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Possible QMX TX/RX switching race condition?

#qmx #receiver #smoke

N1TR All Messages By This Member #141721 I believe this is a question specifically for Hans :) ? Having recently had the receiver mux chips be destroyed seemingly without any other failure of the switching circuit controlled by Q508, I'm wondering if there is a potential race condition such that the transmitter "switch on" code may be reachable without the receive switch pin on the microcontroller being pulled low. ? I assume that transmit is almost certainly gated behind a command changing that pin state, but I'm wondering if there's a machine code level race condition that would let the transmitter operate without that pin being guaranteed pulled low? ? Just a thought, as this seems like a strange failure mode. ? Greg N1TR?
Hans Summers All Messages By This Member #141804 Hello Greg As far as I'm aware there isn't any race condition. Something else must be at fault here. The TX line is deactivated and after some short delay, RX is activated. And vice versa on key down.? 73 Hans G0UPL toggle quoted message Show quoted text On Wed, Mar 26, 2025, 16:51 N1TR via <gregoryjz=[email protected]> wrote: I believe this is a question specifically for Hans :) ? Having recently had the receiver mux chips be destroyed seemingly without any other failure of the switching circuit controlled by Q508, I'm wondering if there is a potential race condition such that the transmitter "switch on" code may be reachable without the receive switch pin on the microcontroller being pulled low. ? I assume that transmit is almost certainly gated behind a command changing that pin state, but I'm wondering if there's a machine code level race condition that would let the transmitter operate without that pin being guaranteed pulled low? ? Just a thought, as this seems like a strange failure mode. ? Greg N1TR?
N1TR All Messages By This Member #141836 Ok thanks for the confirmation. ? I only suspected a microcontroller switching fault is that the failure happened after first performing the SSB calibration into a dummy load then testing SWR with the terminal tools also into the same dummy load. ? I didn't find any other hardware faults? in the receive chain during the repair. It's working fine now so I'll have to see how it holds up over time. ? Thanks, Greg N1TR?

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