|Dec 11, 2014, 06:26 AM|
Joined Dec 2014
Fixing Modelcraft 4-CH TX RX 40.675Mhz Problem and Modification....
I brought Modelcraft 60.475 Mhz Transmitter receiver set t this during my stay in Germany for 42" Glow plug trainer , From Conrad... probably in 2009-2010. I never used...
Due to Recent need I had tried it, it has problem....with 3rd channel and 4 channel, ch-1 and ch-2 works fine.... here is video link
Observations please see in video (ref link above)
Rx has crystal of 40.220 and Tx 20.3375, I think both Rx and Tx crystal should have same frequency right ? and Frequency mentioned on set 40.675 Mhz
Already Tried[LIST][*]Potentiometers seems ok and checked variable resistance shows correct on multimeter[*]interchanged servos....and used different set of servos...[*]Low battries cause problems with servos.... I tried with new and full batteries....but no success /LIST]
If you have any idea how to fix this issue please advice. how to identify the ppm and bind wire going to tx.... there are four wires as shown in attached image Tx_module_marking_VDD_VCC_Fr.jpg .... i guess red(marked ad VDD on pcb) and black(marked with negative sign) for supply other twos, yellow marked as(VCC) and white marked as (FR), so which one is ppm and bind ?
ImagesView all Images in thread
|Yesterday, 03:08 AM|
To prove that the entire encoder is working properly you could view the ppm signal with an oscilloscope. If you don't have an oscilloscope then feed the ppm signal into a PC sound card and use a program such as winscope.
Another possibility is that the Tx and Rx are not on exactly the same frequency (modulator out of tune, bad crystal?). When FM TX and Rx frequencies are not aligned the signal gets distorted and you may see interaction between channels and/or some channels not working properly.
Vdd (Drain supply Voltage) is a regulated voltage (+5V?) which powers the logic chips on the encoder board, as well as the FM modulator on the RF board. This is used because the modulator needs a stable voltage to minimize frequency drift.
Vcc (Collector supply Voltage) is a higher voltage (probably direct from the battery) which supplies the RF power amplifier.
FR is the only wire that doesn't supply power, so it must be the PPM signal!
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