Switching a relay with Q X7

[benaresq]

I'm fleshing out an idea here, I want to hook up a small relay to my radio and I want the relay to switch with the radio.

I was originally thinking about using the 5v from the s.port on the bottom, but that appears to only be powered when the radio is actively flashing a receiver.

Poking around inside the radio with a multimeter, I've found 5v powering what I assume is the amplifier chip for the speaker:

Chip is a LM4875M which (according to Google is an audio amplifier).

Not being an electronics guru, what are the chances of spectacular failure if I switching a relay like this using this pin?

Thanks

[MikeB]

You don't want to use that pin, it is a filtered 5V for the audio. See if you can find C521 and C522, the main filter capacitors for the output of the 5V switch mode regulator.

Mike.

[benaresq]

Thanks, I'll have a look when I get home from work tonight.

[benaresq]

Hi Mike,

I've found C521/522, they look easy enough to get to. While I was poking around I noticed a pad under the kapton tape next to the power connector with +5.0 written next to it:



It looks like the trace goes through D504 and stops. The multimeter shows 5v on this pad and the inner sides of C521/522, would it be OK to use this one? It looks really easy to get to...

[MikeB]

Yes, that is fine to use. D504 provides power (5V) to the board from the USB connector.

Mike.

[benaresq]

Awesome, thanks for your help.

[3kouet]

Hey guys, i was looking infos about this D504 connnector. On my mainboard, it does not come with yellow cover and i don't have any componant like resistor on this pin as you can see on picture.
It look like it have been unsoldered.. I was afraid to had nroke it when removing the battery or opening tx, but looking close, there is not damage, only old melting point and the old shape of a square componant which has been removed after melting.




so i was wondering about the utility of it.. The strange things is that i got a signal between +5.0 and the right part (arround 350 ohm), so it should be connected somewhere from behind, cause in front it's cut !!

I also did a clean-up cause some old rest pieces of iron where stuck somewhere, and im wondering they can fall and touch connectors somewhere and make a "ziiiiiit".. (i can see one on your picture, between the big letter B and C, 1mm under the big iron point)..

My tx is the new version X7S but on all the pictures i had found for the moment (very few), there is the yellow tape and a resistor on the D504 place..

An idea ? like to understand more about electronic, that's very interesting.

Nicolas

[MikeB]

That is a diode related powering the radio from the USB connector power.

Mike.