142gtl transmits works modulation works pa works squelch works.just doesn’t have receive radio has been recapped and I have followed the alignment procedure not getting receive
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142 gtl no receive
- Thread starter kaos513
- Start date
Obviously your audio amp is good if the PA function works, and that also tells you the audio path is good as far as the CB/PA switch. In CB mode, is the audio leaving the CB/PA switch and getting to the External Speaker jack? If it gets that far, is it getting to the speaker? In each case if the audio arrives at a given part and doesn't go beyond there, you have the spot to start looking.
I'm assuming you have an oscilloscope, although I supposed a speaker with some wires attached could be used for this.
I'm assuming you have an oscilloscope, although I supposed a speaker with some wires attached could be used for this.
Does the S-meter kick around on channel chatter or line noise?
Crank the volume to max, then turn the squelch knob end to end. Should hear a gentle "thump" at the point on the squelch knob where the audio is being muted.
First question would be is this just an audio problem in a receiver that's pulling in signals? If so, you'll see S-meter movement.
Or are there no signals being fed to the volume control at all?
The volume control is a good dividing line to find out if you check downstream from there, or upstream from it for the failure. I'll apply the "Manual Digital Signal Injector" to the clockwise lug of the volume control. That's your finger laying alongside the shaft of a small screwdriver. Touching the tip to the volume control's clockwise lug should get you the AC hum you'll get from an electric guitar with a bad cord on it.
73
Crank the volume to max, then turn the squelch knob end to end. Should hear a gentle "thump" at the point on the squelch knob where the audio is being muted.
First question would be is this just an audio problem in a receiver that's pulling in signals? If so, you'll see S-meter movement.
Or are there no signals being fed to the volume control at all?
The volume control is a good dividing line to find out if you check downstream from there, or upstream from it for the failure. I'll apply the "Manual Digital Signal Injector" to the clockwise lug of the volume control. That's your finger laying alongside the shaft of a small screwdriver. Touching the tip to the volume control's clockwise lug should get you the AC hum you'll get from an electric guitar with a bad cord on it.
73
I can hear sound from speaker But not the usual static recieve also the volume does work as that noise goes up and down with volume control
I have my signal generator hooked up to antenna jack I get signal at the jack with my signal tracer
Kaos, I am wondering if the frequency alignment is that far off. In other words, your radio is on channel 19 am and you are injecting audio at the antenna jack on channel 19 am but the frequency alignment is so far off that the radio internally (not the dial) is on another channel.
When you switch modes, what do you hear in the speaker?
Diagnostics here....
Typical AM gives you a lower toned hiss, while USB an LSB are sharper higher tone in the hiss...
If you don't get these "tones" on your TV set...
Let alone the 142...
There may be a problem with the Routing of the Signal, make sure your IF'sections are working - not just in TX - but RX too.
The 142 - if you hear tones and hiss like the conversions are working, then that means something further towards the front end.
Could be something as simple as a blown input cap - 22pF or thereabouts.C29 onto an electrolytic in the PIN section called C169 if its value is not right - will "quench" a receiver to a point it seems too sluggish.
Hows the RF Gain control?
Does TR9 Diode D15 - that section even see any variability from that RF Gain knob when you rotate it?
Diagnostics here....
Typical AM gives you a lower toned hiss, while USB an LSB are sharper higher tone in the hiss...
If you don't get these "tones" on your TV set...
Let alone the 142...
There may be a problem with the Routing of the Signal, make sure your IF'sections are working - not just in TX - but RX too.
The 142 - if you hear tones and hiss like the conversions are working, then that means something further towards the front end.
Could be something as simple as a blown input cap - 22pF or thereabouts.C29 onto an electrolytic in the PIN section called C169 if its value is not right - will "quench" a receiver to a point it seems too sluggish.
Hows the RF Gain control?
Does TR9 Diode D15 - that section even see any variability from that RF Gain knob when you rotate it?
Another thing I would look at,
Usually where there's Fire - there's the smoke - but usually it's the other way around...
I'm referring to what section needed any repair to even get it to work?
IF it's pristine and no scorching - well then we're guessing...but if you have to fix a final or the tuning was way off...knowing the repair history can lead you to the right Bunny Trail and Stop up the Hole before Bugs' n' Friends make more...
So, if the Final had to be replaced, and now the receive quit, well, what else is in line with the Final?
ALC comes to mind - people change the values there in the circuit to "punch down" the clamping effects - so look past the final - into the out-there, the output network. - for is it not using the same input connector?
Elon in making Tesla - used Mel Brooks for a crutch to help people understand the effects of speed, - using a sense of humor
Why are we talking about Speed?
Well, it can also apply to troubleshooting conditions; you think are ok, but if not - one has gone back and revisited - even I have caught myself as well as others pointed out - errors done before - it's nothing new.
