off and power cord disconnected, of course).

Then it's time to take some resistance measurements!

[TinCanAlley]

Taking the resistance measurements was a bust. About 3 out of 16 pins had values noted in the SM. There was supposed to have been 2 that were supposed to INF, but had minor resistance. Others weren't even close. I figure that if they were this far off, there would be other major issues, so I decided to get a replacement IC just to see if that helps. I am also going to remove the individual metal socket pins on the board and replace with a modern socket. Then I'll revisit the resistance measurements.

I got the new bar generator and just tested it. I created exactly what the SM stated and I should be able to get the scope to show the waveforms from the SM. I think someone here, years ago, stated that the horizontal width is preset and cannot be changed. The color bars at each end are halfway off the edge of the screen. Normal?

Anyway, I need to figure out what the AFT might have to do with tint and color as I turned it off and slightly adjusted the channel and turned it back on. The tint went back to normal and has stayed there. This might just be coincidence, but it's worth a look.

Attached a couple pics. Colors in pics aren't exactly as seen in person. Tried several settings on camera, but this is the best I can get.

[TinCanAlley]

Oh, and this generator makes much tighter dots and lines. I now need to redo static convergence.