Yes. Backwards. I'm trying to think of an excuse. I'll let you know if I find one.

“jr tech: Yes, voltage is low on both sides of R36.”

Is this still true when the contrast control is adjusted properly for voltage table comparison? Should be about 24 volts across the resistor. :scratch2:

jt

I'll check that now. Could be up to 30 minutes after now.

Twenty-seven volts. 143V on the pin 6 (grid) side. 116V on the pin 5 (plate) side.

So r-36 is apparently connected correctly, and post 34 was in error, as the measurement across r-36 should have shown the 80 volt difference measured between pins 5 and 6 of v-9, as notimetolooz stated in post 37. :scratch2:

jr

The voltage difference between pins 5 and 6 of V-9 is dependent on the setting of the contrast control. When contrast is set at midrange as directed in the instructions, the voltages are consistent with the specifications in the voltage chart.

The 80-volt difference is correct when the contrast control is at its max setting.

Have C-37 and C-39 been replaced with mica caps yet? :scratch2:

jr

Yup. C37, C39 are now .001pF mica, but no improvement. Reassessing the problem. Set worked before I started restoration. Intended to do nothing but replace paper, cardboard, electrolytics, and defective components. But after I started work, the set didn't work. Two possibilities are (1) I inadvertently changed something, or (2) There are one or more failing components which have not be identified. So, my current plan is to restart the project using the 200 chassis photos I took before I touched anything. I think I can reproduce its original condition (from the previous restoration), and recheck every connection and component. This could take a few weeks. Hope you all will be there when I start posting again.

Thanks for all the help so far.
Winky.

Back in the Saddle Again.
 

Hello again. I've spent a lot of time ensuring that this set is in exactly the same condition as when I acquired it. Also checked the values of 20 original ceramic caps and replaced one disk that showed more than twice the specified capacitance and one with possibly overworked leads. Also repaired and reinstalled the original horizontal size pot. Other than replacing defective parts and upgrading parts to comply with advice from this forum, the set is exactly the same as when I bought it.

Now, to address one issue at a time, please consider V15, 6SL7, Balanced Vertical Output. I have inconsistent voltage readings going back to when I first started working on the set. Now, rather than trying to describe my difficulty in reading the voltage, here's a quick video of the multimeter on one plate and one grid.

https://live.staticflickr.com/31337/...c78fa437_m.jpgAdm 17T12 9015 V15 Jitters by H Boyars, on Flickr

I checked it with another meter and with another tube, but both grids, both plates, and one cathode still give the same result. What might cause this phenomenon?

Here's a link to the 17T1 schematic:
https://flic.kr/p/2mv3Wrm

The plate voltage for the 6SL7 comes from the HV supply thought a string of voltage dividing resistors. If the RF HV supply isn't working properly or any of those resistors are off, you can get strange results. Like the voltage may fluctuate with the screen brightness if the HV rectifier tube is weak.

Thanks. I've been looking things over. Retested the 1B3 and even though it's quite strong, I tried switching out another strong 1B3. To no avail. I'm rechecking the resistor chain(s) and everything connected as if I've never seen it before.

Possibly your dmm is measuring the dc value plus the instantaneous value of ac vertical sweep voltage present on the tube elements mentioned. :scratch2:

Do you have an old meter with a needle (slower response time) such as they likely used when making the voltage measurements in these ancient service documents?

jr

RF HV Supply, Vertical Sweep Voltage
 

1. Regarding the HV supply to the 6SL7, the circuitry is correct and all components are the right values. I followed the voltage from the tube back through the resistor chain until I reached 500V at R73. The voltage readings were still fluctuating.

2. Regarding "instantaneous value of ac vertical sweep voltage" (not sure what or how that happens): I have no analog meter. But wait--I do have a 15 volt panel meter! I set the needle at 1 volt so I could see negative deflection, checked the grids and cathodes, then reversed the leads and repeated the readings. The readings were perfectly steady: G1 1.5V, G2 zero, K1 zero, K2 4.5V. So, does that mean the vertical sweep voltage is the cause of this issue, and I can ignore the irregularity of the voltages?

“-I do have a 15 volt panel meter! I set the needle at 1 volt so I could see negative deflection, checked the grids and cathodes, then reversed the leads and repeated the readings. The readings were perfectly steady: G1 1.5V, G2 zero, K1 zero, K2 4.5V. So, does that mean the vertical sweep voltage is the cause of this issue, and I can ignore the irregularity of the voltages?”

Perhaps... the ac voltage (vertical sweep signal) may be disrupting the measurement of the dc voltage, as your fast response dmms may be sampling the dc voltage as well as the value of the ac signal at the instant(s) the samples are taken.

Or perhaps the dmm is attempting to auto-range to track the varying voltage :scratch2: .

On the other hand, the jumping could be caused by a noisy resistor in the hv circuit (popcorn noise), but it seems that your panel meter would have indicated fluctuations.

Do you have a high voltage probe?

jr

Yes, I would think it's the sweep voltage causing those readings. It's a pretty large sweep sawtooth wave on the plate and grid.

