Chinese Timegraphers

[Kalanag]

2 hours ago, mikepilk said:

I'm checking the capacitors and getting odd results with C4,C5,C6 and C10. So I tried them in beep mode, and can get them to beep with the probes connected in either direction. Is that a faulty cap, or could it be a faulty C108? …

If you got at least the beep the capacitors should be o.k.!

I also think that the CM108 is defective

If you were nearby I would be happy to investigate your device further having my working device for comparison. I even have a hot air station

[mikepilk]

1 hour ago, LittleWatchShop said:

Indeed. I would double check. Now you have a new meter to aid your teating.

I did, and it is actually working. If I ignore the instructions I can get it to work. I set the voltage to 5V and limited the current to 0.5A. When connected directly to the board, SPKR (GND) and R3, the board is drawing 0.02A

I put the meter in line - reads 0.025A (and 0.28V at C1)

Edited February 1, 2023 by mikepilk

[Kalanag]

0,02A seems to be a bit low. It doesn‘t indicate a short circuit.

Edited February 1, 2023 by Kalanag

[mikepilk]

1 hour ago, Kalanag said:

If you got at least the beep the capacitors should be o.k.!

I also think that the CM108 is defective

If you were nearby I would be happy to investigate your device further having my working device for comparison. I even have a hot air station

But a beep in both directions ?

Thanks for the offer and help. It only cost me £27 including postage, so no great loss, and not worth trying to change the chip. It only lasted an hour, but has given me hours of entertainment.

[Kalanag]

2 hours ago, mikepilk said:

But a beep in both directions ?

That‘s o.k.!

[xyzzy]

3 hours ago, mikepilk said:

I did, and it is actually working. If I ignore the instructions I can get it to work. I set the voltage to 5V and limited the current to 0.5A. When connected directly to the board, SPKR (GND) and R3, the board is drawing 0.02A

The key is follow the correct instructions!

In CM108 datasheet version 1.3, suspend mode power consumption is 320 mA.  I don't believe that.  Way too high.  Speaking of specs that are way too high, can your new "60 MHz" meter measure the crystal frequency?  Then I found CM108 datasheet version 1.6, and now suspend mode is 300 µA and total power consumption is 70 mA.  That makes more sense.

But we must also consider the the LM386 amplifier section is drawing power too.  This part is a little more analog than what I work with.  But I have another Chinese 3d printed microphone with a LM386 amplifier section and an analog out.  At 5V it draws about 4 mA.  So assuming it's the same here, that leaves 16 mA for the CM108.

That's too much for suspend mode.  But not an obvious short either.

Depopulating R6 and C16 would disconnect the CM108 from the amplifier.  The idea is somehow the amp section is drawing too much power from the mic bias output.  Other than that, I think the CM108 dying is the only other explanation.  Probably some flaw in the board design allows the maximum limits to be exceeded, rather than a piece of silicon just up and dying for no reason.  Voltage from the lm386 out of limits?  Or maybe the amp continues to supply power from the big cap after USB is disconnected and Vdd is 0V, so it exceeds a MICIN > AVdd or VBIAS > AVdd limit?

On 1/31/2023 at 5:23 AM, TGX said:

Do you know anything about the SPK pins? Since this is a USB audio interface, maybe you could play audio from PC?

Yes, it can.  It even showed up on the computer as an output while it briefly worked.  The CM108 recording function can be disabled, but the line out can't be. Two 470 µF capacitors should be in C2 and C7 to connect the line out pins to a socket that would mount into the holes by SPK.

6 hours ago, mikepilk said:

I'm checking the capacitors and getting odd results with C4,C5,C6 and C10. So I tried them in beep mode, and can get them to beep with the probes connected in either direction. Is that a faulty cap, or could it be a faulty C108? 

Measuring the capacitors in situ isn't going to work well.  But it's not really necessary as they aren't going to fail by having an incorrect capacitance.  They are just a point where a solder bridge could exist and create a short.  They could also become disconnected from poor solder joints.  But I think the band gap and regulator in the CM108 should still work (and they aren't) even with most, if not all, of the capacitors removed.

[mikepilk]

13 hours ago, xyzzy said:

The key is follow the correct instructions!

It was following the instructions on the power supply that led me to the conclusion it was faulty. To set the current limit the instruction is to set the voltage to 3-5V, short the terminals, then set the current. But that doesn't work, it never registers a current. So now I set the voltage to the desired level, use the meter as a load in current mode to set the current limit. 

13 hours ago, xyzzy said:

Speaking of specs that are way too high, can your new "60 MHz" meter measure the crystal frequency?  

 No, I think you are right about the limits of the meter, I got something but it didn't make sense.

Thanks for your knowledge and patience. I love learning new things, and I have. I'm watching lots of Youtube vids on fault finding electronics - I'm probing everything 

[LittleWatchShop]

1 hour ago, mikepilk said:

I think you are right about the limits of the meter, I got something but it didn't make sense.

If you measured at the crystal, you may have stopped the oscillator

[xyzzy]

7 hours ago, LittleWatchShop said:

If you measured at the crystal, you may have stopped the oscillator

It's an oscillator module, rather than just a crystal.  That be less likely to be affected by the meter, right?

[LittleWatchShop]

3 minutes ago, xyzzy said:

It's an oscillator module, rather than just a crystal.  That be less likely to be affected by the meter, right?

Yes, absolutely.  I did not notice that it was a module.  My bad.

[mikepilk]

11 hours ago, LittleWatchShop said:

If you measured at the crystal, you may have stopped the oscillator

What does that mean - would it have damaged it ?

Not that it matters now, but useful to know. 

[LittleWatchShop]

22 minutes ago, mikepilk said:

What does that mean - would it have damaged it ?

No, it would not have damaged it.  Just might have stopped it from oscillating due to load impedance.  But as noted earlier, this is an oscillator can, so it has a low impedance output and would not have been disturbed but the loading of the meter.