Broken RC Unit, any electronic experts?

[fresko]

Hi all!

My RC Unit broke a couple of weeks ago, after mulitple malfunctioning problems.

I bought it about 4 months ago (mid July) on Bricklink, and it worked perfect when I received it. I just had to clean up the battery compartment: some batteries of the previous owner leaked.

I buildt some MOC's with it during the summer (I didn't use it intensively), until school started in September again. Like everybody knows, school/work=less time for hobby.

During a period of 3-4 weeks, it layed on my Lego worktable (with batteries).

I got some time, and I builded a MOC with it. When I wanted to try it out, it turned that the 'gas'-button (the left) of the remote didn't work porperly, in forward direction.

Sometimes it just worked (I could drive forward and backwards), other times (mostly) it doesn't (I could only drive backwards, with sometimes a 'shock' in forward direction).

When you went from 'backwards' to 'forward' the motors were braked. When you went leased the lever from 'backwards' to 'neutral', the motors were coast. The auxilaury plug worked fine.

I tried to change the batteries (remote AND receiver), switched to other channels, tested with other motors (also not the 5292), another remote (my remote works perfect, I tested it with the RC unit of a friend), etc.

When I was trying to find the cause of the problem, by trying to drive forward, it suddenly started to smoke.

I immediantly removed the batteries and let it cool down. I tried again if it works, but it has still the same problems, with the exception that it doesn't drive, in any case in the 'forward' direction

(of course I know I could just turn the cables 180° to drive forward, but then I couldn't drive backwards) AND if you press the 'forward' button long enough, the motors will turn with little shocks in the 'backwards' direction. It can be noted better when we attach a multimeter on the ouput, it sometime give some weird, very short tensions in the opposite direction. Moreover, the motors weren't braked anymore, they just coasted when you went from 'backwards' to 'forward'.

I sent an email to Lego, and of course they doesn't sent replacements anymore.

So, I screwed it open and I noticed the cables are melted a bit (both: the auxilaury plug AND the 'normal' plug), but I think that can't be the cause, because in the opposite direction everything works fine.

Meanwhile, I bought a 'new' second hand Supersonic RC, but I'm still wondering if I could repair this unit?

Are there any electronic experts on this forum?

Kind regards,

Fresko

[Lakop]

It sounds like bad wiring, it's certainly a fault causing it to burn the wires resulting in smoke. Maybe the previous owners did some DIY on it. Buy a new one from the lego shop website, your nearest lego store or ebay. Maybe someone on the forums here might be able to help you obtain a working one.

H

[DrJB]

Can you take pictures of cables/connections and post them?

[clarkdef]

I tell you I have had a lot of experience with these units, I have three currently and each has needed a repair job done on them, and Horace is most likely spot on, the wires fray and end up touching inside, these things are not build to last they are all expiring, and the transmitters and receivers are starting to wear also even without use (causes jump stutter).

If it was smoking or smelling then the transistors are most likely gone, this most likely means a short internally, as normal AA's can't do it through normal operation.

Hold tight I am looking at internal revamp of the things, something that would allow better more reliable operation, though finding parts that can fit has been hard...

The transistors are on the smaller PCB face down, not all units use the same type, they are replacable.

[Junpei]

It sounds like bad wiring, it's certainly a fault causing it to burn the wires resulting in smoke. Maybe the previous owners did some DIY on it. Buy a new one from the lego shop website, your nearest lego store or ebay. Maybe someone on the forums here might be able to help you obtain a working one.

H

You can do that? On the subject of the broken RC unit though, I agree that it's probably bad wiring, but I'm probably not the one who can help you.

[fresko]

I'll place some photo's tomorrow.

@clarkdef:

Is there a way I can test the transistors? With a multimeter or something else?

Fresko

[clarkdef]

I'll place some photo's tomorrow.

@clarkdef:

Is there a way I can test the transistors? With a multimeter or something else?

Fresko

Well I am not expert on transistor testing, but yes they can be tested, but first you have to take them off the pcb, which isn't easy, just sniff it, if it's burnt out then some smell should remain. To take the transistor of the pcb a good method is coating all 3 joints with solder then melting the lot at once and having someone else pull the component off with a tool, then you need to suck up the excess solder with a syringe, also a two man job.

Set to ohms lowest possible, if the transistor is burnt it should show high resistance if not low resistance.

[Lakop]

I'm sure there will be a youtube video demonstrating everything you need to know about testing and removing transistors. You will more than likely need a small workshop vice or a set of helpiing hands and all the usual soldering kit, if you don't have them already. Why not use this faulty one for experimenting and buy a new one.

