Does anybody know how to properly adjust the AGC delay on this Chromacolor II set (chassis 25EC58)? The picture tends to shift at the top, and it sometimes makes a humming noise depending on the intensity of the shift. The intensity depends on what movie I put in or what show I turn on. Sometimes the picture looks good, other times it is awful. The AGC adjustment doesn't seem to do anything except make the picture fuzzy when it is turned too far. Any ideas?

Hi ghjkl67.
i don't think AGC DELAY is your problem.sounds more like primary agc issue.

iirc-to adjust AGC DELAY-you run the tv on the weakest channel and adjust agc delay control so you see the picture get "noisy"(snow) then back it off to get rid of the noise/snow-hope this helps,
RonL

I did try adjusting it so the snow just goes away. That didn't work, so I tried turning it all the way in either of the directions. That didn't work either. It looks like something to do with the AGC, but the delay adjustment doesn't fix anything and seems to have no effect on the picture (other than the snow). What else should I try?

I think the problem may be your source video that may be copy-guarded combined with your TV that was not designed to handle video with reduced sync pulses.

Is there anyway I can "clean" my VCR signal so that it would work better? Since they stopped broadcasting analog, I can't get the signal that the TV was designed for. It is an old top loader VCR, so I assume it was made for use with TV's that were already out at the time.

VCRs do the best that they can, but without some digital circuits they can not fix the problem. The problem is that when the VCR switches heads, the now new head may be playing back a slightly different part of the picture than the one that was just switched away from. Making the problem worse is that as VCRs age, the back tension on the tape tends to decrease. With decreased back tension the mismatch when switching heads gets worse. Also causing trouble is that different tapes are recorded slightly differently. The back tension on the tape is an adjustment, but to do it right you need specialized test equipment.

Different TVs differ in how quickly the horizontal can re-sync to a jump in the position of the sync pulse. After VCRs became more popular, TV manufactures speeded up the recovery for a jump in the position of the sync pulse. At the time VCRs were introduced, some TVs were already quite fast and others not. You might be able to modify the TV to help with this problem. You would have to find the horizontal loop filter capacitor and reduce it's value.

There are devices called video stabilizers that claim to fix such problems. I have no experience with them. Perhaps someone else can talk about them.

You could try other sources of signals such as DVD players or digital converter boxes for over the air signals. Both of those will give you a stable signal.

Oh, by the way, go back and adjust the AGC delay to the position that just eliminates the snow.

Tom, thank you for the info and advice. I have a few more questions.

I don't quite understand what it means when a VCR "switches heads" and is out of sync. Is that what directly causes the AGC issue on the TV, or is that a completely different problem? I do notice that some tapes play better than others when hooked up to this TV, but they all look fine on my other TV.

Where can I find the horizontal loop capacitor and how can I identify it? Is it on the horizontal module? If I find it, would you recommend trying to bypass the capacitor entirely? The main thing that I am concerned about is, why would I be messing around with the horizontal if the problem is with the AGC?

I have a stabilizer that I use to record tapes with tracking issues. I haven't thought about using it for this, but it might help. The only problem is that it uses RCA jacks, so I would have to use another VCR as a coax adapter which might be defeating the purpose.

I did try a converter box and the picture looked okay, but I don't have much use for it. There just isn't anything on television worth watching. Haven't tried a DVD player yet. I would have to route it through a VCR as an adapter which (again) might be defeating the purpose.

Back when I did TV service work, I used a 9" Zenith as a "bench TV" to check video/RF output quality. I'm not sure what it was about Zenith's, but they just did not like some VCR's. I often had "flag-waving" at the top of the screen.

I had a Zenith that did exactly what is described, but only for certain commercial video tapes (copy protected ones). I consulted my old boss who was a Zenith shop owner and repairman. He told me that there was an updated horizontal module that fixed the problem and gave me the number for it (long gone). I dropped in the replacment module and the problem was resolved.

Curtis Eickerman

My horizontal module number is 9-57. There is another number that reads "837258B." The chassis number is 25EC58. Maybe somebody here knows what the updated horizontal board is.

The bottom 2 postings in the thread below might shed some light on the subject. I have not located any other good information. http://www.videokarma.org/archive/index ... 47395.html

I see a lot of adds for 9-90 modules, but I doubt they are a plug in substitute based on the above. The 9-70 definitely was a substitute for the 9-57, but I just don't know if that had the correction in it.

Curtis Eickerman

I looked at the thread, and it seems that somebody has a replacement. I will try contacting him and see what I come up with.