I've had this sitting around for about 15 years and decided to get it going. I recapped the power supply first as a precaution. I plugged it into a variac and slowly brought up the voltage until it had a full raster except for a small 3inch spot in the top right corner. With a vcr hooked up, it had a good picture and sound then I lost horizontal sweep with a vertical line in the center of the screen. I immediately unplugged it and noticed the 12DQ6B horizontal output tube was red plating. All of the tubes were replaced when I got it. It's covered in Sam's 439. I do have the Sam's. I've worked on solid state TV's for about 30 years but am not very experienced with tube sets. Anybody have some ideas about what might be causing the red platiing and loss of horizontal sweep? I have a Motorola VT-71 next in line as well as 3 others. Thank's in advance for any help. Dan.

if the horz out is red plating I would start with a check of the horz osc tube, pull the horz out tube out of the circuit and check the wave from going to the grid. Possible problems would the horz osc tube quit working, or the couplate that couples the horz osc to the grid of the horz out is leaking.

if you only replaced the power supply caps and not all the paper caps, then that could cause a lot of problems.

Pull the top lead off of the H output tube and check the grid for the proper waveform with an oscilloscope, and also do voltage checks.

Replacing just the electrolytic type power supply caps is not enough to safely run a tube set. You need to replace all the paper dielectric type caps as well or the set will either not work or is left as ticking time bomb counting down to failure and possible destruction of other (often unobtainable) parts.

When you say a vertical line do you mean it's side to side or top to bottom?
if the line is from side to side it means the Vertical sweep has quit, if the line runs top to bottom that would be the Horizontal sweep but that's a nearly impossible scenario on a flyback set.

As the others have said it will need a complete recapping, not the most fun on a Predicta because you have to remove the PC board to do it, therefore it makes sense to do them all and check the resistors while your at it.

I don't have a scope anymore, I sold pretty much of all my test equipment when I retired from the repair service. About all I have left are some digital and analog VOM's and a cap checker. Looking at the Sam's, it looks like the grid of the horizontal output tube is connected by a 3,300 mmf cap from pin 6 of the 6CG7 horizontal oscillator tube. Am I on the right track? Also, would 3,300 mmf translate to .033 uf ? I'm going to check it in a couple of minutes. Thank's for the help so far. Dan.

that cap is not a discreet part, but rather built into a couplate (a part that has all the resistors and caps built into a ceramic looking package.

I would 1st try recapping the paper caps as that needs to be done anyway.

Then I would check the voltage at the grid of the horz, should be neg, 30-50v, if not then either the horz is not working OR the couplate cap is leaking.

Some folks have had those couplate go bad, i have only worked on a couple predicta's, they were fine.

When you say a vertical line do you mean it's side to side or top to bottom?
if the line is from side to side it means the Vertical sweep has quit, if the line runs top to bottom that would be the Horizontal sweep but that's a nearly impossible scenario on a flyback set.

As the others have said it will need a complete recapping, not the most fun on a Predicta because you have to remove the PC board to do it, therefore it makes sense to do them all and check the resistors while your at it.

The line was top to bottom, then lost all raster. I'm going to check the coupling cap and let you know what I find. Thank's. Dan.

Look for shorted .047 cap in the boost to B+ circuit.
Clip screen resistor pin 4 and check for -45 volts on 12DQ6, pin 5. You can trouble shoot without cooking 12DQ6s with screen voltage disabled.

If still no answers, check for low resistance from damper cathode to ground. That points to shorted electrolytic or less likely, yoke.

Remember to re-solder the screen resistor once you find the trouble.

If no neg 45 volts, clean freq and hold controls, look for open lug ground near 6CG7, controls. Oscillator shut down could be a number of causes. Let's explore the other options first and let us know.

Thank's,Don. I'll try and check the cap later this afternoon. If not, it will be Wednesday before I can get back to it. I was thinking it was losing the -45 volts but wasn't sure. Sounds like a good place to start. It probably might not be a bad idea to replace the 12DQ6 while I'm at it. I'll have to dig out my Hickock and see if I have a decent used one. I think I have a few lying around in my tube boxes. If not, I can get a couple while I'm in Casper. Thank's again. Dan.

This article has restoration notes for the 9L37 chassis that may be helpful:

http://antiqueradio.org/philc12.htm

As others mentioned, it's pointless to expect much in the way of performance until you have replaced all of the paper (or plastic-coated paper) capacitors. The article also shows how I replaced a couplate, if you find that necessary.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I can't contribute much more to what needs to be done. However, when in the horizontal osc circuit, check both the horizontal hold and range pots and verify continuity. Wiring and connections as you may have noticed are not the best. Even though my couplates have been ok, I've had issues with bad pots.

I've had to replace/substitute the vertical linearity and contrast controls. Even though my set is in playing condition, I don't know when I'll ever consider it complete!

And be on the lookout for broken tube socket contacts -- I recently had a failure of the 6CG7 socket in a Predicta I worked on.

3300 pF is 0.0033 uF.

I've done several Predictas and haven't had a bad couplate yet, so that would not be my first priority.