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 Circuit Diagram for Dick Smith Q-1312 RF signal generator
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 Return to top of page · Post #: 16 · Written at 10:17:45 AM on 5 August 2019.
Keith Walters's avatar
 Keith Walters
 Location: Sydney, NSW
 Member since 16 January 2008
 Member #: 219
 Postcount: 61

FINALLY cracked it!
After being driven completely up the wall trying to find where the voltages were going on the oscillator PCB, I discovered that the plates of the 2-gang air-spaced tuning capacitor were touching.
On closer examination I found that the tuning capacitor frame is simply soldered together, and one of the joints had given way!
The reason this wasn't so obvious was because the oscillator ground PCB foil also had a high-resistance contact to the tuning gang frame, because the screws were loose! So instead of getting 0V I was getting something like 1V.....
No doubt my other Q-1312 has the same fault, and the "inexplicable" is now explained.
The 2SK55 FET is a real weirdo; no US-types (2N5485 etc) will work.
 
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