B&K 1077B Tough Dog Problem

[Tom9589]

I finally got my B&K 1077B where I want it except for one pesky thing. I have vertical deflection instability. The amount of vertical deflection jumps up and down. It gets better as it warms up, but never goes completely away.

Here is what have done so far:

1. Replaced all the electrolytics in the vertical and power supply sections (including B Boost capacitors)
2. Replaced all non-electronic capacitors in the vertical section.
3. Replaced all out of tolerance resistors in the vertical section.
4. Cleaned all the tube and tube socket pins with Deoxit.
5. Tried a NOS tube in the vertical circuit.
6. Re-flowed all of the PCB solder joints in the vertical circuit.

Waveforms:

1. Vertical plate and grid waveforms look steady with no bouncing around.
2. Vertical cathode waveform bounces around in sync with the raster bouncing on the TV.

There is a new capacitor in the cathode circuit of the vertical output stage and I have tried a fixed resistor in place of the vertical linearity control. No change.

Does anyone know if vertical output transformers are a problem in these units? At one time, I thought I could repeat the problem with freeze spray.

[old_tv_nut]

You replaced the V lin control. You didn't mention V size/height control. I'd guess there must be one.

[Tom9589]

The height control is set up like a volume control: one end to the vert. osc. plate, the other end to ground and the wiper to the vert. output grid. The grid waveform looks rock solid. I'll try to gen up something to try tomorrow. It's a 3 meg pot. It's always the last rock you turn over, isn't it?

[kf4rca]

My schematic shows 2 transistors ahead of the 13GF7. And ahead of that is a vertical integrator network where it gets its reference off the filament supply. I'd check out those components in that network next.

[Tom9589]

Old TV Nut wins the cigar. I had attempted to clean the height pot early on. It is a 3 Meg CTS 201 consumer grade pot. I jury-rigged a 1 Meg pot of the same brand with suitable resistors on both sides to achieve a total of about 3 Meg. That cured the vertical instability! I then took out the original 3 Meg pot and got a better angle at shooting DeoxIT on the resistance element. I put it back in and lo and behold, the problem was cured. I thought about replacing the pot, but it seems that no one carries a small screwdriver adjust consumer grade pot. Mouser was the only one to carry any 3 Meg pots and they were in the $12-$20 range. Drop down to 2.5 Meg and you can get the pots for under $1. There must be something difficult about making a high resistance, low cost pot.

KF4RCA, I had checked the derived sync pules early on and found them very stable. BTW, the signal to the integrator comes off of the HV winding on the power transformer, not the filament winding. It is labeled "HVAC" on the schematic.

[Electronic M]

With CRT sets out of production and reasonable expectation of maintenance and no other real HV (anything over 60V) applications in consumer electronics the market ends up being mostly scientific and industrial gear where cost doesn't matter as much. Try finding an assortment of 2W or higher resistors between 1M and 15M and you'll watch price climb a mountain and availability jump off a cliff...
I've been building an assortment of new stock 2W resistors for TV work and I have everything between 62 ohms and 1M... Above 1M there's no kits and finding some values (especially some common ones in early color) fuggedaboutit...And that's just fixed resistors, Pots are much worse.

[kf4rca]

Thanks Tom. I see that now. Had a senior moment. My 1076's are similar.
Well, that's why I pick up every piece of electronic junk on the roadside. Who would have ever thought Radio Shack would go out of business. And then Fry's went under. (They were about 8 miles away from me.) But I remember going there in the middle of the week and there was hardly anybody there.
But fortunately there's Audiolab which is about 3 miles away. But I don't know how much longer they will last.
https://www.audiolabga.com/

[Tom9589]

We must live close to each other. When you mentioned Fry's and AudioLabs of Georgia, I knew we were close. I'm in Tucker, GA.

[Electronic M]

I've heard of fry's but never been there, haven't even heard of audiolab.
Radio shack had cool stuff but a heck of a markup, and as they shifted to cellphones that and their inventory gradually got worse. When you can get a much better selection of much better parts at much better prices online brick and mortar tends to fail... Except in cases of convenience which isn't often in electronic parts.

[Tom9589]

Fry's started out in the Bay Area and were pretty big, They carried a lot of components, computer hardware (assembled and DIY), TV, audio equipment and appliances. I spent a lot of money there. Although in the latter years, their stock in components was going downhill - lot of empty bins. I heard somewhere they would rob stock from an established store to start up a new store, but never replenish. Without warning, they shut down every store they had. Never heard what happened to the inventory.

AudioLabs of Georgia is a one-off store in the Atlanta area. Pretty good prices, but not the largest selection. They really specialize in audio equipment and repair.

[kf4rca]

I'm near Spaghetti Junction. The colonists have taken over around here. Tucker is nice.
I knew Fry's was in trouble. They didn't have enough traffic to make the electric bill on that big store. They had a pretty good supply of ECG (TCE) semiconductors.
AudioLab used to do flatscreen repair but they've gotten out of it in recent years.

[Tom9589]

Finally found the real gremlin. I had narrowed it down to the vertical output transformer. A member on the Antique Radio Forum came up with a way to simulate peak DC current loading on the vertical output transformer to see if it was the cause of the instability. Nope. It was rock steady.

I reconnected the transformer and still had the instability. I go back and tap and wiggle parts on the deflection board again and notice that wiggling the horizontal oscillator tube makes the instability worse. That doesn't make sense. I get my magnifiers out and start looking at every solder joint and PC run. Then I find it. Hidden under a component mounted on a nearby terminal strip is what looks like a break in a PC run. I didn't have continuity, but I suspect that there was some high resistance connection. I scraped away the solder mask and bridged the break. That cured the problem. The PC run connected the Boost B+ to the 390K vertical charging resistor.

Glad I didn't need a vertical output transformer after all.

[Tom9589]

Thought I would pass one several things I learned while working on the 1077B.

Bean Current. B&K specifies 75 uA. Mine was setting at slightly over 100 uA. Going to 75 uA improved the spot size and sharpened things up somewhat.
Sync Level. I never could get the display on the TV set to have enough brightness or contrast like I could with my old 1076. B&K specifies 0.7 V p-p for the 1077B and 0.5 V p-p for the 1076. I settled on the 0.5 V setting and now have good brightness and contrast.
Working on the vertical circuitry. If you are working on the vertical circuitry and need to keep the CRT from coming on, just use a clip lead and connect it across the CRT's filament. Both ends of the CRT's filament are readily accessible underneath the chassis. No bright thin horizontal line on the CRT.

[kf4rca]

Thanks for the update on the 1077.
If it worked before, it can work again!
An old CE taught me that. He was a pretty good transmitter tech. We didn't have a backup or spare. So he had to be pretty good!