New enclosure for the MST400 40m SSB transceiver

Last year I completed an MST400 MK1 SSB transceiver from Ozqrp.com - see post here

This worked well but I was not happy with the plastic box I used for the enclosure .  Sometime later I cam across a nice metal box on eBay and decided it would be more suitable for my MST400 .

Here is the finished product in the new enclosure -

Trio TS-120S PLL unlock fault

I recently acquired a Trio TS-120s HF transceiver with an intermittent fault - when powered up the PLL would fail to lock , resulting in no TR or RX and no digital display - just two dots.

PLL Unlocked

Once the set warmed up the PLL would eventually lock , first on 14MHz then  on the other bands.  Once the set had been switched off for a while the PLL would return to the unlocked state on power up .


I checked the PLL board for cold solder joints but nothing obvious was found.






Tapping on the boards when the PLL was unlocked made no difference , so I tried gently heating the boards using a hairdryer , this helped pinpoint the problem - the PLL came in to lock whenever the area near the back right hand side of the AF board was warmed up .
I didn't expect that a fault on the AF board would prevent the PLL from locking , but underneath the AF board is the carrier board which produces a ~8MHz signal which is fed to the PLL board .

Testing J19 CAR signal

I attached a frequency counter to Pin2 of J19 on the PLL board and a volt meter to TP1 on the PLL board .  When the PLL was unlocked there was no 8MHz signal reaching the PLL board . When the CAR board was gently heated  the 8MHz signal appeared and the PLL locked .

An article on mods.dk indicated that there was a common fault where the  carrier board would fail to oscillate due to the Q1 transistor going low gain, so I removed the AF board to gain access to the CAR board to replace Q1 .

AF Board

AF board removed 

CAR board removed

I removed Q1 ( 2SC460)  and tested it on a transistor tester - the device was ok , but the gain (hfe) was very low at around 29 . It should be about 100 for this device.

Original Q1 - low gain

After warming the faulty transistor the hfe came up slightly to 36

Original Q1 warmed up

This additional gain was probably enough to get the oscillator to start up once the transistor warmed up.  I tested the new replacement transistor prior to installing it - it had a hfe of 107

Replacement Q1 

After re-installing the CAR and AF boards I powered on the set - the PLL locked immediately on all bands !

PLL Locked

Codan 9780 HF Transceiver

I recently acquired a used Codan 9780 HF transceiver. This is a commercial HF SSB transceiver that provides 15 user programmable channels in the 2.25 to 30MHz range.  Power output is 125w of USB or LSB.

Codan 9780

The radio was purchased without a microphone and I thought it would be straightforward to find a suitable replacement microphone, however a search online only found original replacement microphones at AU$ 389  - way more than I was prepared to pay.

I found the schematic of the Codan keypad microphone on the aboutcodan.blogspot.com blog - this is a very useful blog with lots of information on Codan 9xxx series radios , including how to enable programming of channels from the control panel.
The microphone schematic is here .
The schematic indicated that it would be possible to connect a normal dynamic microphone to the radio , leaving out the custom keypad controller.  I had an old Pama dynamic CB microphone that looked suitable , so the next problem was to find a suitable microphone plug. Unfortunately the 9780 has a very custom 7 pin connector - I wasn't able to find a suitable connector at a reasonable price , but I found an eBay seller in Australia that had a replacement Codan microphone cable and plug for AU$ 65.  This was ordered and it arrived about 2 weeks later .  Mic plug shown below.

9780 mic plug

I found the pinout of the MIC socket in the Codan 9360 reference manual available here .
Note - this pinout is viewed from the perspective of the radio front panel, not from the microphone plug.

Microphone socket pinout

It was necessary to link pins 1 and 7 together in order to route the received audio to the front panel speaker.  This is illustrated in the microphone schematic .

On connecting the microphone I found I was still not getting any audio out of the front panel speaker , so I plugged in an external speaker into the LS jack on the back .  This worked.

