How stupid can I be?

[Jim Hearnden 1]

As a new return to RC flying I bought myself a JR X9303 TX the other week. I've bound it to a few DMS 2 receivers happily. I rejoined Medway Model Flying Club and they fly indoor, last time this Sunday. The chances of me building anything before then is low, so ordered a Night Vapor from Leeds Models which was delivered very quickly. Did a Bind & set up with this at the weekend, all worked 100%. 

I charged the TX up using a proper JR charger. I then was playing around with my multicharger with a 12 to 1 lead. I have no idea why but I plugged the multilead TX charger into the 9303 & phut! The 9303 now doesn't work. How damn stupid of me. I phoned Mike Ridley and he hasn't fixed a 9303 before, but reckons it could be the main processor board. 

I've managed to source another JR 2.4GHZ Tx on EBay which the guy is couriering to me for Friday. So Hopefully I should be flying Sunday. But that's cost me 95 quid plus if its fixable Mike's charges to fix the 9303! 

 

So morale is & I now this is remember the JR is negative centre pole the opposite of every other user of these jacks. 

 

I checked both poles of the TX jacks of the 12 in 1. Both are positive centre pole, so expensive lesson learned...... 

[Andy Stephenson]

If it was one of these, then it's ridiculously easy to short it out when one of the connectors is connected to a battery.

My guess is that it's simply blew something in the battery circuit like a fuse or a diode.

[Phil Green]

I wouldnt expect it to have done much damage Jim, there is most likely a crowbar diode & fuse across the power input.

The fuse is likely to be just a thinner PCB track but could be a physical fuse, either way it should be visible and costs you nothing to look.

If so its an easy DIY repair to solder some fuse wire across the blown fuse track, or replace the physical fuse if there is one.

 

[GaryW]

The trouble with many of these types of leads is when connecting them to the charger quite often the TX charge plugs are wired for futaba tx's where the center pin is positive whare as the centre pin in JR tx's is actually negative so with the tx plugs on multi leads the polarity at the charger neads to be reversed... Safest way to charge a JR / Spektrum tx battery is to remove it from the tx and connect it directly to the main charge lead

 

 

Will se you at the indoor on sunday @Jim Hearnden 1  I'm also a Medway Club Member

Edited February 14 by GaryW

[Brian Cooper]

Take the back off the transmitter and see if there is a "plug in" fuse. 

JR had these on many of their TXs and it is quite common to blow one by connecting a charging lead with the wrong polarity. 

[Frank Skilbeck]

10 hours ago, Jim Hearnden 1 said:

 

 

So morale is & I now this is remember the JR is negative centre pole the opposite of every other user of these jacks. 

 

And Spektrum, bit surprised your charger didn't alarm reversed polarity.

[Outrunner]

My old JR388 had a fuse on the charge circuit. I'm sure it was a clip in replaceable fuse as I managed to blow it once and it didn't go away for repair!

[Jim Hearnden 1]

Thanks for the commiserations, I'm still beating myself up over it. As A. it was charged, as I have quite a few proper JR chargers, B. I've had JR for around 34 years, as my first was a X347 which I still have!. C. And the most embarrassing, I'm an electronic tech!

As for the fuse/diode, doing a google it appears the 9303 doesn't have one as the Americans didn't like their inability to cycle the nicad through the side port.

But I've ordered some fuses and will whip the back off when they come. Unfortunately although "qualified" these days my eyesight is not up to changing small surface mount components.

 

@GaryW See you Sunday, hopefully with a brand new Night Vapor and a TX that works.

[Chris Walby]

Lesson learnt the hard way is never forgotten!

 

45 Years ago I used to work on forklift trucks, even the big narrow aisle 72V ones and we were issued very nice Fluke digital multi meters that with a lead swap could measure current (unfused). After a few weeks I made the mistake of measuring the battery voltage while fault finding after measuring the current through a relay. No display nothing, took the cover off and the vaporising circuit board track totally destroyed any components as it straighten up from terminal to terminal!

 

Popped it in its box and sent it back to Fluke (Watford IIRC) asking what the repair cost would be as it was my mistake, blow me it cam back the next day FOC! it even had new leads and the film on the display! I mentioned this to our controls engineer and he just said as customer service it was not even worth them looking inside, just replace with new.

 

I still have the multi meter and it still works although I do have to change the battery once every 5 to 10 years!

