UNIDEN GRANT
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UNIDEN GRANT
Radio Make.Uniden
Radio Model.Grant
PCB number.PC-409AC
PLL number. MB8719
Hi I have just acquired a Uniden Grant (basically a president Grant) Like brand new, with pc board number PC-409AC, But it has a problem i do not have any audio rx or tx on usb, yet am & lsb work 100% perfect.I can hear a bit of a hiss on rx usb with volume full up,but not registering any signal level on the s meter & totally nothing on t.x!, Any idea's folkz??? as i really want to have it working 100% as even though its just 40 channels on midband i want to band it up,Thanks beforehand,Shaun
Radio Model.Grant
PCB number.PC-409AC
PLL number. MB8719
Hi I have just acquired a Uniden Grant (basically a president Grant) Like brand new, with pc board number PC-409AC, But it has a problem i do not have any audio rx or tx on usb, yet am & lsb work 100% perfect.I can hear a bit of a hiss on rx usb with volume full up,but not registering any signal level on the s meter & totally nothing on t.x!, Any idea's folkz??? as i really want to have it working 100% as even though its just 40 channels on midband i want to band it up,Thanks beforehand,Shaun
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There can't be that much wrong with it if it's only USB that's not working, should be easy enough to find the fault with the circuit diagram (see link below):
http://www.cbtricks.com/radios/uniden/grant/index.htm
Maybe start at the mode switch and, and then follow the diagram from there.
Regards,
Brian.
http://www.cbtricks.com/radios/uniden/grant/index.htm
Maybe start at the mode switch and, and then follow the diagram from there.
Regards,
Brian.
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Hi Brian , i already tried the mode switch & that seems fine as i swapped the lsb & usb wires around & it still did'nt work on usb.I already have the circuit diagram & block diagram, but i am not that well electonically minded in knowing how to read or understand the different componants/stages etc,hence why im here to ask,cheers,Shaun
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It sounds like there is a problem with either the Balanced modulator, or the actual USB offsets (the L.O. or I.F.).
I would suggest that you check for any bad solder joints around the adjustments of the oscillators, specifically at:
Loop Oscillator:
L22,L23, CT1 and D33 (USB)
I.F. Oscillator:
L30, L31, CT2 and D39 (USB)
I would suggest that you check for any bad solder joints around the adjustments of the oscillators, specifically at:
Loop Oscillator:
L22,L23, CT1 and D33 (USB)
I.F. Oscillator:
L30, L31, CT2 and D39 (USB)
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Hi again Brian mmm i see maplin actually do stock something that i may need for once, as they actually stock 1n4148's.Brian Morris wrote:They are probably just standard silicon diodes, in which case a 1n4148 will be fine as a replacement. Definitely worth cheching that L25 isn't open circuit as well.
Brian.
Is there a way i can test the d33 d37 & d39 diodes & how do i do this,
i would like to test them rather than a wasted journey to craplins.
I have also tried swapping L25 with L26 & it maade no difference,
Cheers, Shaun
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Check L28 and D38 too.
If you have a continuity tester, put both probes accross the diode, then swap them round, it should conduct one way but not the other way.
These days most multimeters have a diode test setting on them, in which case the meter should show 0.6 to 0.7 volts one way round, and nothing the other way round on a good diode.
If you're going to be fixing rigs on a regular basis, a multimeter is a must. They're cheap as chips these days.
Brian.
If you have a continuity tester, put both probes accross the diode, then swap them round, it should conduct one way but not the other way.
These days most multimeters have a diode test setting on them, in which case the meter should show 0.6 to 0.7 volts one way round, and nothing the other way round on a good diode.
If you're going to be fixing rigs on a regular basis, a multimeter is a must. They're cheap as chips these days.
Brian.
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Right Brian, i have tested D33,D37,D38 & D39 All only conduct one-way like you said at 0.6 volts or just above, so thats one we can cross off the list.As for can L28 I had already resoldered that.Brian Morris wrote:Check L28 and D38 too.
If you have a continuity tester, put both probes accross the diode, then swap them round, it should conduct one way but not the other way.
Brian.
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Hmm, seems a bit strange that, if anything I would have expected to see 8 Volts on AM and LSB since you say that AM and LSB are working properly.
You should see 8 Volts on the appropriate tag for the selected mode, if you don't then either the switch is knackered, or something has gone short circuit and is dragging down the voltage for that mode. Anyway, you've said that you already tested the switch by swapping the wires around.
By the way I think L25 is the USB choke and L26 is the AM choke.
I am running out of ideas Shaun, the last thing I can suggest is that maybe one of C125, C126, or more likely CT2 have gone short circuit and this is dragging down the 8 Volts for USB mode. If any of the caps show continuity on your meter then they're buggered.
Good luck,
Brian.
You should see 8 Volts on the appropriate tag for the selected mode, if you don't then either the switch is knackered, or something has gone short circuit and is dragging down the voltage for that mode. Anyway, you've said that you already tested the switch by swapping the wires around.
By the way I think L25 is the USB choke and L26 is the AM choke.
I am running out of ideas Shaun, the last thing I can suggest is that maybe one of C125, C126, or more likely CT2 have gone short circuit and this is dragging down the 8 Volts for USB mode. If any of the caps show continuity on your meter then they're buggered.
Good luck,
Brian.
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The alignment procedure and info is on the main site in the alignments section, I suggest that you look it up and try to go through it, and let us know if anything does not appear to be correct with your radio.
The alignment info is here:
http://www.radiomods.co.nz/grantalignment.html
The alignment info is here:
http://www.radiomods.co.nz/grantalignment.html
Re: Grant PC409 no LSB.
Check at R150 for 7.800 Mhz in AM, 7.985 MHz in LSB and 7.8015 MHz in USB.
Check at TP21 or the Emitter of TR20 for 33.975 MHz in AM, 33.9765 MHz in LSB and 33.9735 MHz.
If the 33.9765 and the 7.985 are missing then you will probably find that the mode switch or wiring is the fault.
My diagram for the Cobra 148GTL classic may help as it has the same Osc's
http://www.cbtricks.com/radios/cobra/14 ... redraw.pdf
Check at TP21 or the Emitter of TR20 for 33.975 MHz in AM, 33.9765 MHz in LSB and 33.9735 MHz.
If the 33.9765 and the 7.985 are missing then you will probably find that the mode switch or wiring is the fault.
My diagram for the Cobra 148GTL classic may help as it has the same Osc's
http://www.cbtricks.com/radios/cobra/14 ... redraw.pdf
Rick.
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