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2970dx stuck on tx

9wire

Member
Dec 20, 2016
26
15
13
60
I have a 2970dx, it had echo and talkback. Pulled the echo out, removed the talkback, now when you turn the raxio on its in tx mode, and none of the buttons do anything. Can't change frequency either. Does this with or without the mic connected. Does this in am mode.
 

You shorted the tx to ground somewhere when removing those items. Recheck. Then recheck again. If it was working before and not now you have the transmit pin grounded somewhere.
 
It had been working really well, was thinking about selling it, and when I turned it on it had a buzzing (sort of) on keyup with the mic gain turned up, had to turn it back to about 50٪ to get rid of the noise. I thought the echo might be the issue.
 
This radio doesn't activate the radio circuit board's transmit circuits directly from the mike socket. The mike only "keys" an input on the computer. The program in the computer senses this input pin when your mike grounds it. If the program feels like it, the computer then feeds a ground signal out another one of its pins, activating the transmit-switching circuit on the main radio pc board.

One hazard unique to this type radio is the brain death of the computer chip. It runs from 5 Volts DC. If a voltage higher than that is accidentally fed into pin 3, this clobbers the input circuit in the computer chip.

Been there, seen that.

There is a small symbol on the display marked "tx" that is only visible when the mike is keyed. If this symbol is still there with CN605 pulled out, the transmit-input pin on the CPU is fried.

Pray that the little "tx" goes away when CN605 is pulled.

Sounds like your noise toy somehow pumped 12 Volts or so into the fragile 5-Volt input pin on the CPU chip.

Dern!

Powering down the radio, clipping the black lead of a multi meter to the radio's pc-board (not chassis) ground and probing the hot pin of CN605 will show a low resistance if I'm right. That resistance is inside the processor chip, since the hot side of CN605 feeds directly to it. This means that the tiny transistor INSIDE the chip connected to this pin is fried, transformed from a transistor to a resistor.

73
 

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