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Yamaha TX-930 modifications

Posted: 08 Oct 2014 14:18
by daveB
I'm copying the notes from my project book in case it is of help to anyone. I posted something similar on the old forum in Jan 2014 and you can access a number of posts there by typing CSL into the search box which give further detail. Having the service manual is a must as it gives detail of expected voltages for alignment purposes
1.Replaced F1 and F4 with 150 kHz filters and F2, F3 with 110kHz filters. In SIL sockets
2. Re-aligned IF Offset - re-did after re-fitting filters the right way round.
remember a)tweak b) turn off and back on c) check effect on freq - re-do until satisfied
the method of aligning IF offset is different in wide and narrow modes - the above is for narrow mode.
3. played about with osc coil - and later lined it up properly. 25.1volts
4. tweaked discriminator to ensure CSL properly set up
5. Added switchable disabling of CSL - 5 volts taken from pin 26 of the LC7210 chip - fed to pin 17 of the same chip via a 270k resistor with a minature toggle switch in line.
6. Fitted RDS decoder board.
Audio input taken from pin 6 of the op-amp feeding the MPX decoder - soldered to adjacent jumper
Ground taken from pin 5 of same op-amp - soldered to adjacent jumper
5 volt for board taken from the live side of the CSL switch - note board draws under 5mA
The CSL toggle switch is fitted to the underside of the tuner - into a small CAREFULLY drilled hole - using a hand-drill to avoid metal swarf being thrown about.

With regard to RDS decoding and filter bandwidth - there is a noticeable difference in the abilty of RDSSpy to decode between wide and narrow settings. So I do most of my searching in narrow mode - but switch to wide mode when I want to maximise chances of the pi code being decoded on a weaker (clear) signal.
Yamaha TX930 mods annotated resized.jpg
Yamah TX930 CSL switching resized.jpg
Yamaha TX930 audio feed to RDS resized.jpg