How to inject a signal into a TV?

[Kamakiri]

This is one procedure I have yet to nail down, can anyone explain how it's done?

I've seen it explained as injecting a signal into the grid of the 1st video tube, but what, if anything, has to be disconnected to do this....and what type of source do you use?

A step by step explanation with, say, a common chassis would be most helpful in trying to learn this

[old_coot88]

OOPs. Misread the question

[Gregb]

I have a B&K Television analyst and I can inject an RF, IF, or video signal anywhere I need to in the set and it works AWSOME! It has helped me many times. It also has horizontal and vertical pulse outputs as well as 4.5mhz and audio signals as well.

Gregb

[Kamakiri]

Well, that's great....but you didn't answer the question.......

How and where do you inject a signal *into* the set? Where's it done? Give me an example with a chassis, so I can see, for example, what exact tubes and what pins.

For the moment, let's just talk about a video signal....say if we were trying to diagnose a dead tuner.

[old_coot88]

Originally Posted by Kamakiri

...For the moment, let's just talk about a video signal....say if we were trying to diagnose a dead tuner.

When you say 'video signal', do you mean downstream past the video detector, or 'upstream' from it in the IF chain and tuner?

[Kamakiri]

Well remember that in this case I'm playing with hypotheticals, so let's say either or, or both.

The reason I'm asking is two fold....first, to know how to do it, and secondly as a reference resource for all of those that, like me, know that this has to be done in some cases but don't know the procedure.

[Electronic M]

I'm not going to use tube numbers, but lets assume you have a B&K 1076/1077 analyst like I do (or a ballsy test pattern generator, and a way to modulate it to IF and RF).

You DO NOT need to disconnect anything...But if you are working on a hot chassis set powering that set through an isolation transformer is recommended.

Lets start out with a video chain (in a monochrome TV) and assume it has (and starts at) a SS diode video detector diode, a 1st video amp tube and a second/output video tube. You would start by injecting at the detector diode or grid of the first video amp tube (in the common case that the diode is hidden in a can). If you can see video on the screen assume everything between that point and the CRT is working correctly...If you don't get video move down stream and inject at the plate of the first video tube, then the grid of the second video tube, then the plate of the second tube then the video modulated element of the CRT until you have signal on the screen... You will need to start with a low video level from the generator and crank it up as you head down stream to the CRT. Feel free to test points in the signal flow between the plates and grids...You can sometimes isolate the individual component at fault that way.

Now lets assume a set with a standard 2 tube tuner and 3 stage IF. A B&K analyst's IF generator should have the stones when injected at the antenna terminals to pass through the tuner all the way through the IF and onto the screen in a working receiver (assume tuner or AGC issue if it does this on a bad set). Assuming that does not work inject into the IF end of the tuner to IF coax cable and then the grid of the first IF. If you get signal there assume IF cable and or tuner are bad. If no signal there inject at the 1st IF plate, then 2nd IF grid, then 2nd IF plate, etc till you hit the detector. The parts just before the first injection point that gets you first get signal on screen are suspect. On dead IF/tuner work I set the RF/IF output of my B&K on max so something will get through if it can. On some sets there is not enough IF gain between the plate of the second IF and detector to get any signal to the outputs....This is where using a scope in conjunction with the generator can be important. When looking for intermediate points of injection I use the schematic to get a feel for signal flow and select points of interest.

Using your gear on a working set (especially if it is the same chassis as the bad set) is a great way to get the hang of the process and a feel for what to expect from which points.

I don't get much bad tuner problems so I'll let those that know how to fix a tuner chime in on that.

On tuner and IF issues always remember that the AGC sets the gain somewhere between max achievable and zero gain/attenuation so a good IF can act like a bad one if the AGC system is screwed up.

Hope this helps.

EDIT: since conversation occurred while writing the above I will address that. You can NOT trouble shoot a dead tuner/IF with ONLY a video generator. You need a source of modulated RF/IF signals (such as a B&K 107x series) to do that.

[earlyfilm]

Originally Posted by Kamakiri

This is one procedure I have yet to nail down, can anyone explain how it's done?

If you wish to learn how to inject a signal with the B&K Analyst 1000, 1076 or 1077, first get a manual:

The Bunker of Doom, run by a sometimes poster in this forum, has PDFs of the instruction manual.