On removing the front panel and testing the speaker I found that it was open circuit .  The speaker is a 66mm diameter mylar speaker  - maplin had a suitable replacement ( code VC86T)  . 

front panel speaker

Once this was replaced I tried the radio out and made a number of contacts on 80m , 60m and 40m and received good audio reports.  

Having only 15 channels is a limitation, but I plan to use it mainly on 60m where we only have access to 5 spot frequencies in Ireland.

TS-120v repair - part 2

I spent some time today continuing my attempts to repair the TS-120v I described in part 1 here .

The radio is now usable on SSB on 80/40/20M however it still has no output on 15M and 10M , other faults are a non-functioning S meter and no output on CW.

One of the common faults that can cause a none-functioning S meter is the relay on the IF board.
There is a well written article on the replacement of this relay on the Kenwood TS120_130 yahoo group  - "TS130v Omron relay removal/replacement" Based on this I ordered 2 NF4EB-12v relays - these are a drop in replacement for the original Omron LZN4 which is now obsolete.
It seems that the Matsushita NF4EB relays are also obsolete , so it was hard to find a source for them.
I eventually found an ebay seller in China  that had them in stock for $6 each - see ebay item 381034198000

Omron LZN4 on left. Replacement NF4EB on right

IF board removed from the transceiver

I replaced the relay using the instructions in the link above.  It was fairly straightforward however I needed to use solder braid and liquid flux to cleanly desolder the 15 pins.

IF board fitted back into TS-120v with new relay (orange)

After replacing the IF board and carrying out an on-air test I now have a working S meter.

working S meter

Next I need to fix the CW problem and the lack of output on 15/10M

MST400 QRP SSB Transceiver

A couple of years ago I built a DDS VFO from ozqrp  - see post here.

I was pleased with the design and decided to buy the PCB for the accompanying 40M SSB transceiver the MST400 v1 .

MST400 v1

This is a 40m SSB transceiver that has a power output of at least 5 watts of SSB.
from the manual , the specs are -

1. Complete SSB transceiver on a single PCB (just add a VFO).
2. Superhet receiver using a 4 pole 10MHz crystal filter.
3. 5W PEP minimum power output using a rugged power MOSFET output stage.
4. Unwanted sideband suppression is typically 40dB.
5. All spurious transmit outputs below -45dBc.
6. AF and microphone gain controls.
7. Easy to adjust and set up.
8. Front panel LED transmit power and modulation indicator.
9. Plenty of audio output to drive a loudspeaker.
10. High quality double sided PCB with groundplane, solder mask and silk screen.
11. Simple and easy to build using all through hole components.
12. No complicated coil winding required. Uses inexpensive commercial coil assemblies for tuned circuits.

I just bought the PCB and was able to provide most of the components from the junk box , the rest were purchased from bitsbox in the UK - my normal source of components.

Construction was completed over the course of a couple of evenings and was very straightforward thanks to the well written manual .

I boxed it up in a plastic case with aluminium end panels. I would have preferred to use an all metal case but this seems to work ok .  I may line it with self adhesive copper foil for screening purposes at a future date.

My heatsinking on the IRF510 output transistor is probably not ideal , but it didn't get too hot in use while producing about 8w power.

MST400 in case

While it is not fully finished it works well and I have had many contacts throughout Europe on it. .

The MST400 v1 has since been superseded by the v2 version and is now available for 80M, 40M and 20M as a complete kit .  Well worth a look for anyone interested in building their own QRP SSB transceiver. 

Sinadder 3 and Pye SG5U, SG3V signal generators

One of my radio interests is modifying ex-PMR radio equipment for use on the VHF and UHF amateur radio bands.  PMR radios tend to cover quite a wide frequency range, so once they have been programmed or crystalled on the desired frequency they normally need to be aligned to achieve good sensitivity. This can be done while receiving a signal and adjusting the front end for best quieting but better results are achieved using a signal generator and a SINAD meter .

