sweetpea01

My Feedback: (10)

Please read the following thread from beginning to end........I think I have a transmitter crystal that is walking off its freq once it get warm

[link]http://www.rcuniverse.com/forum/RADIO_HELP%26gt%3B%26gt%3B%26gt%3B%26gt%3B%26gt%3B/m_2621644/tm.htm[/link]


warm=using the radio in numerous flights(or ground equivelant) and moving the sticks


Does a crystal exert more if it is tranmitting an input to the signal (stick movement) vs. just being on?
Have you ever heard of the problems I'm having?

[email protected]

famousdave

My Feedback: (61)

A crystal circuit is pretty basic.. see below for a simplified oscillator. It consists of a bias voltage, the crystal (C0) and either a passive capacitive / inductive loop or a loop controlled amplifier. The simple C/L version is shown. The crystal only oscillates at its native, or harmonic frequency, and is coaxed "into oscillation" using the inductors and capacitors as shown below.

In a nutshell without going into why - it is very unlikely the crystal can "vary" with heat or energy changes within the circuit if it is in certifiable working order. It is however possible for feedback loop amplifiers and multipliers to vary if there is a defect or some other anomaly in the control circuit. This would cause a drift in the carrier or center frequency. JR would have done an extensive test on this however and if they found nothing it is very unlikely there is anything wrong with the circuit.

You have done everything anyone would have done. Here is what I would do first:

Foremost - check and double check ALL connections (make sure all extensions are heat shrunk and use Ernst safety clips on all removeable connections (i.e. ailerons). Make sure there is not as much as a pinhole or any kind of chafing on your ignition lead and that all of those connections are heat shrunk as well.

PUT IN A PPM (NOT PCM) receiver! Troubleshoot the problems with that using your TX and RX crystal set. With the PPM receiver in place - when the problem arises, start unplugging channels until the problem goes away.

My gut feeling says you have a problem at the RX , not at the TX. It could be genuine RF interference on your channel. You had indicated you "checked" the channel for interference, however those cheapo channel scanners are useless for crosstalk and spurious noise - they only monitor carrier frequency and not sidebands more than -3db. They are not fast enough to catch transient interference, the kind that could confuse a RX but not put it into failsafe. The only way you would ever detect that kind of interference is with a spectrum analyzer and chart recorder...(way expensive) ..

Interference more often than not, comes from a faulty device or connection on board, rather than over the air.
Using a PPM receiver will allow you to see the issues, without masking them away with failsafe.

You probably think you are chasing a ghost, trust me, you will find the issue. Since you said that someone else flies all day on the same freq I am going to lean away from true channel interference and lean more toward something on board. Some wierd things I have seen in the past you might want to check -

Carbon buildup inside engine (no, I'm not kidding, it can be a real RFI generator)
Cracked Spark Plug
Carbon Track on plug boot
Chafed through ignition lead(s)
Poor Ground on engine
Loose servo extension(s)
Antenna too close to metal objects or wires
Bad ignition module (RF leaks)
Noisy Regulator
Noisy / Failing Servo Amplifier (i.e. bad servo)

Many of these things develop and degrade over time!


Try the PPM route, run the tests with engine on and engine off and by unplugging channels. I am almost certain you will find your problem.
Anyway, hope this helps and let us know how you make out!
DP

sweetpea01

My Feedback: (10)

My receipt for repairs says nothing except vibration tests........This is why I'd like someone from JR to comment, I've heard they frequent this thread.

Now back to your suggestions DP--

That all sounds good except.........

I've already done what you suggested.


Todays ground check had this........I left my engine at home, so it wasn't even at the field. Today I also undid the pull-pull cables so I could rule them out also. And 2 weeks ago when it happened I unplugged everything from the RX and went to an external nicad battery, and just plugged in one elevator, then the other and same with ailerons..etc....it still did it. I also tried a different rx and a diff rx crystal (same freq as orginal) and it didn't help. My goal then was to isolate the problem to something electrical in the plane. I couldn't isolate it, it happend on every surface, and with everything else unplugged and no power. I also bypassed all switches, and regulators using the external nicad battery. I also ran the antenna wire in several diff places.


Also you speak of a "cheap" scanner........its no osilascope (sp) but on the one we used you can tell the diff between static, PCM and PPM. We had nothing better to do today and we were playing around with it.

