A Lemon Pro 93? Or Squelch FUBAR?

[hastingsmedic]

Hello everyone... I just picked up a mint pro 93, and I think the squelch is inop.
When I turn it on it boots up fine, and everything seems to work fine, but I have no audio. I get keypad tones, and if I listen REALLY carefully I can hear slight static, but I can't hear anything... even with zero squelch on the NOAA bands I still can't get a loud white-noise sound out of it.

What gives? Did I get a lemon? I tried rebooting it but no change. Help!

Andrew
Hastingsmedic

 

[Al42]

You have audio - what you don't have is signal. Do you have the antenna connected? Do you have it programmed to an actual NOAA frequency? The receiver may be dead, or you may just not have it programmed to anything.

(Turning the squelch control should get you a point that the noise stops. That's where you want it - just at the point it stops, no further.)

 

[mancow]

Actually, I think he's saying the opposite. He has very little audio.
It sounds like a bad audio amp or a bad descriminator chip. I've seen that chip go out on three different RS units. However, when it does it usually results in loud open squelch that can't be closed with no audio even on a channel with a signal.
I wonder if your audio amp or something in the audio chain went out. Do you hear the proper audio signal that is just very low in volume when tuned to an active channel?


mancow

 

[Al42]

Actually, I think he's saying the opposite. He has very little audio.

even with zero squelch on the NOAA bands I still can't get a loud white-noise sound out of it.

How do you get "very little" from "loud"?

I wonder if your audio amp or something in the audio chain went out.

If it did, what's causing that loud white noise?

 

[mancow]

Hah... man I don't know, maybe I'm reading this to the point it no longer has any meaning.

Isn't he saying it's very quiet (no loud rushing squelch noise) but no demodulated audio. The only audio heard in the (very quiet) noise at all produced is the keypad tone.


mancow

 

[RadioMarkW]

Bring it back and exchange it. I had a Lemon 93 too.

But my new one works GREAT!

I like how you can costomize the chain search and even the ranges in the banks for chain search!

Take care,

Mark

 

[Al42]

Hah... man I don't know, maybe I'm reading this to the point it no longer has any meaning.

Isn't he saying it's very quiet (no loud rushing squelch noise) but no demodulated audio. The only audio heard in the (very quiet) noise at all produced is the keypad tone.


mancow

He said "loud white-noise sound ".

I agree that if the discriminator goes, the squelch is dead - because there's no noise for it to detect. But then you don't hear "loud white-noise" either. It sounds more like a dead IF, RF or synthesizer. Or ... it could just be that it's not programmed for anything in the area. No signal and a dead front end sound pretty much alike.

 

[hastingsmedic]

Hmmm, doesn't sound good....

With every other scanner I have, even if it isn't programmed for anything, I can turn the squelch to 'min' and hear the loud white noise.... this one won't do that... it is like the scanner is squelching everything.

I've tried programming in our local EMS freqs and standing next to the ambulance while I key the mike, and nothing...

I was hoping that it was a simply Pro-93 quirk, but I think you folks might be right about something inside being fried... guess I'll send it back!
Thanks for the input everyone!

Andrew

 

[Al42]

With every other scanner I have, even if it isn't programmed for anything, I can turn the squelch to 'min' and hear the loud white noise.... this one won't do that... it is like the scanner is squelching everything.

Okay, that helps.

Next step:

I assume that if you put your ear to the speaker you hear very low noise. If you turn the squelch control, can you get that noise to stop?

 

[hastingsmedic]

Still Trying

Okay, tried that, nope no change... the very low audio I can hear is the same faint electrical hum that you can hear from pretty much any speaker when a system is on... definately not the unmodulated white noise from an empty channel...

Andrew

 

[hastingsmedic]

Well, that would do it.

I gave up, and opened my 'mint' Pro 93 that had "Never Been Used", to find that one of the capactitors ("C156", one of three in a row on the left side) was literally blown all to rat poop. There was insulation from the capacitor from one end of the scanner to the other, and only a trace of the foil left on the board.
Well, that is just frigging great!
National Parts doesn't have any of the specs on these capacitors, and it looks like there are two or three different ones used on the board, so it is impossible for me to know which of the three is the correct one to order from Digikey.

If anyone out there has their Pro 93 open any time, can you tell me what colour the three capacitors are in a row, so I can re-order? When you remove the back of the scanner, you'll notice a silver box about 1" x1" fastened to the board. Along the left side of this box, there are three little tin cans about the size of a pencil eraser. One is light Blue, one is Black... I need to know what colour the third one is, because it is the one that exploded.

Andrew
Hastingsmedic

 

[pro92b]

C156 is 100uF 16V and you should be able to get one at an electronics store. The bad news is that something had to be very wrong to make the cap explode. From the schematic, the only thing that seems able to cause this kind of problem is if someone put the batteries in backwards. Chances are that much more is fried than just the capacitor and in fact if nothing else was wrong the radio would still work without the cap. You could send it in to Radio Shack for repair or sell it for parts. Trying to repair it yourself will probably be an exercise in frustration.

 

[Talktech]

lemon Pro93?---

If you replace the cap, use a 25 volt one and be SURE that the polarity is correct, or it will blow as well. Check for output of the audio amp chip--it is probably blown as well. If this model can be run by a plug-in wall wart, someone probably tried to use one with reverse polarity. T/T