Could someone me identify a burned-up resistor

[carlos468]

hi,
I am am hoping someone maybe able to help me identify a resistor the middle is slighty ( fell off) from heat i suspect i will add photos the only coulors left are very end cream then a gold band then cream then middle no there any more then we have a dark brown band then light brown hope that sounds right ?
one end of the resistor was connected to a diode the diode is a 1n4001 which reads uf=671mv c=11pf

this came frome a mainboard in a origami stroller i cannot seem to find anything to do with service or schematics
thankyou for any help

 

[dlgoff]

You measured 12.68 KΩ and since heat general will cause a resistor's value to increase, my guess is, it was originally a 10 KΩ resistor.
But it really depends on how many bands there were originally.

 

[davenn]

You measured 12.68 KΩ and since heat general will cause a resistor's value to increase, my guess is, it was originally a 10 KΩ resistor.
....

tho 12.68 k would still be well within the tolerance range of a 12k resistor
and it's either a 1/2W or 1 W rating ... most likely 1/2 watt

 

[dlgoff]

tho 12.68 k would still be well within the tolerance range of a 12k resistor
and it's either a 1/2W or 1 W rating ... most likely 1/2 watt

I've never seen a resistor looking like this one staying in specs. Just sayin'

 

[davenn]

I've never seen a resistor looking like this one staying in specs. Just sayin'

you may be right, but I wouldn't discount the possibility :)
specially since it is a higher wattage one ... if it was only a 1/4 or 1/8 watt, I would 100% agreeof course a schematic for the unit the thing came out of would help

im am hoping someone maybe able to help me identify a resistor the middle is slighty ( fell off) from heat i suspect i will add photos the only coulors left are very end cream then a gold band then cream then middle no there any more then we have a dark brown band then light brown hope that sounds right ?

soooooo, Carlos ... have you got or searched for a schematic for your device ? ... what is the device, make and model ??Dave

 

[jim hardy]

Can you post a picture of what it was removed from?
4001 is a general purpose power rectifier. Maybe we can guess by tracing out the circuit.

gold is likely tolerance, 5% per dlgoff's table
here are standard 5% values per https://ecee.colorado.edu/~mcclurel/resistorsandcaps.pdf

You'd read bands right to left because tolerance is always last (unless there's a reliability band )
if that dark brown band was truly brown before overheating
the only standard values ending in "one" start with a "five" or "nine",
and first band doesn't appear to be green but maybe was white before cooking...

so what other possibilities are there ?

To make a whole Watt across 12k ohms would require about 109 volts.
Is the circuit capable of that?
If not, your resistor was considerably lower ohms before the smoke got out of it.

Those are some thought steps toward figuring out your puzzle.

 

[dlgoff]

you may be right, but I wouldn't discount the possibility :)
specially since it is a higher wattage one ...

Check out the pictured socked he used. I believe it's this one (from https://www.digikey.com/catalog/en/partgroup/textool-series/7883 ). Note the hold spacing, which to me, says it's not a physically big resistor.

SIP, ZIF (ZIP Style):

• Can be used in sets of two or more to create a socket for non-standard leaded packages on .100" (2.54mm) centers
• Accepts pins up to .025" (0.6mm) square

 

[davenn]

Check out the pictured socked he used. I believe it's this one (from https://www.digikey.com/catalog/en/partgroup/textool-series/7883 ). Note the hold spacing, which to me, says it's not a physically big resistor.

I seriously doubt that that is the device the resistor came from ... hence why I asked for the device make and model
it's a tester that is giving a test value

and the size of the resistor is better gauged by its appearance with the diode, a standard 1N4xxx and it's much bigger than the diode
I still go with the at least 1/2 watt rating

 

[dlgoff]

and the size of the resistor is better gauged by its appearance with the diode, a standard 1N4xxx and it's much bigger than the diode

Good point.

 

[dlgoff]

I seriously doubt that that is the device the resistor came from

I was just speaking of his tester device that I pictured. But you may be right about it being a 1/2 watt.

