Sync Separator Diode Replacement

[zeno]

Does the vert lock in ? If so odds are its not in the sync sep stage.
Diode probably could use any little signal diode like the one
used as the video detector. It should just pass the positive H sync
pulses.
BTW any markings or part #s in the Sams ?

73 Zeno

[Jon1967us]

Originally Posted by zeno

Does the vert lock in ? If so odds are its not in the sync sep stage.
Diode probably could use any little signal diode like the one
used as the video detector. It should just pass the positive H sync
pulses.
BTW any markings or part #s in the Sams ?

73 Zeno

It’s weird but after some component replacements yesterday, on stuff that had drifted way out of tolerance, I can’t adjust the vertical anymore. After these replacements the picture seems to have degraded, even though the replacements are close to spec. I’m using a BK NTSC pattern generator and it’s almost impossible to get just the horizontal lines dialed in, let alone the staircase pattern as that pattern is repeated vertically. This set is a nightmare.

Nice strong CRT and deflection though.

[old_coot88]

Originally Posted by Jon1967us

I’m using a BK NTSC pattern generator and it’s almost impossible to get just the horizontal lines dialed in, let alone the staircase pattern as that pattern is repeated vertically.

What kinda display do you get using a regular signal source (e.g., VCR, cable box etc)?

[Jon1967us]

Originally Posted by old_coot88

What kinda display do you get using a regular signal source (e.g., VCR, cable box etc)?

Pretty much the same. Barely discernible, washed out image that repeats horizontally.

Note this set is some kind of transitional model or oddball. Aside from an occasional different value, the set, although it matches the schematic that I posted, looks more like a later model, with the tuning knob on top, not on the side.

The dead diode I replaced was a dual diode (series arrangement) with one leg unconnected, just as in the year later schematic. The year later schematic has an almost completely different tube compliment. I can post that one as well.

I’ve pretty much replaced every wax and electrolytic capacitor and only left in originals that tested within tolerance. I haven’t really messed with the ceramics.

[old_coot88]

"Repeats horizontally" suggests the horz sweep is 'waay off frequency. I wouldn't use a pattern generator, but rather a regular signal source to get it on frequency first. Then see what the actual video looks like. You can tell a lot more that way.

You indicate absence of any waveforms at the sync sep. Sync is picked off the video chain right after the video output. Check peaking coils L7 and L9, and coil L8 for continuity for starters. And check plate voltage on the video output (pin 9).

[Jon1967us]

Originally Posted by old_coot88

"Repeats horizontally" suggests the horz sweep is 'waay off frequency. I wouldn't use a pattern generator, but rather a regular signal source to get it on frequency first. Then see what the actual video looks like. You can tell a lot more that way.

You indicate absence of any waveforms at the sync sep. Sync is picked off the video chain right after the video output. Check peaking coils L7 and L9, and coil L8 for continuity for starters. And check plate voltage on the video output (pin 9).

Thanks. I have indeed used a regular signal source, RF on the antenna terminals, IF, and composite in the IF chain and after the detector. Same result.

Per your suggestion, I did test resistances on coils L7-9 and everything tested fine.


Plate voltage (varies with Contrast control) tests normal.