Help identifying 405 fine tuning control

[Hunts smoothing bomb]

Hi all,
I haven't posted on here for a while, but need help identifying the fine tuning control for 405 lines on the following set.

The set in question is a Philips 19TG153A dual standard model, I bought it at the NVCF this year, I powered it up the next day with the aurora connected and the set needs loads of caps changing as the raster is small and an odd shape plus smoke came from somewhere, the problem is that the signal also needs fine tuning, the question is how do I fine tune this set as the VHF tuning knob does not appear to push or pull and rotate in the way expected.

Here is a picture of the tuner.

Cheers

[G8KBG Tony]

Hi Lee,

Put a screwdriver in the little hole. Press in and it will engage in the pre-set fine tuning mechanism. Turn to adjust.

Hope this helps,

Tony

[Hunts smoothing bomb]

Thanks Tony!
Cheers

[Hunts smoothing bomb]

Hmm, tried this but it doesn't seem to work, the plastic screw presses down but will not turn in either direction. I did find the tuning instructions in the red R&TV servicing book, vol 1964-65 models eventually.
It didn't mention depressing the screw though, just turning it which I tried to no avail, (the screw turns but nothing happens on screen) I guess I'll have to take the tuner out and dismantle it to see whats jammed.

I have stopped the set smoking though, two caps in paralell across the efficiency diode that were leaking worse than a sieve!

Cheers

[G8KBG Tony]

I've just had a quick look at the Trader sheet. There may be a bit more information than in the red books. PM me your email address and I'll send it on.

Cheers Lee,

Tony

[Hunts smoothing bomb]

Thanks for the info Tony,

It turned out that the individual screws on the tuner that the front panel plastic screw locates into were just stuck with age.

I removed the tuner, freed them off, powered up, tuned the signal and with a tweak of the line hold resolved testcard C.

The picture is very wishy washy and lacking in contrast though, the contrast control does work but has very little range, I have noticed this set has a different timebase panel to all of the ones listed in the publications too, the circuitry around the contrast pot is different, the components are not laid out the same and also there is a germanium diode in the circuit there somewhere.

I will try and post a pic of the panel tonight to see if anyone can give any pointers on the circuit.

Cheers

[G8KBG Tony]

It sounds like the slightly modified version used in the xxTG154A etc,. That has a diode in the contrast circuit. I'll email you the Trader sheet.

Regards,

Tony

[Hunts smoothing bomb]

Tony,

You have been a great help, the 19TG154A data seems to be correct for the TB panel I have I'm wondering if my set has the wrong back cover actually as my set looks just like the 19TG154A pictured in the data you sent me!

Cheers

[Hunts smoothing bomb]

I got the chance to do a bit more on this set last night and it's looking promising.

The faults I needed to sort out were,

lack of contrast (washed out picture)
lack of frame hold (probably will be cured when I sort the contrast issue)
lack of sound on 405 (haven't tried 625 yet)

I managed to prove that the audio amp (PCL83) was working fine by injecting a 1KHz sine wave into the grid of the triode section, there was plenty of volume so I next focused on the AM sound demodulator, this diode is hidden in one of the cans of the I.F. section and was not easy to test as the PCB is very populated in this area.
The Ge diode was found to be open circuit so a hunt through my bits box produced a very similar looking diode but with different coloured bands, the original (OA79) had a white and purple band I think but the replacement I was to fit had a white and black band. (Anyone know what type this is?)

I had to de-solder the I.F. can and remove it from the main PCB to replace the diode which was quite a fiddly job.
After the diode was replaced the can was soldered back into circuit, the set re-assembled and switched on, the result was restored volume and plenty of it too!

I found by flexing the I.F. panel by pushing on the valves I could make the contrast fault come and go so a note of where all the wires to the board was made and the board has now been removed from the set for inspection and repair.

That's all I had time for but good progress none the less.
The set will have to wait now as we're are off on holiday to the Isle of Wight this evening and not back until Sunday.

Cheers

[Tazman1966]

And you're not taking the set with you for something to do in case it rains?!!!