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Help! What is this component and why is it getting so hot!

superjon

Apr 18, 2014
7
Joined
Apr 18, 2014
Messages
7
Alright,

I need some professional help here. I am currently modifying a Hubsan "FPV Transmitter" (an RC controller that transmits commands on 2.4ghz and has an color LCD display that shows a live video feed from the helicopter...the video is received on 5.8ghz) to accept a large capacity 3s LiPo battery in place of the original 4-AA arrangement. I am doing this to increase operating times between charges.

What my intention is to do is to install the 3 cell LiPo Tx pack, the one from Turnigy designed for the 9XR transmitter, fed into a BEC (Battery Eliminator Circuit = DC-DC converter) that is rated for 6volts/3amps output.

Here is where things went south. I, in my foolish carelessness, hooked up the BEC backwards with regards to input and output. I did not notice this until I attached the battery and was not getting any signs of life from the Transmitter. I measured the voltage coming out of the BEC only to find 39 volts coming out. As well, the BEC was getting warm quickly. I disconnected the battery, and realized what I had done.

I swapped the BEC around and tested it for proper output before turning the Tx on again. The BEC, fortunately, was still putting out a steady 6 volts and was not heating up anymore. But now I have two new problems!

When I turn on the Transmitter power switch, the LCD display never shows signs of life. And, there's a little surface mount module directly after the power switch that gets extremely hot in just a few seconds. I have included a few pics of the device below. I'm guessing it's a linear voltage regulator. The label on the part is "0B21." I can't find anything about this module online. The component in question is the little module mounted between the two push button switches, just below the main power switch. If it is, in fact, a linear regulator, I am quite surprised that it does not have a heat sink installed from factory.

So now I'm wondering if I jacked up my Tx or not. What do you guys think?

1) What is that component and why is it getting so hot when I'm feeding in the same voltage as the 4-AA batteries would have? Unfortunately, I do not know if it got so smoking hot when the 4 AA batteries were connected. Did I damage the regulator via over voltage input and now it's ruined?

2) What may have burned out that might keep the LCD display from working?

Thanks in advance for all your help!

Jon
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
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OK, first thing, please clarify what the normal input voltage and source of power is for the "BEC".

Now, you've applied 39V to a piece of equipment rated for 6V. Now it doesn't work.

At the very least, you may have damaged the voltage regulators on board, and possibly anything up to *everything* on the board. How much is a new one? It might be better to simply replace it.

The part that's getting hot will have failed internally and is now (with any luck) close to a short circuit. I say "with any luck" because if you are really lucky it died to protect the rest of the board.

My guess is that the 0B21 marked part is a 2.1V regulator. There are a large number of parts with 0B21 in their names and many are 2.1V regulators. However I cannot find one that is specifically marked 0B21, or is in the type of case you have. An example is the LN6201B212P (and that may actually be the case used...) It may even be one of these.

Assuming this is not the regulator for the entire board (seems unlikely that it s) then there are either other damaged regulators, or other components that were connected directly to the 6V rail that are now badly damaged.
 

superjon

Apr 18, 2014
7
Joined
Apr 18, 2014
Messages
7
OK, first thing, please clarify what the normal input voltage and source of power is for the "BEC".

Now, you've applied 39V to a piece of equipment rated for 6V. Now it doesn't work.

At the very least, you may have damaged the voltage regulators on board, and possibly anything up to *everything* on the board. How much is a new one? It might be better to simply replace it.

The part that's getting hot will have failed internally and is now (with any luck) close to a short circuit. I say "with any luck" because if you are really lucky it died to protect the rest of the board.

My guess is that the 0B21 marked part is a 2.1V regulator. There are a large number of parts with 0B21 in their names and many are 2.1V regulators. However I cannot find one that is specifically marked 0B21, or is in the type of case you have. An example is the LN6201B212P (and that may actually be the case used...) It may even be one of these.

Assuming this is not the regulator for the entire board (seems unlikely that it s) then there are either other damaged regulators, or other components that were connected directly to the 6V rail that are now badly damaged.

Steve,

Thanks so much for getting back to me. I have posted this on several forums over the past 10 days and you are the first person to even respond. I greatly appreciate it! Here's what I have to your replies...

The BEC is rated to accept an input voltage range of 6-23v DC. I had a 3 cell lipo attached to it. Fully charged the lipo puts out 12.60 volts DC. Here is a link to the BEC:

http://www.hobbyking.com/hobbyking/store/__17158__6V_3A_UBEC_2_5S_Lipoly_6_23v_.html

Sadly, I believe you are EXACTLY right about the failed components from the over-voltage situation...such an amateur mistake! I still cannot believe I did this! I attached a 6.6 volt LiFe battery to the BEC and checked the regulator operating temp again and it still gets scolding hot.I cannot even touch the back of the double sided circuit board underneath of the regulator after about five seconds.

I agree with you that there are several regulators on this board, but this one is the biggest and most prominent. Its also the only one in the immediate vicinity of the power switch. The transmitter can still control the helicopter, but the video section is dead.

One thing that upsets me is the manufacturer of the transmitter will not sell parts. A complete new transmitter assembly sells for $99. Its really not that advanced of a circuit and construction quality to justify that price; but, I cannot go anywhere else for an alternative...so, they have me!

I was really hoping I could get a new regulator or two and install it (them) and be good to go! But, I have been down these roads too many times to know that never seems to happen.

I'm really bummed to call this whole transmitter worthless over this.

Thanks again for your input,
Jon
 

superjon

Apr 18, 2014
7
Joined
Apr 18, 2014
Messages
7
Steve,

Also, I looked at the data sheet you provided a link to. The case design of the regulator in question is SOT-89-5. The product name according to the spec sheet is S-1170B21UC-OTGTFx.

I definitely know this part is bad according the the pinout found on that datasheet.

Do you have any idea where to source a small quantity of those for a few bucks in the US?...I really only need one!

Thanks,
Jon
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,505
Joined
Jan 21, 2010
Messages
25,505
I'm sure this is a regulator, and it looks like the pinout may be similar, but I can't be sure that's exactly the same part.

I'd look on digikey for that device. It probably can't hurt to try replacing it. However I can't find the exact part or anything close :(

At least you have a lead...
 

KrisBlueNZ

Sadly passed away in 2015
Nov 28, 2011
8,393
Joined
Nov 28, 2011
Messages
8,393
I think you're right, superjon. It's probably a write-off. I can't find a suitable replacement on Digikey or Mouser, and they're the biggest electronic component etailers around. If you're really keen though, you could replace the regulator with an adjustable LDO regulator with two feedback resistors to set the output voltage. There are many more options in adjustable than in fixed 2.1V regulators.

If you want to go that way, you could use a small piece of prototyping board to build up a 2.1V regulator module, and wire that into the main board.

The original regulator is a Seiko S-1170B21UC. Important specifications are: output voltage 2.1V ±1%; output current 0.8A maximum claimed, but in practice, 0.5A maximum; active-high enable input ("ON/-OFF"); package SOT-89-5; dropout voltage at 0.3A: 0.15V typ, 0.22V max.

A suitable variable regulator would be the Micrel MIC5209xM. It comes in an SO-8 package, and needs two resistors to set the output voltage to 2.1V. It's rated for 0.5A maximum output current, and has an active-high enable input. You would need extra decoupling capacitors on the board as well, so the board would have 1x MIC5209xM, 2x surface-mounted resistors, 2x surface-mounted multi-layer ceramic capacitors (MLCCs).

Let me know if you want to go down that road and I'll check for better alternatives and give you some more details.
 
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