Philco 51-T1601 - Videokarma.org TV - Video

bigaudioal · #1 03-12-2015, 12:03 PM

Well after working great for a few weeks (after full recap, all resistors tested and replaced as needed), this set gave up the ghost somewhere last night. No raster. Cannot hear the horiz osc running at all and the 6CD6 horizontal output tube is hot plating something awful. Not sure what failed. My lack of test equipment (well I lied - do have a scope, but no clue how to use it yet) may limit me in diagnosis. Don't want the set on with this condition so testing voltages is out. I did pull the two 5U4s to eliminate the B+ and run the set like that. Power transformer ok, all tubes lit normally then, including the 6CD6. Seems like the set lost horiz drive maybe. Or - dare I say, flyback pooped out?!

Anyone want to suggest how to try and find what failed in order of likelihood??? Or offer any suggestions of diagnosis techniques with no test equipment except a multi-meter and an cheapy cap tester (does not test under voltage). Schematic is here:

http://www.earlytelevision.org/pdf/p...sams_138-7.pdf

Electronic M · #2 03-12-2015, 12:32 PM

Pull the top lead off the HO tube to stop the red-plating. Then start checking voltages at the HO tube and osc.

bigaudioal · #3 03-12-2015, 12:39 PM

Thx. First time I have dealt with a red-plating horiz osc tube. Removing the cap to the fly stops this condition?

Electronic M · #4 03-12-2015, 12:48 PM

Yup. With the plate lead disconnected it should not draw much current...There is a possibility of the HO Tube screen grid being overloaded (if the osc. is dead) though so it may be worth wile to disconnect the screen grid lead from the tube as well.

bigaudioal · #5 03-12-2015, 01:15 PM

Ah ok. That makes sense. I think something may have been up with osc now that I think about it. May have been on its way out. This osc has two adjustment lugs on it. One is the osc, other is listed as the horiz stability, I think. then to either side of the 6CD6 there are two trimmers. One is Horiz Drive, other is Horiz lock.

When I first got the set up and going, the horiz control on front would produce a nasty squeal when turned to one side and the pic would get majorly scrambled (sometime even a dual image), even shrinking horizontally and darken. So I centered the front control and ever so slightly tweaked the osc and stability lugs (counting half turns). Well only after a half turn or so of the stability control the pic locked in and looked pretty good. So I did not continue to mess. However, when reading the proper Horiz adjustments in the set's literature, I noticed that both lugs were way farther out than they should be. Literature gives measurements on how far out stability lug should be when doing proper adjustments. Maybe with the recap and replacing all the out of spec resistors, it finally failed? Definitely a possibility I guess. Horizontal was never quite right on this set. So I am not totally surprised this happened.

earlyfilm · #6 03-12-2015, 01:27 PM

Bigaudio

I looked at your schematic and wrote this just before you posted #5 above, but this still is a good way to resolve your problem.

Don't operate the set with only the Horiz Output plate connection removed for a long time, as that can overheat the screen grid and you will never see any indication of this happening until it is too late. Normally this won't happen, but since they ain't making these tubes anymore, it is a good precaution.

If the set worked after the recap:

Substitute the Horiz Osc, Horiz Output and Damper tubes and plug back in and see if the plates in the new tube get hot.

Then go to below.

If the set failed on the first power up:

Remove Horiz Osc and Damper (both could be shorted) and do a resistance reading as shown in the Sams for that section of the set.

If nothing suspicious, power the set up with Horiz Output and Damper tubes removed and see if the voltages on the Horiz Osc look normal. Then wrap an .01 capacitor on your AC volts probe and see if you get any AC on the horizontal output plate. (Yeh, this test would be so much easier if you had a scope.)

If so, see if most of the AC is also visible on the grid of the Horizontal output tube.

The grid on the horizontal output (no tube in socket) should not be more positive than the cathode.

If nothing suspicious has appeared so far, take a break and come back and recheck each connection in these circuits against the schematic. Let us know the results.

James.

bigaudioal · #7 03-12-2015, 01:41 PM

I do have a scope (recapped), but have never used it and do not know how to use it. Something I plan on getting to soon (NOW may be the time).

Got an RCA WO-33A, with original funky looking probe.

https://www.youtube.com/watch?v=Xczvo9ftS0g

Thanks for your suggestions. I already substituted the damper, horiz osc and horiz output tubes and fired it up and it gave me same condition. No raster, no horiz osc noise at all and red-plating 6CD6. Also tested every other tube in power chassis and all seem ok. But I substituted out these three with others I had and got the same condition. Set was worked fine for about 3 weeks after recap, estimate - put about 15 hours on it. Like I said the Horiz was never quite right. Seems like the whine of the osc was a bit louder than my other sets. It was stable but not perfectly symmetrical. Would be elongated to the left or to the right, could never get it centered, where it did not look out of whack one way or the other. Almost like it would drift out over time.

