Capehart Troubles... - Page 2 - Videokarma.org TV - Video

Chad Hauris · #16 01-20-2007, 08:18 PM

Do you have a scope...it would be good to check the AC waveform at the horiz output grid and compare it to the sams.

kbmuri · #17 01-20-2007, 08:20 PM

Your power-supply readings are excellent, pretty much identical to mine when I was working on it, before I had the whole set going. The deviations are because the set isn't loading it down until it's working completely. The PS is done correctly. Good work.

Could get a little expensive, smoking 6BG6s. They normally do get very hot though. I guess just keep the tests short until you know it's all correct. Your -71VDC on pin 3 is excellent. Pin 4 isn't used on a 6BG6, so I assume the socket lug for pin 4 is just used as a soldering tab for some other circuit. Without pulling my chassis, I'm not certain what you ought to see there, except that the Sams spec says you're pretty much on track.

Your black screen certainly isn't the brightness control's fault, excellent readings there. The low voltage on pin 10 of the CRT is suspicious. Maybe focus there a bit...?

You're close though.

- Kirk

kbmuri · #18 01-20-2007, 09:37 PM

Sams wants you to have 1.5K Ohms between V20 pin3 and ground, not 136K. The path to ground is thru R98/99, R109A, and R109B, which add up to (roughly) the 1.5K. Because your PS voltages are correct, I have to assume R109 is in good shape. Your R98/99 pair must be smoked open from 110 ohms to more than 100K Ohms. Replace them. R97, at 1 meg, will likely have drifted high too. Check and replace if necessary. R96 you already know is bad. Replacing these ought to get you back to a safe grid bias voltage and you won't blow any more HO tubes. I assume the capacitors in this circuit, if paper, have already been replaced with orange drops. If not, do so. Hope this helps.

- Kirk

jpdylon · #19 01-20-2007, 09:39 PM

I am without a scope. The last one I had stopped working, so i sold the remains.

There is no width pot on this chassis. Its stamped on the rear of the chassis, but the hole has been plugged with some cap. It looks like it was factory, but I could be wrong. The last owner was an electronics technician. I have no idea what else he did to this set. If he wasn't dead, I would ask him!

jpdylon · #20 01-20-2007, 09:41 PM

Quote:

Originally Posted by kbmuri

Sams wants you to have 1.5K Ohms between V20 pin3 and ground, not 136K. - Kirk

OOPS. There was supposed to be a decimal point in there. its 1.36k. R98 and R99 are reading just under 115 ohms

kbmuri · #21 01-20-2007, 10:09 PM

Rats. Or I guess good. I'm still leaning towards your CRT is just bad and you really do have raster. I'd feel better if you had more V at CRT pin 10. I'll measure mine tomorrow, just to make sure.

jpdylon · #22 01-20-2007, 10:13 PM

I'll measure it with the socket off the CRT and see if I get better voltage --after changing the resistor. I figure the CRT is the culprit it registers near nothing on the tester. Good chance its the tube, but I won't know for sure until I try everything else and get voltages where they are supposed to be.

hope I win that 16KP4, crossin my fingers I can snipe it

Chad Hauris · #23 01-20-2007, 10:17 PM

You need to check whether you definitely have HV before suspecting bad CRT.....
Do you get a spark when discharging CRT anode after power is disconnected?

jpdylon · #24 01-20-2007, 10:23 PM

haven't tried discharging yet. I do notice a blue glow around the HV rectifier and HO tube with the lights out. Its gota be making some kinda HV...

I'll give that a shot tomorrow.

jpdylon · #25 01-20-2007, 11:07 PM

NO HV at the connector, hmmmm.

HV rectifier filament is not lighting. I pulled it and it tests great, so its either a bad socket, or open heater winding

kbmuri · #26 01-21-2007, 10:29 AM

The anode lead itself possibly shorting to the HV cage where it exits? or just open somewhere internally? Use standard precautions to discharge the HV at pin 2 or 7 of V22, or at the flyback secondary. Then test the anode lead for continuity, or short to ground.

Then do a continuity check from pin 3 of V21 to the top cap of V22. Ought to be the 500-600 Ohms of the flyback primary only, and will verify the wiring around it. With V22 removed, make sure there's continuitly in the flyback's secondary (socket pins 2 and 7 ought to be near 0 Ohms).

You should always be able to drag the back of your hand or forearm across the picture tube screen and feel the hairs raise from static electricity. Even if the tube is "dead" from lack of emission.

The blue glow of the HV tube is normal (and quite lovely to look at). It's the easy way to set the horizontal drive control. When the control is set minimum the blue glow will not be there, turn it up just until the blue glow appears, and leave it there. that's what I called "conducting", although there's probably a better term. The go/nogo point is where the blue glow is either present, or not. Oscillator singing will appear at the same time.

The HV Rectifier has a very small, 1-volt filament, under a metal "bell" internally. You can't see it glow, over the other tube light in the set, and even on a tube tester, in pitch black darkness, it's hard to see. If it tests ok. it could be glowing in the set too, and you just can't see it.

Best of luck on the 16KP4.

- Kirk

kbmuri · #27 01-21-2007, 10:35 AM

C82 was bad on my set. Normally the micas and ceramics you don't have to worry about, but this one takes a beating. Check it with your Ohmmeter for infinity reading. Mine was about 500 Ohms and pretty smoked-looking. That would definitely drag your HV down...

jpdylon · #28 01-21-2007, 02:10 PM

pin3 of V21 to the top cap ov V22 is 531 ohms

resistance across pins 2 and 7 of V22 socket read .3 ohms

Fly looks good. however, i cannot find C82 anywhere on the chassis. Could you shoot me a pic of where its located? I'm not sure if someone pulled it out of the circuit, or where it is at all. I'm following the scat, but when I get to the tie point where C82 might be, its not there. The service notes say that not all models have this cap, and some models have it connected between V20 plate and chassis to increase width.

maybe mine was without C82 in production?

jpdylon · #29 01-21-2007, 03:18 PM

missed the 16KP4

I clicked placed bid and confirmed, but my connection shat and it didn't go through. would have been 60 dollar max too

kbmuri · #30 01-21-2007, 05:54 PM

Pity. Oh, well, you're connected here for a used one I'm sure. Your flyback's fine, not much left! If you get HV and still dark screen, maybe toss in a tube brightener.

C82 on my set(s) is just sort of strung across the top of the HV cage. From Flyback primary to a pop-riveted solder tab on the left side of the cage. Can't miss it if it's there. Your (early) set, it probably isn't there.

Trace the lack of HV from the CRT anode cap back. Should be 0 Ohms from the cap to pin 2 of the 1B3GT. Fly is good. It really should be working.

- Kirk