RCA 630TS - no high voltage - Videokarma.org TV - Video

dcl0 · #1 02-15-2023, 07:22 PM

I'm stumped! I've been working on an RCA 630TS for about 3 years now (I treat my radio/TV repair projects like someone might do a jigsaw puzzle. I leave it on a work table in the spare room and work on it off and on when the mood strikes). This one originally came from shore road in Great Neck Long Island according to the service tag. It was probably stored in a humid environment all its life but the chassis didn't look too bad. Before I could even think about testing it with power, I had no choice but to change out all the leaking electrolytic caps, all the wax paper caps (all later tested as shorted at well below their rated voltage) and most of the resistors which had drifted upward. After all this, I turned it on and got sound (reception) from the digital converter box, but no picture.
The picture tube tests well into the green (Heathkit TC-2) but the high voltage as measured at both the top of the doorknob capacitor and the anode button are only a laughable 400 volts. I confirmed that my high voltage probe (Heathkit IM-18 with high voltage probe) was working correctly by measuring known ~300 volts elsewhere on the chassis. I've looked everywhere I could think of in the high voltage circuits for a fault and cannot find any.
The ringing test of the flyback with a Sencor VA62 gives me only 4 rings with everything connected, but 24 rings with everything disconnected. I can't really pin down which leg is dragging the rings down because its all interconnected (only pin 3 through the high voltage rectifier socket is a separate circuit). However I disconnected, in turn, various points in the high voltage section and measured resistances throughout the primary winding, damper circuit and high voltage winding and all were almost spot on. Continuity was also what it was supposed to be where it was supposed to be. I disconnected the yoke and that resistance was within spec.
I've swapped out 3 sets of damper, rectifier and horizontal output tubes (all I have) with no effect. Voltage checks give me 325 volts on the cathode of the damper tube and -101 volts on the grid of the horizontal output tube. The cathode current of the horizontal output tube is 90 mA.
http://www.videokarma.org/attachment...1&d=1676509703
Shown below is the oscilloscope trace of the grid of the horizontal output tube.
http://www.videokarma.org/attachment...1&d=1676509706
I've taken oscilloscope traces of everything shown on page 269 of the RCA-Victor Service Data 1943-1946 (available for free download on the Worldradiohistory.com website) except for the high voltage/pulse stuff, and it matches except for the screen of the horizontal output tube and the cathode of the damper. The peak-to-peak voltages are OK, but the peak profile is very different.
Screen of HOT
http://www.videokarma.org/attachment...1&d=1676510127
Cathode of Damper
http://www.videokarma.org/attachment...1&d=1676510127
Can anyone point me in a direction to look next?

nasadowsk · #2 02-15-2023, 08:34 PM

Check the rectifier socket, and HV cap - try the set with the cap discoonected. They act weird at times…

Electronic M · #3 02-15-2023, 10:44 PM

Quote:

Originally Posted by nasadowsk

Check the rectifier socket, and HV cap - try the set with the cap discoonected. They act weird at times…

+1.
If you can draw a decent arc from the plate lead for the HV rectifier with it disconnected from that tube but with it connected you don't get HV it means the rectifier is bad, the HV doorknob cap is bad, the HV rect heater winding is bad (in one or more ways) or the connection between the tube pin and the point of measurement has failed.

If you happen to have a CFL bulb or a small neon indicator lamp you can place it in proximity to the flyback and the tube plate leads coming off it and see if it lights up. It normally should in those areas.

Yamamaya42 · #4 02-15-2023, 11:13 PM

make sure the 2 resistors 235 1m and 233 3.3 ohms are good, on my FADA 895,(630TS clone) they were both bad, with carbon burn inside them, that killed the HV, I had to replace both using 2w carbon film

dcl0 · #5 02-16-2023, 05:20 AM

Many thanks guys. I'll test this all when I get home from work today.

Yamamaya42 · #6 02-16-2023, 10:27 AM

These are the ones I mean, they are almost always a source of trouble.

https://antiqueradio.org/art/RCA630TS20.jpg
https://antiqueradio.org/art/RCA630TS19.jpg

Pics from here.
https://antiqueradio.org/RCA630TSTelevision.htm
very good info on the set.

dcl0 · #7 02-16-2023, 06:47 PM

Well the results are in! Again, many thanks for your help.
With the plate cap of the high voltage rectifier disconnected, I got a nice arc off of it (about 3/4 - 1 inch) with a grounded screwdriver. I was a little leery of doing this because the set in this production run does not have a 1/4 amp fuse protection for the flyback. I did some resistance checking with the rectifier removed and found that between pins 7 & 4 (across the 3.3 ohm resistor) its 3.5 ohms, but I was using an empty tube socket adapter and had to really wiggle it around to get that - otherwise the resistance was higher (38 ohms). So something is up with the socket. Between pins 2 & 6 its 980k (across 1M resistor) and between pins 2 & 4 (winding in flyback) its 0.1 ohm. I did some resistance checking from the pins of the socket to ground and found that there is 12M resistance between pins 2,4,6 and 7 and ground. Is this normal? I want to rebuild this area this weekend, but all I have are 3 watt metal film resistors. Will metal film be OK?

