I traced to white wire from the switch to a small board and measure that contact against the ground. Could you help me find TP7 or 8? I am not good with schematics.
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Cobra GTL 2000 Power up Issue
- Thread starter AJAY0618
- Start date
Shadetree Mechanic
Delaware Base Station 808
On some radios, the clock can be set to turn the radio on at a certain time. I am not sure if it is a feature on your radio.
Remember that the power switch in this model opens the ground side of the power feeding the radio circuit board. The hot side is always connected.
The power switch is a famous failure in this model, and not a lot of trouble to test.
It is a two-circuit switch and only one circuit is connected. Two jumper wires will put the unused side into the circuit if the factory-wired side of the switch has failed. Gets you a few more years before having to find a replacement switch.
73
The power switch is a famous failure in this model, and not a lot of trouble to test.
It is a two-circuit switch and only one circuit is connected. Two jumper wires will put the unused side into the circuit if the factory-wired side of the switch has failed. Gets you a few more years before having to find a replacement switch.
73
I'm with you Shadetree, sometimes my Uniden Madison with the digital clock just turns off. I push buttons on the clock and the radio comes back to life. It's some kind of alarm clock mode.
I have checked continuity in the off position vs the on and the switch works as it should. When you switch on, there is a break in continuity from the terminal at the off on both hot and switched hot. Also, you now have continuity on the second set of terminals to hot and switched hot. In other words, when you depress the switch there is a change in continuity.
I tried this no avail. I do see very dim illumination of the CB channels so far but not on the meters. I almost think the old caps have given out.
Do you have an external source of 13.5 Volts DC? My first check when this happens is to plug a mobile power cord into the back of the radio and select "DC". If the radio now runs okay from an external source of DC power, the radio's internal regulator would be suspect.
And if the radio is just as dead when powered from a DC power cord, the fault is not only with the radio's internal DC supply. Won't prove that it's good, only that it's not the only fault.
73
And if the radio is just as dead when powered from a DC power cord, the fault is not only with the radio's internal DC supply. Won't prove that it's good, only that it's not the only fault.
73
Update:
Checked the switch and that is good!
Removed bridge rectifier and checked with meter on diode setting and that is good.
Replaced bridge rectified and established the same baseline clock works, faint CB channel, and no power.
Replaced 4700uf 35v main cap and still the same
Next step is to look at the 1000uf caps (10v and 25v)
I'll keep you posted
Checked the switch and that is good!
Removed bridge rectifier and checked with meter on diode setting and that is good.
Replaced bridge rectified and established the same baseline clock works, faint CB channel, and no power.
Replaced 4700uf 35v main cap and still the same
Next step is to look at the 1000uf caps (10v and 25v)
I'll keep you posted
the next step should be to check the voltages on the MB3756 voltage regulator and post them here.
its the smaller vertically mounted IC on the right side bolted to the wall.
the one toward the front of the radio.
it has 8 pins.
pin 1 is toward the back of the radio.
measure those DC voltages and post your results.
LC
its the smaller vertically mounted IC on the right side bolted to the wall.
the one toward the front of the radio.
it has 8 pins.
pin 1 is toward the back of the radio.
measure those DC voltages and post your results.
LC
Okay, I believe I have the correct IC. The voltage is 6.4v but it fluctuates just a little then back to that voltage from pins 1 and 8. This does not surprise me because the voltage from that one smaller board in my previous post is only 4.5v!
please measure all 8 DC voltages starting at pin 1 (rear) and list the voltages you get on each pin. they should not fluctuate.
LC
LC
if you want to see how much voltage is coming out of the power supply make sure the switch on the back is in the AC position and measure the DC voltage at the fuse itself.
remember that you cant use the metal chassis for a DC ground for any of your measurements because it's isolated from the main PC board.
you can use the metal tuning cans on the board itself for a good ground.
LC
remember that you cant use the metal chassis for a DC ground for any of your measurements because it's isolated from the main PC board.
you can use the metal tuning cans on the board itself for a good ground.
LC