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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 12th Jul 2018, 3:57 am   #1
Francis
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Default How do you test a chip-on-board (COB)?

Hello, everyone,

I bought this very large radio controlled toy car, but it doesn't work.
I checked every component on the board and they are all within their right tolerances. I unsoldered every single SMD component (to test them) and soldered them back again (as in the image). It's the first time I removed these tiny parts and I think I did quite a tidy job soldering them back in place, if I don't say so myself. After all that work, it still won't go. The only part I wasn't able to test was the chip-on-board (COB). Is there any way of testing this part. I'm quite certain the transmitter works okay.

In one of the images you will see a large resistor near the chip-on-board. There used to be a SMD resistor there, but I lost it, so I replaced it with large one, which is of the same value.

I have a quite good basic knowledge of components and how they work and I can correctly test and replace the faulty ones with new ones of the correct value etc., but that's about it.

Much help would be appreciated and thank you in advance.

Francis
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Old 12th Jul 2018, 5:19 am   #2
Argus25
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Default Re: How do you test a chip-on-board (COB)?

One thing to do would be to put an oscilloscope on the output pins of the COB (which you could figure out or find by trial and error) There should be an output level change , a DC level, or possibly a carrier signal, when the transmitter button is pressed.

This test would simultaneously show that both your transmitter & the COB is working.

The output signal from the COB would be expected to pass to a detector & comparator or possibly just some transistors and then to the relays.

If you cannot find an active output from the COB then it would be either the transmitter or the COB that is faulty. If your scope had a wide enough bandwidth you could see the transmitted signal from the transmitter.

Without test gear it could be difficult, though a crystal detector diode and earpiece might demodulate enough of the transmitted carrier to hear a faint signal to prove the transmitter is definitely outputting something. But for it to work the transmitted signal has to have the correct frequency and modulation and the receiver has to be correctly tuned to that frequency. Are there any optional channel settings in the transmitter & receiver ? There might be some so two or three of the same model cars can be used together. If its on the wrong one that could also explain it.
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Old 12th Jul 2018, 11:27 am   #3
Refugee
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Default Re: How do you test a chip-on-board (COB)?

The go for check on that is the joints between the little board and the main board.
The pads come off with monotonous regularity around those type of joints.
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Old 21st Jul 2018, 7:38 am   #4
Francis
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Default Re: How do you test a chip-on-board (COB)?

Hello, everyone,

I apologise for the delay in replying and thank you for your great answers.

I bought another similar working model complete with transmitter. When it arrived I checked to see if it worked, it worked great. Then, I tried the transmitter from my car to it nothing happened, but when I tried the transmitter from the bought car to my car it burst into life! Everything worked just great! I'm very happy with this, because as I said I'm just an amateur. Nothing 'popped' on the board, which means I tested everything thoroughly and I also soldered those 'micro' components in correctly.

I'm very pleased with the result and I don't need anymore answers.

Thanks, again, for your help.

Francis
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