 

[carlos468]

thankyou for all the replys it is appreciated this came out of an origami stroller (its a pram that folds itself up and down) i can not find any schematics it runs on a 11.1v lithium battery at 1A
this is the board circled in red is where the diode and resistor was pulled from...

and this is what it came from
About the product

• Opens and closes itself at the touch of a button
• Self-charging via generators in the rear wheels
• Daytime running lights. Automatic pathway lights
• LCD dashboard including thermometer, speedometer, trip and lifetime odometers

looking at the board the resistor was the only thing that looked wrong there was power to the board but nothing was working so I am just going though the process of elimination The chap i bought it from said there was no charger so thinking he just tryed one and that is what fryed the resistor when testing the battary it was charged to 11.5v but then this buggy charges itself when being pushed

again thans for all your help.

 

[UsableThought]

Interesting puzzle. So far the most useful guesses to me are those made by @dlgoff in comment #2 and @jim hardy in #6. Clearly this is a smallish power resistor compared to all those SMC's on the board. I too searched for a schematic and/or service manual (yes, I have a lot of time on my hands some mornings) and like the OP I came up empty.

As Jim points out, that sort of diode is often associated with a power supply. A DC battery wouldn't require rectification, but what about a generator working off the wheels (wild guess)? If the OP (@carlos468) were extremely obsessive-compulsive and had no other real-world responsibilities to attend to (e.g. no job, wife, or child), he could sketch a partial layout (and from that a schematic) for that part of the board, getting values for other nearby components by inspecting them; hopefully the board is no more than double-sided, which means you'd still have to look for via's (little holes which connect traces on the opposing sides) and also identify the ground plane. You wouldn't have to do the entire board, just enough that someone could take a good guess at this part of the circuit. I once drew both sides of a PCB for a guitar amplifier, just so I could analyze the layout; so it can be done.

However - one thing that gives me pause is, the fact that the resistor burned out in the first place - as the OP says, apparently when the previous owner somehow plugged a charger in (no details given by the OP on what this entailed). Sometimes a resistor will literally "take the heat" and protect the rest of a circuit by burning open, almost like a fuse; but often even when that is the design intent, it isn't always enough. Thus the possibility exists that even as the resistor was toasting, more sensitive components such as ICs and transistors were getting killed; typically this happens without leaving visible evidence. Possible support for this theory is that if the resistor still measures as having resistance, rather than being open-circuit, that means it didn't get sufficiently fried to stop conducting or even to alter its value as hugely as it might have; which in turn may mean that it's not be to blame for the circuit not working. I am guessing there are at least transistors on that board, as I see a lot of three-legged creatures in the photo that seem to have "Q" associated with their part label; but that's just a guess as my solid-state knowledge is pretty limited.

At any rate I would be wary of committing a huge amount of time to worrying about exactly what resistor it was, without a better sense of what the previous owner did as well as a plan for identifying and checking the status of the semiconductors on the board. Without a schematic and some experience at checking voltages for transistors & ICs and so forth it would be very difficult to tell. You could just get yourself a half-watt 10K resistor and a new diode and solder them in place & see what happens. If no joy, then the most efficient option might be to find a service shop that could at least take a quick look (good service shops will do that). Some product companies will supply replacement boards to repair shops; others won't. But this little board looks simple enough that potentially a capable repair shop could replace bad parts and get it running again.

 

[carlos468]

thankyou for the reply UsableThought i may have to sketch a partial layout but i may go for the bung a 10k resistor on the board and see what happens :) this board has a clear film (glue) over it i would say it was for water proofing so putting a solding iron to it is not very nice i think if that does not work ie putting a 10k resistor on it imay then go for the capacitors they don't look bad but I am thinking for what there is on the board it wouldn't be a hard ship to swap the whole lot for new i was just a bit stuck on the resistor
but open to ideas and help thankyou all again :)
more photos

 

[UsableThought]

i think if that does not work ie putting a 10k resistor on it imay then go for the capacitors

Do you mean the SMC caps, or the big electrolytics?

When big electrolytics get subjected to reverse polarity, typically you will see damage - the ends bulge or leak goo; or even explode. If subjected to excess voltage that is high enough, my guess is you'd also see damage. If you don't see this sort of thing those caps are probably fine.