H

[fresko]

Here are some photos: 1, 2, 3. I couldn't make them more clear.

I noticed one of the transistors is deformed: it looks like there is something melted inside and it show a 'knob' on the outside. Something like this.

The code on the transistor is O3420 , but when I googled it, I didn't found much information.

Does someone knows with which type of transistor I can replace the faulty one?

@Horace T:

Like I said above, meanwhile I bought a Supersonic RC, so I got a working RC Unit. But if I could repair this one for a low price, I got 2 working RC Units.

Fresko

[fresko]

Correction: The transistor number is C3420

[clarkdef]

Try this search http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm if you can't find a replaement you have to spec the PCB and make an assumption...

[nibor]

Full part number is 2sc3420.

You should be able to find loads of inexpensive suitable replacements.

Data sheet to get you started http://www.jbprojects.net/projects/wifirobot/c3420.pdf

I would replace all the transistors.

[fresko]

Thanks to all!

I have searched for replacement parts that I could order in Europe, but it seems it won't be easy to find it.

Probaly because I'm not really familiar with those things.

I find some good (web)stores, but they mostly have the 2SA1357 but don't have the 2SC3420, which is the most important.

Does someone know which component I could use as replacement, or rather: which details are the most important?

Of course I know I may not use a component with a lower Max Voltage or current.

Greets,

Fresko

Edited November 25, 2013 by fresko

[Boxerlego]

Full part number is 2sc3420.

You should be able to find loads of inexpensive suitable replacements.

Data sheet to get you started http://www.jbproject...robot/c3420.pdf

I would replace all the transistors.

That is a npn transistor so you maybe need the other type of transistor pnp to complete the other side of the H-bridge.

Edited November 25, 2013 by Boxerlego

[fresko]

On the other side of the H-bridge (if I understand you well ), there are 2 2SA1357.

So the small PCB contains 4 transistors (far as I can see), 2x 2SC3420 and 2x 2SA1357

The 2SC3420 are npn indeed, ther 2SA1357 are pnp's.

I just don't know which details in the Datasheet have to match with a replacement, with other words:

If I don't find a 2SC3420, with which transistor I could replace them? Have the V_CBO, V_CES, V_CEO, I_CP, T_J and so on to match exactly or may they hav(e)(n't) an higher/lower value?

Fresko

[Lego Otaku]

In USA I would have suggested 2n3904 as generic replacement as they are dirt common. 2n2222 is also common and also works as general NPN transistor. For Europe I think BC547 should work as well.

I don't have the RC unit so I don't know if those transistor is good enough or if you need different type for higher current.

[1974]

Those are in no way powerfull enough

BC547/2Nxxxx (as suggested) is around half a watt, the 2SC/2SAs here are 10 watt. They're not heatsinked and thus must be derated by 'bout 75%. TO-92 transistors don't like working all that hard and the 2SC/SAs types are the proper ones for the job. But they're not critical at all, you could probably run it with BD139/140, but let's keep it original shall we

I have some at work. PM me your adress and I'll send you a couple of pairs for you

Cheers,

Ole

Edited November 26, 2013 by 1974

[clarkdef]

Do you work at a transistors r us warehouse? If so I need a wheel barrow full!

[1974]

We have many zillions of transistors, yes

I've found both .. beam me Fresko

[fresko]

I sent you a PM

[Lego Otaku]

I didn't know the original transistor had a rather high power rating. I should have checked the spec before suggesting 2nxxxx transistors.

[DrJB]

Typically from the 'box' type you can 'guess' it's a high current/power ... especially the metal part at the top that needs to be attached to a heatsink. I got this from the last photo ...

Edited November 27, 2013 by DrJB

[Boxerlego]

Have you figure out what caused the transistor to burn up in the first place. No sense in putting a new ones and burning them up by the same problem.

[fresko]

Well, I got presumption: I made a MOC where I used the servomotor as steering motor (trick via auxilaury plug with aluminium foil)

Probably I (or rather the box) pressed the wrong button once too long, while my remote layed in a box and I was testing my MOC.

Fresko

[OmenGda]

Hi,
sorry for topic reactivation. I have a similar problem. One of integrated circuit has been burned. It's placed near by the cables of the rc engines. It's only marked as a 1930 3Q9 :( Have anyone suggestion what element is this? 

Best regards 
Michael

Edited October 27, 2017 by OmenGda