JR PCM9 Module/Rx change... - RC Groups
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Apr 19, 2013, 01:08 PM
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yorkiepap's Avatar

JR PCM9 Module/Rx change...

To those who really comprehend Tx's/Rx's & configurations/applications:

Being a senior, as with many other seniors, the newfangled technology & attempts to have a good comprehension of "How/Why" Tx's & Rx's intertwine to operate & function together can be a bit frustrating. Please enlighten me......

Ok...here's the issue I am unable to understand. I have a nice JR PCM9 72MHz Tx that, for some reason, will not operate with a JR Select-Scan module & JR 790 Sel-Scan Rx.

1) The Tx will operate with no issues with the original module/Rx(72.030) on my test board. All functions/motor operate correctly.

2) I changed the module to the JR Net-JS72 Sel-Scan Synthesized module & started with a JR R790 Sel-Scan Rx. I plugged in the servos & Throttle(power) leads, had the module set to Ch55, turned on the Tx, then plugged in the battery cable. As soon as the Rx had the blue light solid, I pressed in on the scan button, waited till it went out, & then within 3sec, pressed the button again to lock the frequency as I do with all my 790 Rx's. There was no movement of servos, the blue light began to flash, & the motor was beeping. I left the Rx plugged in, turned off the Tx & turned it back on, & the Rx blue light went to solid blue. Still no indication of a bind as nothing functioned. Unplugged the Rx, re-plugged it in again & the blue light started to flash again.

Ok.....what's happening that I cannot understand? The Sel-Scan module indicates PCM/PPM, the Rx shows S-PCM & the Tx is a PCM format. I read the owner manual 4 times to see if I was missing something I didn't do, albeit, nothing I did was incorrect. On the rear of the Tx, the (2) access panels were removed to insure the "Failsafe" switch was set to "Off" & the Act switch was set to "Lock".

Any suggestions? Sure would like to get the Sel-Scan Module & 790 Rx's to work with this radio. Thanks for any help you can provide. Pics of the Tx, Rx's, Modules, & my test board attached.

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Apr 19, 2013, 01:24 PM
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GBR2's Avatar
I don't know for sure but the transmitter is probably using the older Z-PCM modulation and so would be incapable of supporting the S-PCM modulation that the Select a Scan receiver requires. The Synthesized Tx module is capable of both Z and S modulation codes but which one to use is determined by the transmitter programming.
Apr 19, 2013, 02:51 PM
Registered User
I'll second GBR2 opinion. Your transmitter came out before I had switched to JR. I had to pull up a manual for it on the web. There is no reference to S-PCM and Z-PCM in it so your transmitter is probably Z-PCM. You could try using your transmitter and syn module with your old PCM9 receiver to check out the transmitting side of the equation. If it works, then you have a PCM mismatch between your transmitter and the 790 S-PCM receiver.

Apr 19, 2013, 03:11 PM
Registered User
Yes - Tx predates S-PCM and may not in fact be compatible with Z-PCM marked receivers.
Apr 19, 2013, 03:53 PM
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yorkiepap's Avatar
Hey guys,
Thanks much for your replies, & yes, GBR2 was correct. After a phone call to Horizon, the tech did indeed indicate that the Tx was setup for Z-PCM. Quite a learning process as I use JR exclusively & like them a lot. They did say the later "G"-Series single & dual stick(PCM-9) Tx's were S-PCM & could use the Sel-Scan modules/Rx's. Never too old to learn(70 this year)....... Thanks again.


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