[Alan Hilton]

JR tx charging sockets are negative centre post, which is the reverse of normal, connect a normal charger and its a problem .There is probably a fuse as mentioned before .Have a look in the battery compartment , if its not there take the back off 

[FlyinFlynn]

What could possibly have been the reasoning behind this?

In my eyes it isn't so much a case of how stupid can you be, it is a case of how stupid can the JR designer be!  What possible benefit could there be to design something like this that is a polar opposite to everybody else's design norms.( I mean outside radio control circles as well), other than bolstering their repair business at their users expense.

[Brian Dorricott 1]

I've still got a works issued Fluke with a calibration sticker dated around late 90s which works fine except the case is araldited together and has tape around the case ( hard life) .

[Geoff S]

My commiserations.  I did something equally stupid when I tried to charge my first Frsky Taranis with a 'smart' charger, not realising there is an inbuilt charge circuit and blew a SMD device on the mainboard. Also, like you, I am (was?) an electronics engineer, so equally shaming.  However, I did succeed in replacing the SMD mosfet myself but it wasn't easy.

 

It's certainly worth having a look.  It's certainly odd that the centre pin is negative, when the almost universal convention is that it's positive in just about every case. Rather like Sanwa(?) using a different servo pin allocation from everyone else, which cost me a servo on one occasion.

[Andy Stephenson]

Sony UMatic camcorder batteries had a negative centre pole connector back in the 1980s when they used Cyclon lead acid batteries. Maybe JR thought that was the way to go.

[Paul De Tourtoulon]

Can't you rewire the plug to give you the + in the middle ?.

 

 Like the time when I sold a Futaba battery to a customer who asked for a Futaba TX 9.6v pack, it blew his new Hitec Tx up 😨

[Tom Gaskin 1]

If I recall, Futaba are the only RC firm to use that polarity on their chargers, all others use the JR orientation.

 

Tom

[David Elam]

A mate of mine, sadly not now with us, was setting up his F3F glider and made his own wiring loom to connect all the (expensive) wing servos to the Multiplex sockets. Then the exciting moment of connecting power when to his dismay all four servos started smoking. A quick disconnection of the battery followed but by then the damage was done. To be fair he did admit that the bottle of Stella may have contributed to the issue.

[Engine Doctor]

Easy mistake to make Jim. The multi leads can be problematic. As a rule i dont charge Tx's on a smart charger through the jack as there is usualy circuitry that prevents the smart charger from reading the voltage. Hope you get sorted for Sunday.

When i  came back to RC in the late 70's there were a few popular brands around all on 35 meg. It was common practice then to mix and match the tx's , rx's and servos. Unlike today the cost of the radio was comparatively high so if type A would work with type C or B we would use it.  Everybody seemed to know about the differences in polarity between the brands and modified the wiring and ctystals accordingly . Futaba, JR , Hitec and Sanwa were the main players then an JR and i believe Sanwa had the different charge polarity although back then they also had a different sized jack plugs that couldnt be used on another makeof Tx. Sanwa used to wire thier servos differently , a simple fix and JR servos would burn out if more than 4 cell packs were used. Hitec were generally easily interchangeable with Futaba unless you conected a Futaba and Hitec tx with a Hitec buddy lead. It would instantly blow components on the buddy board mount in the Futaba tx . How did i find out ? When the magic smoke came out ! I was assured by a LMS that the Hitec lead was compatible who then denied saying that . Simple fix and Ripmax sent a pack of the components FOC  to change, very helpful . All surface mount then and easier to replace.  I stick mainly to Futaba now with FrSky 2.4 module and recievers and tend to remove Tx batteries for charging.

 

[Cuban8]

It's very easily done particularly when in my experience, the convention is, and for sound technical reasons, to have +V on a centre pin and 0V to the outer terminal or shield.

For the sake of a few extra components costing pennies, all this can be avoided, but I guess that the manufacturers like to try to lock their customers into using only their own approved accessories.

My old DX7 had a 'reversed' charge port and it was only a couple of minutes work to swap the wiring at the socket to accept a 'standard' Futaba charger. I accept that not everyone will be confident enough or equipped to do the same. My DX8 G2 came with its own charger and an odd skinny plug - I must admit I haven't checked for polarity on it as it's unique to my DX8.

[GaryW]

2 hours ago, Jim Hearnden 1 said:

 

 

@GaryW See you Sunday, hopefully with a brand new Night Vapor and a TX that works.

