Sounding like you have a bad crystal somewhere... The servos will twitch as you turn on the RX no matter the condition of the crystal. The TX's RF board is de-energised in certain sections wen the TX crystal is pulled... and so is the RX board when you pull its crystal... but the servo positioning section will "blip" even without a crystal.

The servos should twitch a little even with the TX off. They should jump again when the TX is turned on, then go to the stick positions. This isnot the ideal way to turn on... but it checks if the RX is getting any signal at all They COULD jump even if the crystal is bad.... and then not go to the stick position because the bad crystal will not allow it to decode the positions info.

The 127DF RX SHOULD work fine with the 7UAP That's the type RX I use with mine. (well... one of 4 types...) the same RX with the same crystal works fine with another Futaba TX (cheap 4-channel) on the same frequency. (I tend to buy my radios on just one frequency when I buy new)

The TX module is the correct one, and might be the original that shipped with the TX.

All of my PPM Futaba crystals are type 72-10

My PCM RX's crystal does not list a type... and looks like its the original for the RX (I bought the system used and don't know if its the original RX)

The type number appears to refer to the crystal's intended useage.... the band is the first 2 digits.. then the other number seems to refer to the radios it will work in. Color seems to be linked to the series code... but that's not clear from what I can find.

http://www.futaba-rc.com/radioaccys/futl20.html

I have not and will not open the TX module to look at the crystal type number.

There is a chance you are trying a TX crystal in the RX... and that is not supposed to work... The TX crystal should say "TX" on the tag though.

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There is also the possiblity you are putting a high band crystal in a low band RX... this could drive the tuning off enough that resuslts can be unpredictable.

Look in the RX right beside the crystal socket. there should be a dot near the socket if it is high band. (visible without removing the plastic case if you are careful and have good light.) the dots in my RX's are red... I have read that some have white dots.

Ch 36 or higher is high band. Ch 35 or lower is low band.

ALSO... Futaba made some 127DF RX's that were tuned to 50 mhz (ham band channels 01 to 09) and some tuned to 75 mhz (surface use RC... no airplanes 62 to 90) and some on 35 mhz (for other countries... could be more too... I don't know all the bands used in other countries) and none of those will work correctly with a 72 mhz crystal.