pyromaneyakk

I have a JR XF622 transmitter (with NER-226X receiver) used for a chopper which was given to me last year. Sadly, a poorly-constructed battery plug caused the TX to turn off as i was tuning the engine of the chopper, allowing it to take off and crash. Now that i have the chopper about 98% fixed, i recently discovered that my transmitter is no longer working.

What luck! Anyway, i'm not sure what to do. I know the radio is very old, probably at least 4 years, so it's out of warranty. I have changed the fuse (looked good already) and changed the battery (still had over 3v left) but it still is not working.

My question is -- would i be better off sending this in to service, or trying to find a new radio (either transmitter to use with my current receiver, or new system as a whole)? As much as i'd like to buy a nice system with more channels, i really can't afford it now.

Any idea how much repair would cost in a worst-case scenario? And how about repairing it myself, any ideas? I'm quite skilled with soldering and electronics...

Rodney

The battery should be at least 9 volts, if a typical 8 cell, 9.6 volts with nearly 11.6 volts right after charge.

pyromaneyakk

I checked the battery with my DMM, it's just under 11 volts (was charging for almost 2 days). The lithium battery also appeared to be fine -- 3.01 volts. I may have accidentally plugged the TX into my Futaba charger a while ago and forgotten about it has been quite a while since i've messed with this (heli crashed just under a year ago). So my guess is that the TX needs repair/replacement.

Anyone know which components on the board 'die' when you plug the wrong charger in? I'm sure i could replace them myself, i just need to know which ones and what types of components they are (for example, NPN transistor, etc.)

Rodney

In the US, you must have the proper license to work on your RC transmitter unless you are a HAM and on 6 meteres. There are a couple of radio repair shops in the US, check the ads in model magazines as well as the manufacturers themselves. Radio South is one.

Ladyflyer

My Feedback: (2)

I think the 622 has a separate memory battery. You will need to return it to Horizon to have the cell replaced and the memory reset.
You could check with JR at Horizon.

pyromaneyakk

I disconnected the RF modulator circuit while i was working on it, so *technically* i was not working on a radio, just a computerized pulse generator. I see no harm in that. In fact, i still have yet to reconnect the modulator (probably won't unless i either get it working or send in for service).

I checked the battery, it's at the right voltage (3.01v, for a 3v battery) so it's probably something else. Most likely a dead board.

Anyway i'm thinking about just getting a new radio altogether, maybe with 7 or 8 channels. I will probably sell my current receiver (NER-226X with 5 NES-507 servos and a 1400MAh pack). Any reccomendations on a good replacement radio or price to sell the receiver/servos for?

Ladyflyer

My Feedback: (2)

If you momentatrily shorted the memory supply or the voltage was interrupted even breifly the memory is likely to have been erased.

pyromaneyakk

Here's what i've decided to do:

1. Send the radio to Horizon for inspection. If the repairs cost too much ($70 seem like a reasonable limit?):

2. Try to find a used radio (either from this forum, Ebay, or local hobby store/flyer). If i can't find one:

3. Wait until i can afford it, and buy a new sytem (preferrably a good one, 8 channel futaba maybe).

I work with microcontrollers, which are what the TX uses as it's "computer" and i find it VERY odd that the system would "die" from the battery losing power. Most MCU's are programmed in Flash-EEPROM which theoretically retains it's data for over 100 years without power. I suppose they could have rigged it somehow to lose it's default settings whe power goes out. Seems like a very bad engineering practice though IMO...

FLYBOY

My Feedback: (11)

I think it is a good choice to send it in to make sure. I have found that horizon is pretty good for service on everything I send in. If you don't like the price, and look for a new radio, look at the 9C futaba. It is a great radio. Hope they take care of it for you though. 4 years old isn't that old for a radio.

pyromaneyakk

Any idea how much the repair cost would be? When i was working on it i accidentally murdered the battery plug header, and the fuse rolled unfortunately under the wheel of my chair (#crunch#). I'm usually better at preventing mistakes but this damn thing is driving me to the edge of insanity!

