Carrier On Indicator Modification

[SpectreOZ]

I've done a few of these COI mods without issue, you can very quickly locate the on/off logic pin on the IC and take it forward, well that method has fallen short on my current project a Pro-2011...

According to the specifications this IC controls squelch via "hysteresis" and thus the pins are all over the place positive & negative voltages on each, the only method that permitted a stable positive voltage was bridging my DMM between the squelch input pin (14) and either the audio mute (16) OR ground (17) pins recording approximately 0.7v when a signal was received (this didn't effect operation of the scanner).

Does anyone know how can I manipulate this IC to provide the necessary input for my transistor?

Thanks in advance

 

[SpectreOZ]

Solution found... after a good night's sleep LOL :lol:

This particular scanner doesn't utilize the chassis for a common ground, thus once a common ground was located a stable signal could be routed to the NPN transistor controlling the led's grounding path.

The IC pin chosen is actually the squelch control input and has a low voltage present at all times (unless signal detected) so I had to opt for a larger resistor value as a buffer between the transistor base and IC pin.

This radio has been chosen to supersede the Pro 2021 currently supplying my Broadcastify feed.