Could someone please help me identify a burned-up resistor

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  • #26
jim hardy
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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.
 
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  • #27
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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 im 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 :)
 
  • #28
jim hardy
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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 dont 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.
upload_2017-5-24_22-42-16.png

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 dont 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?
 
  • #29
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thankyou jim i afraid it shows nothing at all no voltage
but the rest do
00.jpg

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 im 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 :(
chip.png

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
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  • #30
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Have you tried googling the make and model number of the pram? You may be able to get a circuit diagram.
 
  • #31
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yes Dadface there is nothing that i or another member could find shame it would have made it abit more simple.
 
  • #33
jim hardy
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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
 
  • #34
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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
 
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