With the generator's amplitude turned down, I'm clearly zero-beating the video at exactly 61.25 MHz. This makes sense to me because the TV is obviously processing the 61.25 MHz video signal perfectly, so it must be tuned there exactly. The picture is crystal clear. The zero-beat is when the generator perfectly matches the video signal -- the TV under test isn't really part of THAT experiment. We just demonstrated (again) that my frequency counter is very nicely accurate.

The fine tuning knob doesn't change the local oscillator 6 MHz, but the oscillator tuning slug A14 sure does. I was able to put the Ch3 video on channel 2 and channel 4 with it. I watched the video signal come down from the topside to Ch2, and up from the bottomside to channel 4, and all across the slug's range on channel 3. Volume at max, not one peep of audio signal. I even turned the generator's tone modulation on, set it at exactly 65.75 MHz, and tuned the slug for maximum sound. Turned the generator off, STILL no audio. The generator tone is apparently only getting thru because it's AM. Completely assuming the audio of my Rat Shack receiver is accurate, at 65.75 MHz, and present. Just doesn't get thru the system. Only difference is AM vs. FM.

I didn't see any point in messing with the coarse-tuning slugs in the tuner turret. Those are for adjusting a single channel once A14 gets most of them right, if one or two is off. The sweep of A14 ruled that out to my satisfaction.

Still stumped.

Another thought, using another TV set, see if you can "jam" the sound carrier with your signal generator, at 67.75MHz. Only a few dB stronger signal on the sound carrier should be enough to achieve "capture" of the FM detector, thus blotting out the normal sound signal. You should hear only a faint detection of the generator's AM modulated signal on this other TV set. And if you have the set under repair also receiving the same TV channel (or the VCR RF output) and see the same video and hear the generator's modulated AM, I'd suspect that the FM detector is somehow misadjusted or broken and can only hear AM and no FM. That would be the final sound transformer. If you can tweak the detector for max AM detection, and the VCR sound carrier is jammed on the other TV, try turning off the generator and try tweaking the detector to see if you can get some FM sound.

I bought a couple of B&K Television Analysts with the intent of fixing one of them.

http://cgi.ebay.com/ws/eBayISAPI.dll...m=140136583787
http://cgi.ebay.com/ws/eBayISAPI.dll...m=170128981748

Reading the manual, I gather it's a pretty amazing tool. Seems as though it can inject a signal at just about any point in any (vintage) TV and give a go/nogo indication for that stage.

I'm putting the Admiral aside while I restore one (or both) to working, then maybe I can learn more with it to fix the Admiral. The manual claims any seasoned idiot can easily diagnose any TV problem with it. Including audio. We'll see if it's true.

What's the proper local-oscillator frequency for channel 3?
The Admiral from Hell uses a 6J6 as the oscillator/mixer tube (it's a twin-triode). Side A is the mixer, side B is the oscillator. The plate of side B is pin 1, the control grid is pin 6. I put my frequency counter on pin 6, and also thru a 100pF cap to pin 1. The results were troubling.

Try a loop or two of wire around the tube. VHF circuits get very unhappy when a big chunk of stuff comes a-connectin' to easily-detuned or easily-loaded-down nodes. Hopefully your counter has enough gain to deal with the lower input level.

Thanks Einar. Just inductively taking readings from around the tube I got:

Ch2: 79.53 - 79.94
Ch3: 85.71 - 86.16
Ch4: 91.02 - 91.50
Ch5: 101.50 - 102.04
Ch6: 106.50 - 107.08

They were a lot more stable than poking probes directly onto the VHF circuits. The counter had plenty of gain to deal with the lower input level.

According to Adam's 721 thread and Steve M, the oscillator frequency should be at 87.0, so I'm currently a bit low. Now that I know what to target, I'm sure there's room on the tuning slug to get it dead-on. So I can at least eliminate that.

The "lame" fine-tuning adjustment does what I said earlier -- it only ranges the oscillator about 1/2 MHz, not a lot of room for adjustment.

I recapped B&K Analyst #1. The electrolytics only. It almost works. Probably needs a few paper caps replaced too.

Good thing about it is it broadcasts 400Hz tone, FM modulated at any IF frequency from 15 to 50 MHz. Except it doesn't work yet.

Will likely recap the other one too.

Pic shown is it running on the Magnavox. I know it has issues. After this, it should be easy to tune the Magnavox up.

Finished the B&K Analyzer. Two small 10V electrolytics on the audio-osc PCB were open too. Once replaced, the 400Hz tone is present. Actually it's at 438Hz according to my frequency counter, but for now, close enough. I'm sure there's a trimmer under there, later.

Shown working on the Admiral from Hell. Unfortunately I was mistaken, the only audio-only signals from the B&K are straight 400Hz tone, or 400 Hz tone FM-modulated at 4.5MHz. Not terribly useful for split-sound audio problems. I did inject the 4.5MHz onto either of the cathodes of the 6al5 FM discriminator, and it discriminated (i.e. I heard a pretty reasonable 400Hz (I mean 438Hz) tone at a reasonable volume).

Injecting the 4.5Mhz signal at the grids of either sound-IF 6au6 amp yielded nothing (no sound). Not sure if it would or not though, even on a working set.

In IF mode, I injected at the grid of the first 6au6 and swept up the range. There were a few places where I was able to get tone out the speaker, but not at great volume (muffled and far away, like my original "tune it by eyeball" results of some weeks ago). One point in the sweep yielded that very loud poppy 60-Hz buzz that all TVs make when you tune the fine tuning too far right. That was the only full audio level I've ever heard out of the set (other than injecting transistor radio directly into the first audio amp).

I've ruled out the LO being off, ruled out the discriminator not discriminating, and ruled out the audio amp itself. Have ruled out any power-supply issues (all plates in the sound-IF strip are at voltage spec). Have ruled out all resistors (they ohm out to spec). Have replaced all paper caps in the strip with orange drops. Have double-replaced the sound-IF tubes, have ruled them out. Leaves very little. Those caps that are buried in the IF transformers, maybe. Or the IF transformers themselves (windings shorted maybe, not open, because they ohm out ok).

The B&K is a pretty cool tool though, and will be indispensible later on other projects, I'm sure. After I toss this freekin Admiral in a dumpster.:sigh:

http://cgi.ebay.com/ws/eBayISAPI.dll...m=150166963510

I gave it back yesterday because I'm expecting a couple of new projects this week, and need the workbench space back. She didn't waste any time listing it.

All the hard work's done, it's a good little set. It's not mine to sell, so I'm not pushing any of my own business. Just letting you all know it's available if you want to take a stab at it. The 12LP4 and NOS tube set is worth more than the starting bid. And 50 bucks worth of new JustRadios.com capacitors too. Not to mention the warm fuzzy of knowing the tuner and video and the audio power-amp all work. Good set for one of the "pros" out there. Just fix the sound-IF and you're golden.