Quote:
Originally Posted by BeamT
+1 Horiz osc is way off frequency. This is almost entirely contained on 9-57 Horiz Board, with the exception of the horiz osc coil/hold control and the attached capacitor that forms the circuit that determines the osc frequency.
+1 on the Q803 121-755 Horiz Driver transistor not being the cause. ECG 190 is a closer substitute.
The question is, can the osc run on frequency or is the AFC driving it off frequency.
Do you have a spare 9-57 Board?
Is the plastic stop still in place on the horiz hold control? Has it already been forced past the stop?
Have you replaced any other components on the 9-57 Board?
Re-examine and tighten pins and connectors A11, U4, T13, that connect to the coil.
Common problems:
R808 330ohm 1/2w replace and upgrade to 1w
R821 2.2k 1w replace and upgrade to 2w
Lead sockets for the transistors are always problematic, most people will either remove the pins and solder the xsistor directly to the board, or solder the leads in the pins. Every rebuilt board I've ever seen, Zenith or PTS, soldered the leads into the sockets.
From there you need to troubleshoot the board. At least its not intermittant anymore?
On the Video Proc IC, I've had luck gently scraping with an Exacto knife, also taking a small piece of green scotchbright soaked in DeoxIT or CRC Cleaner, held with a needlenose and gently scrubing. Be care not to over manipulate the pins.
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The horizontal hold still has the stop on it and it hasn't been turned past it. The image does show slight change as I rotate the control.
I replaced the 755 on the current board yesterday, no change, so I have to agree, it's not the issue.
I have replaced all the transistors on the board in the past month, other than that, it is unchanged. Could a bad transistor in another part of the board cause it to loose synch? If so, I have all the original transistors. Maybe one of the new transistors is bad. I also have the original 9-57 board, but after 13 years I can't remember why I had to replace it. Guess I could swap it and see what happens.
The lead sockets on the current module have one crimped socket per transistor. I guess they did that to make sure they were secured.
I tested the resistors. R808 is 310 ohm and R821 is 2.4K ohm.
I was given a "new" video processor board years ago, but it never worked. Then I noticed the top corner of it had a red mark on it. I'm betting it was the bad one put back in the box and that mark was to let them know that. Somehow it got out. Never got around to finding out what was wrong with it, but I remember the board yesterday and took the IC out of it and put it in the existing board. Problems solved for that one.
Okay, I'm going to put the old horizontal in right now and I'll post my results. I'll also retest the transistors I put on the current board and see if any have gone bad.