Wednesday, 25 May 2016

Clansman RT-351 Refurb and Mod

I had planned a very busy day today - a bit of radio work, and lots of gardening. But, its not stopped raining all day, so instead the hours have been spent in the workshop continuing with the Clansman refurbishment.

So first the outer case sleeve of the RT-351 got its second coat. Although i'd masked the labels on this, they are likely to be coming off anyway, as ive ordered nice shiney new ones. I will transfer the serial numbers over, and also engrave my callsign on them!

I also decided that, since dismantling the -351 is such a bloody ball-ache, I would carry out the 10m modification whilst I was about it. This involved removing all the electronics from the chassis. But then I had to do that anyway in order to paint all the casings.

With everything dismantled, came the delicate and scary task of modifying the flexible PCB. This as can be seen below connects everything in these sets together, and can become brittle with age and risk cracking, destroying tracks. Well, theres a good chance this set is over 30 years old! So I was taking no chances and handling it very carefully

I had to desolder and lift half of the flexi in order to modify the connection. This gave me a chance to try out my new £1 chinese solder sucker, which did a passable job. With the pads unsoldered I slowly expanded the hole for synthesiser pin 15 using small drill bits. The white wire was soldered to pin 15 and insulated from the surrounding PCB flexi pad with heat shrink. The pad then had the pink wire soldered to it. Finally, a grey wire for the ground connection was added, and the flexi replaced and resoldered.

In order to install the toggle switch to select 10m, I had to remove the drying plug and drill out the thread. This was a pig! It turns out the thread is a carbon steel insert! I'd painted the casing by this time and reinstalled the control knobs.  The switch can be seen in the photo below. Once they come from China the nut will be replaced with a waterproof rubber boot. This will be much more in keeping with the style of the radio, which is generally devoid of chrome.

With the mode done, the switch installed, and the paint dry, I began to reassemble the unit. Here I realised a problem - the switches have no end stops! I couldnt align the knobs and switches. Any other equipment i'd have winged it and just redone them if wrong, but thats not a good option here where its a real bitch to put together, and each time it has to be opened risks damage. I eventually discovered that each switch has two tiny dots molded on it, and when these are aligned, the 25kHz, 100kHz and 1MHz switches are all set to zero. The 10MHz switch when these dots align is set to 3. I had to resort to metering out the connections to discover that about the 1MHz switch! Essentially, with the knobs set to 30.000MHz, and the switches all with the dots aligned, they all fit together.

So, I reassembled the radio - and it didnt work!

Ok, so it kind of worked. As I tested the switches one of them slipped before starting to click, this was the 1MHz. I soon discovered that the setting was 5MHz out. I had to take it all apart again! But this time, I was more careful and the switches all aligned properly. There were just two problems now - abysmal modulation and no rx audio! This was down to poor earth from the audio module, solved by reinstalling the back part of the case.

Time to test the mod! I set the frequency, flipped the switch - Dead! No Rx, No Tx!

It took me reading the service manual, the operators manual, and taking Sam to karate and back to realise what was wrong! I'd set the wrong frequency! The mod fools the synth into setting the tens of MHz divider to 20MHz and not 30MHz. I'd set 36.9MHz, which gave 26.9MHz - well out of VCO lock range! I should have set 39.6MHz! That gives 29.600MHz - the 10m FM calling frequency. I'd just got the 6 and 9 the wrong way around!

With 39.600 set on the dials, I flipped the mod switch - perfect reception and transmission on 29.6MHz! A bit of checking revealed that the set now will lock right down to 27.750MHz!!!

Before putting it all back together, I want to look at doing one final mod - setting the Tx deviation to +/- 5kHz on both W and L audio settings, thus making my Tx signal good on both and making it just a volume control.

I also rebuilt and tested the newly pained RT-320, this is essentially finished now. The LiPo battery pack has got a coat of fresh paint, thats still drying.

And the GS carry frame and adapter plate are finished and the straps replaced. 

A few more days and the Clansman system will all be refurbished.

No comments: