Help Understanding ACC
 

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?

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.

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?

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.

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).

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.

"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.

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?

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.

The video processor, subcarrier and chroma modules have ICs.

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?

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.

The particular waveforms you should get depend on what kind of color bars you have. The instructions are referring to a "keyed rainbow" or "gated rainbow" pattern that has 10 vertical bars of color with black inbetween. Is that what you have? I am disappointed that pictures of this pattern can no longer easily be found online. I've attached a couple of pages from the RCA Color Pict-O-Guide, which you can find at https://www.worldradiohistory.com/AR...Guide-1964.pdf

But really, if you know what the pattern is supposed to look like, you can just see if it's correct on the screen and checking the waveforms is not necessary.

https://live.staticflickr.com/65535/...NTIiLCJ2IjoxfQ

https://live.staticflickr.com/65535/...MDAiLCJ2IjoxfQ

I know for certain my generator doesn't create this pattern, but if I'm understanding things correctly, as long as the color generated pattern has the three basic colors displayed, I should see the waveforms as noted in the SM.

I have a couple different calibration discs and each has a bunch of different color bar patterns. If I display one of these patterns, is it the same to the TV and testing as if it came from a generator?

Wish I had more use for a bar generator. I found on on ebay that does the those bars and more, but can't justify spending on it for occasional use. The one I have not has been used about 5 times in 10 years or so.

Is there a source for the type of wire used in older sets? I'm guessing it's a hybrid type of woven covering. Not quite plastic and not quite cloth. If I strip enough cover off the red tap wire, once soldered back on, it won't reach the "HI" connection. I'd really like to use the same color wire so it won't look out of place. I know the set is closed 99% of the time, but it would bother me.

If not, another option would be to strip enough off to solder on bare wire to length it, wrap that wound the post and then solder it. Won't be perfect, but should get the length to the point it reach to all three points of connection.

I'd be surprised if a solid-state era set had cloth wire, but somebody here should know better than me.

I'd think the usual would be PVC, and later solid-state chassis would have PVC with the temperature/fire rating printed on it (after UL tightened their requirements). Exceptions could be teflon-insulated wire in the high-voltage section.

The signal from a DVD will be even more accurate than from most service-grade test generators. Cheaper generators will have simple sync signals without all the FCC details like vertical equalizing pulses.

As long as the pattern has all three colors, you should SEE all three colors ON THE SCREEN, but if the pattern is not the one specified in the service manual, the waveforms will be different from the service manual.

Example: If you have the color bars shown in the lower left of the link below, you will have the luminance, B-Y, and R-Y waveforms shown in the upper left.

https://en.wikipedia.org/wiki/EBU_co...Barras_YUV.JPG

Maybe not cloth, but seems to have a braided covering. I found a seller of wire that matches pretty much in color and braiding, but it is 18ga and the original is 22ga. Also found a seller in Greece that has 100' of original 22ga wiring in all the colors, but it's over 500 delivered. Would be worth it if I had a business of restoring older sets and wanted to keep things original. :lmao:

I have a blu-ray player with composite output and will run it into the RF converter. This way I can use the Spears & Munsil calibration disc that has a number of different color bars. There is one that has all the color bars.

Well, I learned something today!
This is a Zenith 25EC58? (Your first post said 2SEC58.)

Yeah, typo on my part. Been fixed.

I was going to scope things today, but I got lazy and tried with the handheld Fnirsi unit. It couldn't display it correctly and I think it was all about setting the proper time/division. The user manual isn't much to speak of. I'm going to have to bring down my old school Tektronix tomorrow.

I know it's been a while since I've had the scope out, but I tried using it with the color bar generator to check the wave forms for R G and B, but what I get looks nothing like the ones in the SM. I set it for 10V/Div, 20us (even tried 10us), DC then AC coupling, calibrated 10x probe and used the external trigger from the generator (even tried without). I found the generator creates all the necessary bars for the keyed rainbow by pressing a button that gets rid of all the other parts at the bottom and leaves only full bars top to bottom.

The forms I get are stable, so I am locked in, but like I wrote above, the waveforms aren't even close to what the SM shows. I guess the handheld digital scope I tried was working as they looked the same.

I'm not chasing perfection, but I want to be as close as I can with old technology. I want to button it up knowing I've done all I can and it's as close to perfect as it can get.

"gets rid of all the other parts at the bottom and leaves only full bars top to bottom"

does not sound like keyed rainbow to me.

Sounds like primary and secondary bars (like SMPTE bars):
white, yellow, cyan, green, magenta, red, blue, black.

Is this what you had before "getting rid of the parts on the bottom?"

https://en.wikipedia.org/wiki/SMPTE_...Color_Bars.svg

The bottom was a bit simpler than that, but yes. So this isn't a keyed rainbow pattern, darn. I found a generator on ebay that does the keyed rainbow, but not sure I want to add another generator to my collection for one purpose. I guess if it works, I can get rid of my Leader unit.

On another note, my tint is stuck in the poor control now. When it was working properly, it went from overly magenta, to more neutral and then to overly green. Each of those took about 1/3 of the pot travel, so to get from magenta to neutral, I had to move it at least 1/3 from fully counter clockwise. Now from fully counter clockwise it is magenta, then only a slight turn to neutral and another slight turn to green and the rest of the turn gets really green. The neutral section doesn't fully get rid of magenta or green, it's the best I can do to balance them.

I think I need to remove the subcarrier module and lift a leg of each capacitor and resistor for proper measurements. Then the same for the chroma module. Not sure about the coils and ICs on the boards (how to test or if they're even play a role in the tint adjustment).

The Heathkits do gated rainbow.

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.

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.

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!

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.

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