High voltage probe-no. I should mention that with the dmm set for AC, when reading what should be 300VDC, then I get the erratic reading in the neighborhood of 30 volts-whereas I would usually expect less than one volt.

Popcorn noise? Is that audio? I have been getting some crackling noise (with no signal) which I didn't notice previously. To rule out noisy resistor, I could do a temporary switch of ALL suspects if you could tell me which ones to do.

Thanks. I'd better leave it that. I can't deal with much more than one thing at a time.

30 volts fluctuations, or 30 volts signal?

Can’t point out a particular resistor, any can become noisy/erratic.... high meg ohm resistors are likely the worst offenders.

je

30 volts signal--fluctuating within the 15 to 40 volt range. Nearly all of the resistors in the megohms have been replaced with new. I may start replacing the old ones to see if that helps. Beyond that, I have no direction to go with this project.

30 volts signal??? is this measured on pin 5 and/or 2 of the 6SL7? I woud expect hundreds of volts of vertical sweep signal. :scratch2:

jr

Sorry. I wrote this reply earlier but apparently failed to post it.
Repeated those readings several times with similar results for the plates, pins 2 & 5. The readings are from numbers erratically flashing on the meter for less than half a second. Always ranging from 10V to 65V when the meter is set for AC. (Actually, one time I got steady readings of .8V and 1.0V, but the set wasn't turned on.)

Interesting! what do you see on the screen while you make this measurement?

I’m really scratching my head on this one!

jr

On the CRT? Nothing! All the rear controls are set a mid-range. Without more brightness there is nothing on the screen. Most recently, with a lot of adjusting, I could see an oblong blob in which you tell, if you knew what you were looking for, that the TV was trying to show of a test pattern.
Thanks for sticking with me. I'll have to pick this up tomorrow morning.
Winky, "The Eternal Novice"

OP can you repost the schematic you're using with this repair so I can follow along? I'm have quite a bit of confusion which schematic we're using.


It would be a good idea to pick up a regular multimeter. Even a cheap harbour freight / hardware store grade one. They deal with some measurements that a DMM is just too sensitive to get proper readings compared to the schematic.

This is the 17A1 schematic from Wallace-Telaides:

https://flic.kr/p/2mv3Wrm

The set I have is a 17T1 chassis. There were relatively few of these made compared to the 19A1 chassis. They're very similar, but the 17T1 has some additional circuits and some production changes. The catch is that the previous restorer probably used a 19A1 schematic. Apparently they knew what they were was doing. It's a sloppy restoration, but it worked when I got it. I'm trying to replicate what the previous restorer did.

Here's another link that may be helpful. It's the 17T1 schematic overlaid on a 19A1 schematic. Printing that's only black (not black with red overprint) indicates a difference between the two chassis.

https://flic.kr/p/2mv7qkt

Thanks for the tip about an analog meter. It never occurred to me that they still made those.

jr tech asked what I saw on the screen.
 

This is 13 seconds of a test pattern video from 09 Jan 2022:

https://flic.kr/p/2mY1fbd

The four following links show one second of the video frame-by-frame. The time between each image is approximately .029 seconds.

Frames 1-9
https://live.staticflickr.com/65535/...b2114b18_m.jpgAdm 17T12 9031 01-09 by H Boyars, on Flickr

Frames 10-18
https://live.staticflickr.com/65535/...89402ed2_m.jpgAdm 17T12 9032 10-18 by H Boyars, on Flickr

Frames 19-27

https://live.staticflickr.com/65535/...f65008e9_m.jpgAdm 17T12 9033 19-27 by H Boyars, on Flickr

Frames 28-36
https://live.staticflickr.com/65535/...9368daa1_m.jpgAdm 17T12 9034 28-36 by H Boyars, on Flickr

That is very interesting how it goes from a stretched vertical to a full collapse and back at random like that.

I would be looking with a fine toothed comb in the vertical oscillator circuit.

I'll have to put more thought in on this one.

I would start with the power supply to the vertical circuit.

I think, unless you are very lucky and stumble onto something, you are going to have to get some more test equipment.
Many times when something is seen on a TV screen it will give a more definite cause of a problem and a scope will not be necessary. Where the image is distorted in both the horizontal and vertical directions however diagnosis is very hard. A scope would straighten things out rather quickly.
I believe your meter was trying to follow a moving target when looking at the vertical output. An interaction between the measuring cycle of the meter and the vertical signal.
Normal trouble shooting methods would look at the power supply to the suspected circuit stage first, however in this case the power for the vertical output originates in the HV CRT supply (after going through the voltage dividers). You can't measure the HV without a HV probe for your meter.
It looks to me that some supply or something else is cycling up and down over a second or two.

Definitely looks like a noisy/erratic power supply problem.

Can you see/hear any evidence of arcing/corona discharge in the HV supply and related components including pots and resistors as well as capacitors?

Is the low voltage supply stable and noise free (audio ok?)

Very nice video and photo work.:thmbsp:

jr