Cracking the 320 Case and Fixing a Turret Fault by Stewart Gebbie G8YQN

Developing a Fault

This might be interesting for those of you that have a UK/RT 320 that is having issues with the band changing turret switch.  In my Clansman collection I have two 320’s. One modified for LSB, still needing the case restored and the other I have restored, and it looks like a new one.  I take the latter out with its brand new Clansman battery, whip antenna, headset and Bergen. This set up is good for working the higher frequency HF bands and I go for walkies with it.

In early January we had a window of milder weather so I thought I would go out onto the cliffs above the sea near my QTH and make a few contacts.  The radio worked fine for the first 10 minutes but then it gave the high pitched whistle (or  not ready tone) indicating the band selection turret was in the wrong position.  I wiggled the switch and it would spring back into life…for about five seconds and this was subject to putting pressure on it anti- clockwise.  When I got home, and the radio had been sitting at room temperature for half and hour it worked perfectly.  SO – I was either going to have to figure out a repair or it was a summer outdoor radio only!

Going In…

I open the case, finding it best to remove the hex bolts from the back and slide off the back first, then remove the front. The main radio slides out of the front of the casing.

DO NOT GO INTO THE BACK SECTION AS THERE IS A WARNING THAT BERYLLIUM OXIDE IS PRESENT

Fault Finding

Once the case is removed there is a small cover on the top of the band change turret. Remove these six screws. You will now see the mechanism.  Now turn the band switch clockwise and you will see little metal fingers making contact with the turret.  For those of you old enough, this is just like the tuning turrets in the old VHF 405 line TV’s.  Each of the contacts rests in a little black receptacle. Turn the band switch clockwise until it is halfway between two tuning positions and the little metal fingers should all be resting against the black plastic retainer.  In my case two of the fingers were missing.  While in this mid way position use a strong light to check the metal fingers that have gone AWOL. In my case, they were hanging downwards.  Fortunately I always turn the turret clockwise as I knew that was the direction that put the least stress on the contacts.  With these two hanging down and if I had turned the control anti-clockwise I would have snapped them off.

Repair

With two little screw drivers I gently teased the fingers back into their correct positions sitting alongside the others in the black plastic retainer.

I rotated the band switch many times and they worked perfectly every time.  Problem solved.

Reassembly

I then started to re-assemble the radio for test.

Note that when replacing the back part of the radio, there is a tuning capacitor and this has to engage with the turret. This has a little half moon shaped black plastic projection that engages the back of the turret.  Make sure you have this aligned or you will damage this fitting to the point where the capacitor will not be suitably engaged.

The back panel also has two connectors to mate when reassembling so be gentle and make sure they engage otherwise you could bend the pins of the connectors.

Do not forget the gaskets when re-assembling. Then it is the boring task of putting back the zillion hex bolts on the front and back.

Testing

My test was then to stand the radio out as the temperature was a bracing 3C and leave it for an hour.  I then operated the turret and set, and it was back to its old self, working perfectly.

Lessons Learnt

The important lesson I learned from this is that you should always turn the band switch turret clockwise because it puts much less strain on the contacts.  If a contact does come adrift then you minimise the chances of breaking  a contact.  If this happens it is a much more difficult repair.  (A further risk of damage can be avoided by putting the set out of use immediately you experience the symptoms above and investigating the fault – ed.)

Post Mortem

What I believe happened is that I inadvertently turned the band switch anti clockwise and this pulled two of the contacts out.  In spite of their dodgy positions they were “kind of” making contact. The temperature change going outside and the resultant metal contraction or reduced springiness in the lower temperatures was just enough for them to lose contact.

Finally – ALWAYS TURN THE BAND-SWITCH TURRET CLOCKWISE IF YOU WANT TO PROLONG THE SECOND LIFE OF YOUR UK/RT 320.

Cheers

Stewart G8YQN