7E power to RF modules has disappeared.

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28 Aug 2016 13:04 #53196 by jonrev
Not having much luck with questions being answered but thought I'd just see if anyone could help on this forum.
I have a Devo7E which I have modded with NRF, A7105 modules and the resistor power short mod. All went well and I have been using it with several V2x2 quads.
Recently I bought a F450 with Lemon Rx, Naza-M lite FC with GPS etc. Been struggling to set this up as I'm no programming wiz but got to the stage of getting the Devo to operate all channels of the Naza albeit not in quite the right way but I was slowly making progress.
After one of my attempts to alter the .ini via USB I turned off the Tx and when I turned it back on it had lost all modules including the CYRF- none were recognised as being installed. Everything else on the Tx works fine and all buttons and sticks are working but just no RF modules.
I've tried all the software settings and all are fine so I took out the add-in modules and left just the CYRF and altered the .ini file to suit- still nothing. The 7E always seemed to get fairly warm after a bit of use and I assumed this was normal but the thought struck that maybe it shouldn't have and something was wrong
Thinking I may have a burned component or track I had a good look with a magnifier but found no signs of problems. Unsoldered the shield from the CYRF and had a look in there and again all seems OK.
Had a probe round with my DVM and can find no voltage supply inside the CYRF module anywhere. I assume one of the external solder points along the bottom should be supplying power but none of them has a voltage present. The VDD pin at right of the line of points below the CYRF has 3.3v.
Has anyone had similar symptoms or can anyone suggest a possible failure I should check for? Should I be getting a voltage reading from somewhere on the bottom pins of the CYRF module or somewhere on it's board? Is there a component which is supplying the power to the RF modules which may have died and if so which one?
I'd be really grateful if anyone had any ideas as the alternative is to scrap the 7E which I'd be unhappy about after all the time and money spent modding it.
Thanks.

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28 Aug 2016 13:43 #53199 by jonrev
Replied by jonrev on topic 7E power to RF modules has disappeared.
Well a bit more searching and it seems there should be +5v on pin 6 along bottom of CYRF module. I have nothing so maybe that's my problem? Question now is where does the 5v come from. I assume there's a 5v regulator on the main board somewhere which has gone down but I can't see it (or at least I can't recognise it). Could someone point me at it?
If I can't find it or can't replace it for some reason would the Tx be likely to work if I were to put in a 5v regulator somewhere to feed that pin 6 of the CYRF module???? Not recommended I'm sure but at a pinch it may be my last resort and may show up any other problems? What do you think?

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28 Aug 2016 13:44 - 28 Aug 2016 13:46 #53200 by Cereal_Killer
Replied by Cereal_Killer on topic 7E power to RF modules has disappeared.
On the 7E power is supplied to the CYRF module by the right most pin. It's [strangely for an RF module] a 5v device (the devo module has its own on-board regulator). It comes from the SOT-123 package diode below and slightly to the right.

Verify it's receiving 5v.ibe had that diode go bad on mine and had to replace it


EDIT: I only saw your first post when I replied... 5v is pin 7, the far right one. Do not apply + voltage to any other pins!

Note again the stock devo module has a built in 3v3 regulator and as such is supplied with 5v.

Taranis X9E | DEVO 10 | Devo U7E | Taranis Q7

What I do in real life: rivergoequestrian.com/
Last edit: 28 Aug 2016 13:46 by Cereal_Killer.

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28 Aug 2016 15:46 #53206 by jonrev
Replied by jonrev on topic 7E power to RF modules has disappeared.
Thank you very much for the reply. The diode you point to has 5v on RHS and 0v on LHS and it seems to be LHS that's connected to the CYRF module pin.
I'm not an expert but suggests that the diode has gone OC? I'll remove it and test. I presume it's just a rectifier diode and I can replace with anything similar from another board? I have some dud toy FC's with similar diodes.
The CYRF module in my Devo has the far right pin (No.7) as ground. You can see it is directly connected to the groundplane and shield pads so must be slightly different to the one you mention.
I'll let you know how I get on later. Would be a real bonus if that's all that was wrong. My luck is seldom that good!
Thanks again.

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28 Aug 2016 16:35 #53207 by jonrev
Replied by jonrev on topic 7E power to RF modules has disappeared.
Ah well it was a good call and it certainly worked. Tx started up as normal with no warnings but a quick 'finger check' showed the diode heated up very quickly but so did the chips in the CYRF module. Hot enough to burn skin within ten seconds! Seemed like pretty much everything on that small daughterboard was ready to glow red so switched off quickly.
Tried it again with VM on the pin and the current was so high it was dropping the supply down to 3.8v.
Seems the CYRF board has failed catastrophically and my limited knowledge is too limited to try component level fault finding on that.
Guess I could get a replacement module and make it a full power one so no micro soldering across that resistor. I'll have a look round and see what's available.
Meanwhile I'll order a cheapish DSM2 compatible Tx which will make setting up the F450 a bit easier too.
Thanks Cereal_Killer for pointing me in the right direction. Really appreciate it.
John

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