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1 hour ago, xyzzy said:

Keep in mind that the displays on the power supply have two modes.  One shows the max values you are setting, the other shows the actual values as it supplies power.  You can't get both current and voltage to be specific values, it would violate Ohm's law.  You get one, then the other is forced based on the resistance of the load.  You set maximums for both, but only one max, V or I, will be reached and the other will be whatever V = I * R produces based on the load's R.

So maybe the power supply needs to have its outputs off to show the set points?  Most seem to let you adjust while on, and the digits will flash to let you know you are in set mode rather than measured mode.

If the power supply isn't connected, it should read 0 A when on.  How can it supply current when there is no circuit?

My power supply works in either Constant Voltage or Constant Current.  I was trying to set the current to 0.5A, then adjust the voltage.

To set the current, you first set the voltage to 3-5V, then turn the current knobs to zero, and short the output terminals. Then adjust the current to the value you want.  Problem is, I can't get it to show any current, it just switches back to Constant Voltage mode. There's a known problem with this power supply blowing the MOSFETS. It has 4 and I was trying to figure out how to test them. I found this link https://electronicsbeliever.com/how-to-know-if-mosfet-is-defective/

I don't know if these tests are good/bad/useless, or if there are any others you could point me to?

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On 1/29/2023 at 6:24 PM, Kalanag said:

My test result: The LED doesn‘t light up if the device is just connected to an USB charger. Connected to my PC the LED lights up.

I measured the voltages according to @mikepilk

The results (just) on the USB side of the board are very different! The REGV output of the CM108 has the correct voltage of 3,3V where the faulty board just has 0,64V.

2DAA9C1B-8F7F-4898-8DC4-6570076E5070.thumb.jpeg.52f8d7fedf7eb1417bebf726e722da73.jpeg

 

Thanks Kalanag,

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

One can potentially turn this into a beat amplifier (with a speaker or headphones attached).

 

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1 hour ago, TGX said:

One can potentially turn this into a beat amplifier (with a speaker or headphones attached).

I‘m sure that is feasible. „SPK“ should mean „speaker“.

CC565D19-147C-49B8-A3C6-854EC2AFB569.jpeg

20 hours ago, mikepilk said:

The article does say MOSFET testing, and starts with the diodes. I assume they are part of the MOSFET? Looks like 2 of mine have failed.

https://electronicsbeliever.com/how-to-know-if-mosfet-is-defective/

MOSFET testing (video)

Edited by Kalanag
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On 1/29/2023 at 6:53 PM, Kalanag said:

You are right! But if the capacitor is o.k. the C108 is shot 😞

My new meter has arrived, which can measure Capacitance. Can this be used to check C1 in situ, or does it only work with 'free' components - there's a little gizmo to sit them in.

It can also measure Hz, diodes test,  and transistors (hFE), if that's of any use.

20230131_150551.thumb.jpg.06066c9c5c028c424cdad4bd0a335acd.jpg

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6 minutes ago, Kalanag said:

My C1 reads 3,8 microfarad constantly! It never drops to zero. I‘m not sure your C1 is fine!

IMHO...those caps never go bad...they just don't.  It is two metal plates separated by a bar of ceramic.  If it is not a dead short or an open circuit...it is just fine. My bet is that the chip is bad.

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4 hours ago, Kalanag said:

I‘m sure that is feasible. „SPK“ should mean „speaker“

I've already seen a variation of this microphone where it does have the speaker output jack. But is it connected to the large IC that in this case isn't working? if you want to use it for beat amplifier just connected to the output of the ICU of the input is connected to because that will work just fine. Is actually designed for a crystal input and driving a speaker output so it works perfect for making a beat amplifier you don't need the rest of this at all

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7 minutes ago, JohnR725 said:

I've already seen a variation of this microphone where it does have the speaker output jack. But is it connected to the large IC that in this case isn't working? if you want to use it for beat amplifier just connected to the output of the ICU of the input is connected to because that will work just fine. Is actually designed for a crystal input and driving a speaker output so it works perfect for making a beat amplifier you don't need the rest of this at all

The speaker output is connected to the CM108 line out pins 30 (left) and 32 (right) via two (missing) capacitors.

33 minutes ago, LittleWatchShop said:

IMHO...those caps never go bad...they just don't.  It is two metal plates separated by a bar of ceramic.  If it is not a dead short or an open circuit...it is just fine. My bet is that the chip is bad.

You are right most likely. But I don’t wanna give up yet 😉

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10 minutes ago, Kalanag said:

The speaker output is connected to the CM108 line out pins 30 (left) and 32 (right) via two (missing) capacitors.