Sinadder 3

SINAD refers to the measurement of 'Signal and Noise plus Distortion' and is a useful way of measuring the performance of a receiver.  The Sinadder 3 manual provides a good description of how this measurement is used to quantify FM receiver performance, but in summary an FM RF signal at the receiver frequency is modulated with a 1KHz audio tone at 5KHz deviation and fed in to the receiver.  The SINAD meter is connected to the audio output of the receiver under test and samples the demodulated 1KHz audio tone.  This can detect the amount of distortion introduced to the 1KHz audio tone bu the receiver. The lower the measured distortion the better the receiver performance.
Typically a measurement of 12dB SINAD is considered a usable received signal, so the aim of alignment via SINAD is to adjust the front end of the receiver to achieve the 12 dB measurement for the minimal level of input signal.


Professional radio service shops tend to use integrated communication test sets or service monitors costing €1,000's for this task but it is possible to pick up older test equipment for a reasonable price which is still very usable for amateur use.

I bought a second hand Helper Instruments Sinadder 3 meter to perform the SINAD measurements but I needed a VHF and UHF signal generator capable of producing an FM modulated output.  My existing signal generator only did AM modulation and more recent signal generators cost hundreds of Euro.
I contemplated trying to build some form of DDS synthesized signal generator using an Arduino and an si5351 device but couldn't see an easy way of frequency modulating it with the required 1KHz tone.  Instead I found a pair of vintage Pye VHF and UHF signal generators going for a good price on eBay.  Shipping from the UK wasn't cheap due to the weight of these devices - way more than the cost of the signal generators themselves , but it was still a good deal for some classic test equipment .

• The Pye SG3V covers VHF 66MHz to 150MHz
• The Pye SG5U covers UHF 300MHz to 480MHz

Both are capable of FM modulation with a 1KHz signal with variable deviation from 5KHz to 15KHz . Still useful for wideband amateur equipment, however modern sets tend to use narrow 2.5KHz deviation . If I can find a circuit diagram for these I may see if I can modify the deviation range to go from 2 to 5KHz , but it will do for the moment.

They both have a high quality signal attenuator to allow the output signal to be reduced to a low level , these are graduated in uV. Not sure how accurate the calibration is - the calibration label says it was last calibrated in 1986 ! however it is not critical as I will be tuning for maximum sensitivity rather than trying to perform an accurate measurement.

The signal generators were both manufactured by Pye Dublin - I hadn't been aware that Pye had a factory in Ireland , but it seems that they did have a manufacturing facility in Dublin which closed in the late 1960s.


Using this configuration I have successfully aligned several PMR sets including a Kenwood TK-859
, Kyodo KG107, Tait 2020, etc.

Pye SG5U and Sinadder 3 aligning UHF Tait 2020

The alignment procedure differs depending on the radio being aligned - a search on the Internet should turn up the service manual for most common radios. At a high level the procedure is -

• connect the signal generator to the antenna input of the radio being aligned. 
• connect the SINAD meter to the speaker output of the radio. 
• adjust the frequency of the signal generator until a signal is heard in the receiver
• set the signal generator to produce a 1KHz tone with 5KHz deviation. 
• adjust the signal level until 12 dB is indicated  on the SINAD meter
• adjust the front end of the radio according to the radio's service manual ( using an alignment tool not a screwdriver - the ferrite cores can be fragile) try to get the meter to swing as far to the left as possible. 
• next reduce the signal level from the signal generator to bring the sinad measurement back to 12 dB and repeat the adjustments. The aim is to achieve 12 dB SINAD for the minimum amount of input signal level. 

Trio TS-120v repair - part 1

I recently picked up a used Trio TS-120v that was listed as 'spares or repair' on eBay .
The TS-120v is a low power version of the TS-120s HF transceiver and it provides 10w of USB/LSB/CW on the 80/40/20/15/10M bands.

On receipt of the TS-120v I powered it up and connected it to my HF antenna - it received well on all the HF bands which was promising , next step was to try the transmitter.  The radio did not come with a microphone , so I wired up an old Shure 527B microphone using the wiring information available in the TS120v operators manual. When I tried to transmit into a dummy load there was no output on any of the bands on either SSB or CW.

