Clansman PRC320 problems
 

Hello,
I have a Clansman PRC320 USB only.
I seem to have 2 problems.
Fault 1:-
It receives OK ish. Sometimes difficult to manually tune into an amateur received signal. Sounds like listening in a bucket!!! CW is fine though. (The band selector switch works and the unit out of tune tone stops very quickly on correct band selection.)
I thought the audio was wonky but when I tune into Shannon Volmet on 5.505 or 3.413 it comes over crisp and clear so no problem there.
Are these units difficult to accurately tune in to amateur band USB or AM?

Fault 2:-
When checking my transmitted signals on my general coverage receiver I find that on CW my transmission is very CHIRPY and on SSB it is unintelligible.
I have checked my PSU voltages and the tantalum caps measure ok on both the PSU and ramp unit.
Can these capacitors measure ok but still cause instability?
Is it worth changing these capacitors anyway?

Also if its not the PSU or synth capacitors what can it be?

Any advice is welcome.

Kind Regards

Dave
2EOEYR

Re: Clansman PRC320 problems
 

Your CW TX. Do you by chirpy mean that the tone of the DAH raises/gets lower towards the end of the sign but if you keep the key pressed a couple of sexonds, sending a continuous tone, will it then stabilize? Or does it keep going all over the place also on a prolonged tone?

The PRC-320 doesn’t sound ”pretty” on the first sign when starting a TX. But If you keep up the transmission and keep up a speed which doesn’t let it to back to RX, then it should sound ok. What you describe sounds more like not staying on frequency than just chirping to me. Does it behave the same on both low and hifh power?

Re: Clansman PRC320 problems
 

If you have a spectrum analyser then I suggest you have a close look at the carrier to see what exactly is going on.

It could be random jitter of the synth for some reason. One possibility I have run into on a Syncal was faulty logic ICs in the synth resulting in bizarre behavior. But it could just be a problem with the PLL.

Re: Clansman PRC320 problems
 

The tantalums may 'test' OK with a typical capacitor-tester that only puts a few volts on them - they can still be defective when shown 120V or so.

Apart from failing short-circuit [which does bad things to the transistor in the +120V inverter which works itself to death trying to pull the rail back up to +120V] the problematic failure-mode is minute and continually-varying leakage - which causes the synth VCO-rail to have a random wobble superimposed on it. The VCO will remain in-lock (so you don't get the 'unready tone') but will wander about over a few hundreds of Hertz in a way which makes CW/SSB reception impossible, and will get you some nasty comments if you transmit.

Replacement 'official spec' Tantalum capacitors are available but at a price of something like £80+VAT each! I replace mine with modern 160V 105-degree-rated low-ESR electrolytics which are available from the likes of RS at a much more wallet-friendly price.

Re: Clansman PRC320 problems
 

Chirp is a known symptom of the high voltage capacitors failing. Replace them in the synth and the PSU with modern electrolytics as soon as you can. Much better to catch it now than risk a damaged synthesiser!

I've recently had issues with low voltage tants in Clansman sets as well - these caps are not aging well!

Re: Clansman PRC320 problems
 

Hi All,

Thank you for replying with much needed advice.
I have tried 3 different PSUs with no improvement. All volts read ok.

I then replaced the tantalum capacitors in the PSU and the synth.
Tested yesterday and my transmission on AM mode is ok when I TX and listen in on my Yaesu HF transceiver.

But my TX on CW is not a tone but a squeal.

SSB transmission is unintelligible and almost like heavy whistle/feedback the moment the handset TX is pressed. Cannot be handset because it works on AM.

GMB asked me if I have a spectrum analyser. Unfortunately I don't and I admit I would not know how to use it effectively.
GMB also said it could be a problem with the PLL. Please explain ,what does PLL stand for?

I shall continue playing but Please keep the advice coming in.

Kind Regards

Dave
2E0EYR

Re: Clansman PRC320 problems
 

Have you tried a different handset/headset?
Have you tried a different, fully charged battery? (or PSU?)

I know this sounds basic, but these are the very simplest things to check and you'd be surprised how often such things are the problem!

I'll look at the EMER tonight see if I can work out any pointers for you. Do you have the EMERs for 2nd and 3rd line servicing?

Re: Clansman PRC320 problems
 

PLL stands for phase locked loop.

Well, I would actually not necessarily rule out feedback right away. I’we also got the VHF little brother of the PRC-320 (Plessey PTR-1851) and it had a bad feedback problem. Try disconnecting the headset/handset/mike and key an ssb transmission using the CW key. Does it still squeak?

Re: Clansman PRC320 problems
 

Listen to your carrier wave in AM TX using the CW mode on your Yaesu. Is the carrier a squeal too?

Re: Clansman PRC320 problems
 

Hello all,

Thank you again for your kind advice.

I thought yesterday that my TX freq was different than the RX freq!!! I found that detuning my Yaesu a bit reduced the CW squeal.

I checked the battery volts ok but to be certain changed it.

Today, I followed the possible feedback trail and found that when my Yaesu was turned down to barely audible then all my PRC320 transmissions were OK !!! On frequency, intelligible SSB and no squeal on CW. same with both headsets and both handsets I have.

