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Need a little electronics assistance...

Gadget

Gadget

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Any of you SMD heads out there care to make an educated guess as to the value of R1? I can't see with my magnifier what I can see now that I shot this macro. It looks like the burned resistor has a 2, then a burned out number, then either a 4 or a 9. Anyone care to extrapolate from the rest of the circuit, and the burned component, what R1's resistance is? This is a single cell LiPO charging circuit powered from 5v USB.

Thanks in advance,
-G

(Edit) Looks like the burned out character may be an R, as in 2R4 or 2R9? Maybe? (/Edit)


LiPO%20charger%20board_zps2lq43xlo.jpg
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Alaskan

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If all else fails, you could solder a small potentiometer across it and adjust from a high to lower resistance value until the board starts working correctly. Might not be worth it, unless you have a bunch of pots in your junk pile already.

Edit: Although I wonder what caused the failure to begin with, if it is still present that trick might just make something else burn out. That and I don't know what the top end resistance of the pot should be, put too large a resistance pot in there and tiny movements at the low end might overshoot too much.

My wild guess is it is 274 ohm? Or maybe that is a code number and not a resistance? Where is cyparagon when we need him? If I am wrong, he will surely help.

http://www.hobby-hour.com/electronics/smdcalc.php
 
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lasersbee

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Where did you get the PCB ?
The seller must have more of the same and
could give you the R1 ID from a new PCB.

Jerry
 
Gadget

Gadget

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Yeah, I thought about that, as well. Problem is, it's from a pretty large Chinese company and the truth is I'd probably have better luck just gruntin'' real hard and shittin' one myself than I would trying to get ahold of someone who actually knows what a resistor is. Good advice in most situations, tho.

Thanks,
-G

lasersbee said:
Where did you get the PCB ?
The seller must have more of the same and
could give you the R1 ID from a new PCB.

Jerry
Click to expand...
 
Alaskan

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I feel your pain on that one, near impossible, even if you went to the vendor.
 
Cyparagon

Cyparagon

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Where is the picture of the bottom side? All I'm seeing here is a current limiting resistor, and a transistor to change the color of the LED when a certain voltage is reached.

If this board has no components on the bottom, throw it out - it is a death trap.
 
paul1598419

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My guess is that it is part of a charging unit for batteries, but that is only because of what I can see on the front of the board. If that is what it is used for, you can probably live without it and still use the charger.

Edit: oh crap. I just reread the OP and it is from a charger. Yeah, I'd guess you can throw it away and use the rest of the charger.
 
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Benm

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I can't really tell from the pictures, but i presume it is a 2.4 ohm resistor due to the markings you got and the fact it burned out.

The middle character must have been R, since the last character is 4 or 9, resulting in value of numerous kilo-ohms in case of for or something rediculous in the order of giga ohms if 9.

2.4 ohms is a pretty common value, though it must have burned out for a reason, and simply repacing the component will not solve that problem.
 
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