Motorola 19k14wa Possible Arcing?

[mr_rye89]

Thanks M

something's goofy in the IF as I wiggled all the IF tubes and the picture came back, I'll check the solder joints and clean the sockets tomorrow, but it's playing fine now.......

[mr_rye89]

Yaargh! this TV is frustrating...... it seems the vert/horiz is locking but the washed out contrast look goes in and out, but can sometimes be "fixed" temporarily by jiggling the channel selector.

I might try injecting video past the detector diode and rule out any problems there. I'm still thinking the tuner might be troublesome, but the card edge connectors at the back of the PC board might be problematic, but I've cleaned those several times. I have cleaned the tuner, but I've been gentle (maybe too gentile) trying not to screw it up.

[Electronic M]

When I clean a tuner I use De-Ox-Id and a white rubber eraser...The De-ox loosens the crud and the eraser gently scrubs it off and polishes the surface...Hasn't failed me yet. There is something nice about seeing a black terminal become completely shiny metal once more.

[mr_rye89]

Well I feel dumb. I found another 3BU8 (agc keying/sync sep/noise limiter) in my tube stash and swapped it in and the picture is back. I woulda tried this earlier but I hate throwing tubes at a TV set.

The tube tested ok in my tester, but it was slow to get into the green zone

[Electronic M]

Originally Posted by mr_rye89

Well I feel dumb. I found another 3BU8 (agc keying/sync sep/noise limiter) in my tube stash and swapped it in and the picture is back. I woulda tried this earlier but I hate throwing tubes at a TV set.

The tube tested ok in my tester, but it was slow to get into the green zone

Sometimes tube substitution is a better approach than testing...I had a CTC-15 clone that had low HV and sweep issues. That set I tested all the tubes, nearly drove myself nuts checking all the passive parts a couple of times, then had it spring to life when I subbed all the sweep tubes from another working CTC-15 clone. Once I narrowed it down I retested the tube and found it still tested good...Buuut if I held down the test button for nearly a full minute it would slump into the bad end of the scale.

[dieseljeep]

Originally Posted by mr_rye89

Well I feel dumb. I found another 3BU8 (agc keying/sync sep/noise limiter) in my tube stash and swapped it in and the picture is back. I woulda tried this earlier but I hate throwing tubes at a TV set.

The tube tested ok in my tester, but it was slow to get into the green zone

If you look at the pin-out of the tube in a tube manual, you'll see it's a rather unique design with a few common elements. I don't think it can be checked properly with a tube checker. Best is substitution.
IIRC, the circuit is a Zenith design, as they used it first.

[ronl]

Working on tvs/radios...etc since the early 70, s in my basement shop for a large part of my career (made more working for myself)(tough to keep new stocked tubes) i used pretested in tvs or whatever used tubes i knew were good in a set.saved me a LOT of trouble.i would recommend that any tube set every member has in this forum,stock used tubes tested on a tube tester AND tested in your known workining (or once you got it working sets. A lot easier. Maybe this should be a stiicky post. RonL

[mr_rye89]

Well the sync went funny again. So I pulled the board and found a crack in the ground plane trace around the edge of the board (near the horizontal output tube - high stress area), solder bridged it back and got sync again

The sync circuit must have been dropping the ground there intermittently.

Now the horizontal linearity is a bit off, but I screwed up the noise gate (sync stability) pot so now to fix that.....

[dieseljeep]

Originally Posted by mr_rye89

Well the sync went funny again. So I pulled the board and found a crack in the ground plane trace around the edge of the board (near the horizontal output tube - high stress area), solder bridged it back and got sync again

The sync circuit must have been dropping the ground there intermittently.

Now the horizontal linearity is a bit off, but I screwed up the noise gate (sync stability) pot so now to fix that.....

That PC board job wasn't one of Motorola's better efforts. They made a few years of those and then went back to the hand wired chassis. The tuners were also trouble prone. Yours is probably the last year of that chassis.