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Compatability problem

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Old 08-01-2003, 12:03 AM
  #1  
crashlessons
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Default Compatability problem

I recently purchased a couple extra rx's. One is a hitec platinum series and the other is a hitec 555 RCD 8200. Both say dual conv.

They don't work with my hitec focus 4 tx. I was told they would. Both cause the servos to flutter violently and end up all the way to one end. I've tried several combinations of crystals and no go. I took the platinum to the hobby shop and they said it and the crystals check out ok. The tx works fine with the rx that came with it. The paperwork says that it's gold label and dual conversion. The only combination I haven't tried yet is the new crystals with my old rx cuz that rx is difficult to get to inside the plane and I don't want to disassemble it.

What am I missing?

Thanks!
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Old 08-01-2003, 12:40 AM
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strato911
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Default Compatability problem

There are two things I can think of...

1. I found that my Hitec receiver (3500 I think) doesn't like some servos. Mine did the same thing as your description when I tried to test some new GWS servos. When I turned off the flourescent lights it got better, even though the lights never caused a problem when I had Hitec servos connected.

Perhaps you're faced with the same problem. If you have flourescent lights, try turning them off, and I also found it worked better if I had several servos connected, instead of just one.


2. Hitec makes their receivers available in both varieties of frequency shift:
- Positive shift for JR / Airtronics
- Negative shift for Futaba / Hitec

Perhaps you got receivers designed for positive shift transmitters.
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Old 08-01-2003, 01:10 AM
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Default Compatability problem

Well, I'm gonna get a new 8u radio soon, that should solve the problem. But it'd be nice to use what I have now.

Didn't know hitec made the other shift, I knew the new rx's are available with a plug you pull and flip over to change from neg to pos.

No florescents in sight.

It seems worse when all 4 servos are hooked up. Tried just one servo in all holes available. Same thing.

I tried with futaba servos and hitec. Same results. Haven't tried my one and only JR servo yet. That one is still in the box waiting on rest of the components for a real nice plane.

Thanks for the response!

I'll keep checking back, maybe someone will pipe up with more ideas.

Maybe this old focus 4 ain't what the box says it is. I got it 4 years ago and who knows how long it was on the shelf.

Thanks again.
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Old 08-01-2003, 01:19 AM
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strato911
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Default Compatability problem

Originally posted by crashlessons
Didn't know hitec made the other shift, I knew the new rx's are available with a plug you pull and flip over to change from neg to pos.
That is the Supreme Shift Select, which allows the user to select which shift it works with. Their other models have to be ordered for your particular application (+ve or -ve shift).

Only the HFS-04MG micro 4-channel is not available with +ve shift.
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Old 08-01-2003, 04:34 AM
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Default Compatability problem

The Positive shift (JR, Airtronics) 555 is the RCD 8600

The negative shift (Hitec, Futaba) 555 is the RCD 8500

Check that number agine.


John
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Old 08-01-2003, 12:24 PM
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crashlessons
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Default Compatability problem

It definately says RCD 8200 FUT J. Must be an older model rx than the 8500 and 8600 ?!?!?

The box my original radio system came in says; focus 4, digital proportional, fm, dual conversion, RCD-3500 receiver.

Is there a difference in the crystals from a few years back? Can't see that being it but the only way to test is pull the rx from the plane so I can get to the crystals. I'm probably just going to have to do it, then I will have exhausted all possibilities and tested all possible combinations.

Maybe I'm not plugging everything in right. Don't see how it could be that either. It's not like it's a complicated thing.

?????????
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Old 08-02-2003, 02:42 PM
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Default Compatability problem

Ok,
I pulled the radio late last night. All the servos I was using function flawlessly. My tx works just fine with crystals and rx that it came with. All tests perfect. Then I tried the other two (new) rx's with the crystals that came with the focus 4 radio system. Both new rx's work perfectly with the old crystals and any combination of servos. Then to double check, I put the new crystals in the tx and rx (the ones came with the new rx) and I'm back to the servos going nuts as soon as I power up.

Both rx's came with crystals in them, only one has a tx crystal to match. Naturally I cannot test the one lone crystal but the other set will not function properly with this tx and any of the three rx's (my original hitec or the two new ones).

Evidently, from tests I have performed, this older focus 4 hitec system will not work with the crystals that came with the 2 new rx's.

Both guys that I purchased these new hitec rx's from used futaba transmitters. I of course have the hitec transmitter. Is this where my non-compatibility issue rests? I thought crystals for fm futaba and hitec systems were universal.

It appears the crystals are the problem, so that is a cheap and easy fix. I'll just get a new hitec rx crystal for each of the new rx's that's same channel as my original system, then when I get my new transmitter I'll buy it with same channel and everything should be good to go right? To reiterate, I'm looking at getting the 8u futaba transmitter.

Thanks again for the help! Sometimes I'm slow on the uptake with electronics but this shouldn't be difficult and I think I've covered all bases with the testing. If you see an error in my experimenting please let me know.

T
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Old 08-02-2003, 04:27 PM
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Default Compatability problem

I'm not clear on just what is happening here.

Are You trying to change the crystal in your "Transmitter" to a different channel?

Did you say you are trying to use a Futaba crystal in your Hitec transmitter?

If no to both of these questions,I'm sorry.I don't understand what your trying to do.

If this IS what your trying, I think you just found out why the FCC does not allow changing the Transmitter crystal "without sending the transmitter to a repair shop for retuning".
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Old 08-02-2003, 06:11 PM
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crashlessons
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Default Many thanks!

I was not aware of any FCC rules about that.

We're out in the sticks in the middle of nothing. Not much around but cattle and rattlesnakes.