My own opinion is that caps are the least likely component to be your problem. I speak from limited but relevant experience: aside from troubleshooting various cap/resistor issues in a guitar amplifier built mostly on a PCB, I once subjected a small battery-powered audio amplifier to an over-voltage input & had to troubleshoot that as well. I was lucky enough to locate a schematic; plus I had an excellent DIY book on how to repair solid state consumer electronics. I then checked the circuit's single transistor and single IC to see if they registered expected voltages; they did not, so I replaced them & the amp worked again. It's key to know what voltages you should be getting when you check particular nodes against ground w/ a voltmeter.

Again, if replacing the resistor doesn't help and you don't have a methodical plan of repair based on at least a basic understanding of consumer solid state circuits, you are likely to be wasting your time. Of course it's your time to do with what you wish; but I would suggest doing what you can to make it a learning experience rather than just a frustrating experience. E.g. if this sort of thing is new to you, maybe get a book of the sort I linked to above & start reading. Forums can't teach you everything.

P.S. As for the waterproof coating, just chip or scrape it off the areas you want to work on, being careful not to damage traces. Shouldn't be a problem if you work carefully.

 

[davenn]

Clearly this is a smallish power resistor

that's what I said !

As Jim points out, that sort of diode is often associated with a power supply.

yes so ?

A DC battery wouldn't require rectification, but what about a generator working off the wheels (wild guess)?

probably, very wild ... diodes are used for lots of other purposes other than just rectification
it could just as easily be used for polarity reversal protection

but i may go for the bung a 10k resistor on the board and see what happens :) this board has a clear film (glue) over it i would say it was for water proofing so putting a solding iron to it is not very nice

it definitely wouldn't hurt and it would be interesting to see what happens, just be ready to pull the power connection quickly

yeah, some of those conformal coatings can be yucky

can you please take 2 more pic's of the board, closer up ... take care with the focus, well lit. If the pic doesn't look clear to you once taken
try doing another pic till it loos good before uploading
and just the left hand side of the board from the edge and up to those 2 higher power resistors. Both sides of the board in that areaDave

 

[UsableThought]

that's what I said !

No slight intended; I liked the comments I mentioned for their overall perspective. And certainly the diode could be for another purpose; it's just that I am tickled by the thought that this stroller charges itself by being pushed.

Also, for the benefit of @carlos468 - I assume that when you advise being "ready to pull the power connection," you mean to turn the scooter off (and remove the battery) if either (a) he smells smoke, or (b) the stroller's electronic functions don't immediately come back to life? Smoke seems unlikely with just the lithium battery, but I agree, if no signs of life kill power on general principles.

 

[carlos468]

thanks again for taking the time to reply
Dave i have taken the photos you asked for hope they are ok

 

[Asymptotic]

Take a closer look at the "LEG2" connector with the black and white wires - it appears to be a bit smashed up. There are two "LEG" connectors, and I'm guessing they go to DC generators built into the rear wheels.

One trick when powering up dead, "black box" boards (ones that you don't have schematics for) is to carefully mark and record how all wiring is connected, disconnect everything except for the power supply, then flip the switch. If nothing blows up, the board itself probably doesn't have short-circuited components. Individually reconnect each wire connector, re-test, and repeat until all wiring has been reconnected. If things go awry after the n_th cable has been reconnected, that's a good place to focus on.

 

[carlos468]

yes i tested that for continuity as the leds for that just go to a little jack plug (i agree the board and plugs And soldering look abit naff for an $800 buggy) anyway i think that one is for little leds at the front, thing with unpluging and trying one at a time is the lcd near the handlebars should come on as soon as you move the stroller or as soon as you twist a knob on the handlebars there is a button in the middle of that knob that makes the stroller go up and down but nothing works at all
here are a couple of photos of it still in the buggy

im going to try and do a photo of the board listing where all the wires feed too thanks to all for the help and advice
as you all seem really helpful i would also like to write what i have done and going to do and fingers crossed i can get this little thing working as is should :)

 

[jim hardy]

Did i see the resistor and rectifier joined up in the air, above the board ? As in parts added after the board was built ? Which means they're a fix for some "Design Oops" ?