I do not know what I have done but all is fine now. The strange thing is that I had had CW squeal / unintelligible SSB with my Yaesu off and with my wife walking around the garden listening in on a small general coverage short wave receiver.

So, I wonder if something is loose inside or switch contacts are dirty. I don't know and maybe tomorrow it will play up again!!!

I have yet to make contact with anyone to check it properly but I am more hopeful now that I think it is transmitting ok.

So, I have to eat humble pie and thank you all once again for your help.
I do hope I have not wasted anybody's time on this.

Kind Regards
Dave
2E0EYR

Re: Clansman PRC320 problems
 

The problem I had with my PTR-1851 using the Clansman handpiece was feedback from the earpiece part to the microphone. The clansmans (as most military rigs) have a monitoring audio going to the earpiece also during TX. The microphone was able to pick this up. Especially if the sound levels around the microphone otherwise were low. This meant that if I was silent and didn't speak into the microphone, then it picked up it's own sound from the earpiece. Since it picked it up as a sound with low volume the automatic gain control of the mic line stepped in and increased the gain. This raised the output level on the earpiece which then again was picked up better... The feedback loop was born and the TX modulation was a squeal.

I'm not 100% sure of what the real cause for the problems were in my case. Either the AGC had become "hot" raising the gain a bit too much. But I also found that the rubber gasket around the earpiece speaker probably helped the feedback. It had become stiff making the sound transfer much easier to the plastic body of the handpiece. Loosening the speaker a little from it's fitting made the problem disappear.

What I ended up doing was putting a small electrolyte over the speaker line. Can't remember exactly but it was probably something like a 15uF. What this does is that the speaker reacts a bit slower, not "popping" so loudly when sound is applied. It was enough for the feedback not to appear any more.

Re: Clansman PRC320 problems
 

I have also encountered this handset problem.

I got the impression that the handsets that did this were Racal-type handsets rewired for Clansman (they look like regular telehpone handsets rather than the smaller Clansman kind). I fixed it with a lowish resistor across the microphone.

I had meant to see if blocking up the hollow bit between the mic and speaker would help as the problem did not seem to be feedback through the air.

Re: Clansman PRC320 problems
 

Hello again !

Thank you for all your advice on my last problem. Which is now sorted as previously described. The set runs well.

I have bought another 320 for a good price and have tried this one out. It is slightly different in that the front panel is brown and not black as on my other one. Another manufacturer or a later build perhaps??

Anyway, this one has a fault which I ask for advice on before I open it up.

It receives well but does not appear to transmit.
Also, no tone heard when pressing the pressel or morse key when I try to tune.
The meter does not move on TX or tune.
It shows battery volts ok.
The ATU works by me tuning by EAR for the loudest noise.

The synth works, I think, because the out of band tone goes when the band switch
is placed in the correct position.

Any advice before I start will be welcome.

Kind Regards
David 2E0EYR

Re: Clansman PRC320 problems
 

A few things to check:

When you press the transmit-pressel, you should be able to clearly hear a relay click inside the PRC320. Does this happen?

If so, when in SSB/AM mode, do you hear any "sidetone" [your voice in the earpiece when you press transmit and speak into the mic] ??

If the relay's not changing-over you will not see much happening on transmit.

Re: Clansman PRC320 problems
 

Thank you for replying so quickly.
In answer to your questions.

When I press the pressel I hear a I hear a click inside the 320. Also what transmission I am listening to goes off as I press transmit but I hear no side tone in my headset or my hand set.(both headset/hand set work on my other 320).

So in summation. Something happens when I press the pressel on ssb / am but no TX,
side tone or meter movement.
When pressing the pressel in tune mode no noise or meter movement.

Where to start?
When I open up the unit soon I will look for anything disconnected/loose or any obvious damage and of course the PSU but really I am at a loss after that.

Kind Regards

David

Re: Clansman PRC320 problems
 

A few things here -

You are testing with the T/R link removed and a power meter and dummy load attached to the Tx BNC?

You have obtained the EMERs that describe the internal workings of the radio?

So, are you measuring ANY output power at all? Are you seeing an increase in current draw when keyed up?


Brown front panels are a result of fading due to UV exposure, which suggests your set was deployed to somewhere sunny.

There are three relays involved in Tx/Rx switching, one of which acts as master and drives the other two. If the set is working on receive, but absolutely dead on Tx, then the PSU module 5 should be fine but one or other of the supply rails is not being switched to Tx mode somewhere

Martin

Re: Clansman PRC320 problems
 

Thank you Martin,
I was testing with link in and watching the front dial meter.
I know there is no TX as my general SW receiver picks up nothing.
I will do as you say and remove link and fit power meter/dummy load.
I have had cases off nothing loose and all plugs mate ok. PSU spot on but as you say as its ok on RX then its something else.
I will read up and investigate the relay switching.
Thanks once again.

Kind Regards

David

Re: Clansman PRC320 problems
 

Do you have the EMERs? I can forward them to you in pdf if you PM me an email address (they are quite large)

You have checked for power in CW and AM modes? A fault like this is probably best investigated in CW mode at first so you know you should have a Tx carrier.

I would look to see if the 6v Tx rail is present when keyed up at first