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View Full Version : Whats wrong with this PCB? Board Repair Mystery..


Customizer
2013.01.02, 11:13 AM
I have a an rc car (an MR01 clone picked up used in a lot recently). It never ran extremely well but it officially died 48 hrs ago. It stopped responding to commands from the transmitter. Nothing is burned on the PCB. Everything was stock.

I attached its motor to another car and the motor isnt dead.
I pulled out the soldering iron and disassembled the car expecting to find a wire that had popped free from its soldering point. Upon inspection i found none.
I pulled out the multimeter and performed continuity test (first time !) expecting to find a broken wire. Every wire path from the toggle switch to the battery terminals made my multimeter beep. No broken wires so far .

I tested the positive and negative battery terminal wires that led to the PCB for continuity. Both made the multimeter beep.
I tested the positive and negative wire terminals on the PCB itself and ...no beep. No continuity. I get a number fluctuation on my multimeter LCD screen but no beep.
I assume this means that the short is on the board itself and not a wire (as all wire paths made my multimeter beep). Does this sound correct?

monkeyZ
2013.01.02, 06:29 PM
I have a an rc car (an MR01 clone picked up used in a lot recently). It never ran extremely well but it officially died 48 hrs ago. It stopped responding to commands from the transmitter. Nothing is burned on the PCB. Everything was stock.

I attached its motor to another car and the motor isnt dead.
I pulled out the soldering iron and disassembled the car expecting to find a wire that had popped free from its soldering point. Upon inspection i found none.
I pulled out the multimeter and performed continuity test (first time !) expecting to find a broken wire. Every wire path from the toggle switch to the battery terminals made my multimeter beep. No broken wires so far .

I tested the positive and negative battery terminal wires that led to the PCB for continuity. Both made the multimeter beep.
I tested the positive and negative wire terminals on the PCB itself and ...no beep. No continuity. I get a number fluctuation on my multimeter LCD screen but no beep.
I assume this means that the short is on the board itself and not a wire (as all wire paths made my multimeter beep). Does this sound correct?

Can you check voltages instead of continuity? The board probably has a reverse polarity protection diode on the board so you would not be able to check continuity on the actual board. What you really need to do is put one probe on the gnd of the pcb and then probe around the power supply section of the board and see if you are actually getting power to the board. If you post pictures I can tell you where to probe.

good luck,

Bryan

Customizer
2013.01.02, 11:40 PM
Thanks for the reply :) Yes i can check voltage with my multimeter so feel free to direct and i'll do my best to follow along .

Below is a picture of the board :
http://i148.photobucket.com/albums/s14/TradeItems/Myboard_zps47b36e4d.jpg

It's only when i touched the probes to the far left black ground and red power wire on the pcb (someone may read this next year with the same problem so i'm trying to be descriptive lol) that the multimeter did not beep.

Edit:
While waiting for your reply i gathered a bit more information.
* With all 4 AAA batteries in place i checked for voltage. Both battery cases on either side have unbroken circuits (2.4v registered. Actually 2.7 as these are NIMH Rayovac batteries and each battery reads as 1.3 volts)

* Both battery cases registered voltage when using the probes to touch the positive and GND wires on the PCB as well (i.e. - probe on the GND wire on the pcb and the + probe on the opposite side positive battery case contact. I repeated the same process with the positive side PCB wire and the negative wire on the opposite side battery case).

* All wire circuits read voltage when using the contacts on the toggle switch as well.

All that is left is figuring out where else i can probe on the board itself to see if i get a voltage reading. Nothing on the board looks burned or damaged at all.



Thank you very much for the reply and input.

P.S. I have 2 LOSI boards (AM27) that i might as well use if i cant repair this board. Do you know if anyone has used a Losi Micro T board in a Mini Z before?

Draconious
2013.01.03, 03:59 PM
Did the crystal Die? Cheap crystals do not last long...

Customizer
2013.01.03, 05:19 PM
I believe i performed a check just in case that was the issue already but i'll double check just to be on the safe side while i wait for MonkeyZ to tell me where to place the probes on the board to check for voltage. It never hurts to double check :)
Thanks for the suggestion.

Customizer
2013.01.09, 04:32 AM
I'm posting this for that "One Guy" or kid who will google search the same problem 8months to 2 years from now. We've all been "that guy" behind our pc screens when some mystery problem strikes. Hopefully this helps.

You'll need a multimeter and you'll need to know how to use it . Watch this video for instructions and a suggested multimeter:
http://www.youtube.com/watch?v=bF3OyQ3HwfU


With that said - The car is working again. I have no clue why. Here is what i did:
1. Cleaned the car completely (removed carpet fiber from every location i spotted it) . Disassembled the car (separated front half from back half. Did not remove motor from it's back half location).

2. I used my multimeter to first check for "continuity" (i.e. if there were any breaks in a wire or circuit). I checked the battery terminals, the on off switch , , the motor wires and all power/red and gnd/black wires. All test showed the wires were functioning as they should.

3. I connected the motor (back half of car) to another car to check if it worked. It did.

4. I used my multimeter to check for "voltage" (i.e. if power was being received from the AAA batteries). I checked the battery terminals, the on off switch , the batteries themselves and all power/red and gnd/black wires that led to the board. All test showed power was being received as it should. Specifically 1) my batteries read at 1.3 volts individually and 2.7volts in series 2) The power (red) wire on the board was receiving 2.7 volts and the black wire on the board (GND) was also receiving 2.7 volts 3) Most importantly IMO when touching the GND wire with the black probe and touching the red probe on many points on the board the multimeter reading fluctuated showing the board was receiving power. I touched mosfets, diodes...i touched everything.

5. Once every test was completed and i was convinced there was nothing wrong with the board i decided that i would solder new thicker wires to every contact point in the vehicle. That would have taken some time so before i did that i decided to reassemble the vehicle one last time. Upon reassembly it began working again and responding better than it had before taking it apart.

SMH. Thus is life.

Customizer
2013.01.12, 10:51 AM
I rewired the IW01 and no more problems :)

I replaced the stock Power wire and GND wire with new thicker gauge wire and used relatively generous amounts of solder heh.

I ran it for at least 25 minutes straight with no unexpected power failures during that time. I ran it into a few things to see what might happen and it still kept responding and running. I think i now understand why some RC owners really enjoy tuning. I have better RC's than this IW01 but for some reason its my favorite.