Swinburne DR600 Airband Radio Tuning Problem - Help!!!!

[HEAVY747]

I purchased a Swinburne DR600 airband monitor off a old gentleman who had obvosly tampered with it. The LCD display does not increment with the movement of thumb wheel but I get hiss output from speakers and some airband transmissions.

See links:

YouTube - bizzwhizz's Channel

YouTube - bizzwhizz's Channel

Circuit diagram:

esp@cenet original document

I have turned it on for nearly 24hrs to drain battery with hiss still coming out.

What could be wrong please help!!!!!!

Many Thanks
HEAVY747

[Comint]

Originally Posted by HEAVY747

I purchased a Swinburne DR600 airband monitor off a old gentleman who had obvosly tampered with it. The LCD display does not increment with the movement of thumb wheel but I get hiss output from speakers and some airband transmissions.

What makes you think that the set has been tampered with.

It is fairly common to get hiss from unsquelched AM audio when not in receipt of a strong RF signal.

Assuming the referenced circuit is for the subject radio, I notice there are a few errors in the diagram. For example, TR 6 only has 2 connections instead of three.

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A casual analysis of the circuit diagram, would seem to indicate that the diodes and associated trimpots in 31, serve as 'fine-tuning' of the crystal frequencies. And VR1 (the thumb wheel) provides the variable voltage to the two Varicaps (aka varactors) in the Variable Frequency Oscillator 32, to change the frequency when in Manual mode. The fact that movement of the thumb wheel does not invoke movement of the frequency would imply missing voltage by way of 'open circuit' or 'failed component/s'.

Do you get any frequency indication, when on one of the crystal channels.?

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Comint

[HEAVY747]

Many thanks for your reply - it turned out to be bad solder joints which were done back in 1982 last!! Also after re-soldering I adjusted the local oscillator and its associated variable cap trimmer and bingo it all works fine. To sum up bad solder joints.