( http://www.bunkerofdoom.com then scroll down to "Electronics" and select B&K, for either 1076 or 1077)



To find the gold standard set of instructions, primarily geared toward the B&K Analyst, you want "Television Analyzing Simplified", by Milton S. Kiver.

http://oldtubes.net/library/free_man...Simplified.pdf

If you want a paper copy and my mind sure works better while looking at paper, rather than at pixels, a quick search showed the four (maybe more) editions that are priced from $7.99 and up on the usual auction sites.

To search on Google use "Television Analyzing Simplified" Milton S. Kiver

Note use of quotation marks to reduce stray hits.

James

[old_coot88]

In addition to the sage advice given by Electronic M, you can also work 'backwards', beginning at the CRT injection point. Bear in mind that some designs inject video via the cathode, others via G1.

Then work back point-by-point to the plate of the vid. out tube (there may be a peaking coil or two in the signal path). Then go to the grid of the vid. out tube, attenuating the genny as needed.
Be aware that phase inversion may occur, i.e., if the display is photonegative, that's normal.

Then to the plate of the 1st vid tube, then to the grid, attenuating as needed. Then point-by-point back to the vid. detector diode, which may be either a tube (e.g., 6AL5) or a SS diode.

The same staging process would apply back thru the IF strip, except you gotta use a moduated carrier, not raw video. Start at the last IF plate, then the grid, attenuating as needed. Then likewise back thru the preceding stages, attenuating as needed, and finally to the plate of the mixer tube in the tuner.

[init4fun]

And then , when ya want to go all Frankenstein on it , you can kill the vertical osc and inject a music signal on the vertical output's control grid and have a flat line that dances to music

[Gregb]

Originally Posted by Kamakiri

Well, that's great....but you didn't answer the question.......

How and where do you inject a signal *into* the set? Where's it done? Give me an example with a chassis, so I can see, for example, what exact tubes and what pins.

For the moment, let's just talk about a video signal....say if we were trying to diagnose a dead tuner.

Sorry, your right, I didn't answer your question. I have a spare copy of Television Analyzing Simplified by Milton Kiver and it really explains how to use the B&K or really any test signal source to do exactly what your asking. PM me with an address and its yours.

Gregb

[ChrisW6ATV]

First, you need to have a device which can make different types of video, IF, and RF signals. A B&K 1077 or Sencore VA62 are good examples, and there are others as well.

The basic procedure, which is probably explained well in Milton Kiver's book, is to power up the set (with its own separate isolation transformer if it does not have a power transformer itself!), decide where you need/want to inject a signal, and then pick that signal type from the generator, which may have more than one set of output jacks/connectors. Typically, you use a cable or cables from the generator that have alligator clips on the ends. One clip (from the black or shield wire) goes to the chassis as a "ground", ideally near where you want to inject the signal, and another clip (from the red wire or the center wire of a coaxial cable) goes to your injection point. That point might be the grid pin of the video amplifier tube, or right after the video detector diode, for example. It is not an exact location, and it does not always have to be "just one right place per circuit". The one thing to avoid is connecting to the plate circuit of a tube (until you are using a device intended for that, such as a horizontal-output tester). Always put a voltmeter on the pin/connection you plan to use before you connect the generator. Then, adjust the generator while looking at the CRT or otherwise testing for the results you hope for.

[ChrisW6ATV]

Quite often, you cannot actually clip the signal to the circuit but have to just hold it there while looking at the screen.

[Electronic M]

Originally Posted by ChrisW6ATV

The one thing to avoid is connecting to the plate circuit of a tube (until you are using a device intended for that, such as a horizontal-output tester). Always put a voltmeter on the pin/connection you plan to use before you connect the generator. Then, adjust the generator while looking at the CRT or otherwise testing for the results you hope for.

Quite often, you cannot actually clip the signal to the circuit but have to just hold it there while looking at the screen.

That depends on the signal generator. My B&K 1077 has no issues with signal plate circuits....The video signal output socket on it has a large series capacitor feeding it signal to block DC....I've used and X10 scope probe for the RF/IF lead (the only thing I have with BNC on one end and clip-leads on the other to act as a test lead for it ), and used that to feed signal to IF plates without issue......Even generators not meant to feed signal to plates or the like can do so safely WITH a proper DC blocking capacitor added in series.

[old_coot88]

Originally Posted by ChrisW6ATV

The one thing to avoid is connecting to the plate circuit of a tube...

Yeah, that's one thing I forgot to mention. If the probe tip isn't already DC-isolated (or if you don't know whether it is or not), use a cap to inject through. Anywhere from .01 - .047 or thereabouts.