Uniden Grant gray plastic faceplate. Board number PC409AC. TP21 ( L21 secondary) I am lost and it probably is something simple
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Looking for test point on a old Uniden Grant
- Thread starter Low_Boy
- Start date
look for a resistor that has no paint on the lead in the vicinity of L20 it is TP1.
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TR20 is the loop mixer. You are trying to align the BFO's..... right? The alignment data you have is internet bullshit. What are you using to adjust these points? Freq. counter with what as a probe? Service monitor? AF gen? Try using the old Cobra 148 GTL alignment procedure on CB Tricks.
So I found a schematic the test point is the emitter of TR20. I am still having problems. First of all I am not using the right manual for the radio. I am using Sam's 221. I do not think the frequencies are correct. I can align it by zero beeting it against a known good radio. Of course I have all the test equipment. But I have another problem for some reason the radio keeps going out of lock. Someone has been in this radio before me. They unlocked the clarifier and did it wrong. I straightened that out. Then put that back to factory until I find the next problem. So tomorrow is another day.
That board is quite different than a 148 GTL. It is closer to a 136 GTL or a 140 GTL but still different.
The 8719 Grant and 148 GTL are close cousins. The 146 is not even close and the 140 is same as 142. The Grant and 148 are double conversion RX in AM. The other variants are single conversion. You say CB-221 is not the correct manual. Why not? Is your radio a *UNIDEN GRANT*? PLL MB8719? Is the CB-221 not for this chassis?
I'm at home, no Sams library here. Is L21 the tripler coil being fed from the 11.3258 crystal?
Best way to peak the tripler is to 'scope pin 17 on the 8719. Touching a probe to a circuit tuned to 34 MHz tends to change its resonance, such that if it's peaked with the probe tip touching it, that peak is lost when the probe is pulled away. The probe tip adds capacitance to the tuned circuit.
The tripler coil feeds into a mixer circuit, which feeds into pin 17. Probing the chip pin isolates the probe tip from the tuned circuit. Keeps the peak setting from being disrupted when the probe tip goes away.
73
Best way to peak the tripler is to 'scope pin 17 on the 8719. Touching a probe to a circuit tuned to 34 MHz tends to change its resonance, such that if it's peaked with the probe tip touching it, that peak is lost when the probe is pulled away. The probe tip adds capacitance to the tuned circuit.
The tripler coil feeds into a mixer circuit, which feeds into pin 17. Probing the chip pin isolates the probe tip from the tuned circuit. Keeps the peak setting from being disrupted when the probe tip goes away.
73
It must be Sam's 121. It is a MB8719 PLL. I believe my new problem is a bad solder connection. AM floats all over while SSB stays in tune. All modes can not be set to the specs in the Sam's 121. Someone was in this radio years ago. Unlocked the clarifier and did it wrong. They may have moved or changed something I have yet to find. I tried a new varactor diode and that was not the problem. Also PLL and all crystals are good. I just have to keep on it. I need 33.9765 USB, 33.9750 am, 33.9735 lsb. So Sam's says. I am getting 34.98xx and can align all 3 modes which puts receive off center with the clarifier. It has been driving me crazy. The only thing I see is a purple wire on the mode switch that may have been moved but I have no way to double check it. I do not have another radio like this and Sam's does not show a purple wire in the schematic.