That sounds like either:
a 'flywheel' diode for an inductor such as a motor.
or
reverse polarity protection across a voltage regulator IC, to keep a downstream filter capacitor .from discharging backward into the regulator's output terminal on power down, which could become forward biased should he attempt to charge with a wrong polarity charger... That'd wreck the voltage regulator and if he's real lucky nothing else.

The chap i bought it from said there was no charger so thinking he just tryed one and that is what fryed the resistor

Another observation Carlos can make:
Look at those capacitors on the board, the round cans wrapped in plastic. What voltage is printed on them ?
If none are marked 100 volts or more, then i don't think there's enough voltage on this board to possibly hurt a 10K resistor and I'd suspect it was closer to 10 or 100 ohms before cooking.

What do you guys think about replacing the resistor with a 1/10 amp 12 volt lamp ? With a millivoltmeter he could see what traces are carrying high current.

P.S. As for the waterproof coating, just chip or scrape it off the areas you want to work on, being careful not to damage traces. Shouldn't be a problem if you work carefully.

For just measuring, I use a straight pin from Fair Anne's sewing basket as a meter probe to push through that varnish-ey stuff.

 

[carlos468]

hi jim that resistor was like that when i got it, one end sat in the board the other on top of a diode which i thought was strange id be surprised if it had been repaired in the past but is bad to think this was done at the factory considering the cost of this buggy $800 only made in the usa so you have to have them shipped here to the uk
as for the caps all the small ones are 16v 220uf range and the one large on is 50v 220uf i may just pull the to test but I am thinking i really should start with the resistor as that was the only thing with any real damage that i can see should i just go put a 10k back in on top of that diode (1n4001)
here is the diode in the tester

 

[dlgoff]

That sounds like either:
a 'flywheel' diode for an inductor such as a motor.

Could be as there must be a motor in the thing to make it fold.

or
reverse polarity protection across a voltage regulator IC, to keep a downstream filter capacitor .from discharging backward into the regulator's output terminal on power down, which could become forward biased should he attempt to charge with a wrong polarity charger...

That was my guess after @carlos468 posted the additional pictures.

 

[carlos468]

dlqoff there is in each side of the front wheel arms but the promblem is before that so i think it is the amin brain problem as i sure you have concluded :)

 

[jim hardy]

as for the caps all the small ones are 16v 220uf range and the one large on is 50v 220uf i may just pull the to test

I only asked to find out of there's 100 volts on the board that could toast a 10K resistor. i wouldn't pull them yet.

That you found the resistor/diode tacked onto the board , an apparent afterthought, suggests to me they are a factory fix for something that cropped up after they'd finalized the design of that circuit board. That's not really uncommon in manufacturing, especially consumer grade stuff.

We don't yet know if the board has a series diode to block reverse polarity from the charging receptacle, do we ?

So it's still plausible that a voltage regulator sacrificed itself to save the rest of the board. I can't see clearly enough to guess which package it might be,
and I'm unfamiliar with modern SMT types

It's scary because they can be this small, about a quarter of an inch end to end..

................................

I think this is where you found the resistor/diode ?

Top left IC looks like a candidate. Ohm him in circuit on RX10 scale and see if he's shorted 3 to 4. Then you can decide if it's worth trying to unsloder him.

 

[dlgoff]

see if he's shorted 3 to 4. Then you can decide if it's worth trying to unsloder him.

Should he replace the tacked in resistor+diode if he finds the MOSFET shorted (3 to 4 shorted)? I'm asking just in case those were NOT put there as "a fix for some "Design Oops"".

Edit: The original problem may have been the motor(s) them self's since

... there is in each side of the front wheel arms but the promblem is before that ...

i.e. there was a problem with the front wheels before it totally stopped working

 

[jim hardy]

Hmmm good thinking.
I assumed those two 0.1 ohm resistors (brown black silver) are to measure motor current. They don't appear to have got hot.
Still, it's probably a good idea to unplug the motors for troubleshooting.

Replace the diode and resistor?
I probably would,
on the premise that whoever put them there at least figured out where to put them to achieve something,
which means he knew a lot more about that board than i do , even if he only had an inkling.