And please explain how this can happen........

the plane works fine.......then after continued use (thus heat buildup) it stops working. Leaving everything on, and switching crystals in less than 20 secs......everything works fine for 10mins(that was how long I kept checking once on.) Then another 20 secs back to orginal crystals and its back to not working? To me this screams crystal issues not RF interference mainly because with my experience when you get radio intererence from your plane, it gets feed into your rx as noise, not a specific freq, so normally you have problems on whatever channel your on. Also when flying my shockflyer I was getting "hits" constantly, and since it doesn't have a failsafe we were able to fly through them (though it stopped us from hovering over the pool)



Now what I really think is that something in the radio or module is causing the crystal to go bad......whether thats heat or bad output. That is why I really want the module replaced. I'm not saying I know the exact process of how a radio or crystal works, but from all the testing I've done the only conclusion is that the crystal is somehow being affected. My concern is that possibly something else is happening causing the crystal to be intemittant (heat is my guess as its a time thing). And I really don't want to just throw a new crystal in and have it happen all over again.

So far I've ruled out these things
-Lithium batteries
-regulators
-kill switch
-any of my switches
-ignition
-ignition battery
-motor on or off
-motor not even installed
-any servo (unless they are all bad)
-RX
-RX crystal
-my module (as today it worked with diff crystal)
-my radio (same as above)
-smoke system
-pull-pull cables
-antenna position
-PCM (since my shockie was glitching on a gws micro)

There are only 2 possiblites left.......TX crystal or the freq # And since someone else is flying on the same freq with no problems and its a JR radio also........And I flew my shockie over 10miles from the field at got glitching on the same freq....would seem odd the whole city has a channel 17 issue. This is why I really want to do one more day of ground testing with faulty equipment then switch the crystal to the same freq. Then go through the whole testing process again, to be sure before I fly. I also want to go to the new module incase the module is whats causing the crystal to fail. Oh and I've never taken the crystal out of my module before any of this happend.

Next.......what and how do they really test equipment? When I orginally called all they said was they vibration tested it and checked the module. I don't think what is happening to me they really testted for.

Does any of this make sense?[

famousdave

My Feedback: (61)

Yes, it does make sense.. looks like you have the bases covered.

If it were my radio, I would change out the TX module and both crystals. If this fixes the problem, then get on the phone with JR and argue it with them to get credit if your radio is still under warranty. If they don't give you credit .. .TOSS the module and crystals!!

It is possible that the TX module is acting up and from all other accounts and motions you have gone through, it points more and more to that scenario. Not all problems are detected on the bench and it is possible to miss intermittent problems.

I called over at Horizon - the part number is JRPTXM - XX (xx= channel #) cost is $59.00 includes the crystal.
Ships same day.. .I'de say its cheap insurance. I will stick to my original hunch though - I doubt it is the crystal. But even it the new TX module does not solve the problem, you wont go wrong having a spare around!

DP

sweetpea01

My Feedback: (10)

That was my plan........I already orderd a new module with crystal. (I got it from my old hobbyshop). It just hasn't shown up yet. It should be here in the next couple of days.


I plan to send back the old module and crystal and demand a new set (going to try to get a new freq but I will take what I get).


Thanks for your advice.

famousdave

My Feedback: (61)

This was a very interesting thread (well this one and your link) let us know what you finally found out. I share your frustration, but hopefully you fix the problem with the module swap!

DP

sweetpea01

My Feedback: (10)

None of my friends have ever seen a situation like this either. We went through everything in the plane trying to find out what the problem was.


And of course......you lose a $3000 plane to a $15 dollar part that probably cost 2cents. At least my damage was repairable.

sweetpea01

My Feedback: (10)

I should get my new module sometime today or tomorrow. Then I can retest and prove that its tx crystal.

sweetpea01

My Feedback: (10)

Just got my new module............Tomorrow or saturday I'll start another round of testing to make sure its the crystal and not the actual channel.

canavanbob

My Feedback: (20)

I had a similar problem with a new radio. I extended the antenna, turned it on to start setting up models and after 5 minutes it started jittering and in another minute was totally inoperable. Turned the radio for a minute and turned it back on. Same thing! Repeated several times. Sent the radio back. They said it was a bad solder joint. Never had another problem. Good luck!

Bob

sweetpea01

My Feedback: (10)

Got off the phone with JR today............Talked with one of the Reps.

He had never heard of whats going on with my Radio, infact he talked to the tech that first worked on my radio..........the two of them couldn't figure it out. They had no idea on how to test for the problem. They also noted that in the work order it showed the tech tested out the module and the rX and found no problems, yet a problem exists.


He said that if I send in my old module and crystal that he would replace it though. So after this weekend I'll do that.


I want to do one more round of testing.........

---use all the old equipment and get the problem to show again.
---Then once it has shown.......use my radio and crystals on someone else's plane that has never had a problem (this is to verify that its not a plane issue)
---switch out crystal and run exented tests on my plane with the old module.


IF all the results are good or what I expect I should be flying by Sunday or Monday. (depending on weather)