Resurrecting an old Kenwood TS-50 HF Ham radio

Resurrecting an old Kenwood TS-50 HF Ham radio

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I’ve had a full ham radio license since I was a teenager, and when HF radio was popular in the 1990’s I bought a Kenwood TS-50 HF transceiver.

Since my last house move, its been gather dust, so this week I decided to to fire it up and see if it still worked after well over 10 years on the shelf

 

The first problem, was that long ago I got rid of the large heavy 12V 20A PSU that this radio needs, but I have been accumulating a stock of ATX power supplies, salvaged from PC’s.

 

 

Looking at the output voltages it has two separate 12V outputs, +12V1 which can deliver 14A and +12V2 which can deliver 15A.

Both these have a minimum load 1A.

However when I opened the case and looked inside, I realised that both +12V1 and +12V2 were connected directly together on the PCB, so there was an artificial distinction on the label which implied that these were 2 independent supplies.

There were only 2 wires connected to +12V2 (Yellow with a blue stripe), and I unsoldered these to save confusion.

Whether this PSU requires a load is also a matter of speculation, as it seems to output voltages on 3.3V, 5V and 12V even with no load, and they are all exactly the voltage they should be.

Initially I connected a 12V 50W filament lamp, as it was the easiest way I had to create at least a 2A load. However this lamp was very bright and got quite hot, so I removed it, and the PSU still seems to work OK.

In the longer term, I cost effective source of load resistors, as 50W 6 Ohm resistors seem to be sold to fix problems on cars where people have replaced their flashing indicators with LED replacement versions.

These can be found on eBay etc, by searching for

50W 6OHM LED Load Resistor

So I have ordered a pack of these, and intend to put two 6 ohm resistors in series, to provide 1 Amp of load.

 

Having resolved the lack of a power supply, I applied power to the rig, only to find that it turned on immediately and all the VFO band presets had been reset.

This wasn’t much of a surprise, and I guessed that an internal memory backup battery must have gone flat.

So after looking around on the web, I found that the normal solution is to use a button cell in a holder, and either solder it in place of the existing battery location, or use flying leads to the new battery.

 

 

In my case, the button cell holder, was one I had salvaged from another computer and it was too tall to solder directly onto the PCB, so I used the flying lead method, and encased the battery in a small plastic bag to prevent it shorting to the case etc.

I initially just covered the battery in insulating tape, but as the rig gets warm even just listening, the insulating tape tended to go soft and would eventually become unstuck. So the plastic bag is a better option.

 

With the new battery in place, when I applied power to the rig, it does not turn on straight away, and it also remembers the VFO frequencies etc when the power is removed.

 

The next job was to remove the TX frequency limiting that the rig had. This limits it to operate on the HAM bands that were valid in the UK in the 1990’s but since then, there have been changes to the bands, new bands have been introduced and band frequencies changed slighly

On my particular version of this transceiver, it has 3 diodes which need to be removed D3,D4 and D5 (earlier models only have 1 diode that need to be removed).

After this mod, I was able to transmit on the bands which previously I could only listen.

 

I managed to unsolder these from by heating with my soldering iron from the top of the diodes, as accessing the underside of the PCB would require removal of several ribbon cables, which could be hard to refit.

(The extra black wire seems to be some factory fitted modification, and I’ve no idea what it does, but it connects to a transistor on the other side of the PLL board via a diode)

 

With the modification, I was then able to access frequencies on the 40m band between 7.1 and 7.3Mhz and also the 2200m and 630m bands.

 

The final modification was the addition of computer control. Luckily the transceiver has a serial control “interface” port which is accessed by connecting to a 6 pin micro JST socket on the PLL board, via a removable plug on the base of the transceiver.

As I didnt have any micro JST connectors and none of the local components shops stocked this part, I ordered a plug (set of 10) from eBay, but it was going to take weeks for the plug to arrive.

So as I wanted to get this working as soon as possible, I managed to unplug the PLL board and partially remove it, while still keeping the ribbon cables attached, so that I could solder wired to the underside of the micro JST connector.

Only 3 wires are needed for serial TX, RX and GND. I use wire-wrap wire as its small and it also it breaks before the track on the PCB would break, if I pulled on the wire too hard. To stop the wires breaking I put some hot glue on them where they were soldered to the PCB.

 

At the moment these wires run out though some air holes in the case and are connected to a CP2102  USB to serial adaptor.

 

 

Initially this didn’t work as I followed some instructions I found online which suggested that TX on the transceiver needed to be connected to TX on the USB to Serial adaptor, however in the case of my adaptor this was not the case, and I needed to connect TX  <–> RX

Additionally I shorted the serial flow control pins on the socket, as my USB to serial connector did not support them.

 

With these connections the correct way around, I was able to use the free (old) version of Ham Radio Deluxe to control the rig.

I was initially hoping to be able to put the USB to serial adaptor inside the transceiver and perhaps have a USB socket on the back panel or the side. However I’m not keen on drilling holes in the bottom panel, as the rig is still in mint condition, and hand drilled holes never look as good as the original cutouts, mainly because the paint is applied after the holes were punched.

So the next best thing appears to be to either re-purpose the external speaker 3.5mm jack socket on the rear panel, or possibly drill a hole in the rear panel and fit another 3.5mm jack socket, and fit a stereo socket, and then use an external USB to serial adaptor

However, neither option is particularly easy, because I would need to remove the PA tuning switching board from the underside back of the rig to access the back of those sockets, so I will have to leave that until I get some more free time, and some courage to take the rig apart a bit more.

 

 

Finally I’d like to try out some digital transmission modes, but that will need to wait for a mic plug to arrive in the post.

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