Quote:
Originally Posted by earlyfilm
Horizontal sync that locks as the set warms up, but won't relock after a channel change is a relatively common problem on the early RCA sets using this and similar horizontal circuits.
The cause is misadjustment of the multiple controls in horizontal sync.
I don't have a factory schematic on this set, so take look at the Sams 74, fol 8:
http://www.earlytelevision.org/pdf/R...-Sams-74-8.pdf
If the .01 Mfd cap on the exposed end of T3 Horizontal Oscillator coil under the chassis is original, you can bet that this set was taken out of service before it was 10 years old. But, you say, this cap is paralleled by a 22K resistor, how could a little leakage hurt? Well it can cause some well-intended person to mess up the other horizontal sync adjustments!
After you have finished recapping the set, follow the alignment procedure on page 18 of that Sams. If you are lucky, you won't have to use a scope. |
Well, the cap was indeed original....all of the wax caps have now been replaced with new mylar jobs. Since the set was working prior to this, I decided to plug it in at this point, and check my work. Everything's up to snuff, and the picture is much crisper than it was.....now for the last leg, the electrolytics.
The issue that brought about earlyfilm's post was my set losing horizontal lock when I change the channel, and having to power down the set for a period of time to get it to lock back in. The picture locks in fine as long as the set is left on the channel that it's set at when I power the set on.
Now I probably shouldn't have done this, but I did it anyway.....without a scope available, I applied the "golden screwdriver" technique, and tweaked B6 all over the place, using the rest of the controls to try to tune everything in......
Well, it worked, kind of. Whereas before I had to power down the set for an hour or longer to get the horizontal to come back, now I just have to flick it on and off, and it pops back into alignment. If I made any improvement, it was by dumb luck more than anything else. Picture size, linearity, etc, all seem close to dead on.
At the moment, the horizontal hold is at the end of its range clockwise....I can now bring it counterclockwise almost 1/2 turn without affecting the picture, and before I had to leave it buried to the right for the picture to lock in.
In the setup procedure, it says "If more than 9 bars are present Just before synchronization, turn the horizontal locking range trimmer (B5) slightly clockwise. If less than 7 bars are present, turn B5 slightly counterclockwise. Turn the hold control counterclockwise and momentarily interrupt the signal and check the number of bars present at the pull-in point. Repeat this procedure until 7 to 9 bars are present."
I never got down that low, there were about a dozen bars at best, maybe 20+ at worst. The horizontal locking range control seemed to have almost no effect on anything.
Something is telling me that I'm dealing with a resistor out of tolerance rather than a setup procedure, but I could be WAY off in that assumption. Thoughts?