Help Understanding ACC

[TinCanAlley]

I'm trying to adjust ACC on my 25EC58 chassis and I don't know if the values I'm seeing are correct and the SM doesn't say what voltage I should see, or at least a range. When I follow the procedure, I'm supposed to be in align mode, then short two pins and read voltage from another pin (chroma board). From there I remove the short and adjust the ACC pot until the voltage I'm reading matches what I saw when the pins were shorted. However, if I look at the schematics for the boards, the two pins to short are ACC pins with voltages of 8.7V and 8.55V. The point to be measured is the burst line and it shows 11.7V. When I take my reading shorted, I get 17.6V and I adjusted unshorted for that same voltage. Is this correct? I'm not sure if the voltage is supposed to be that high, seeing as how the schematic voltages are well below that point.

Anyway, just trying to figure out if 1 of the 2 boards where tint is might be bad. The burst leaving the chroma shows as 11.7V going to the subcarrier module. If I'm reading 17.6V, then isn't that out of spec?

[old_tv_nut]

I wish I could help.
I'm afraid I'm not familiar enough with this chassis to figure out what's going on.

Not even sure what "ACC" is in this case. It sounds like "Automatic Color Control," which would control the strength of the colors, not the color oscillator lock or wrong hues.
Also not sure what the "burst line" is unless you point to it on a schematic.

If you could link to a schematic and service manual, it would probably become instantly clear.

Finally a hint about VK: starting a new thread about a problem that apparently has been discussed to some degree in another thread is not a good idea.

[TinCanAlley]

Originally Posted by old_tv_nut

I wish I could help.
I'm afraid I'm not familiar enough with this chassis to figure out what's going on.

Not even sure what "ACC" is in this case. It sounds like "Automatic Color Control," which would control the strength of the colors, not the color oscillator lock or wrong hues.
Also not sure what the "burst line" is unless you point to it on a schematic.

If you could link to a schematic and service manual, it would probably become instantly clear.

Finally a hint about VK: starting a new thread about a problem that apparently has been discussed to some degree in another thread is not a good idea.

Yes, I know about multiple posts, but I felt that maybe the title of the current one is keeping some from viewing by thinking it's only on that topic.

[TinCanAlley]

Don't know if this is enough of the schematic to help, but just in case, here it is.

I've circled the ACC and Burst sections in red, shorted points for testing in green and the point I measured voltage in blue. If I'm not mistaken, the Burst is used for a color signal/image?

[old_tv_nut]

Is this a tube set with some transistors and/or ICs? I see B+ on the chroma module = 22.6 V and B+ on the subcarrier regen module = 12.36 V. I als see125 V being looped through both modules.

So, you are following the procedure of shorting J and JJ, at which time you get 17.6 V on the Burst line. Then you remove the short and adjust the ACC pot (where is that? is it on the Subcarrier Regen Module?) to again get 17.6 V on the Burst line. Correct?

1) this adjustment is definitely to control the level of color based on the strength of the color signal. It has nothing to do with colors turning the wrong hue or being unlocked (that would be APC).
I'd think that if you turn the ACC pot with the switch in NORMAL position, you should see the color level change as the DC voltage on the BURST line changes. Is that correct?

2)Without seeing the schematics of the two modules, I would have no guess as to whether 17.6 volts could be out of tolerance.

Once you have made the adjustment, is there anything wrong with the set's operation?

Chasing after schematic listed voltages without a malfunction to suggest doing it could be a waste of time if the 17.6 is actually within tolerance (like, it's actually compensating for differences in circuit components, especially tubes, and therefore should differ from the marked voltage on the schematic.)

Finally, I have no idea why a line marked simply Burst has a variable DC voltage on it. If it's normal for it to vary widely from set to set, it should be marked as such.

[old_tv_nut]

By the way, I'm guessing that the NORMAL/ALIGN switch section on the right disconnects the burst from the subcarrier regeneration module in the ALIGN position so the oscillator free-runs, and the section on the left sets the chroma and burst gain to maximum (so you can see the color that's free-running).

[TinCanAlley]

Fully solid state TV.

This is what I've been able to figure out. The subcarrier module has the tint pot connected to it. It changes the phase of the burst signal sent to the chroma board. Now I don't know if the tint shifting I'm seeing is being created by the subcarrier in the burst, or the chroma module. I would imagine that when the tint is adjusted, the burst voltage would change. I just wish I knew what the range of the burst voltage should be to know if what I'm seeing is in range.

When I adjusted the ACC, I didn't have the color bars up, or anything for that matter, as the instructions only noted to put it in align mode and do the adjustment. Now the APC did use the color bars as it was a purely visual adjustment. Once I get all the modules back, I'll try the ACC with color bars.