Yamamaya42 · #8 02-16-2023, 08:37 PM

Quote:

Originally Posted by dcl0

Well the results are in! Again, many thanks for your help.
With the plate cap of the high voltage rectifier disconnected, I got a nice arc off of it (about 3/4 - 1 inch) with a grounded screwdriver. I was a little leery of doing this because the set in this production run does not have a 1/4 amp fuse protection for the flyback. I did some resistance checking with the rectifier removed and found that between pins 7 & 4 (across the 3.3 ohm resistor) its 3.5 ohms, but I was using an empty tube socket adapter and had to really wiggle it around to get that - otherwise the resistance was higher (38 ohms). So something is up with the socket. Between pins 2 & 6 its 980k (across 1M resistor) and between pins 2 & 4 (winding in flyback) its 0.1 ohm. I did some resistance checking from the pins of the socket to ground and found that there is 12M resistance between pins 2,4,6 and 7 and ground. Is this normal? I want to rebuild this area this weekend, but all I have are 3 watt metal film resistors. Will metal film be OK?

If you are going you have that socket pulled up, its best to replace both resistors, and clean the area, and even a new style 3 watt metal film 1 meg would be about the same size that the original 1 watt was, so no loss there, important ting is to get new ones in while it is apart, and get it cleaned like in the pics above.

old_coot88 · #9 02-16-2023, 09:47 PM

Quote:

Originally Posted by dcl0

... I got a nice arc off of it (about 3/4 - 1 inch) with a grounded screwdriver.

Yee-ikes!

No need to ground it. An ungrounded screwdriver (with an insulated handle of course) will draw a nice "air arc" of 1/4 to a half inch without throwing a gruesome load on the fly and HO tube.

dcl0 · #10 02-17-2023, 02:06 AM

Oops, OK I won't do that again. Since this never had a fuse, I'd like to add one. (According to SAMS later examples came with one wired between pin 8 of the damper and one side of the horizontal linearity coil L201). Does anyone know of a source for 1/4 amp pigtail fuses? What would be a good cleaning agent here?

dcl0 · #11 02-17-2023, 02:12 AM

Oops, OK I won't do that again. Since this never had a fuse, I'd like to add one. (According to SAMS later examples came with one wired between pin 8 of the damper and one side of the horizontal linearity coil L201). Does anyone know of a source for 1/4 amp pigtail fuses?

Yamamaya42 · #12 02-17-2023, 05:42 AM

Quote:

Originally Posted by dcl0

Oops, OK I won't do that again. Since this never had a fuse, I'd like to add one. (According to SAMS later examples came with one wired between pin 8 of the damper and one side of the horizontal linearity coil L201). Does anyone know of a source for 1/4 amp pigtail fuses?

http://suzaku.live-evil.org/0225202240.jpg
This is where the fuse was on my FADA.

Yamamaya42 · #13 02-17-2023, 08:42 AM

Yeah, there has to be something strange going on under the socket, corona arcing or whatever, the only active pins are 2 & 7, with tie point 4 at heater potential, all other pins should have almost infinite resistance, meaning there must be a buildup of carbon or conductive dust or something in the socket.

Electronic M · #14 02-17-2023, 09:24 AM

Quote:

Originally Posted by dcl0

I did some resistance checking from the pins of the socket to ground and found that there is 12M resistance between pins 2,4,6 and 7 and ground. Is this normal?

No that is not normal. Either the doorknob is leaky, the insulation on the HV rect filament winding failed, or dirt and carbon tracking made a new path somewhere.
I'd de-solder the filament winding and check it...If there is any measurable resistance to ground from the winding replace the winding. Any wire rated for 15KV or better should be fine.

Yamamaya42 · #15 02-17-2023, 09:40 AM

Quote:

Originally Posted by Electronic M

No that is not normal. Either the doorknob is leaky, the insulation on the HV rect filament winding failed, or dirt and carbon tracking made a new path somewhere.
I'd de-solder the filament winding and check it...If there is any measurable resistance to ground from the winding replace the winding. Any wire rated for 15KV or better should be fine.

That could also be the case, like it was in my Hoffman Colorcaster (ugh, what a mess.) but I find it a strong sign that he stated that he saw 12m on pin #6, which should have nothing connected to it, that there is krud under the socket.