I was in fact trying to change the crystal in the tx. I purchased 2 new rx's and one came with both crystals (tx and rx) I thought I could just change tx crystal to fly another plane.

If a retuning is required to change channel on a tx, then this would explain the problems I've encountered. I was not aware of this either.

I'll just get new rx crystals so all rx's match my tx and I should be good to go!

Thanks.
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Old 08-02-2003, 06:28 PM
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Default Compatability problem

Crash

Are the crystals in the 555's Futaba? If so that is likely the problem. It is unwise to use a crystal of another brand in your Rx. and all the manufacturers warn aginst this, in some cases it may work but with a degradation of performance that possibly may not show up on a range check. There are differances in the way differant brand crystals are cut even though on the same channel.

The after market Hitec Rx's are not sold with crystals and that was confusing the picture when you said they came with them.
There have even been cases of LOH's selling new Rx's with Futaba crystals.


I have checked and rechecked the 8500 and 8600 model numbers with both Rx's in hand and is correct. Not a big deal but as a matter of curiosity I had to read that number on the front label with a magnifying glass (the printing font is very hard to read) and it would be interesting if you double checked with a glass.


John
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Old 08-02-2003, 08:37 PM
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Default Compatability problem

I'll definately be getting new crystals very soon. And they will be hitec to match the tx and it's crystals.

When I get the new futaba transmitter (8u) will I want futaba crystals in it to match the transmitter, or hitec crystals to match the hitec rx's and crystals in them? By the sounds of things, I'll want futaba crystals and they will operate the hitec receivers with hitec crystals in them. Right? (This is obviously more complicated than I thought.)

I checked with some magnification. Looks to be about 3 or 4 power. It definately says 8200. Has someone ever manufactured knock-offs with hitec "looking" labels? The label and logo on it sure look authentic. Now you got me curious too!
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Old 08-02-2003, 09:12 PM
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strato911
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Default Compatability problem

ALWAYS use the same brand of crystal as the equipment it is plugged into.

- Use the same brand of crystal as your transmitter IN your transmitter.
- Use the same brand of crystal as your receiver IN your receiver.

Changing transmitter crystals is illegal in North America, unless the Tx is sent to an apropriate service center for tuning.

The differences in model number may simply be earlier revisions.
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Old 08-02-2003, 10:28 PM
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You know, the amazing thing about this is NOT that I had no idea changing crystals in a transmitter would cause problems or was illegal, but that I had asked at least a dozen people about this all with a great deal more experience with RC than I and not a one of them knew either. The transmitter crystal is just as easy to get to and remove as the rx crystal. Easier actually, it's right on front of the transmitter and requires no tools to remove the cover or the crystal itself.

I read the instruction book cover to cover when I bought the radio system (4 years ago or more). I don't recall it being mentioned there either.

I will double check on that.

What I'm saying is, it looks as though this is not a commonly known thing. It is however a very important thing.

Thanks, that's why I came here. Another successful mission!! And another successful "lesson" (without a crash this time)
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Old 08-02-2003, 11:01 PM
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Default Compatability problem

Originally posted by crashlessons
What I'm saying is, it looks as though this is not a commonly known thing. It is however a very important thing.
Yes, it isn't as well known as it should be. That's why those of us who do know have a hard time convincing people of the error in their ways.

My thanks to John Buckner for his continued support in educating the masses on this problem.

As for using Hitec Spectra modules in Futaba radios... Both Futaba and Hitec have posted notices on their websites that this is contrary to FCC regulations. As soon as I informed a few on-line stores of the illegality of using them this way, they promptly changed their web-sites (one changed in under 8 hours).

http://www.futabarc.com/faq/faq-9c-q504.html
http://www.hitecrcd.com/product_fs.htm
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Old 08-03-2003, 12:38 AM
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Default Compatability problem

Don't forget also that transmitter crystals and receiver crystal are different....you cannot use a dual conversion receiver crystal in a transmitter...


And to sum up... use the same brand crystal as the piece it goes into... Hitec crystal in a Hitec receiver, Futaba crystal in a Futaba transmitter, etc...
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Old 08-03-2003, 01:11 AM
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Quote: "Those of us who do know have a hard time convincing people of the error in their ways."

That's unfortunate, I'm sorry to hear people would be stubborn enough to require "convincing".

Error indeed. Only thing is, I would have never suspected any difficulties. Most others are probably like minded BUT, should make the correction IMMEDIATELY upon hearing the facts of the matter, just as I have.

Sounds like I was one of the fortunate ones who unwittingly tried changing tx crystals. Those less fortunate could have experienced what appeared to be a functional system only to find out once it's in the air that it was not. This could be very dangerous and at least cost them an airplane not to mention much more serious consequences.

I echo your thanks going out to John Buckner and I thank you as well strato 911. I don't have contact with very many RC people out here in the sticks, but I'll do my part to educate those few I do know.

Thanks again!
T

With all the warning labels in recent years on pretty much any product available, I'm surprised this situation isn't clearly advertised. Especially since it could end up with serious bodily injury.
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Old 08-03-2003, 03:06 AM
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Default FCC regulations

It's a subject that comes up frequently during the off-season months.

As a Canadian, I am not affected by the FCC regulations (we have our own regulatory board), but the topic bothered me enough to do my own research. After numerous discussions this winter, I almost had the FCC regs memorized by spring. Some people like to ignore the parts of the regulations they don't agree with.
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Old 08-08-2003, 02:10 PM
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Default Compatability problem

The trouble is that they(someone who has changed the crystal int their transmitter) could fly for years without seeing a problem. The problem "could" show up in other radois trying to operate at the same field. With the output not tuned to the operating frequency ,the power output "on frequency" is reduced, But the "OFF frequency" output is greater.
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