Fixing a Receiver

[natkcirred]

Hi Everyone,

I was wondering if it's possible to fix a GWS R-6NII Receiver that I have and thought that this was probably the best place to post this question. I received it as part of a package in an unfortunate Ebay dealing. The person I bought it from decided to ignore me after he sold this one to me after implying it was fully functional which it is not.

Anyhow, down to the receiver. It seems to receive signals but mixes them somehow. I checked all channels and here's how it currently functions: I can control channel 6 but channel 5 seems to have a "trim" effect on channel 6. For example, if I transmit a movement on channel 5, it moves the servo on channel 6 slightly. Transmitter movement on channel 6 creates large movements on channel 6 which is good. The same effect goes for all the rest of the channels. Channel 4 affects channel 5 slightly, channel 3 affects channel 4 slightly, and so on. Any ideas if this is fixable or what could be going on? Any help is appreciated. Thanks.

[jeffs555]

I am having a hard time figuring how a bad receiver could do this. What transmitter are you using? Are you sure the receiver has the correct shift? It should have a sticker on it; J for JR shift, or F for Futaba shift.

[natkcirred]

I am using a Futaba 9Z with synthesizer which I know functions properly since none of my other receivers do this including GWS ones. As for the receiver, it did not have a sticker on it so I actually don't know what shift it is for sure. I just assumed it was negative shift since it sort of worked with my transmitter. Would a positive shift receiver respond to my Futaba? Thanks.

[MatC]

That receiver comes in F and J versions, depending on the shift. Absence of sticker means nothing, because the sticker may have "come off".
Going out on a limb here: it's possible the "low" pulses vary in length along with the "high" pulses (invert the previous as necessary)... possibly in an attempt to fit 9 pulses into a "standard" 20ms PPM frame. Only a 'scope will tell you for sure. Do you have access to a more standard transmitter with 7 or less channels?

If that's the case, having the wrong shift would include a small proportion of the previous channel into subsequent channels, although the frames would still look to make sense (eg if the receiver only looks at positive edges).
In terms of what to do about it... maybe someone here knows how to convert that receiver to the other type? Can you alter the shift on your transmitter? Can you reduce the number of channels it sends? Are you an electronics genius?
Let us know how you get on :)

[natkcirred]

Yep, the sticker is gone as it is a used receiver. Your explanation for the receiver's behavior is logical but doesn't the ppm decoder look for a certain start signal either high or low for a certain time before it starts to read the transmitted info? This start signal being some kind of sync time. I'm no electronics genius but I would think a positive shift receiver wouldn't respond since it never receives the correct start sequence. I currently do not have a more basic transmitter that can transmit on the correct frequency so I can't test that. My 9z also does not shift select so I can't test that either. Anyone have any other ideas?

[MatC]

It wouldn't respond... unless it is only looking at the edges. If it times everything based on just the positive going edges, pos or neg shift looks pretty similar (because the "off" pulses are short and constant width), and there is still a valid sync pulse.

This is a reasonable way of getting a receiver to work with pos or neg shift (as may be the case with yours), the only difference being whether the previous or next "off" pulse is included. Which shouldn't matter either, unless the transmitter is monkeying around with those, in which case it matters whether you look at the positive or negative going edges, because you need to include the correct "off" pulse.

Well, that's the best guess I can make anyway... can anyone jump in and suggest whether the 9Z actually does this?

[helikalle]

Sorry to jump in on your thread but I have a 9Z with synthmodule too. It has never worked with any other reciever then Futabas. Anyone with the same experiance?

/Christian

[MatC]

Even receivers with the same shift?
A quick search on t'web shows similar problems: 9Z having PPM that's just not that compatible with other receivers. Anyone know how they cram 9 channels into a PPM frame? 9*2ms + 3ms sync = 21ms, so they've clearly altered something somewhere.
No easy solutions spring to mind, but if my guess is correct, the receiver isn't actually faulty.

[Marion]

He says "I am using a Futaba 9Z with synthesizer which I know functions properly since none of my other receivers do this including GWS ones."

[rc404]

He says "I am using a Futaba 9Z with synthesizer which I know functions properly since none of my other receivers do this including GWS ones."
My 9ZS works fine with all my GWS receivers and with my Blade CP. My buddies 9ZS does not work with a Hitec 05S and FMA says they don't work with most of their receivers. Look at the 6th FAQ here

http://www.fmadirect.com/faqs.htm?category=1

Looks like its hit and miss.

Ed

[natkcirred]

My 9Z with synth has worked with all Futaba, Hitec, and GWS receivers I've tried with it and that's a lot of receivers. I've even gotten it to work with a Berg. I hope this helps.

As for my present problem... I still have no clue what the problem could be. Could a broken component cause this behavior?

[Captn Don]

Nat:sounds like its the transmitter is at fault.Sometimes the channel pots can be out of calibration and will cause a pulse from one channel to mix with another channel. U need to scope the pulse train in the receiver and see if one pulse is mixing with another.Most transmitters have a frame rate pot and main pulse width pot and they interact with each other if turned too much in a certain direction.I surmise you have a TX problem.

[fritzthecat]

Look at the SRV Servo screen on the TX. If the bars indicate movement of other channels when you move just one stick it's the TX's fault. If the bars remain still but the RX still mixes channels then it is the RX's fault.

Fritz