 

If your night vapour arrives but new tx doesnt arrive intime... bring your night vapour along on sunday and you can use my DX7S for the day so you can have a fly

[Jim Hearnden 1]

23 minutes ago, GaryW said:

 

If your night vapour arrives but new tx doesnt arrive intime... bring your night vapour along on sunday and you can use my DX7S for the day so you can have a fly

Thanks a lot Gary. The Night Vapor is here with 3 battery packs & working. I hope the new TX arrives but if it doesn't I'll take you up on this offer.

 

[David Davis]

While not so expensive as Jim's problem, I have a little incident to report. I've been trying to teach a seventy year-old Belgian friend how to both build and fly for a couple of years. He was keen to build a model rather than buy one so when a Radio Queen kit became available, he bought it. The Radio Queen is a vintage three channel model with a wingspan of over two metres and I used to have one powered by an i/c engine. It was ideal for giving elderly beginners their first taste of r/c flight. He made a nice job of the build then we reached the stage of installing the electric motor. Now I'm an engine man and not very enthusiastic or knowledgeable about electric flight so we fitted a motor of equivalent power to that recommended for the Radio Queen by a well-known supplier of electric flight equipment.

 

It was far too powerful, something over 500 watts. When Frans flew it, flight consisted of a series of barely controlled stalls. We tried a smaller motor, different props and a change of cg position all to no avail. Vintage model experts suggested that 50-60 watts per lb would be adequate so we weighed the model and bought a Roxxy 28-34-08 1120kv motor. On a 10x7 prop she produces 320 watts. As the model weighs 4.8 lbs, thats about 67 watts per lb. We had to install a different mouning plate for this motor and we had to do it on Monday last because Frans was going away for a week the following day. Having fitted everything on my dining room table and having  glued the mounting plate into position with cyano, we retired to the flying field.

 

I was anxious that we might not have had enough power and that I would end up driving a car but we fitted the wing, connected the LiPo checked the controls and carried it down to the club's tarmac runway. I progressively pushed forward the throttle stick and the Radio Queen shot backwards! Oh how we all laughed! 😄

 

I told Frans to swap a couple of cables between the motor and the ESC and we were good to go in the diminishing daylight. The model rolled down the runway, took off and climbed well until I'd reached a good altititude when I was able to throttle back. The old girl floated about magnificently with the throttle stick at just over the halfway point.

 

So now at least I know something about how much power is needed to fly a vintage model.

 

Pictures of both my old Radio Queen and my much younger self and Frans' model below.

 

PS. With a 10x5 prop the motor produces 285 watts which is about 59 watts per lb so it should fly well on that too.

 

Edited February 14 by David Davis

[Jim Hearnden 1]

1 hour ago, Cuban8 said:

It's very easily done particularly when in my experience, the convention is, and for sound technical reasons, to have +V on a centre pin and 0V to the outer terminal or shield.

For the sake of a few extra components costing pennies, all this can be avoided, but I guess that the manufacturers like to try to lock their customers into using only their own approved accessories.

My old DX7 had a 'reversed' charge port and it was only a couple of minutes work to swap the wiring at the socket to accept a 'standard' Futaba charger. I accept that not everyone will be confident enough or equipped to do the same. My DX8 G2 came with its own charger and an odd skinny plug - I must admit I haven't checked for polarity on it as it's unique to my DX8.

Very old RAF words "You cannot make things foolproof, as fools are too ingenious!"

 

[Jim Hearnden 1]

1 hour ago, Engine Doctor said:

Sanwa used to wire thier servos differently , a simple fix and JR servos would burn out if more than 4 cell packs were used. When the magic smoke came out ! I was assured by a LMS that the Hitec lead was compatible who then denied saying that . 

 

Yup before I was bought the X347 I used to fly Sanwa Stac 4. Which served me well. Then I had a big fleet & Rxs' were expensive. SO I still flew the Sanwa. 

I had a Nieuport 17 bought s/h from a shop, it wasn't the Flair one as it had foam wings. Anyway that flew with Sanwa servos. One day installed a JR RX into it with JR servos. When I got to the flying field & attached the wing, plugging the aileron servo in as I went. Switched on & smoke poured from the wing. YES! I'd changed all the servos except for the aileron one which was elsewhere on the bench. Words like Oh deary me, issued forth. 

[Jason Channing]

I used to have a JR 9303 as it was the same tx as the PCm9Mxii but hell of a lot cheaper (not legal in the UK as its the USA version with higher output) The good news is that inside on the main board is a 3amp glass slow blow fuse which normally blows before anything else.