Findm-Keepm · #8 03-12-2015, 02:05 PM

Quote:

Originally Posted by bigaudioal

I do have a scope (recapped), but have never used it and do not know how to use it. Something I plan on getting to soon (NOW may be the time).

Got an RCA WO-33A, with original funky looking probe.

https://www.youtube.com/watch?v=Xczvo9ftS0g

Read the XYZs of Oscilloscopes by Tektronix. Great starter, and available online for free:

http://ecee.colorado.edu/~mcclurel/txyzscopes.pdf

I intentionally didn't link to the most recent edition - it is full of sales mumbo-jumbo for Tek, and doesn't add to the analog oscilloscope module.

bigaudioal · #9 03-12-2015, 02:15 PM

LOVE IT! Thx!

Electronic M · #10 03-12-2015, 02:51 PM

To be honest the horizontal osc. transformer adjustment is best done on a scope so you can match it to figure 6 in the sam's. Just make sure it is in synch when you are done getting the waveform right.

bigaudioal · #11 03-14-2015, 02:08 PM

Ok guys, I decided to test voltages and resistance on the 6CD6 tube b/c I was comfortable doing that. This being my first time trying to diagnose a major issue in a set. I have one of the octal test sockets, so could test the voltages from the top of the chassis and very quickly. Set it all up, popped the plate cap off the 6CD6 and fired up the set. No red-plating so proceeded with the testing. Below are the results of the voltage testing:

Pin# / Correct Voltage / Actual Voltage
1 /0 /0
2 /0 /0
3 /0 /0
4 /-23 VDC /-18 VDC
5 /-23 VDC /-18 VDC
6 /310 VDC /222 VDC
7 /6.3 VAC /7 VAC
8 /115 VDC /71 VDC
9 /do not test /did not test

I then tested the resistances as outlined in the SAMS:

Pin # /Correct Resistance /Actual Resistance
1 /Inf. /Inf.
2 /0 /0
3 /0 /0
4 /488K /1 meg
5 /488K /1 meg
6 /50K /55K
7 /.1Ω /Inf.
8 /9K /12K
9 /35Ω /Inf.

Not sure if you guys can look at the schematic and tell anything from these readings, but the biggest things I see amiss are in the resistances. Pins 4, 5, and the plate cap.

I did also test the two doorknob caps and they were both in the 500 PF range. Like 530 pf each. Rated at 500 pf. Also the 1b3 and 1x2 tubes in the HV cage tested fine. Damper and HV osc tube tested fine as well. I also did swap the damper, 6CD6 (HV output), and HV osc tubes and still have same condition.

Let me know if anyone has any suggestions.

Thx.

miniman82 · #12 03-14-2015, 09:24 PM

This is easy, not sure why you're making all these funky readings but...

Your horizontal oscillator probably stopped running. Easiest thing to do is remove the 6CD6 and scope the grid pin for a waveform, if it's there you have other problems. If not, investigate why and trace it back. If the coupling cap between the oscillator and output tube is leaking, you will have 0 or positive DC voltage on the grid of the output tube when it's installed whether the waveform is there or not- that's BAD. There should be normal negative grid voltage on the output tube when things are working like they are supposed to. This is the #1 cause of melted output tubes in TV sets.

DavGoodlin · #13 03-14-2015, 09:38 PM

That test socket on the schematic is where you want to plug in your scope.

kramden66 · #14 03-15-2015, 10:59 AM

did you check the micas in the horz section ?
i had a mica go bad in a set like this and caused issues
mike

bigaudioal · #15 03-16-2015, 09:15 AM

For us new guys "this is easy" is not a very helpful statement or comment. I am trying to learn and absorb as much as I can. For me, no troubling shooting is "easy" as of yet. I did these voltage and resistance tests on the advice of others on this forum who are trying to help a new guy trouble shoot issues that he has not dealt with before.

Now, thanks for the rest of your comment b/c now I think I understand what might be happening. If the coupling mica cap (think it is a 220 pf/500 v) between the osc and output tube is bad, it might cause this issue, and thanks to your comment I now understand why. Appreciate it!

Quote:

Originally Posted by miniman82

This is easy, not sure why you're making all these funky readings but...

Your horizontal oscillator probably stopped running. Easiest thing to do is remove the 6CD6 and scope the grid pin for a waveform, if it's there you have other problems. If not, investigate why and trace it back. If the coupling cap between the oscillator and output tube is leaking, you will have 0 or positive DC voltage on the grid of the output tube when it's installed whether the waveform is there or not- that's BAD. There should be normal negative grid voltage on the output tube when things are working like they are supposed to. This is the #1 cause of melted output tubes in TV sets.