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-   -   Sencore SS105 - sweep troubleshooter question (http://www.videokarma.org/showthread.php?t=269947)

DavGoodlin 01-04-2018 10:53 AM

Sencore SS105 - sweep troubleshooter question
 
Has anyone used one of these before? A very portable Horiz and vert sweep signal substitution like part of a B&K analyst. It sounds ridiculously simple to use from the SS105's manual, "just touch it to suspected components until sweep appears" probably because it makes a 100-200 v p-p v-drive sawtooth.

I have a 1958 Sylvania-made RCA-branded metal 17" portable that lost vertical sweep. The vertical osc-out tube is a 10DE7 in a standard multi-vibrator circuit. Osc plate voltage is 2 volts, should be 120vdc. So osc section must be conducting because the whole stage has stopped oscillating. I need to clear the output transformer and yoke as well as try a tube before looking for more component trouble.

Height and boost dropping resistors are good. Boost is 400v because horizontal sweep is working.

Background - I recapped this 100% a year ago and I was using it daily until spring, then I moved it to the shop for a long-hours test before I call it done. The burn-in must have been too long, and it lost vert sweep.

DavGoodlin 01-09-2018 01:35 PM

I have been working on the RCA "chassis 5377" and since found the vertical linearity pot's wiper arm is open. This vertical multi-vibrator circuit is ridiculously simple and if any one component fails*, MAJOR hard fails-not minor symptoms, present like no sweep.

Looking at the SS105, which has a 12AU7 dated 59-35, it also needs to be recapped before I test it on this TV.

* Muntz's rule = remove parts until it doesn't work. known as "Muntzing" a circuit.

bandersen 01-09-2018 02:28 PM

I had one of those SS105s but sold it before I ever tried using it. Looks like a useful device. Here's the old thread.

http://www.videokarma.org/showthread.php?t=251847

DavGoodlin 01-10-2018 01:14 PM

Thanks for the thread link Bob, the schematic will help.

Update: The vertical linearity pot did not fix the RCA, so its time to restore this sweep generator, and inject a signal at the output tube grid to confirm its NOT the yoke or VOT.

DavGoodlin 01-12-2018 09:53 AM

1 Attachment(s)
Our weather went from 0 degrees 3 days ago to 60 this am with drizzle. My barely heated work spot was actually comfortable not all soaking wet from the condensation. So I decided on an extra 30 minutes to get somewhere with this.

I fired this little box up this morning after a re-cap I did a day ago and the neon lighted to indicate the oscillator is running. I did not try the HOT cathode current socket on the 'DQ6, or measure the HOT screen grid voltage on the socket with the voltmeter function. I need a functioning vertical oscillator:yes:
Attachment 196299

I touched the ball-hook connector to the grid of the 10DE7 output and saw some action. About 140 v-pp of vertical sawtooth brought sweep to 75% of the screen with a 3 inch fold-over.

Moving to the plate of the oscillator brought a similar sweep return, but the TV's oscillator grid did not. The vertical feedback, vertical hold control ties this point, so removing the grid connection may bring it back, pointing to a loop issue.


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