Need assistance with vertical troubles on my silvertone - Videokarma.org TV - Video

jpdylon · #1 05-28-2009, 11:58 PM

This one I got about a year ago:
http://www.audiokarma.org/forums/sho...d.php?t=154960

I finally got around to recapping the chassis and bringing it up. Everything actually looks pretty good except for the vertical problem at the top.

Its not a foldover, but rather a compression at the top. The linearity control changes the bottom of the picture from acceptable to huge. The height control has little to no effect.

I'll be pulling the chassis again this weekend. It appears to be a CTC-15 chassis, not a 12 like I had thought. Any pointers before I dive too deeply in it?

andy · #2 05-29-2009, 12:17 AM

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sampson159 · #3 05-29-2009, 08:27 AM

nice picture! looks like a really sharp crt.i had a similar issue with my ctc 15.there is a resistor off the linearity control that may solve this.mine was almost identical.also a cap in the vertical by the output tube.good luck and that is a good looking roundie.keep us posted on this.

jpdylon · #4 05-29-2009, 10:07 AM

All of the paper and orange drops have been replaced. I checked the 150k resistor on the vert lin control which is ok at 152k. There are a few out of tolerance resistors that I'll replace and then go back and check some voltages.

roundscreen · #5 05-29-2009, 02:47 PM

Check the vertical center control and the yoke. See if by chance you put in a wrong value cap when you replace the orange drops. I know I have seen this and I think it was a cap I replaced with the wrong value. Cool set and it does have a good picture.
Ed

jpdylon · #6 05-29-2009, 11:05 PM

Quote:

Originally Posted by roundscreen

Check the vertical center control and the yoke. See if by chance you put in a wrong value cap when you replace the orange drops. I know I have seen this and I think it was a cap I replaced with the wrong value. Cool set and it does have a good picture.
Ed

Ding ding ding! We have a winner.

I double checked my work, and found that the decoupling cap from the plate of the vertical amplifier to ground was the incorrect value. It was supposed to be .001 and I had a .02 in there. Don't know how I managed that.

Going to change that out along with the few out of tolerance resistors and give it a go.

*zenithfan1* · #7 05-29-2009, 11:33 PM

Good luck Jordan! That's a cool looking set!

jpdylon · #8 05-30-2009, 12:47 AM

ayup. The vertical is fixed now.

I notice the width is a bit short and the HV is low at startup. The HO tube is a bit tired and will get replaced. then I can continue with the rest of the setups.

Thanks for the pointers guys.

Tony V · #9 05-30-2009, 01:40 AM

Nice set Jordan! Post a pic when your done so we can see the end result. Do you have any chassis pic's?
-Tony

jpdylon · #10 05-30-2009, 01:49 AM

I can get some pics later. You'll undoubtedly see a finished thread when It's done.

jpdylon · #11 05-30-2009, 11:24 AM

ok, well the vertical is kinda fixed. The distortion went away when I put the proper capacitor in, but there is still insufficient height - now with a supplementary problem. Intermittently I loose sweep for about a half a second. Tube swapping has no effect on the problem.

The low width / low hv problem also seems to actually be a power supply issue. I also loose brightness and the vertical is somewhat shrunken too. B+ is low while this symptom occurs and it too becomes more intermittent as the set warms. Perhaps its just a bad solder joint. I resoldered just about all the boards in this thing already!

Looks like its time to pull the chassis again.....

Tony V · #12 05-30-2009, 11:39 AM

Several craft stores sell a nice foil paper that would work if you ever wanted to tackle the foil behind your knobs problem. Otherwise your roundie is near mint. The unfrosted faceplate gives this one a different but nice look. These roundie clones have a neat look to them and glad they're finally getting some recognition. My latest Truetone roundie purchase gave me a whole new respect for the clones and makes me want more.
-Tony

jpdylon · #13 05-30-2009, 12:12 PM

well, the top on this one is pretty beat up. It iwll need to be refinished at some point.

I do like the out of the ordinary roundies. Its the only reason why I haven't parted out my packard bell. I've had more trouble getting that set to work than anything else I've ever owned. It was a rain victim and had a bad power transformer. I get to that when I have absolutely nothing else to do

I just need to put my thinking cap on. With some effort and time I'll get this one right.

Tony V · #14 05-31-2009, 01:35 AM

I dont blame you on the Packard Bell...its a nice set also. You'll get there...you always do!
-Tony

jpdylon · #15 06-01-2009, 01:21 AM

ok, so here is where it stands. The vertical oscillator and output tube is getting incorrect voltages. The result is lack of height and poor vertical lock. Here are the measurements taken with everything in circuit.

No bias on pin 9, supposed to be -20
low plate voltage at 22 volts, supposed to be 140. With the tube out of circuit its near 300v.
low grid voltage on the vertical amp section. 27v vs 65v Does not change with the tube out.
no cathode voltage. 1.5 where it should be 120v.
Height and linearity controls are fine. Neither have any effect on voltage.