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I just got my PRO and after five minutes the screen don't light, the FrSky module Led is lighting and the "ready" Led also...

I can measure around 5.5 volts on black and grey wires of U12 with no HF, but this go down 3.4 with the HF load; it seems the issue come from the center power board ?

Thank you for your help

Michel

First thing is probably to check all the connectors are fully seated on the main board.

You say "the screen don't light", does this mean no backlight or no text on the display?

Mike.

Refer to this diagram:
viewtopic.php?f=122&t=5659#p80407

There are spots labeled on the Main PCB near the 5V switching regulator pcb
as 0V , 5V , 3.3V
Are these at the correct voltage?
Does it work with the RF Module removed?

-Brent

Hi Brent,

Well, after a glance to that circuitry it appears the main board is powered directly by the pack through the black wire of U10; something strange is the screen turned off during I worked with the Tx; when I measure voltages I can see 10 volts with U10 disconnected and drop down 5 volts when connected, I suspect the thermal fuse since there is 10 volts at entrance and only 5 volts on outside...

I was afraid about a poor solder on the main switch, it seems ok; what do you think ? I have not measured the A drain but I guess the pack voltage would give some burn smell ? it seems there is some unexpected resistance somewhere..It would be nice if you could send me the scheme.

It is a pity your great work is badly realised by those .... workers.

Regards

Michel

I tried to short the thermal fuse but nothing better, I continue my investigations and I can see there is some circuitry with three transistors between the fuse and the switch,for what purpose ?

Which voltage has to be applied on the main board on U10 black wire ?

Regards

Michel

Hi
Revisit the link I gave you...there is a new drawing.

R9 is a 0.1 Ohm current shunt ...to measure battery current , it will blow open in a short condition.
There is a PMOSFET that shorts out the power switch , for soft power function.

Look at the Sky9x board posts for a idea on the circuit diagram.
Brent

Hi,

With no load, HF module and U10 disconnected, I get 10 volts, with U10 connected or module only 5 volts.

I can see U1 is used to switch power, what is it ? Q are transistor but I don't know that chip.

Maybe the issue is there: on one of his leg I have 10 volts, on the opposite leg I have 5 volts with load, on the center leg I have 2.5 volts.

I guess that circuitry is used to connect the trainer mode ?

Do you think I can short the two legs of U1 without risk ?

Thanks

Michel

U1, on the power board, is the current measuring device. Q2 is used to switch the power, but the on-off switch shorts it out anyway.

The power flow from the battery is through FU1 (fuse), through R9 (0.1 ohm resistor), through Q2/power switch, through D2 (diode) to the +12V line on J3 pin 10.
The module power goes through FU1 (fuse), through R9 (0.1 ohm resistor), then the power switch, then D4 to the power pin on the module.

I would suggest checking, with power switched on, the voltage across FU1 and that across R9. There should be very little voltage across either of them. You might also try monitoring the current being taken from the battery, it shouldn't be more than 100mA maximum.

Mike.

Thank you Mike, I shorted U1 and now it works... I don't know what really happened, maybe some chip have to be changed but I don't got that "magic smoke"...is there a hazard to use it with U1 shorted ?

It would help me to understand if I had the electronic scheme; well I have now to transfer the model files from my TH9X and I don't know how to do.

Regards

Michel

R9 is a 0.1 Ohm current shunt ...to measure battery current , it will blow open in a short condition.
R9 is what you have shorted out.

so, what happened? it was a short circuit to blow that resistor, right? How did it happen? this is important to know..

João

No R9 is OK, I had to short U1; I don't know what happened since it shut down instantly.

I don't understand why wouldn't the radio work if U1 is just the current measuring device.. The power for the radio passes through R9 which is the shunt.
Maybe there is some bad soldering somewhere, or even a broken track/via??
João

EDIT: wait there a second.. Isn't U1 in parallel with R9?? If so, You might have a blown shunt resistor (R9).
That's why the radio comes alive when you short U1. I think you are really shorting R9.
Mike (or someone with the schematics) could you please confirm this?
If that is the case, shunting U1, you are making all current for the radio pass through very thin tracks.. Maybe that would be a problem?
João

U1 and R9 are in parallel, if you have shorted U1, then you have shorted R9, as far as the circuit is concerned.
I would check to see if R9 is not properly soldered down.

Mike.

remove the shunt you've made.. Measure for continuity between FU1 and the leg on U1 that is connected to R9. If the shunt resistor is blow or not soldered properly you won't have a reading on the ohm meter.

João

It Has to be R9 , these can burn out faster than you can blink a eye

After removing the strap it seems there is something bad in R9: when I put my test point softly I get around 55 ohms and if I push harder I get near 0 ohm, maybe this is defective or poor soldered.

more and more strange: I desoldered R9 and my Ometer tell me 0 ohm...I have to make a test with a drain of 100 mAh to know what happens...

any idea ?

SkyNorth wrote:It Has to be R9 , these can burn out faster than you can blink a eye

What's the max current to take r9 out and acceptable working current?
I haven't been following the posts.
Thanks


Sent from my iPod touch using Tapatalk, small keys and a big finger.

michel49 wrote:more and more strange: I desoldered R9 and my Ometer tell me 0 ohm...I have to make a test with a drain of 100 mAh to know what happens...

any idea ?

Did you remove the shunt you made on U1? You should

ShowMaster wrote:

SkyNorth wrote:It Has to be R9 , these can burn out faster than you can blink a eye

What's the max current to take r9 out and acceptable working current?
I haven't been following the posts.
Thanks


Sent from my iPod touch using Tapatalk, small keys and a big finger.

Wait a second, shouldn't the fuse blow before this resistor in case of a short? If it is designed like that, then the problem was not a short, but maybe some bad solder job.. Brent??
The fuse HAS to blow before R9, right??
João

(offtopic)
One of Murphy's laws says: Even though you protect a transistor by a very fast fuse, nevertheless the fuse will protect the transistor
(/offtopic)

Klaus

KAL wrote: nevertheless the fuse will protect the transistor

You got those 2 swapped

Sent via mobile

KAL wrote:(offtopic)
One of Murphy's laws says: Even though you protect a transistor by a very fast fuse, nevertheless the fuse will protect the transistor
(/offtopic)

Shame on me!
That must of course be: "Even though you protect a transistor by a very fast fuse, nevertheless the transistor will protect the fuse!!"

Klaus

Of course I removed the strap and I tested R9 on my bench, I believe it is definitely a bad part;I don't know how many mA my Ometer use to test it but I guess it isvery low...

Anyone know where I could find that smd part ?

hmmm...

michel49 wrote:Of course I removed the strap and I tested R9 on my bench, I believe it is definitely a bad part;I don't know how many mA my Ometer use to test it but I guess it isvery low...

I am getting confused here. The resistor R9 is 0.9 Ohm from what has been said earlier. With most meters this would read something like a short circuit or close to that figure on the resistance range.

From your previous post I got the impression that the resistor was okay and the problem was either the solder joint or the PCB track related to it..

SkyNorth wrote:R9 is a 0.1 Ohm current shunt ...to measure battery current , it will blow open in a short condition.
R9 is what you have shorted out.

Please allow me to get the facts right..

João

EDIT: OOPS, sorry, placed this msg in the wrong topic... moved to the appropiate topic...

R9 has a variable value along with the current: around 0 with my DVM ometer -what current ?- and around 50 ohm with 100 mA

Mike can you confirm R9 is 0.1 ? I have to purchase one.

Thanks

Michel