 

[carlos468]

ok so replaced all the caps as i had them here anyways replaced the diode and resistor using a 10k i then put it back in with nothing connected apart from the lcd and power knob tryed it all even spun the wheels to see if it would break into life but sadly not so back to the bench with the board i started to test for voltage on all the 3 legged chaps all but one showed voltage the one top left as advised. so i cleared the glue of and its a UTC 7805AG last part was hard to see but i think it says (01 ROTO) anyway now a problem do i have to find the same ie I am not sure of the voltage as non passed though it when testing is it safe to assume its going to be the same as the rest without cleaning the glue off the others i think this is what i may end up doing to see if it had a mate

all so took off the rear wheel housing nothing but a moter which would be the genarator and just a wee wire sensor i would say this is for when it tells its on the move
thanks all just thought id give you an update

ok thought id just check the others before i post there all diffrent from the one i pulled so there not going to help with what i need, can anyonyone point out a safe course of action :)

 

[jim hardy]

i started to test for voltage on all the 3 legged chaps all but one showed voltage the one top left as advised. so i cleared the glue of and its a UTC 7805AG last part was hard to see but i think it says (01 ROTO)

I don't recognize the UTC
but 7805 is a standard voltage regulator part number
here's a datasheet for it
http://www.onsemi.com/pub/Collateral/MC7800-D.PDF
as you see it comes in a lot of voltages, last two digits tell what voltage , 7805 is on page 3
the DPAK3 case on page 31 looks close to what your picture showed

That OnSemi datasheet doesn't mention this, but TI's does
https://www.sparkfun.com/datasheets/Components/LM7805.pdf
This could be what the factory guys were up to when they added that diode, but I'm speculating. Such things crop up when a product hits the field and people do things to it you never thought about - like charge it with a backward power supply.

Second case is what i was thinking.

Good Luck

old jim

Anyhow, if you've found a dead 7805 that's a clue. A clue to I don't know what , but it's progress.
With voltmeter's black lead on the common tab of that 7805 , what is voltage at each of its other two pin?

 

[carlos468]

thankyou jim i afraid it shows nothing at all no voltage
but the rest do

I have added a link to the image as the forum resizes which makes it hard to see
https://www.dropbox.com/s/uamamx71xsuu77z/00.jpg?dl=0
Whatever happens i think I am going to need to replaace the 7805 before i can any more :(
thanks for your help and links
Oh and this is the dead chap :(

found here but no longer available
https://www.aliexpress.com/store/product/78D05AG/1764337_32700495890.html

I cannot seem to find where i could buy one from or if i cannot get that one what i could replace it with any ideas ?

• Supply Voltage: 1v 2v 2.5v 5v
• 1A

 

[Dadface]

Have you tried googling the make and model number of the pram? You may be able to get a circuit diagram.

 

[carlos468]

yes Dadface there is nothing that i or another member could find shame it would have made it abit more simple.

 

[dlgoff]

I cannot seem to find where i could buy one from ..

If you have or could make an account at http://www.ebay.com/, you can get 10 for US $1.70 from http://www.ebay.com/itm/10pc-SMD-Voltage-Regulator-IC-78D05-5V-0-5A-TO-252-UTC-/131872655850?hash=item1eb43909ea:m:mewwUp7l5Q3g0cQ2z133Efw.

 

[jim hardy]

thankyou jim i afraid it shows nothing at all no voltage

No voltage at output pin? What about input pin?

Here's its datasheet.

http://www.unisonic.com.tw/datasheet/78DXX.pdf

Looks to me like an industry standard part. TI or ONSEMI or anybody's 7805 should work,
usually i suggest getting the same package, dimensions are industry standard too,
but for your repair one of the TO251 's would work if you can bend the leads to make it physically fit so you can solder it in.

You could get one at Radio Shack just to try out. You might find one in a discarded VCR or wireless router, they're a very common IC.

good luck

old jim

 

[carlos468]

Just an update after week of trying I have given up I replaced most parts and managed to get 11.3 volts on the output pins the battery was 11.1v so I thought I was on to a winner but alas no nothing worked I connected my desktop power supply to the knob on the handle bars and managed to get it to light up with 15v I'm not sure what's up but I have put back together before I forgot how it all went still had fun with some soldering and trying to work out how it all worked I failed but it was worth it
Anyway just wanted to thank everyone who commented and tried to help me