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No Power to board? But meters light up.

B

Brian G

Active Member
Dec 21, 2020
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My Cobra 2000 has yet another problem. It’s connected through a DC power supply that has 13 volts in. the radio turns on and all the meters light up nice and bright. But there is no power to the board otherwise.
I changed the voltage regulator but that made no difference. I lifted pins 1 and 2 off the pads and there was no voltage on the pads The frequency counter is showing 92.0000 but I imagine that’s because there’s no voltage getting to the PLL etc.
what else can I check?Help!!
 
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nomadradio said:
Which voltage regulator?

Find the TA7222P audio power chip. The pin closest to the front of the radio is pin number 1. Do you have any DC voltage there?

73
Click to expand...
No voltage on that chip anywhere. But again the meters and clock/frequency counter are lit up bright. (Though the frequency is wrong). No voltage in the main board. Checked that 12 volt rail area and same, no power. It sounds like voltage regulator doesn’t it? But like I said i replaced that and it didn’t change. Question: is the power supply board only in play if you are running it off AC power? If not, could there be a problem there?
 
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You will have to trace and troubleshoot the main B+ and find out where it's missing, that's the ONLY way to do it.Throwing parts into it that may or may not be bad isn't the way to go.
 
techradioman said:
You will have to trace and troubleshoot the main B+ and find out where it's missing, that's the ONLY way to do it.Throwing parts into it that may or may not be bad isn't the way to go.
Click to expand...
Well I’ve been trying to do that and haven’t found it yet. That’s why I was asking for help on where to look.
 
Tracing it from the power supply to the main board isn't that hard.Do you have the schematic on it ? You have to have the schematic to do it.
 
techradioman said:
Tracing it from the power supply to the main board isn't that hard.Do you have the schematic on it ? You have to have the schematic to do it.
Click to expand...
Yes. I run it off DC power, not plugged in. So one question I have does the power supply board (Tr301,401 etc etc) come into play with it running off DC or does it basically bypass that whole area?
 
techradioman said:
Tracing it from the power supply to the main board isn't that hard.Do you have the schematic on it ? You have to have the schematic to do it.
Click to expand...
I tried lifting pin 1 and 2 on the voltage regulator and checking for voltage at the pin and the pad and there’s nothing. If I am not getting 13 volts at pin 2 of the voltage regulator or at the pad or pin itself, then Where is the block? Isn’t that Input to it? I don’t see any component in between that input to the Regulator and the DC source at the switch.
 
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techradioman said:
Tracing it from the power supply to the main board isn't that hard.Do you have the schematic on it ? You have to have the schematic to do it.
Click to expand...
So here’s something, though I don’t know what it means. If I run a jumper wire form the 13 volt source on the Ac Dc switch to the 12 volt rail in the main board , it corrects the frequency counter and shows the right frequency. The transmit light comes on as well. Then when I pull the wire off, the receive light will come on for a second then go off and the frequency counter goes haywire again. So it is definitely something with voltage not getting to the board. I think it might be that 3300 UF electrolytic cap in the main board because that’s where that white wire goes to. Sound maybe right?
 
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