[frsimen]

Hello Mark,

That's really good news. Let's hope that having got to the top of a hill, it doesn't reveal another one which was previously hidden!

The next problem is still on the logic board. This isn’t the fastest approach but it will help with the diagnosis of the fault.

With Fine Tune selected, check for:

+12V on terminal 8.
-6V on terminal 7

Pins 5 and 6 of IC1 should be 12V too. If they’re not, check L3 for continuity.

+2.7V approx on terminal 5.
+7.3V approx on terminal 6.

Terminal 1 should be adjustable over the range 2.7 to 7.3V by adjusting the coarse and fine tuning controls. The voltage should change smoothly as the controls are adjusted.

The approximate voltages depend on the voltage at the emitter of Q11. I’ve assumed 11.4V, that may be out by a few percent. If the voltages you measure at terminals 5 and 6 are much lower than expected, check Q11, C29 and R62.

There should be a 5MHz clock on terminal 3

Check at TP6 for a 5.3MHz signal. The actual frequency will depend on the setting of the coarse and fine tune controls. Check and note the range of frequencies that you obtain there. The output should be present over the full range of adjustment.

Move to the emitter of Q6. Use your oscilloscope and check that there is a signal present, the amplitude of which should be constant as the coarse and fine tuning controls are adjusted. Note the amplitude.

Move to TP7. Expect a 300kHz or so signal of at least 8V peak to peak.

DC voltage readings, based on 11.4V at Q11’s emitter.

Q4 base: 3.5V
Q4 emitter 2.9V
Q4 collector 9.5V
Q6 emitter 8.9V.

Paula