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President Mckinley 1011001 no tx/rx.

J

Josan

New Member
Jun 28, 2022
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Hi to all. I'm new here and new on the hobby too and i want to learn so i bought this president mckinley cb radio. It has no rx and tx. The radio powers in but the green light doesn't turns on but i can see it blink when i switch the radio on and turns it off

Hope the gurus here could teach me

Thanks JM
 

Can't go wrong with an old school President...I may have to drag my old Jackson export out and run it for a while. I think they are one of the best looking radios made.
 
I check the volatge on the MB3756, here is the reading.
1. 6.5v
2. 13.4v
3 13.4v
4. 0v
5. 13.3v
5. 0.5v
7. NC
8. 0.6v
 
That chip appears to be hosed. Either the transmit-only pin 8 will be hot for transmit, or the receive-only pin 6 will be. But if both of them are zero, that's a bad sign. Pin 1 is the kicker. This should be a steady 8 Volts DC all the time, transmit and receive.

Might be wise to check the circuit board pad where pin 1 connects for a short to ground before trying a new MB3756 chip. For that matter, if you unsolder JUST pin 1 and see 8 Volts from the loose pin, that would suggest a short that's overloading the chip's output current. Sure don't want to overload and pop a new chip.

73
 
Thanks for the reply nomadradio. I use the main filter cap as my ground source and i got 8.53v on pin 1 of the regulator but pin 6 still has 0 5v. I ordered a new regulator
 
I checked pin 9 of the and i has 8.59volts but the rest has low voltage pin 6 has only 0.85v.
 
nomadradio said:
That chip appears to be hosed. Either the transmit-only pin 8 will be hot for transmit, or the receive-only pin 6 will be. But if both of them are zero, that's a bad sign. Pin 1 is the kicker. This should be a steady 8 Volts DC all the time, transmit and receive.

Might be wise to check the circuit board pad where pin 1 connects for a short to ground before trying a new MB3756 chip. For that matter, if you unsolder JUST pin 1 and see 8 Volts from the loose pin, that would suggest a short that's overloading the chip's output current. Sure don't want to overload and pop a
Click to expand...
What would be my next step to do after replacing the regulator? Thanks

73
 

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