I still have HV, just no sweep whatsoever. The dot in the center is horrifically bright, the only way I could get it so that it wouldn't put a nasty ion burn on the screen is to bring it way out of focus. Brightness control has zero effect on it.

Have you've checked the brightness control, and the 1M resistor coming off it's center tap? The brightness pot is fed by the same B+ on pin 6 of the 6AS5. The voltage on pin 2 of the CRT should vary from 72-180v(according to Sams) with rotation of that control. Make sure you don't accidentally measure the HV with your VOM.

I'll get on that tomorrow morning and let you know my findings. It's 19 degrees out, and I'm pooped out from moving DuMonts in the cold that weigh as much as a conversion van ;)

My Sams is showing me that the 6V6 should have 3 VDC on pin 8. I've got 6.32. On pin 3, I've got 281 VDC, should be 220.

And now, seems I've lost raster......

:wave: Tim , If this is the same set that's been kickin yer nuts with the selenium replacement and such , here's my offer ;

Next time your gonna be in eastern Mass. PM me and we can spend a couple hours going over it together . I may not be a total rocket scientist , but I did work in radio/TV repair back in the 60s and 70s (and as a special bonus I CAN even spell "rocket scientist" :D )

Definitely will! Wife and I take a LOT of road trips.....we usually combine our interests....she'll look up a Diners Drive-Ins and Dives restaurant, and I'll manage to work a TV in there :D

Nope, different set though.....this is a little 7" from the late 40s. The other one's a Sylvania Halolight.

I quit on the Admiral today, and I've got the RA113 on the bench, doing some more caps. Perfect day for it too.....20 degrees and windy with light snow outside. Wife is working (she does freelance transcription), and I'm all toasty in the basement with my soldering iron, my old Perfection kerosene heater, and a snoozing cat. Sundays were meant to be just like this :)

Can we assume the brightness control checked out OK, along with the 1M coming off it's center tap?

Resistor is measuring 1.13 M, so we're close anyway. Brightness control is within spec. Now, here's the odd part.

I noticed on the brightness control there is a wire that is attached to the terminal of the brightness control opposite chassis ground, that goes right to one half of C1.

My parts chassis does not have this wire.

The plastic on the end of the wire where it attached to the brightness control appears to have melted, and the wire was disconnected. Granted, it could have melted from the previous owner's soldering iron, but I get lost in the schematic right at that point trying to figure out if it should even BE there, as the junction spiders out everywhere.

:dunno:

:thmbsp: Cool , Sounds Great to me . If you are coming anywhere near Boston just give me a PM a day or two in advance so we can meet up . I am sincere in my offer of help when ya got a tough one , like I say I ain't God's gift to all things electronic but I do have a pretty good way with diagnosing and repair of our beloved tube sets .

From the Sams, it appears that the high end of the brightness pot should connect to C1-b. Does the wire indeed go to the "b" section of the cap? Perhaps the set that you are working on has a less obvious connection path... ohm it out, I bet the high end of the brightness pot is indeed connected to C1-b

jr

Agree with JR that the end opposite ground needs to be connected to + side of C1-B. You need that variable control voltage on the CRT's cathode(pin 2) in order to change brightness.

Gotcha. I guess the parts chassis was more of a parts chassis than I thought.

I'll resolder the wire and proceed with the voltage test on pin 2 of the picture tube.

Okay, now we're getting somewhere.....

Powered up after resoldering the wire, and shortly thereafter, a small POP....not big enough for me to shut the set down right away, but now I've got sweep of some kind FINALLY!

Same audio buzz is back in the speaker as in the video. High pitched whine coming from the chassis....I'm not sure if it's the horizontal oscillator going at warp speed, or what. Didn't see anything obvious in the POP, but I assume the next step is to start rechecking my voltages?

Yeah, you've at least got horizontal and vertical sweep now. It'd be interesting to see if your supply voltages came down closer to spec, now. From here it looks like you don't have horizontal lock, so that may be all that's keeping you from getting a stable picture at this point. Hard to say about the pop noise. Sometimes a control can arc if the riveted terminals are making poor contact with the resistance element, or the wiper itself could have poor contact. Does the brightness control appear to be working correctly now?

Sure does! In fact, the set is now passing signal......I've got vertical lock, and perfect audio! :D

The horizontal is all messed up, though. There's a flat spot on the horizontal size control that's, well, most of the control. I'll ohm that out later and change it from the parts chassis if needed be.