Just have to make sure
Because? A 142 has SSB mode, so it uses a sense tap for the ALC control - that means it is wired in back there - at the rear panel - in the output network - that uses the same area to tap it's received signal from - so if one works - you know there's two - make sure you can get a signal from that tap off - from that area.
Usually where there's Fire - there's the smoke - but usually it's the other way around...
I'm referring to what section needed any repair to even get it to work?
IF it's pristine and no scorching - well then we're guessing...but if you have to fix a final or the tuning was way off...knowing the repair history can lead you to the right Bunny Trail and Stop up the Hole before Bugs' n' Friends make more...
ALC comes to mind - people change the values there in the circuit to "punch down" the clamping effects - so look past the final - into the out-there, the output network. - for is it not using the same input connector?
Elon in making Tesla - used Mel Brooks for a crutch to help people understand the effects of speed, - using a sense of humor
- there's "Ludicrous"
and then there is "PLAID"
Well, it can also apply to troubleshooting conditions; you think are ok, but if not - one has gone back and revisited - even I have caught myself as well as others pointed out - errors done before - it's nothing new.
Just have to make sure
And does the conversion process work?
Do you hear changes in Hiss tone as you select the different modes?
For if you do, then locate TR13, that is the 1st place where BOTH the AM and SSB signals combine.
Only in the different modes.
It can be something like D8, or D9 - D10 or D11 (RF Switch) not working like they should.
Might want to look at TP3 (Bare lead of R29 or R28 in there)
TR14 puts current into the Emitter of TR13 when the squelch is on but uses two stages to do this - one is set up with a very high trigger hysteresis to accomplish this.
If you hear the thunk from the squelch as its knob is turned to open and close...
How is TR13 doing?
You say you recapped, but did you bother to check the BIAS, make sure the resistors are NOT out of spec.
TR13 is critical - uses a window for the Squelch to kill signal by changing the potential difference between Collector and Emitter of that Conversion stage - if the resistor (or cap) has gone bad, this changes the TR13's amplification ability and linear range of it - so it would act like it's dead and also would make it hard to hear the hiss.
You also said that the S - meter is dead, so that may mean IF section - this is not a 148 but Unidens next effort to make single strip IF conversions without a ton of Xtals and the PLL does all the mixing - it's not perfect but in this instance - I'm trying to isolate where the condition may be.
Since it uses two different IF strips - their split and the recombining - if you had a bad Mode, it would show up because you hear just fine in one mode- not the others.
But you have some hiss, just not a lot of it.
You have some S-meter - so if the AF strip was bad, it would make any reception weak but not kill the signal.
You don't have a lot of S-meter action - tells me were back to the main RF/1st - IF section - looking for signal.
Maybe...but...there's always the Elephant in the Room.
Does not rule out the D8, D9 and D10 and D11 - Germanium diodes being bad. The S-meter and final output from the IF stages - use these diodes.
But the lack of ability to hear clicks, pops - static noises from the internal noises made inside the radio also bothers me.
Do you hear changes in Hiss tone as you select the different modes?
For if you do, then locate TR13, that is the 1st place where BOTH the AM and SSB signals combine.
Only in the different modes.
It can be something like D8, or D9 - D10 or D11 (RF Switch) not working like they should.
Might want to look at TP3 (Bare lead of R29 or R28 in there)
TR14 puts current into the Emitter of TR13 when the squelch is on but uses two stages to do this - one is set up with a very high trigger hysteresis to accomplish this.
If you hear the thunk from the squelch as its knob is turned to open and close...
How is TR13 doing?
You say you recapped, but did you bother to check the BIAS, make sure the resistors are NOT out of spec.
TR13 is critical - uses a window for the Squelch to kill signal by changing the potential difference between Collector and Emitter of that Conversion stage - if the resistor (or cap) has gone bad, this changes the TR13's amplification ability and linear range of it - so it would act like it's dead and also would make it hard to hear the hiss.
You also said that the S - meter is dead, so that may mean IF section - this is not a 148 but Unidens next effort to make single strip IF conversions without a ton of Xtals and the PLL does all the mixing - it's not perfect but in this instance - I'm trying to isolate where the condition may be.
Since it uses two different IF strips - their split and the recombining - if you had a bad Mode, it would show up because you hear just fine in one mode- not the others.
But you have some hiss, just not a lot of it.
You have some S-meter - so if the AF strip was bad, it would make any reception weak but not kill the signal.
You don't have a lot of S-meter action - tells me were back to the main RF/1st - IF section - looking for signal.
Maybe...but...there's always the Elephant in the Room.
Does not rule out the D8, D9 and D10 and D11 - Germanium diodes being bad. The S-meter and final output from the IF stages - use these diodes.
But the lack of ability to hear clicks, pops - static noises from the internal noises made inside the radio also bothers me.