6-switcher PAL 2600: Sound constantly detuning

[tearex]

Hi "techies",

 

I have a problem with my six-switcher PAL 2600: The circuit that produces the 6 MHz sound subcarrier is constantly detuning itself. I already drilled a hole into the bottom of the case so that I can adjust the tunable inductivity (L2, I think, in the AtriAge provided schematic) with a match or so, without opening the case.

 

However, it's getting worse and worse and sometimes I can't tune it at all. This means the "real sound" will be soft to nonexistent and there will be lots of humming and noise. If I let the console run for a few hours then I can normally tune it after that, but when it's still cold it is very problematic.

 

Do you know of a fix for this problem? I can handle soldering and I can read schematics, but I'm not enough of a "buff" to know an answer myself.

 

Thanks a lot in advance,

[Pixellated Ghost]

There's a transistor near that coil that is connected to it, try replacing that. I can't say for sure exactly what it is, other than that it's NPN. While troubleshooting mine I replaced it with one from my parts bin so the type probably isn't horribly important.

[tearex]

Somehow, someway, bending the capacitors in that part of the circuit back and forth a bit did it for me. Suddenly the noise disappeared. A hair-width tear in one of the capacitor's maybe? Well, whatever it was it has worked flawlessly for some days now, even some good knocks didn't start the problem again.

 

I also fixated that darn coil with some glue once and for all after careful fine-tuning as the core was already getting quite loose from so much "tuning" attempts.

 

And I also learned a new fact, the subcarrier is actually 5.5MHz here in continental Europe, not 6Mhz as it is in the UK.

 

So... NTSC = Never Twice the Same Color, PAL = never twice the same norm, it seems.