So i'm guessing the repair(s) would be new lithium, new fuse, and new plug. If the plug is going to add too much to the cost i will just order a new one from DigiKey (electronics distributor) and replace it myself. Same with the fuse. No sense paying $20 for them to replace a $0.20 plug that would take me about 15 seconds to put in.

I know JR radios are supposed to be good but from seeing what's inside, i'm not too impressed. It should use EEPROM instead of SRAM, and maybe rectified charger input. Also a good voltage regulator. That would add maybe $2 to the cost. Worth it IMO....

Ladyflyer

My Feedback: (2)

Rectified input ?

pyromaneyakk

In electronics a rectifier prevents you from applying power the wrong way. There are generally 2 types -- a regular rectifier which just blocks voltage the wrong way and allows it the right way (typically using a large diode), and a "full-wave" rectifier, which will take any voltage -- forward or reverse -- and point it in the right direction. This can be done using 4 inexpensive diodes, or a single inexpensive "full wave rectifier" chip. A rectifier chip that could handle 10x the power throughput required to charge a transmitter battery costs about $0.55, if you just buy one. Buying hundreds, or thousdands, can cut the price drastically (1/2 or 1/4).

Think about it -- a little chip or diode would go a long way in these expensive transmitters in preventing people from killing them. I don't think that's the problem i have as i don't recall plugging my Futaba charger into it, but it would help a lot of other people out.

Ladyflyer

My Feedback: (2)

I understand the rectifier principle . I was wondering why you preferred it to a fused input. Many people are bridging the DIODE in their Futaba with a fuse so they CAN discharge through the charge connector. The fuse JR provided is actually costlier than a cheap diode. Futaba now uses a fuse type device in some of their equipment so people can cycle their battery from the charge connector. I guess it would be very simple to put a diode in the fuse location if you wee so inclined.

The fuse or diode is really meant to minimize the fire ?burn potential from an unintended high rate discharge from the the charge connector. Earlier transmitters had neither.

I guess they could try to make everything idiot proof. Maybe a test would suffice ?

pyromaneyakk

Probably a better option would be go have a switch going across the doide, with a diode/resistor combo to burn off the power and discharge the battery.

Perhaps i'm out of the loop (i'm no big-time flyer but i would like to get into it once i have more cash flow) but what's the reason for discharging? I'm guessing it's becaues of the NiCD's tendency to degrade in capacity? What would be the disadvantage of using NiMH instead of NiCD other than cost?

Ladyflyer

My Feedback: (2)

Some folks like to cycle their batts . Some THINK NiCads have "memory" (not a worry) others just want to measure the capacity (a good reason). Also you can check the loaded bat voltage at the jack when there is no diode in the way.
There are pros and cons with both cell types. A real driving force behind the promotion of NiMH is the ecological time bomb posed by improper disposal of NiCads. The NiCads are a lot less fussy than NiMH cells and will survive moderate abuse that will total a NiMH cell . NiMH cells will deliver more capacity for their size and are always being improved . There are other battery types on the horizon that may well beat out both types .
For now ,I like my NiCads and I DO dispose of expired cells responsibly?properly.

Lynx

Pyro, the FCC certifies the ENTIRE radio, not just the RF generating portion of it. Changing the way the signal that is sent to the transmitter is modulated can easily over-modulate the RF signal itself in a heartbeat that's why they certify the whole module. If you cause some sort of cascade on the input, there's no telling what frequency it'll end up broadcasting at, so regardless of what you might think, this is still illegal. You still have to have an amateur license to do this and it has to be on 50MHz gear, modifying 72MHz gear isn't legal no matter what HAM license you have (You have to have a commercial license to do that)

BTW Ladyflier diodes completely prevent discharge not limit it. They only let the current flow in, not out. They also cause a voltage drop, of a little more than 1 volt which has to be dealt with. You have to reverse bias a diode pretty badly to get it to conduct. Something like 30+ volts are required before an average diode will avalanche (conduct the other way)

Pyro, what are you trying to do that you need to modify the xmitter for? You're best off getting a micro controller to generate the signal you want and a bare bones xmitter kit (FMA sells 50/72 MHz xmitter RF modules for 50 bucks) Only use 50MHz and AFTER you get your HAM license.

