[EdHolland]

I tinkered at the weekend. With the board out of the radio, I was set to bypass some filters, to help identify troubles. On the underside of the board area where the 2.7 and 6 kHz filters are located, there was a block of foam rubber, adhered to the board using double sided tape. This took quite a bit of effort to remove, carefully picking the tape off with tweezers and then cleaning the residue. That made me consider if the residue was causing troubles, and pressing the meter probes on the foam rubber showed some current leakage (Ohms mode) and also nanofarads indication on the capacitance setting (leakages will sometimes appear as high capacitance). So, before doing anything further, the radio was returned to operation and the band-pass characteristics were checked. At first, everything seemed perfectly aligned, so I left the set running for an hour or two since it does warm up and drift a few hundred Hz when checked against WWV. Assessing it again after this, it seemed as if the slight downwards shift in pass-band had returned. Next up is to work out if this is systematic i.e. related to the frequency drift, or if there is a real change in the 455 kHz IF passband.

Who says modern can't be fun