Motorola 17T21 Flyback & Schematic

[Electronic M]

Originally Posted by Mre12ax7

The set seems to have quite poor horizontal lock.
I have borrowed a HV probe from a friend and it seems to measure a little over 10kV maybe 11kV. The top half inch or so of the picture when locked seems to pull to the right gradually getting worse, eventually the horizontal lock is lost. Vertical is rock solid. Should I go on a witch hunt in the horizontal oscillator section.

Probably. Your not using a VCR as your signal source correct?...VCRs often will cause bad horizontal tearing at the top of the screen on tube era TVs.

[Mre12ax7]

Actually, I am using a vcr.

[mrjukebox160]

I bet the VCR is at least part of your issue. Try a DVD player. It's OK to use the VCR with the DVD as the problem only happens when you play a tape.

[Mre12ax7]

I tried hooking the TV up to a Super Nintendo game system via the composite out and the horizontal lock was solid. No tearing. Now there is a new problem I just noticed. there is a "flag waving" effect in the picture. The left and right edges seem to ever so slightly wave back and forth like a flag.

[Electronic M]

So the width narrows and widens differently as you look up or down the screen, and the whole effect rolls up or down the screen right? On rect color sets that is called pincushion...On monochrome sets that is called bad electrolytic caps or insufficient filtering.

[Mre12ax7]

The left and right sides are straight.
The effect is very subtle, you only see if if you look for it. All electrolytic capacitors are brand new from nichicon. Could I try moving the video wire of the crt away from the rest.

[Mre12ax7]

Well I spoke too soon.
The dreaded horizontal issue is not fixed by not using a VCR.
It would seem that the horizontal oscillator is running off frequency, being that the spot where it locks is at one extreme of the control. I switched out the horizontal osc tube for another one and it just made it worse (new tube checks good), there was different sounds and it was so off frequency that the high voltage died when you turned the hold control.
Should I try and get a hold of a oscilliscope?

[Electronic M]

What I would do is put back the good tube, get the hold as close to center as you can then adjust the H osc transformer/coil to re-sync...If you can't get the front control to center you may have to alternately walk the pair. There is often two adjustments on the osc. can one is for stability. If the service lit lacks a non-scope method of adjusting the osc. then it may be a good idea to get a scope on it.

[Mre12ax7]

Originally Posted by Electronic M

What I would do is put back the good tube, get the hold as close to center as you can then adjust the H osc transformer/coil to re-sync...If you can't get the front control to center you may have to alternately walk the pair. There is often two adjustments on the osc. can one is for stability. If the service lit lacks a non-scope method of adjusting the osc. then it may be a good idea to get a scope on it.

I tried what you suggested. I think that made it worse, there is now no point where it will lock the picture.

[dieseljeep]

Originally Posted by Mre12ax7

I tried what you suggested. I think that made it worse, there is now no point where it will lock the picture.

You have to follow the horizontal osc coil proceedure, per the schematic. The set also uses the horiz phase detector circuit, another 6SN7 next to the 25L6. Check around that area.

[Mre12ax7]

I feel really mad.
I managed to break the fine tuning shaft.
The shaft is broken where it connects to the little plate in the back.
Does anyone have a spare tuner or a way to fix it?

[Mre12ax7]

I fixed the fine tuning shaft.
I also replaced the two 150k feedback resistors from the flyback.
They had drifted up to 195k each.
No change.
Should I check more resistors.

[Mre12ax7]

I have purchased a Eico 460 oscilloscope. I have restored it and built a 10x probe.
Can I connect the ground lead of the scope to the chassis? The chassis is connected to a isolation transformer.

[dieseljeep]

Originally Posted by Mre12ax7

I have purchased a Eico 460 oscilloscope. I have restored it and built a 10x probe.
Can I connect the ground lead of the scope to the chassis? The chassis is connected to a isolation transformer.

Fine, as long as it's connected to an isolation transformer.

[Mre12ax7]

I have scoped out several waveforms in the horiz, osc section and they don't really match the schematic.
The waveform on pin 1 of the 6SN7 multivibrator looked squished vertically and the general
shape did not look right. Is it better to start at the sync separator and go towards the oscillator or vice versa?