If you're looking into PC applications pick up a Realflight Interlink controller. It's a MULTI axis joystick for your PC if you need it. Can decode PPM signals from many manufacturers, and the internals are nice neat and easy to modify.

And there's a good reason they don't put rectifier circuitry in xmitters. It's cheaper to have one way connectors that you can't hook up backward on their hardware. If you make your own and hook it up backward because you weren't paying attention, you learn REAL quick why it's important to check, double check, and then have someone else check your polarity first =)

pyromaneyakk

I wasn't trying to modify the transmitter, just diagnose the problems. I tested another battery in place of the lithium one (same type, CR2032) but to no avail. That's the only thing i really did that could be called "modification", if it is such a thing. I didn't actually change anything in the circuit to non-stock, and i had the modulator unplugged when i was working on it, so i find it hard to believe that i could have caused interference.

As for the connectors, here's the reason why i stated that:

Both Futaba and JR have the EXACT same connector for TX charging. The difference is that they have polarity reversed on the same pins. If you have multiple radios and chargers, you may plug in a cable with the right connector, but the wrong polarity.

Anyway i have the TX packed up in a box, ready to send out to Horizon tomorrow. If all goes well the repair price will be reasonable and i will have my transmitter back in no time.

mbba2002

My Feedback: (10)

to service a jr radio will be at least $50. that includes a cleaning and replacing lith batery and inspection to deturmine problem.you may get a little more work. After that parts+ labor probly 1+2 hr + parts. To replace radio$75-100 look around(same model).

Ladyflyer

My Feedback: (2)

Lynx quote:
"BTW Ladyflier diodes completely prevent discharge not limit it. They only let the current flow in, not out. They also cause a voltage drop, of a little more than 1 volt which has to be dealt with. You have to reverse bias a diode pretty badly to get it to conduct. Something like 30+ volts are required before an average diode will avalanche (conduct the other way) "

............................................
A little quick on the draw today? Perhaps you misread rather than a simple rush to presume error.
Read it again sonny, I said FUSES and diodes LIMIT the POTENTIAL for fire or burn in an accidental discharge. I also said I understand the function of rectifiers (diodes) . BTW, the forward voltage drop is usually closer to .7 volt than 1.0 volt. That is WHY most people replace them with a fuse for the purpose of discharging and or voltage checking . Which is what I said .

I wasn't describing the action of a diode ,just the purpose of the two different types of protection devices . And that IS to limit the potential for fire or burn from accidental high rate discharge . One does it by blocking the discharge the other with a fusible link that will open the circuit in the event of a high discharge. The newer Futaba gear uses a solid state self resetting current limit. Lets try NOT ot confuse the subject OK ?

Peter Khor

My Feedback: (4)

Last I checked replacing battery and re-tuning from Horizon was $20. Call them, they can give you a ball park figure.

pyromaneyakk

I sent the TX in for repair. Should reach them by friday. Hopefully i will hear something right away.

Ladyflyer

My Feedback: (2)

They are usually pretty reasonable . Hope it all works well for you.

BTW : Contrary to what some may say ,if they put a bridge rectifier inside the transmitter case it would be much safer than any arrangement now in use.(from a safety and idiot proofing standpoint) A reverse ,forward or AC connection would pass current with any sufficient voltage present AC or DC.
There would be no accidental discharge potential and the polarity problem is a non issue . I agree with you on that point.
But some people prefer the other options . That preference makes the fuse or polyswitch an excellent compromise.

Vy Best,
EllEff

Peter Khor

My Feedback: (4)

LF,

Great idea with the bridge rectifier! Assuming a .7V drop across a diode, that'll be 1.4V drop ... don't think a wal-wart charger will full charge the TX pack, any idea if a peak charger (say at 1C) would do fine? Don't see a reason why it shouldn't.