The radio was opened up to perform a visual inspection - it was covered in dust and dirt - not surprising considering it is more than 30 years old.  An aero-duster removed most of this and some servisol switch cleaner was used to clean the wafer switches used for band switching.

Once the dust was removed I could see that there was an electrolytic capacitor (C63) missing from the RF board - looks like the capacitor died violently as its legs were still left in the PCB.

missing C63

No sign of it loose in the radio though. The TS-120v service manual was obtained from the very useful Kenwood TS120 and TS130 Yahoo group.  This indicated that c63 was a 10uF 16v electrolytic  - more importantly it showed that it was possible to gain access to the underside of the RF unit PCB without having to remove it and the band switching hardware from the chassis .  This is accomplished by removing the IF unit and a shield plate.

Access to rear of RF unit under IF board

Once I had access to the rear of the board I de-soldered the old capacitor legs and replaced the missing capacitor. Shining a strong light through the PCB from the top down allowed me to see which solder joints belonged to C63.  Unfortunately the replacement of C63 did not resolve the TX problem , so further investigation was required.

Next step in the investigation was to remove the final board from the radio and check the output transistors. On removing the final board I noticed several problems -

Burnt R3 and R5

- Resistors R3 and R5 on the final board were burnt looking and R3 had actually split in half.

- There was a 3 pin connector at the end of a cable from the filter board that was not connected to anything.

- The final board appeared to be installed back to front , the coaxial cable from the RF Unit was connected to the output of the Final board and the cable from the filter unit was connected to the input of the Final board.

unconnected cable from filter board J44

It looks like someone had attempted to repair this radio and had re-assembled it incorrectly .

First step in attempting to repair the final board was to replace the burnt out 15 ohm resistors R3 and R4. At this stage I also tested the final transistors and found that these were both faulty.

Final transistors Q2 and Q3 are 2SC2509 NPN RF power transistors - I wasn't able to find exact replacements , but a search on eBay turned up a matched pair of 2SC1945 transistors which are a direct replacement. Having a matched pair ( same gain) is important in an amplifier such as this that only has a single bias adjustment for both devices.

matched pair of replacement final transistors

I replaced the final transistors and applied some fresh heatsink compound.

Next I needed to find out where the 3 pin cable was supposed to go .  From the service manual I can see that there is a Q5 transistor on the final board that is connected by a cable J41/44 to the filter board .

Schematic of final and filter board TS-120v

This is a 2SD235Y switching transistor that is mounted beside the finals board so that it can share the heat sink. Another trip to eBay found a suitable replacement.

Final board showing mounting of Q5 on right.

At this point it was time to set the bias on the PA .  The manual for the TS-120v only had a bias adjustment procedure for the TS-120s which has a different PA  - 100w instead of 10w, however the TS-120v shares the same final board with the later TS-130v and the service manual for the TS-130v does contain a bias adjustment procedure.

ts-130 bias adjustment procedure 

rather than remove the bias link on the board I just disconnected the supply line from pin 14A and inserted an ammeter in line.  To provide some degree of protection against the possibility of blowing my new PA transistors I placed a 2A fuse in the supply line to the radio.

On switching to TX I could not measure any bias current flowing , so I probed the base voltage of the 2 final transistors and measured only 0.05v irrespective of the setting of VR1 . It should have been somewhere around 0.7v .  Further investigation found that the bias transistor Q4 was also faulty. Back to eBay to buy a replacement 2SC496Y transistor.
I replaced this and went back to setting the bias current , this time I was able to adjust VR1 for 100mA as per the manual .  Things were looking up !

After re-assembling the final board into the radio I tried to transmit again - now I am getting between 8 and 10w out on 80/40/20m on SSB.  Not quite there yet though, only seeing about 2w on 15M and nothing out on 10M.  Also not getting any output on CW but it is still a lot better than when I started .

More to come .....