rca_14pd8053 Strange noise

[jr_tech]

“ no video at this point.”

Does the brightness control have normal range?

jr

[Jon1967us]

Originally Posted by jr_tech

“ no video at this point.”

Does the brightness control have normal range?

jr

Seems to have normal range

[jr_tech]

Good.

Out of curiosity, what signal source are you feeding to the tv when you get sound but no video?

jr

[Jon1967us]

Originally Posted by jr_tech

Good.

Out of curiosity, what signal source are you feeding to the tv when you get sound but no video?

jr

I am feeding a video signal in with a set top D>A converter box, connected to the antenna lugs.

[Jon1967us]

Originally Posted by Electronic M

check your video detector diode and vid amp biases.

Well, it seems that the detector diode is hidden in the metal can as indicated by the left most arrow. I have no way of getting to it other than spending 4 hours disconnecting and desoldering everything to remove the board. This board is totally unserviceable.




Also, the Vid output tube has the test pins INSIDE the tube cover. No way to get to them with the tube in. The Mercury tube checker says the tube is fine by the way. Could I check the bias voltages with the tube out? Otherwise, there are barely visible traces by the socket. I may be able to check the voltages there.

Back to the detector diode, what are the chances it has failed? Do these old Ge Shottkeys have a reputation for failure?

Note, I am feeding a video signal in with a D>A converter box, connected to the antenna lugs.

[Electronic M]

Originally Posted by Jon1967us

Well, it seems that the detector diode is hidden in the metal can as indicated by the left most arrow. I have no way of getting to it other than spending 4 hours disconnecting and desoldering everything to remove the board. This board is totally unserviceable.




Also, the Vid output tube has the test pins INSIDE the tube cover. No way to get to them with the tube in. The Mercury tube checker says the tube is fine by the way. Could I check the bias voltages with the tube out? Otherwise, there are barely visible traces by the socket. I may be able to check the voltages there.

Back to the detector diode, what are the chances it has failed? Do these old Ge Shottkeys have a reputation for failure?

Note, I am feeding a video signal in with a D>A converter box, connected to the antenna lugs.

They make a tool for getting those voltages with the tube installed... called a socket extender or socket saver....they go between the scoket and tube, lift the tube an inch or two and have test points on top.

I'd reckon video detectors prior to the late 60s had a 30% failure rate... the older the worse.
Most weren't shottkeys but Crystal diodes....they predated the transistor in consumer electronics.

[WISCOJIM]

Originally Posted by Electronic M

They make a tool for getting those voltages with the tube installed... called a socket extender or socket saver....they go between the scoket and tube, lift the tube an inch or two and have test points on top.

Sample image. Many are available on ebay, get one that matches the number of tube pins you need.

[Notimetolooz]

I don't know exactly how your chassis is arranged, but sometimes getting to parts isn't easy, its just part of the task. When you have more restorations under your belt you get used to it and perhaps have a better eye for getting to things.
This article by Phil might give you some tips. Maybe in your case also it may make sense to remove the CRT to get to the detector diode.
https://www.antiqueradio.org/RCA_14-...Television.htm

[Jon1967us]

Originally Posted by WISCOJIM

Sample image. Many are available on ebay, get one that matches the number of tube pins you need.

OK, I didn't see the image when I first saw the post. I believe this configuration should work as it appears tall enough to clear the metal shield. I'll look out for one.

[Electronic M]

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.

[Jon1967us]

Originally Posted by Electronic M

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.

Funny you say that bc I considered doing the very same. I've been j hooking the ones where I can access the leads, but the radial ones with hidden leads proved daunting. I will give it a shot with some pliers.

[Jon1967us]

I have decided to tackle the board and try to disengage it from everything that's connected to it, so I can not only get at the diode, but take the opportunity to replace any remaining wonky components and check the traces, etc.

I don't have a video signal generator, so I'm going to have to rely on a conventional video source into the antenna input for now, but will try feeding into circuit in an alternate way, if I need to get to that point.

[Electronic M]

It looks like if you can get that bolt and soldered on under board shield off you can work on the board without removing the board.

Be aware if you plan to power it up before fully reassembling it that you will need to jumper any desoldered board ground to chassis. PCBs of this period usually did not have a contiguous ground plane, but instead had a few separate ground traces that each went to one of the board solder mounts...The board solder mount grounds effectively tied together thru the chassis. If any solder mount is disconnected or has a bad joint the portion of the board it grounds will float and the circuits that use those ground points won't work (until reconnected to chassis ground).

[zeno]

A few notes.
How do you service it ? Almost impossible ! My boss couldnt say
no to anything. There were still some floating around in the early 70's
and he refused to work on them. I dont know how RCA & others
built sets like this. Manuals said to cut out or crush then they had little
spring like things to make the connection.

Video detector diodes were troublesome up till the mid 60's. Often gave
odd symptoms so if any question just change the damn thing. When
built into a can often the can had a 2 piece shield & the top pulled off
so look for that.

BTW tube testers are almost a bigger liar than a politician. A known good tube
is the only way to be sure. We had a TOTL B&K & never used it. It was
for the customers & the biggest obscene profit maker in the shop.

73 Zeno
LFOD !

[Jon1967us]

I was finally able to work free the can hiding the detector diode. I desoldered one leg of the diode and tested it. It tested "normally" with a drop of .275 and no reverse current. I may replace it anyway, as there may be other problems with it undetectable by my multimeter and after 60 years of use.





Another idea that ham friend, who is also very experienced in TV repair suggested, was to inject a 1Khz signal (using a .1 uF) along the signal path and see where there's a hard stop. The 1Khz signal should display black bars (according to him) on the screen. Injecting at a point where black bars don't display on the CRT is supposed to indicate the location of failed component.

I may see if I can get my hands on a tested/NOS 8AW8A to swap out.

Roger on the separated grounds on the board and making sure to clip those to chassis prior to testing. Great call.