Electronic help, ID this component.

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I'm trying to repair a non-functioning playmobil RC motorblock. The motor is good, but the circuit board has a problem. I think I may have narrowed down the problem to a specific component pictured below, by comparing voltages with a good motorblock. The input voltage from the battery was about 5.3 volts on the left side of the component in the picture. It says 'L6' on the component. Can anyone ID this component for me so I can find one to try to replace it with(I'm guessing some sort of transistor?)? Also, if you think the component is good and there may be a different problem causing this anomaly feel free to chime in.
pcb.png
 
PhilP

PhilP

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It is (or was!) a transistor..
From your meter readings, it would appear the junction form left to lower-right, has gone short-circuit. There still being 0.6V across the other junction, that would appear OK. - Unfortunately, you can't just swap the faulty junction! :rofl:

There *should* be a part number on the device, but good-luck in reading it!
 
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actually I just checked and I measure the same resistances across each connection as on the good one, no shorts. weird. The 221 component below it is not shorted either. Now I'm wondering if a transistor can still be the problem while measuring the correct resistance across each leg.
 
Greg Elmassian

Greg Elmassian

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Measuring resistance is not the same as what happens when power is applied, this is an active device.

Hint: the voltage from your meter is not usually enough the bias the transistor to turn on, and then there is the polarity issue when you are measuring resistance.

Pretty much an ohms measurement on a transistor is a meaningless exercise.

Greg
 
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I'm guessing there's an internal problem, allowing the full voltage to pass through, and the resistance I measure is coming from another component in parallel.
Now If I could just figure out how to ID the part to find a replacement... There seem to be a variety of L6 transistors... :-(

I wonder if this would be appropriate:
50PCS 2SC1623 L6 0.1A/50V NPN SOT-23 SMD transistor | eBay
 
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R

Railway42

LGB, Radio Control Model Boat, Electronics
28 Feb 2013
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If you want to test a transistor use the diode test on your DVM. An NPN transistor is two diodes cathode of one diode = C. cathode of the other diode + E. and the two anode of the diodes + B. If a PNP transistor the two diodes are reversed. The transistor maybe a FET so is not the same.
 
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The previous picture I posted was of the good board.
Here are two images of the bad one:

my_photo-376.jpg

my_photo-378.jpg

That fact that the bad board looks less clean helped create some suspicion over that transistor. But I've heard that transistors can have incorrect voltages if the problem is elsewhere on the board. Any ideas on what else might have caused those voltages?

From what I understand, the collector is on the left, Emitter on the top-right and Base on the bottom-right in my pictures.
I have the older style playmobil RC block, without the lighting circuit.

There is a newer version of the board with lighting on ebay here:
RC Motor & Control Module 4010 4011 4016 4017 Playmobil Train Spares #1 | eBay
pcbe.jpg

I can see similar components there and they seem to have marked the C, E, and B on some of the pins of those components. Directly left of the crystal socket you can see one with E and B marked. Towards the bottom-left there is one with the C marked... Another near the top-left with all 3 pins marked. So it is clearly a SMD sot 23 transistor. But is there a way to test it without removing it from the circuit? Is there a good way to determine if it's NPN or PNP without removing it? If I can't be certain I may have to gamble and try one of these: 50PCS 2SC1623 L6 0.1A/50V NPN SOT-23 SMD transistor | eBay Does that seem like an appropriate replacement component for this? It looks the same, but I'm not sure if the voltage ratings are appropriate for this board.
 
Greg Elmassian

Greg Elmassian

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you can determine npn vs pnp.... google a page on how to use an ohmmeter to do so.

Being in circuit can cause issues, but usually you can do it if you are just trying to test polarity and if it is shorted.

I doubt it is a FET

Greg
 
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I'm not getting results expected from the tutorials I've seen, I'm using the diode setting in the ohm section of the DMM and an unpowered board:

Positive on Base, negative on Emitter:
my_photo-380.jpg

Negative on Base, positive on Emitter:
my_photo-382.jpg

Positive on Collector, negative on Base(I think this reading could be from the parallel resistor below it):
my_photo-383.jpg

Negative on Collector, positive on Base(I think this reading could be from the parallel resistor below it again):
my_photo-384.jpg

Negative on Collector, positive on Emitter:
my_photo-385.jpg

Positive on Collector, negative on Emitter:
my_photo-386.jpg


Can anyone make sense of this?
 
JimmyB

JimmyB

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I am a very armature dabbler, but have found false readings when a component is still fitted due to the interaction of other components on the board!
 
PhilP

PhilP

G Scale, 7/8th's, Electronics
5 Jun 2013
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You are pretty much on a hiding to nothing, trying to test in-circuit.. - To many other components, and current-paths, unless you really know what to look for.

Even then, you can be deceived.. :(
 
R

Railway42

LGB, Radio Control Model Boat, Electronics
28 Feb 2013
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As already discussed there is no point in trying to determine the state of a component whilst in circuit. If you do not have a circuit diagram measuring voltages is a pointless exercise! If the transistor shows signs of damage remove it from the circuit and try to determine whether NPN or PNP and then replace it as the board at present is faulty and therefore you have nothing to lose. Personally if I could not measure the transistor I would fit an NPN and see what happens. Hope this helps, best of luck!
 
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Thanks guys. I think I know what I have to do. It would be a pain to replace it only to find that the problem may have been elsewhere on the board. But it's probably a risk I need to take.
 
Greg Elmassian

Greg Elmassian

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Did the tutorial tell you to use the diode setting? If so, please post that link so I can give that guy a piece of my mind.

You need to be doing this with a high-impedence measuring device, normally ohmmeter set for ohms.

Again, there are no guarantees when in circuit, but you can usually extract more information comparing resistance with both polarity than a simple continuity test.

Also, there is no use trying to measure the damaged transistor, I thought you were trying to determine NPN vs PNP... take the good board, remove the transistor, test it.

Greg
 
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My45G

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Did the tutorial tell you to use the diode setting? If so, please post that link so I can give that guy a piece of my mind.

You need to be doing this with a high-impedence measuring device, normally ohmmeter set for ohms.

Again, there are no guarantees when in circuit, but you can usually extract more information comparing resistance with both polarity than a simple continuity test.

Also, there is no use trying to measure the damaged transistor, I thought you were trying to determine NPN vs PNP... take the good board, remove the transistor, test it.

Greg
The collector of an NPN transistor goes to the positive supply line (usually via a resistor)
The collector of a PNP transistor goes to the negative supply rail (usually via a resistor)
 
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The collector of an NPN transistor goes to the positive supply line (usually via a resistor)
The collector of a PNP transistor goes to the negative supply rail (usually via a resistor)
I guess that tell's me it's an NPN, thanks My45G.

Greg, I looked at a few tutorials which all said to use the diode setting, but I think they all had the components removed from the circuit, so that might explain the problem.
 
Greg Elmassian

Greg Elmassian

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Umm... I read those 2 sentences. Neither of them answers my question... did the tutorial indicate to use the diode/continuity setting on the meter as opposed to actually reading resistance.

The point I tried to make is my second and third sentences.

Also, hopefully the 4th sentence registered, more for the person that commented about measuring the damaged transistor, a waste of time.

Greg