TC209V13A Funpack Basic. Tx function stuck

[jorgemef]

Hello,

I have a pair of Funpack Basic Radio with board number TC209V13A, on which one of the units is always transmitting. Intermitently it stops.
I tracked the circuit and could see it is keyid by a group of resistors in series that when key not pressed should stay at 3.2V.
In the "damaged unit" the series stays at 0.1-0.5V. When unsolder Volume up that is very close to TX key, it seems to stay at normal 3.2V.
Measuring the resistance when powered off seems to have normal resistance.
Unfortunately this is a multilayer board with a microchip as a blob. Searched on the network and could not find a schematic for it so I am not sure of the configuration of the keying circuit. Where the 3.2V cames from or how the resistor network is interconnected.
Any hint or do you know where I can find the schematic?

From this page: https://ukspec.tripod.com/446/indexp.html

TC-209 EXTERNAL PIC (OR LOCAL)
Updated TC-109. "FM radio" ?
(black or silver) 38 CTCSS, vox / baby call, key bleeps, monitor, auto power off
Batts: 3AA or 4AAA?!
Seen as Zodiac Me2You Radio, Commodore Fun Pack 40, Alecto FR-30



BR,
Jorge

[jorgemef]

Solved it by reverse engineering. Seems PTT key was presenting a low resistance even not activated (2.5K). After unsoldering/resoldering it was working fine.
Schematic and component positions attached.