Weirdly, the audio level is affected by the contrast control. I know in some of these sets, the circuits affect each other, is that the case here?

Yes! the contrast control varies the gain of the video amp, and the sound IF is driven off the plate of the video amp (through a 2 uuf cap) so contrast will affect the sound.

jr

The POP mighta cleared a tin whisker.

Good point. I've yet to find a control with a tin whisker, which I guess makes me a TV tech rookie. :D

Here's where I'm at now :)

http://www.youtube.com/watch?v=7MkX8...ature=youtu.be

Looks like multiple foldover to me. Any chance you installed a cap that's off by a 10 factor? If so the horizontal osc could be running at some higher multiple frequency.

When you change the horizontal hold, it appears that you're actually get lock at more than one higher frequency.

That's what I was thinking too. I was pretty careful about that, but I suppose anything's possible. I'll double check my work.....

Everything seems fine....

One thing to note....I can't get more vertical out of it than I've got.

Got any more 6SN7s and 6SL7s to try? how are the dc voltages in the vertical & horizontal circuits?

jr

Tubes tested good, replacements yielded no change. I'll test circuits as time permits this evening. Really appreciate you guys sticking with me in this thread :)

I know that I am 24 hours "late for the party" but that very symptom had me pulling my hair out on an Admiral 26R12. It was on the height control. The clue which I failed to pick up on was that varying the control did not change the voltage. The set started out good. But then there was a "POP" and I lost about half of the vertical height. To me, a lesson learned. I was not familiar with tin whiskers at that time. So, you may be good to go for that.

You may want to try brushing the controls G E N T L Y to get any tin whiskers away. They can be from the terminals to the control case and drive you crazy.

In the schematic for chassis# 19A1,
There's four components in the H. osc circuit which, if they've been replaced and one were inadvertently the wrong value, could throw the frequency 'way off. They are:

C36, .01 uf. comes off pin 6 of H. osc tube
C37, .001 uf. connects between yel. and brn. leads of T4
R42, 39K goes to pin 5 of H. osc tube
R43, 39K goes to pin 4 of H. osc tube

(color code for 39K = orange-white-orange)

C36 in my Sams is a .002@600, "de-emphasis", and C37 is a .005 audio coupling cap. I'm working with set 59, folder 2, date 4/49. Matches what is in my set.

I'll just check those specific caps and resistors. Hang tight.

Okay, my diagram numbers them C46 and C47. C46 is fine, C47 is an original Micamold that I never replaced. Time to give that a try.

Translation to Sams numbers

C36 = C46
C37 = C47
R42 = R81
R43 = R82

jr

No change. Should have just done C48 while I was in there. I'll change out C48 and check those two resistors next. I'll get this yet :)

Changed C48. R81 (R42) was at 52K, R82 (R43) was at 73K. Put in brand new 39K 1 watt 5% resistors. No change in the picture.

Did your supply voltages ever come down closer to spec? What DC voltage do you read now on pins 4-6 of V13B(horz osc)?

And if the voltages are *still* too high, perhaps use your variac to reduce until they are normal and see how the horiz behaves.

Is 10 k resistor from horiz hold to the transformer ok? How about the 50 uuf cap to the sync circuit? Does the "parts set" have a good horizontal transformer if you need it?

jr

-69 VDC on pin 4, 2.44 VDC on pin 6. Still high.

Tried it on the variac, and the only thing that happened is that the picture shrunk, and it shrunk as it was, it didn't come into sync.

I'll check the 10K resistor next. Everything on the parts set (except for the frozen controls) *looks* okay? But I haven't tested anything.

Resistor reads just under 12K. Enough to cause what I'm facing? Might as well replace it while I'm in here.

Darn... that actually worked on my 7" Philco... thing made a decent but small picture at about 90 volts line... I found some parts way out of spec!

jr

12K does not seem to be too far off, does the pot have it's full range of 20K?

Which direction are you turning the hold control when it's going 'toward' good sync? Is it the maximum-resistance or minimum-resistance direction?

Pot smoothly ranges to 15K. I tested it in-circuit. Seems about midrange where the sync locks in to where it's shown in the video.

Changing the 10K resistor made no difference, but at least when it's done, the horizontal is going to be REALLY stable :)