I went over all the boards for bad solder joints and found none. I'm going to check all the resistors next. For the video processor module, I am changing the electrolytic caps, but no other module has electrolytics.

I need to create a makeshift tool to speed up the cleaning of all the contacts on the chassis for the modules. Otherwise I'm just going to use deoxit on a tightly wrapped cleaning q-tip and wipe all the contacts and plug the modules back in.

[old_tv_nut]

"When I adjusted the ACC, I didn't have the color bars up, or anything for that matter, as the instructions only noted to put it in align mode and do the adjustment. Now the APC did use the color bars as it was a purely visual adjustment. Once I get all the modules back, I'll try the ACC with color bars."

Aha - I suspect this will make a difference - let us know the result.

Again, I'd like to know if you are trying to fix a noticeable problem, or just chasing a voltage noted on the schematic.

[old_tv_nut]

By the way, why I asked if tube or solid state:
The Subcarrier Regen Module B+ pin says 12.36V (obviously way over-precise reading, suspect the nominal is 12V), and the Chroma Module B+ says 22.6V, high for an analog IC.

When I was developing analog ICs for TV video and chroma circuits Zenith had settled on 12V B+ for all analog ICs.

Do these modules have ICs or only discrete transistors?

[vol.2]

Originally Posted by old_tv_nut

Again, I'd like to know if you are trying to fix a noticeable problem, or just chasing a voltage noted on the schematic.

I suspect OP is still trying to figure out the color tint problem from the other thread. https://videokarma.org/showthread.php?t=277532&page=3

[TinCanAlley]

Originally Posted by vol.2

I suspect OP is still trying to figure out the color tint problem from the other thread. https://videokarma.org/showthread.php?t=277532&page=3

Yes. Is there a way to get a moderator to remove previous posts so I can just start one with a title that doesn't note individual issues? I don't know if people are skipping over some as the title might not give clues as to what is really under discussion. It's my fault for starting so many and I just wasn't thinking.

Anyway, I cleaned and reseated after changing the electrolytics on the video processing module and testing resistors on the subcarrier and chroma. After doing so, I recalibrated contrast, brightness, color and tint. 10 minutes later, the tint shifted again. However, I have noted that when this happens, the tint control range changes. After putting it back together, the tint range was wide. From start it went from magenta, to balanced tone and then to green at the other end of adjustment. When the tint shifted, the control had balanced tones near the start and from there it went up to green at the other end. I know it's not the pot as it does the same with the chromatic pot.

I have the original subcarrier module and will reinstall it tomorrow and see if the issue goes away. If it doesn't, then it might be in the chroma module.

[TinCanAlley]

Originally Posted by old_tv_nut

By the way, why I asked if tube or solid state:
The Subcarrier Regen Module B+ pin says 12.36V (obviously way over-precise reading, suspect the nominal is 12V), and the Chroma Module B+ says 22.6V, high for an analog IC.

When I was developing analog ICs for TV video and chroma circuits Zenith had settled on 12V B+ for all analog ICs.

Do these modules have ICs or only discrete transistors?

The video processor, subcarrier and chroma modules have ICs.

[TinCanAlley]

Originally Posted by old_tv_nut

"When I adjusted the ACC, I didn't have the color bars up, or anything for that matter, as the instructions only noted to put it in align mode and do the adjustment. Now the APC did use the color bars as it was a purely visual adjustment. Once I get all the modules back, I'll try the ACC with color bars."

Aha - I suspect this will make a difference - let us know the result.

Again, I'd like to know if you are trying to fix a noticeable problem, or just chasing a voltage noted on the schematic.

I'll do ACC with the color bars tomorrow. I am also going to hook up the scope to check the waveforms noted in the APC adjustment as I messed with that one by mistake. I'm assuming that when it says "check for proper keyed rainbow waveforms" they mean with the color bars displayed?

[TinCanAlley]

Also noticed something and am not sure it would be an issue, but the red tap used to adjust color in the white areas after G2 adjustments is frayed where it is soldered to a post and it is also a bit corroded (greenish blue colored wire strands). It is only holding on by a few strands. I want to redo it, but I don't think there is enough length to cut off bad, strip it and resolder to post. Is there anything special about the wire used, or can I use just about any stranded pure copy wire the same gauge?

[old_tv_nut]

Originally Posted by TinCanAlley

Also noticed something and am not sure it would be an issue, but the red tap used to adjust color in the white areas after G2 adjustments is frayed where it is soldered to a post and it is also a bit corroded (greenish blue colored wire strands). It is only holding on by a few strands. I want to redo it, but I don't think there is enough length to cut off bad, strip it and resolder to post. Is there anything special about the wire used, or can I use just about any stranded pure copy wire the same gauge?

Any type of wire should be fine.