Weird superstar 3900 squelch/S-meter issue.

[Mudslinger]

Hello everyone.

My EPT360011Z 3900 has a strange issue going on.

Bear with me on this because it is tricky to explain.

On SSB the S-meter constantly reads S-9 of noise, but when a signal appears the needle only deflects slightly more than this, say around +20 even with a very strong signal.

The band is quiet in terms of noise according to my other radios, so I suspected an adjustment issue with the S-meter. When I turn the meter back down to read S-1 of noise (which is the same as on my other radios) the meter doesn't move any further than S-3 even when the station just down the road is on and the pre-amp is on.

There also seems to be an issue with the squelch on SSB, it needs to be at around 3 o-clock to silence the noise, even with the antenna unplugged. Looking at the circuit diagram, it seems the circuit for the SSB S-meter and the squelch are linked.

The radio does seem to be picking up the stations ok and isn't deaf, but the S-meter and squelch on SSB are all to pot.

On AM and SSB modes the radio and meter work perfectly, as well as the squelch which is in the normal position (About 11 o'clock) which seems to suggest a component fault in the SSB/Squelch circuit. Maybe D13 or TR14?


Has anyone have any other idea as to what I should look at? The radio is still useable, but it is really anoying.

Many thanks

[cb4ever104]

Hi Simon .

Never seen that one before , but it sounds to me like an actual issue on SSB RX . If the radio is generating S9 noise by itself on SSB , then the squelch would seem to be working normally . If it's OK on AM , then I'd start looking from where the RX path branches off for SSB , and follow that route .

Sammy

[Mudslinger]

Hello Sammy, thanks for the reply.

I don't think the radio is producing S9 of noise by itself as I can still hear weaker stations above the noise. It is as if the s-meter/squelch circuit isn't differentiating between stong and weak stations. Weak stations are above the noise, stong stations are above the noise but in both cases they give roughly the same S-meter readings.

It is a bit difficult to describe. If the band has some action later I will try and post up a video.

[cb4ever104]

Hi Simon .

So with the antenna disconnected it drops down to S0 on SSB ?

Also . Sensitivity on SSB is better , so you might have the problem on AM/FM as well although it won't be as noticeable .

As you say . Sometimes you need to see it to get a gist of what's going on .

Sammy

[Mudslinger]

Right, just has another look at it. This time there was some proper skip running.

With the antenna plugged in there is S9 of noise, stations are coming over the top of it no problem. With the antenna disconnected the noise drops to zero and the sqelch action is back to where it should be.
AM and FM on the same frequency have zero noise whatsoever, but USB and LSB do. Switching on the pre-amp doesn't increase noise to any level above what I have on SSB.

I stick the Lincoln on the Richard on the same frequency and mode, and noise is zero, but the stations I am receiving are coming in strong like they should be.

It is as if the 3900 is picking up noise from somewhere that the other two are not, even though the rest of the setup is the same.

[163TM847]

Sounds to me someone has been playing with the SSB coils L13/14, Try adjusting L14 slightly on a quiet channel till the meter sits around S1

[Mudslinger]

Nick I might just send it to you for a look. My latest President Richard could do with looking at as well.

I will try tweaking those cans first though when I find my trimmer tool.

[cb4ever104]

I will try tweaking those cans first though when I find my trimmer tool.

Let us know what happens Simon , would you ? I thought "playing with those cans" (no pun intended ) would only worsen the sensitivity , so I'd be interested to know what happens .

S.

[Mudslinger]

I will do Sammy, They haven't been touched since it was last aligned, so I am thinking the radio has somehow gone off tune on its own. Maybe nudged whilst in the post or something?

Normally on SSB when you turn on a pre-amp the noise gets louder and the S-meter will move across. But in this case it makes no difference whatsoever.

It is very obvious that something isn't right when you compare it to one of the other radios I have here.

[astradyne]

Without looking I can't be 100% sure, but aren't there separate presets inside the radio for FM/AM and SSB squelch?

[Mudslinger]

No there is only one.