rca_14pd8053 Strange noise - Videokarma.org TV - Video

Jon1967us · #1 02-08-2019, 12:12 AM

I'm starting the process of restoring this TV. I have just finished a round of replacing several caps and have more to go. Testing my progress after some recapping, I decided to run the set on my isolation transformer/variac, and have noticed an unusual, loud and odd noise. Even with the sound all the way down, it doesn't affect the noise or its level.

I have a link to a clip I took. Sorry the crt is at an angle, as I had the other hand on the power supply and was reaching the other hand to take the video clip. The sound you hear at the end is due to the power supply being turned off.

https://www.youtube.com/watch?v=2flj...ature=youtu.be

I'm interested in what others think this is a telltale sign of or what it may indicate.

I am aware that the picture needs centering and the yoke needs adjusting.

The CRT tests and seems to appear strong.

Looking for any help, as I'm a noob.

Oh, here's the photofact as well, for reference.
https://drive.google.com/file/d/1QYI...ew?usp=sharing

Notimetolooz · #2 02-08-2019, 10:42 AM

Is the sound coming from the speaker? With that loud of sound you probably can feel the cone of the speaker vibrate. It could be that the vertical sweep signal is getting into the sound amplifier. Re-check your work. Some set use the audio amplifier to reduce the power supply voltage to other parts of the set. The electrolytic caps around the audio amplifier are very important. What you are hearing may be the result of changing a few caps at a time.
If you are unsure of where the sound is coming from, disconnect the speaker and substitute a 4 to 10 ohm resistor of a couple of watts size. It could be something else vibrating like the yoke or transformer.

dieseljeep · #3 02-08-2019, 10:49 AM

Quote:

Originally Posted by Notimetolooz

Is the sound coming from the speaker? With that loud of sound you probably can feel the cone of the speaker vibrate. It could be that the vertical sweep signal is getting into the sound amplifier. Re-check your work. Some set use the audio amplifier to reduce the power supply voltage to other parts of the set. The electrolytic caps around the audio amplifier are very important. What you are hearing may be the result of changing a few caps at a time.
If you are unsure of where the sound is coming from, disconnect the speaker and substitute a 4 to 10 ohm resistor of a couple of watts size. It could be something else vibrating like the yoke or transformer.

That's one of those RCA's that use a dual purpose tube, 6CU8 for the IF and vert osc. Maybe there's something wrong with the tube.

jr_tech · #4 02-08-2019, 11:21 AM

Does the pitch of the sound change when you change the vertical hold knob?
I’m thinking that vertical pulses are getting into the audio output stage (since you indicate that the volume control has no effect)... likely bad filter caps in the 275 volt supply.

jr

Jon1967us · #5 02-08-2019, 03:22 PM

Quote:

Originally Posted by jr_tech

Does the pitch of the sound change when you change the vertical hold knob?
I’m thinking that vertical pulses are getting into the audio output stage (since you indicate that the volume control has no effect)... likely bad filter caps in the 275 volt supply.

jr

Yes, in fact the sound changes as I adjust the vertical hold on on the back.
Good call. Most likely the remaining multi section filter cap and or the wax papers on the PCB, which still have to be done.

That sound is a bit intimidating. It sounds like the set is about to self destruct!

Will keep you guys posted and thanks for the help!

old_coot88 · #6 02-08-2019, 08:36 PM

Bad filter caps in the power suppy are the most obvious problem. What caps have you replaced so far?

Jon1967us · #7 02-08-2019, 09:09 PM

I've replaced filter caps and about to replace the multi section C3 (100, 20, 20) I've replaced all wax caps on the chassis facing the crt. Have not touched any caps on the PCB on the side yet.

C3 2 caps go to the audio section and one is in the power supply. So this is probably the main source of this noise

Jon1967us · #8 02-10-2019, 02:00 AM

Replaced C3 multisection. You can see its replacement at beginning of video, right behind CRT. Also made adjustments to yoke, vert lin and height. Previous strange loud noise has been eliminated. Vertical oscillation was definitely getting through the audio section.

Still need to go through the components on PCB board. Set is only passing audio and no video at this point.

https://youtu.be/bV2T3loJL_o

PS the plastic yoke cover has disintegrated and I had to remove it. The yoke is essentially floating on the neck of the crt. I'm thinking I'm just going to fasten a couple large plastic zip ties to hold it in place (?)

Notimetolooz · #9 02-10-2019, 08:46 PM

Here is a link to how someone rebuilt a flyback cover.
http://videokarma.org/showthread.php?t=268978&page=7

Electronic M · #10 02-10-2019, 10:12 PM

check your video detector diode and vid amp biases.

Jon1967us · #11 02-11-2019, 08:16 PM

Quote:

Originally Posted by Notimetolooz

Here is a link to how someone rebuilt a flyback cover.
http://videokarma.org/showthread.php?t=268978&page=7

You mean the yoke cover? Very fancy. Does the cover serve any purpose other than a means of holding the yoke in place and acting as a sort of guide for the adjustment?

Jon1967us · #12 02-11-2019, 08:18 PM

[QUOTE=Electronic M;3208469]check your video detector diode and vid amp biases.

Will check them out. In meantime I have to figure out how to work on the PCB now. Thing is impossible to remove without taking half the TV apart... No idea what the best way to work on this world be.

jr_tech · #13 02-11-2019, 08:18 PM

“ no video at this point.”

Does the brightness control have normal range?

jr

dieseljeep · #14 02-11-2019, 08:40 PM

[QUOTE=Jon1967us;3208504]

Quote:

Originally Posted by Electronic M

check your video detector diode and vid amp biases.

Will check them out. In meantime I have to figure out how to work on the PCB now. Thing is impossible to remove without taking half the TV apart... No idea what the best way to work on this world be.

It's a hard one to work on, period!
I have two of those to work on, one 17" series string model and one 14" power transformer chassis. It's rather hard to believe that RCA would build a set that small with a transformer and a 5U4! I'd have to look at it to see if it's a two or three stage IF chassis, they built both.

Electronic M · #15 02-11-2019, 09:41 PM

Many PCB sets in the tube era were built with the intention that the PCB be serviced while still mounted to the chassis...Most offered some way to get at the foil side to solder, but some makes Like GE and Philco encouraged crushing the body of a failed original part, leaving the original leads as points to wrap/J-hook the replacement parts leads onto. I have service Lit for GE that literally recommends and instructs how to replace a part in that manner.