Problem with MT8870DE DTMF Decoder

[jepoy12]

Im trying to make this circuit then use a N1208 nokia Cellphone as the tone source. I putted a LED to each output to see whats going. It worked at first but without Q2 ouput going high. I dont know why its not working, I checked it with the Volt Meter and it gives me .5V reading. Other outputs work properly only the Q2 is not. When I rechecked I found out that I mistakenly connect the .1uF at pin 17 to the ground instead of connecting it to the voltage source.

I then fixed the wrong connection and try to rerun it again. Here comes another new problem the whole thing is not working. All the output doesnt change state when numbers are pressed and the Q2 pin still on low.

Oh god did I just wasted my 10$ for this decoder? can this problem still be fixed?
Help me please. I ordered this chip from other country and waited 5 days just to destroy it.

 

[OLIVE2222]

Hi, the mistakenly connected 100nF cap (you mention .01µF which is 10nF) should not be the problem root. According to the HT9170 datasheet the available output current is 2.5 mA maximum. Are you using limiting resistors or a buffer at the the data outputs?

Olivier

 

[(*steve*)]

I've looked at the datasheet, and if you only made that small wiring error, I can't see that it would have damaged anything.

However, it is a CMOS chip, and as such may have been damaged by handling it.

I would investigate if my input signal was of the correct amplitude and that the crystal oscillator was operating at the correct frequency first before assuming I broke something.

 

[jepoy12]

Thanks for the reply.
@Olivier
Im using MT8870DE btw. No, I just directly connect the led to it.

@Steve
I dont have equipments to test them. If the problem was on the input why did it run on the first attempt? and why the Q2(I mean the D1 on the diagram) was on low and the rest was high on standby mode.

 

[OLIVE2222]

jepoy12, the MT8870DE don't need the Crystal load caps !
better to add a driver for the leds or as a first test check the outputs with a multimeter.

Olivier

 

[jepoy12]

I already done that. the result are still the same pin 12 still on low.
the TOE is on high so the output pins should be also all high right? but why only Q2 still on low?

 

[OLIVE2222]

Is the Q2 output still low when you set TOE low?
Olivier

edit: and are other outputs working according to the decoded tone?

 

[jepoy12]

When TOE is on low it gives me .5V all output pins.

Yes the other 3 output pins give right outputs but Q2 didnt change. that was before when I put the C2 on ground. but now its all mess up.

edit
I tried to run the circuit this time and number 0, *, # gives right output but again the Q2 did not change still low.

 

[OLIVE2222]

OK. Don't feel this is linked to C2 error but from what I can see Q2 ouput is out of order.
Olivier

 

[jepoy12]

what you mean by out of order? manufactured mistake?

 

[(*steve*)]

out of order = wrong

cause? who knows (yet)

I would try grounding the DTMF input to exclude that the chip is latching on to some noise.

I would also measure the supply current and see if it is within specs.

 

[OLIVE2222]

DEAD!

 

[(*steve*)]

DEAD!

I'd want to exclude some spurious input signal, but yes, literally (and quite possibly actually) true

I would tend to suspect damage from static over connecting that capacitor incorrectly.

You may find that the quiescent current is higher than normal due to a mosfet having a (most likely) destroyed gate insulation. This would be a clincher as far as I was concerned.