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Multiplex Help!

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Stuphedd20/11/2017 09:49:38
636 forum posts
338 photos

I became the custodian of a very old Multiplex Royal MC Soft modul set recently that I require some help with !

It has to be old as the RXes are 4 pin ! It also has more knobs whistles switches plug in modules that the ISS!


No manual , and I cannot find a down load on the net

The TX came in kit form !!

and obviously no info

The reason for the Kit TX , is that I have deduced it was stored with batteries and so black wire syndrome is evident . However I mechanically put it together , direct wired a battery 9.8 volts , hope thats OK, and the PC board has a BATTERY point written on it !! , fired it up , linked it to a JR synth RX and it works !!

So what I need to know , is how is the TX charged ? and why are there 4 wires that appear to be battery oriented ?? all 4 have been cut due to black wire corrosion

Any body out there with any experience of this set ??


Pete W.

Dickw20/11/2017 10:21:34
438 forum posts
76 photos

The archive has a copy of a manual in German that might help:-


The link in full is:-

It seems to have 4 pin servo leads so might be of a similar vintage if not actually the correct model.


Edited By Dickw on 20/11/2017 10:23:58

Peter Christy20/11/2017 10:26:30
1422 forum posts

Pete: I've no direct experience with the Tx you have, but I did have a Multiplex UHF set for many years. That Tx - and other MultiplexesI have seen - used 6-cell packs (7.2V), rather than the more usual 8-cells (9.8V). The extra voltage will probably do the encoder no harm, but I wouldn't run it with the Tx aerial collapsed for long, or you may blow the output transistor.

I'm sure someone will be along shortly to confirm whether your Tx is 6-cell or not!

For many years, servos used a 4-wire connection. The extra wire was a centre tap on the battery. The receiver ran off the usual 4.8 volts, but the servo motors ran off 2.4 volts. One side of the servo motor was connected to the centre tap, and the other switched between either the positive or negative of the battery to drive it one way or the other.

When integrated circuit amplifiers became the norm, these were designed with a "bridge" output, eliminating the need for a centre tap, but requiring 4.8V motors instead of the earlier 2.4V type.

To get your 4-wire servos working, you will need to add a centre tap connection to a standard 4-cell pack.The pinouts are usually the signal pin being out on its own, and the other three being the battery +ve, centre tap and -ve. The centre tap is usually the middle pin. You will need to work out which is +ve and which is -ve!

Best of luck!


(Another) Pete

Robert Welford20/11/2017 12:50:17
153 forum posts
4 photos

I own a Multiplex Royal MC transmitter bought in 1985 from Harry Brooks at the Nationals. A friend also had one and gave it to me so I now have two Mpx Royal MC transmitters.

I still use Multiplex radio, but no longer this gear!

To answer your questions:

The transmitter had 2 6 cell 7.2V nicad batteries hence the 4 wires. They were wired through a latched switch so you could change over battery if one ran low. The current NiMh 7.2V Multiplex transmitter batteries fit. There are Enelope equivalent batteries also available fitted with the same plug.

The radio is later vintage than the era of 4 wire servos. However, the traditional Multiplex plugs were 4-way, but only 3 pins were used.

The radio was well ahead of its time - only Simprop came close.

If you have any more questions don't hesitate to ask.


Stuphedd20/11/2017 13:53:45
636 forum posts
338 photos

You guys are brilliant !

Nearly all my questions have now been answered so thanks very much smiley

I have 2off 7.2 packs , they are now on charge via another charging system , SO One last question for the time being

presumably the TX batteries are charged via the plug on the front ?? which I have , but what power source do you charge it from ?? ( can I say any old 100ma system for a 7.2 stack ??)



Robert Welford20/11/2017 14:43:28
153 forum posts
4 photos


I think I charged it at 100mAH with the latch switch in the centre position, so both batteries were charged together.

The mixing capability of this transmitter was well ahead of its time. As you know the transmitter is configured via a Soft Modul for F3A, F3B, Heli etc. The values were changed in hardware via pre-sets. Some Soft Moduls had memories and thus they stored these values. Powerful stuff for mid-80s. Even now some non-European radios have less flexibility ...

Robert Welford20/11/2017 14:58:21
153 forum posts
4 photos

I believe a 3030/4000 35 MHz RF module will fit directly, so it can be used on 35MHz. I would also expect the HFM3 M-LINK 2.4 GHz RF module to work as well. Note: I haven't tried either option.

Robert Welford21/11/2017 11:36:48
153 forum posts
4 photos


Edited By Robert Welford on 21/11/2017 11:37:00

Edited By Robert Welford on 21/11/2017 11:37:59

Percy Verance21/11/2017 21:14:30
8050 forum posts
154 photos

I think Robert is correct, the 3030/4000 module (and as far as I'm aware, even those made earlier still) ought to fit, as should the suggested M Link module. I'm not sure how easy it'll be to source these now, but someone somewhere might have stock.Multiplex were responsible for developing the interchangeable module concept, and so made much of their gear backward compatible. Even 25+ year old sets can be converted/upgraded to 2.4ghz by the user in a few minutes. There is also a particular module which allows both 35mhz and 2.4ghz operation, with change over at the flick of a switch. Nothing needs to be unplugged or removed.

Yes Pete, you charge through the multi - pin DIN socket on the front. A charge rate of 100 to 200mah should be ok. Any of the current (no pun intended) field type chargers will do the job as long as they have a nimh setting. You can buy a charge lead from an Mpx dealer or make one up Pete. 

I have an Mpx Commander tx from the 80's, which is the less costly stripped down version of the Royal Mc. This one is Cream Crackered though, as the previous owner reverse charged it........ and this one also came from Harry Brooks too Robert.

Here's my old Mpx Combilader charger (the orange box). Could charge several transmitters and receiver packs simultaneously. Quite novel for nearly 30 years ago......


I'd also take a look at Mike Shellim's Multiplex Clinic site if it's still up. He had some useful info on there with lots of history etc. I don't think he offered much technical info for the old stuff, but there were quite a few pics of old Multiplex gear going back 50 years or so....

By the way, if you need the current UK Multiplex agent he's Mike Ridley, and his site is    He's good! yes







Edited By Percy Verance on 21/11/2017 21:43:13

Percy Verance21/11/2017 21:39:17
8050 forum posts
154 photos

Oh, and yes Pete, older Multiplex transmitters run 6 cell (7.2v) packs........yes

Stuphedd22/11/2017 12:14:03
636 forum posts
338 photos

Thanks for all the help ,

I have now got it working , on 4 of the channels anyway , and got rid of the considerable amount of mixing ,

it came with both PPM and PCM,RXes and they all work , when you find the PPM/PCM switch , There were no servos so I "slaved " some to test it out and alls well ,

For its day it must have been expensive !!?? Nicely put together compared to todays plastic !

Whether I will ever use it in reality is another question , but as a learning curve its been "good fun"

thanks again


Percy Verance22/11/2017 16:23:50
8050 forum posts
154 photos

Hi again Pete

Yes, it would have been a premium set when new. Probably about twice the cost of your cooking 5 or 6 channel set. Perhaps even more. When I bought my 3030 back in the mid 90's, that was around the £650 mark just for the tx......

Edited By Percy Verance on 22/11/2017 16:28:23

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