[Premium-Rx] RA-1772 Question.

[David Schofield]

Hi All,

I've just spent most of the afternoon trying to sort out a wierd out of lock fault on one of my RA-1772's without much success, so thought I'd throw it open to the group in case anyone has seen anything like it before. The symptoms are as follows;

1. The out of lock LED is illuminated on every band.
2. The HF local oscillator is 200Khz high on all bands. I.E. Instead of being 35.40000Mhz when tuned to 0.000, it is 35.60000Mhz, it carries on like this right through all the bands.
3. Their is no output from ML11 pin 1 (TP11). Although if pin 1 is isolated the output returns correctly. The signal only goes to two IC's, ML12 & ML6. I have replaced all 3 IC's, assuming first that either ML12 or 6 was loading the output of ML11, and then that ML11 was not capable of driving the other gates, but with no success.

At this point I'm at a bit of a loss. I'm about 98% sure the fault is on the HF oscillator PCB, and do have another Rx that I can borrow a known good board out of, but as they are rather tedious to swap over, I thought I'd ask the group first....

I'm pretty certain that the problem is that the varactor drive voltage to the three HF oscillators is incorrect, due to the logic issue around ML11, but can't get my head around the circuit.

The receiver is working appart from the wierd out of lock issue, in fact it is possible to tune it and receive stations OK, but obviously they are all on totally the wrong frequency due to the incorrect LO.

As usual, any suggestions would be much appreciated.....

Cheers,
Dave.S.