Sunday, 12 June 2016

RT-320 RF oscillator alignment

Phew! Never have I worked on a radio before that way so physically tiring to do!

I realised that this Testbed radio was a bit out of alignment, so this morning before any further mod work, ive at least brought all the RF oscillator sections in the module 3 turret tuner into correct alignment.

I decided probing the synthesizer VCO pin was a bit risky, so followed the service manual and used TPq in module 3a. This required removing the ATU module 4!

The main reason I took the above photo is as a record of where that pink wire goes! Ive unsoldered it to allow me to put the ATU module somewhere safe.

Inside the tuner turret, there are various trimmer capacitors and variable inductors to adjust. The caps proved to be a little sticky but moved ok using a proper trimming tool.

The inductors though are awkward. These have a very odd little adjuster, which required the fabrication of a special tool. For this I adapted an old brass tipped trimmer by soldering on a couple of PCB header pins, and adjusting the spacing between them

All the RF oscillators are now aligned within spec. The only one that is not within the manual specifications is range 1: 2.0 - 3.1MHz, as I have adjusted this to give full coverage of the 160m band, so this is now 1.8 - 3.1MHz! I couldnt get the VCO volts exactly as the mod suggested, going to about 95v instead of 90v at the top of the range, but the set locks at both extremes.

I'll deal with receiver alignment later. For now, I think the final mod, the S-meter, is in order. With that done the only thing left will be to again remove the mother board, physically remove the synthesizer, and add a ribbon cable to its pins to allow connection of the microcontroller in due course.

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