PTT latch external mic audio GD-77

[DF9HJ]

Hi folks,

Has anybody come across this problem?
External mic connected
PTT latch enabled
Pushing thr PTT either on the radio or external mic and release it => GD-77 transmitting but audio is not fed through to the mic amp (no audio on TX signal, no modulation bar)
Repressing and holding the PTT or keeping held at TX start (on the radio or external mic) => GD-77 transmitting audio is fed through to the mic amp (audio on TX signal, modulation bar).
Internal mic is OK.
Both on FM and DMR.
Tried with various mics from Kenwwod, Densei, Chinse headset, and different GD-77. same
Also with serveral FWs from January to devolpemt of 2020/09/27.
I could have swaren it has been working in the past.
So PTT switch has to be closed to get audio on the TX signal, which is obvoiusly not useful for a TX toggle feature.
Does anybody have a clue?

Thanks!!

[VK3KYY]

Did you see the posts about RF pickup in cheap external mics causing the PTT to detrigger.

[DF9HJ]

YesI did see them, but my PTT is not triggered by RF and the audio only fed through only when keeping the PTT switch closed.
Also one of my GD-77 is connected to an external antenna with same symptom and the symtom is same on < 50mW RF with the antenna on the radio.

[VK3KYY]

OK

I think there is probably some small pickup of RF even on 50mW, and probably the PTT detection system reacts too fast, so even a very short spike on the PTT may be causing this.

Does the radio stop transmitting if you don't use an external mic ?

How are you powering the radio ?

[G4EML]

Many external mikes are wired with the microphone ground connection connected to the PTT pin (Outer of the 3.5mm Jack).
The PTT pin is connected to ground (outer of 2.5mm jack) when either the external or internal PTT is pressed. So the external microphone is only connected when the PTT is pressed.

There is nothing the firmware can do about this. The only solution would be to move the microphone ground connection from the outer of the 3.5mm jack to the outer of the 2.5mm jack.

[VK3KYY]

Hi Colin

Thanks for the explanation.

I miss understood the problem because I built my own external speaker by hacking 2 speaker mic cables and wiring them through a PC speaker cabinet.

Hence my mic is always connected even if I release the PTT.

I presume that DF9HJ could just take his speaker mic apart modfiy it, if the problem is the electrical connections

[DF9HJ]

Many external mikes are wired with the microphone ground connection connected to the PTT pin (Outer of the 3.5mm Jack).
The PTT pin is connected to ground (outer of 2.5mm jack) when either the external or internal PTT is pressed. So the external microphone is only connected when the PTT is pressed.

There is nothing the firmware can do about this. The only solution would be to move the microphone ground connection from the outer of the 3.5mm jack to the outer of the 2.5mm jack.

Hi guys,
Thanks that brought me on the track.
The mic ground was only connected to ground when the PTT switch was closed.
Soldered the mic direct to ground. All OK now.

[Zl1XE]

we need a mods page

[VK3KYY]

we need a mods page

Probably best to create a wiki page on github