Hello all.

I have a Klein & Hummel Teletest TV pattern generator model FS-4-A dating from about 1956. I have worked on it, every resistor has been replaced, as they had all gone high or O.C., and all of those Wima capacitors replaced, as they were all very leaky, as well as all electrolytic capacitors. However, it does not work! Tracing out the circuit as best I can revealed that at least one component is missing.
I don't have any service information on this instrument at all, not even a circuit diagram. Can anyone out there help me please?

Cheers, Stuart

I forgot to add that Radiomuseum.org has a circuit for an FS-4, but this is not the same, using different valves and circuitry.

Cheers, Stuart

You'd be lucky to find a circuit for that!

Could you scan and email, or post, what you have traced so far? I might be able to work out what's wrong by asking you to test a few things.

Did you take pictures of it before you replaced parts? It's easy to make a slip-up when you are recapping, especially if the circuit is unfamiliar.

I assume it has a series of locked oscillators to divide down a master clock for the sync and patterns. It could be you'll need to adjust each oscillator in the chain for lock, using a scope.

Thanks Ian for your offer. I know there is at least one component missing because a screen grid is connected to a bypass capacitor but nothing else. Its quite complicated, 12 valves, almost all double types. Trouble is, someone had been there before me and may have made mistakes. Another trouble is that the thing is extremely difficult to work on. I have taken photos but the missing component was not there before I started. I'd like to see if I can get the circuit before I strip it down again. I've added the model to Radiomuseum.org and I'll see if I can get one there. Thanks anyway. Cheers.

Photo uploaded.

Nice looking piece of gear that.

Hi All.

I've got it going! I was able to use the circuit diagram for the FS5B given on Radiomuseum.org as a guide, even though there are significant differences. The circuitry that was butchered I changed to match the FS5B. I got the video section going but had no R.F. output. That turned out to be a broken lead on a capacitor in the turret tuner and a burned out R.F. attenuator probably due to the output being accidentally connected to the B+ of a TV. I had to use an ordinary carbon potentiometer, which is of course less than ideal at R.F.

I still have a slight problem though, some slight vertical jitter, caused by some instability in the vertical synch generator which is a blocking oscillator synched to the mains. I've replaced all the capacitors again, and the valve, but no difference. Interestingly, I replaced a capacitor and the problem vanished, - for 15 minutes, but then returned. I think I'll call it a day. It is still quite usable. Thanks for your replies.

I'd still like a circuit diagram and any other info. though.

Cheers, Stuart

If the circuit is locking an oscillator to the mains, the phase will be affected by ripple control signals ("Zellweger") imposed on the mains by power suppliers for remote control of things like water heaters. Probably not around when and where this was designed. Not a great deal you can do except don't sync it to the mains, that might be the best solution.

Thanks Ian. Yes I thought of that, but it happens when these control signals are absent. I've looked carefully at the oscillator signal and the mains input signal at the same time on a dual channel CRO and can't see anything on the mains waveform (just the 6.3 volt heater supply line) that can account for the jitter.

Sirwin, just a thought adding to Ian's reasoning.

The signal generator was made when the mains was actually sine wave and i'll bet about hi-fi standard!
My mains in Toongabbie in Sydney is flat topped (saturation clipping) and full of spikes ( switching loads and solar junk) with a high harmonic content that may throw a sync circuit whacky.
In the back of my mind was an instrument I once worked on that used the SINE shape curve to phase control/trigger something (too long ago to remember detail) and i'm sure that would go berserk if I applied my present mains signal to it.

Possibly the sync circuit may now need a pass filter to sieve out the rubbish?
Fred.

Yes, Fred, you are right. That kind of filtering is actually done in software in dimmers, where it's VERY important to get a stable trigger point or your lights fade up and down randomly.

What should be being detected is the zero crossing point of the AC waveform. That's easy to do with solid state electronics (although the ripple mucks it up), much harder with valves.

Why not just disconnect the sync and let the oscillator free run? If it was locked to the mains it's random interlace anyway, so nothing is lost except the jitter.

Photo uploaded to Post 9.

Hi Fred & Ian. Yes, I'll look into that. Certainly my mains waveform is noticeably distorted, not just from "electronic" power supplies but also no doubt from the fact that most of my neighbours have solar photovoltaic systems. I will try replacing the mains signal with one from my audio generator, to see if that makes a difference.
I often wonder if the distorted mains waveform makes much difference to my AVO valve tester, which assumed a sine wave input when it was originally designed. I also use a true RMS multimeter now, as I figure the ordinary sort to be not so accurate as they are calibrated assuming a sine wave voltage.

Thanks, Stuart

Hi Stuart

You should be able to disconnect the trigger from the mains and not put any signal into it at all, the oscillator should free-run. Just adjust its frequency to match the hum in the picture so it doesn't move.

Very early in television, it was recommended that TV stations SHOULD NOT lock their frame to the mains, but do just as I'm suggesting.