Bendix - Page 2 - Videokarma.org TV - Video

Charlie · #16 03-02-2010, 09:40 AM

The set was producing an intermittent squiggle in the picture that was quite annoying. Sometimes it was pretty serious. R68, a 15k 10 watt resistor, was put together using a couple of 4700 and a 5000 ohm resistor. It was mentioned in the schematic that they might do it that way. One of the three checked a little high, so I was getting 18k across the three instead of 15k. One of the side notes said to use a wire wound resistor, but the two 4700 resistors were carbon. I pulled them out and place a 10k wire wound in it's place and the squiggles stopped.

I've found the width problem... it was my own fault. There were two caps grounded in the same spot (the blue and orange one in the above photo, lower right corner) that I wired the other ends in each other's spot. One was a .004, and the other a .02 mfd. After realizing this and putting them back the way they were supposed to be, the width popped back exactly as it should have been.

Charlie · #17 03-02-2010, 09:44 AM

Horz linearity is not the greatest on the far left, and also looks like there's some ringing on the left side of the screen. Can't really tell in these photos, but it's there. Books tell me look for issues in the damper circuit... which this set doesn't have much of one. There's no damper tube. It seems, instead, they use a 3000 ohm 20 watt resistor. The original resistor opened and someone installed another in the cage. Also, I was looking for 560 ohm resistors in the yoke, but this set doesn't have any of those, either.

I've changed just about everything in the horz section... there's not a lot left. In the diagram, it shows R64 and C52. Those two components are no where to be found. I'm going to try installing them as per the diagram to see what happens.

Something I've never noticed in other sets... this set uses the 6BQ6 for both the horz oscillator and output. Usually, those are separate tubes.

For the most part, the picture is decent. I've watched it for several hours with no issues. I was thinking it could be a little better, but being a bare-bones set, I might not be able to accomplish much more.

I am, however, interested in getting rid of the retrace lines. I recall it's just a matter of installing something like a .05 cap somewhere on one of the CRT grids. Can someone direct me where that should go? Is there more to it... or is it just a cap?

DaveWM · #18 03-02-2010, 10:17 AM

how did you find that cap swap? did you just go over the schematic again?

I often get antz when doing recaps that involve multiple caps to a single tie point (like a floating ground on a term strip) since I desolder and undo them all at once. I try to insert one leg of the replacement cap in place as a place holder, but I have to admit, its kinda unnerving esp when going at a shot gun recap with out the schematic (which is how I did the TS-14)

Glad you got it up and going. I wonder if the TYPE of resistor is critical on that damper setup as in WW or carbon?

Charlie · #19 03-02-2010, 10:43 AM

I figured there had to be a mistake in there somewhere. There was nothing really left to replace. There might be a couple of resistors in there that are still original. So I decided to go back and recheck everything again and found those two values swapped around. Much of my work was done late at night while I was getting tired. Being tired means I should put down the iron and go to bed... not make more coffee and try to stretch it out longer.

The verticle section was real fun to replace as sooo many caps and resistors were shoved into the same corner and all connected to a 10-section terminal strip. I was suprised that I didn't get that all mixed up.

bandersen · #20 03-02-2010, 02:47 PM

Quote:

Originally Posted by Charlie

... I am, however, interested in getting rid of the retrace lines. I recall it's just a matter of installing something like a .05 cap somewhere on one of the CRT grids. Can someone direct me where that should go? Is there more to it... or is it just a cap?

I think you are referring to this mod: http://www.earlytelevision.org/vertical_blaniking.html

Charlie · #21 03-02-2010, 03:00 PM

Thanks... that's what I was looking for. I'll shoot for that.

Charlie · #22 03-02-2010, 09:23 PM

I installed those parts tonight... and it did not work. In fact, it made the retrace lines worse.

I looked over the Sams some more, and found that the video circuits aren't quite the same as pictured in the diagram for installing the vertical blanking circuit. In the VB circuit diagram, the brightness control is tied to a CRT grid. In my set, the brightness control is tied to the CRT cathode on the other side of a 100k resistor. This is located just above C24 a couple of posts back. It's not seen because that was the edge of the picture.

If someone has an idea for another way of doing this, I'm all ears.

bandersen · #23 03-02-2010, 09:30 PM

Maybe the way I wired it in my Sentinel would work ? http://www.videokarma.org/showthread...=247075&page=2

It has the brightness control on the cathode too. What I did was pick the positive pulse off the vertical output and feed it into the cathode with a resistor and capacitor in series. I determined the values experimentally so you may need to as well.

Charlie · #24 03-02-2010, 11:36 PM

No luck. I tried several value combinations. It seems the lesser the resistance, the heavier the lines got. Going higher didn't change things hardly at all. Tried different value caps as well... that didn't seem to make much difference.

I might try a different CRT. Both of my testers say this tube is weak (although it has good brightness and contrast). Even if I crank it up to 8 volts, it just barely gets the meter up into the green. I have another toob in the garage, and last time I checked, it was pretty hot.

Charlie · #25 03-04-2010, 11:24 AM

I threw in another 10BP4 this morning. The tube was brighter allowing me to turn the brightness control down enough to reduce the retrace lines. They're still there, but only from time to time depending on the scene. Even while there, the lines are not as apparent as they previously were.

I believe I will leave everything as is now. I will be refinishing the cabinet, however, the weather is still to cool and I'll be going back to the ship by Monday. No sense in starting the cabinet now. I should return home again around May 1st, and the weather should be perfect at that time for cabinet work. I'll refinish the Zenith Porthole cabinet at that time as well.