So in other words you wire it direct up to the LM 386 and use it as a beat amplifier

Or even take the output of the LM 386 and run that into the computer input. Which is basically what the original version of this one did it anyway and could probably still powered off the USB port. Only usable to do if your large IC seems to not be functioning otherwise just use it as the way it is.

Then as far as the beat amplifier goes you don't need the output jack because the computer sound will do the same thing. Just be careful not to increase the volume too much because I found it was very sensitive to feedback the microphone is way too sensitive to audio noise around it including the computer speaker outputting whatever you're picking up.

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55 minutes ago, JohnR725 said:

I've already seen a variation of this microphone where it does have the speaker output jack. But is it connected to the large IC that in this case isn't working? if you want to use it for beat amplifier just connected to the output of the ICU of the input is connected to because that will work just fine. Is actually designed for a crystal input and driving a speaker output so it works perfect for making a beat amplifier you don't need the rest of this at all

image.png.fd1ba9f25e8f8c5120bef23fa43f4e6a.png

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33 minutes ago, LittleWatchShop said:

image.png.fd1ba9f25e8f8c5120bef23fa43f4e6a.png

That I'm familiar with as it's currently sitting in front of me were it's been for the past couple of whatever to remind ma'am supposed to make a circuit board to go with it.

That's not what I was talking about I've already seen a modified version of the current design were somebody added in the speaker output so right next to the little USB connector is a green connector for something. But unfortunately all the ones I'm currently looking at don't have it so I have no idea where they saw that previously

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22 minutes ago, mikepilk said:

With the probes reversed it reads 0.0

O.K. so the first measurement was done right. To be sure whether the capacitor is faulty or the CM108 respectively other peripherals it has to be desoldered. But first I would measure the capacitors that xyzzy mentioned in his post at 5:05 yesterday.

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2 hours ago, Kalanag said:

O.K. so the first measurement was done right. To be sure whether the capacitor is faulty or the CM108 respectively other peripherals it has to be desoldered. But first I would measure the capacitors that xyzzy mentioned in his post at 5:05 yesterday.

I assume that capacitors must be tested with no power to the board, and that they should give a steady value?

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1 hour ago, mikepilk said:

I assume that capacitors must be tested with no power to the board, and that they should give a steady value?

Yes.  However, when testing a capacitor "in circuit" there is the possibility of energizing other active components which will interfere with the reading.

Again...testing surface mount capacitors is truly a distraction.

The chip?

4 hours ago, JohnR725 said:

That's not what I was talking about

Same chip...same output. 

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12 hours ago, LittleWatchShop said:

Yes.  However, when testing a capacitor "in circuit" there is the possibility of energizing other active components which will interfere with the reading.

Again...testing surface mount capacitors is truly a distraction.

From @xyzzy

Quote

If the current powering the board is reading new zero, one might think it can't be a short, but that might not be the case.  The CM108 regulator might automatically shut down if shorted.

Possible shorts in REGV are C1 (C5 in the C108 example schematic)

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? 

C4-6 look to all be connected to the same line, so it may only be one? 

Edited by mikepilk
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37 minutes ago, mikepilk said:

I'm checking the capacitors

LittleWatchShop is right, this type of capacitor is exceedingly unlikely to fail and when they do, they tend to leave a crater. Also, testing them in-situ is at best a confusing exercise. You have no idea what the rest of the board is doing so you can't trust your readings.

My money is on the IC having failed.

Edit: the sane thing to do would obviously be to buy another board, but none of us would be here if we were entirely sane and didn't like to tinker. You could acquire a replacement IC and a hot air station (doesn't need to be gold plated, most anything off ebay will do) and try to replace it?

Edited by fellerts
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22 minutes ago, fellerts said:

LittleWatchShop is right, this type of capacitor is exceedingly unlikely to fail and when they do, they tend to leave a crater. Also, testing them in-situ is at best a confusing exercise. You have no idea what the rest of the board is doing so you can't trust your readings.

My money is on the IC having failed.

Edit: the sane thing to do would obviously be to buy another board, but none of us would be here if we were entirely sane and didn't like to tinker. You could acquire a replacement IC and a hot air station (doesn't need to be gold plated, most anything off ebay will do) and try to replace it?

Ok I'll give up and bin it. I'm loathe to buy another and wait for weeks, when the same thing may happen - it only lasted for about an hour. At least I've had some fun trying to fix it. 

Now I've got a new meter, and plenty of time, I'm going to carry on and learn about testing electronics, so I'll know what to look for next time. I've got a long way to go. I need to try and fix my power supply. Apparently the MOSFETs are prone to fail - I spotted two on a large heat sink. One tested OK, testing the other made no sense. After lots of head scratching I Googled the very faint number - turns out to be a "diode array". It looks identical to the MOSFET along side it!  These electronics people don't make it easy. 

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