Just a quick update to let you all know that I have resolved the missing reception on AM - both LW and MW are back!
As I had all three wavebands working previously, checking there was nothing I had done subsequently that appeared to be connected incorrectly in any way and that the AF stage was working I concluded that the problem must lie elsewhere.
I wasn't getting anywhere with David's tests using my Velleman K7000 to check for AM signals - nothing at any of the points indicated in the helpful link to Nostalgia Air: Signal Tracing.
Then I tried Mike's suggestion to try another transistor radio close to the MR10 - there was no interference in the transistor when I tuned through the MW band on the MR10.
Conclusion - there was something amiss with the AM oscillator at V2!
Those with patience and a good memory may remember that I had some difficulties understanding and replacing components on the underside of V2 and how busy things were at that location. I had replaced three Hunts Mouldseals and two resistors here:
C45 (0.01μF) Pin 1 to Pin 7
C44 (0.01μF) Pin 1 to Pin 3
C15 (1000pF) Pin 3 to Ground
R32 (220Ω) Pin 7 to Ground
R39 (22kΩ) Pin 9 to Ground
Only problem was that R39's connection to Ground had worked its way loose and was floating a fraction of an inch above the chassis joint - probably a poor solder joint at this location (
) as it shares this chassis connection with C15 and R32. Fortunately there is a rivet that comes through the chassis at this location and this was used as a new Ground connection for R39 - what a nice, bright solder joint we now have!
V2 now oscillating away nicely on AM while FM reception is still good.
So there we have it - got there in the end with a bit of methodical detective work which was greatly aided and abetted with support from the Forum.
Thanks again to everyone -we're almost there!
