A Narrow Horizontal Hold Control
 

Guys,
I have 2 10L43 Predicta chassis that I have restored. All film, electrolytic, mica, and resistors have been replaced. They both work nice but one has a very narrow H. Hold control. In other words, turning the H. Hold control about 30 degrees either way and the picture unlocks. The other chassis has a nice wide range of rotation to unlock the picture. Both chassis has the diodes replaced with 1N4148. I swapped the 6CG7 tubes between the chassis with no joy. I went through the H. Set up per Sams an each chassis.

Any idea as to what could be the problem?

Thanks.

This is kind of a dumb question, but you've connected the diodes common-cathode (both banded ends tied together), right?

Right.

Caution: I know nothing, just guessing:
Is R7 approximately centered, or at the low-resistance end? Looks to me if R7 is set to low or zero resistance, the H Hold (R4) would have a greater effect vs. rotation.

I looked at R7 on both chassis. They are both near the low end. The chassis with the greater rotation, R7 is closer to the low end. The pots are within 20 degrees of each other.

Good question.

It's time to fire up the oscilloscope. See if you have good horizontal sync pulses at the input of the phase detector.

Just a shot in the dark - does the ground leg (#3) of the dual diode have solid continuity to ground?

OK guys, I found the trouble. It was my Network 30-6035-2. After substituting tubes, checking voltages, checking resistances, checking for proper component values, I thought it could only be 1 thing.....my Network. I removed and replaced the Network. Lucky for me it was located in an open area of the chassis. Bingo, the H' Hold is working great.

I then did an autopsy on the defective Network. All the resistors were the right value and in the right place on the board. The 82pf 1KV capacitor tested bad. This one is a SMD cap. I don't know why it's bad. Perhaps I ruined it soldering it in. Maybe it was bad out of the package, I just don't know. As far as I know, no other 30-6035-2 has been reported defective. I have 2 other chassis here that uses that Network and they all work well.

Problem solved and on to finishing up the TV.