I've decided to contine the story I started in the General Forum here, now a forum dedicated to repair issues exists...
Well, the cassette player is now working 100%. The cause? Faulty labelling in the Dick Smith schematic in the Technical manual
(see http://www.classic-computers.org.nz/sys ... ematic.jpg
In that schematic capacitor 7 is labelled in that schematic as 200uf. 200uf is also what I found IN the cassette player when I first opened it. Given that the schematic said so, and the previous capacitor in there was 200uf, I replaced it wth 200uf.
However, in the board layout in the link below this capacitor is labelled 10uf. http://www.classic-computers.org.nz/sys ... corder.jpg
Also, in the troubleshooting guide, the manual also talks about replacing the 10uf
C7 capactor with a 47uf one (not the 200uf one with a 47uf!).http://www.classic-computers.org.nz/sys ... page54.jpg
After reading that I replaced C7 with a 47uf. Much better!...but not perfect. On occasions the signal was still dropped. I then replaced it with a 10uf one.
No sign of a problem since!
I noticed the C7 10uf on the layout diagram but dismissed it as maybe being an earlier revision. If I'd read the troubleshooting guide earlier I would have been suspicious enough to consider the schematic was mistaken rather than the board layout diagram. Obviously an earlier owner had been caught out by that one as well!
I also opened up my Blue Label model to see what kind of a C7 capacitor it had on the cassette deck. You guessed it. 10uf!