Problem with Logitech Audio PCB (No Sound Output)

[Blackdragonier]

Hi.

I am new to this forum. If I make any mistake regarding the post, let me know.

So, let me start with the whole story. I am using a logitech normal 2.1 stereo audio setup for my PC. Last 1 month I noticed that my right side speaker has less sound than the left side. So, I searched for online tutorials and found not so close but helpful tips. Both speaker goes through one single 3.5mm jack to the back panel of the speaker. I checked the speakers with my laptop and android cellphone, but both speaker sound output is at same level. This is how I came to know that I should check the inside of the PCB of the speaker system.

So, when I checked the PCB there was one capacitor got swollen and from the Youtube tutorials, I learnt that I should remove and replace it with the same type of capacitor. Before removing the capacitor, I used a tester screwdriver to check the responses of on different capacitors. And my left side speaker buzz sounded very high. And the right side had lower buzz sound. Also, it has a 3rd speaker under the bass control system. After doing the tester screwdriver buzz sound test for 2 - 3 minutes, then the sound stopped permanently. I got scared if I might damaged any parts of the PCB or speaker. Then I immediately removed the faulty blue color swollen capacitor and replaced it with the same type of new gray color one (check attachments). After that, I checked if the tester screwdriver buzz sound would work again. But nothing happens now. Edit: the speakers still works fine with Laptop and cellphone but not with the amplifier. Also, even after replacing the capacitor, no sound output is coming of any of the speakers. I checked for the power availability with my multi-meter and it seems fine. I also tried checking the components using tutorials from Youtube but I think I am beating about the bush.

I am actually confused if something happened to the PCB or components that I am unable to check through. Please help me out here. How should I do the checking properly? Any step by step guidelines for checking the PCB or sound system would be helpful. I have attached a short video and some pictures of the audio system.

Thanks in advanced. If I am missing anything also let me know. I am not an engineer, just an enthusiast who is trying to DIY, as there are no known such engineer in my area.

Regards Imran

 

[Audioguru]

Photographs do not "measure" which electronic parts that your "tester buzzing screwdriver" damaged.
We look at the datasheet of a poorly working amplifier and feed in a sinewave of the correct amplitude, then test along the signal path with an oscilloscope to see where the signal is bad.
Logitech products are cheap, buy a new one then keep your buzzing screwdriver tester away from it.

 

[Blackdragonier]

Update:

After replacing the faulty capacitor, I used the tester screwdriver again to check if the buzzsound is produced somehow. But no sound is coming out now. Also, I remembered that the screwdriver lighten up before, I mean before the buzzsound issue. Any pins that I touched with the Screwdriver would lighten up as indicating the voltage availability on the PCB. But after the buzzsound issue the screwdriver never lightens up no.w Also, after replacing the faulty capacitor, the result is same.

 

[BradtheRad]

When a capacitor bulges, it may be faulty itself, or...
Perhaps the initial cause was another component going bad, and then exposed the capacitor to overmuch voltage or overmuch current. Thus it may not help if you only replace the capacitor.

The original cause is not always easy to track down. Since the problem started only in the right channel, then the power supply probably was good. A casual guess is the output stage broke down. It may be a transistor, it may be an IC.
However at this point you get no sound at all, correct? Now there could be a problem in the entire IC, or even the power supply.

Does the unit turn on? Does it light up? It would help if you can extract any audio signal from the circuit board, and run it into a separate amplifier/speaker. This gets into risky territory. You need to protect the units from damaging each other. Jumper wires with alligator clips are handy for this sort of thing. And a small value capacitor in series to ensure that no excessive voltage or current travels between the units.

 

[Blackdragonier]

Hello.

First of all thanks for the information sharing and suggesting. Both of my interchangeable speakers works 100% with my laptop and my cellphone.

So, coming to the important point. I figured that the entire board is dark and has no electricity supply. This made me focus on the Transistor at first. So, I figured that the transistor somehow burnt out and totally zapped. And I also realized the number written on the Transistor has no meaning at all as it says - BR 012. I searched online and I could not find one single source to help me on the transistor. Now, I am really confused if my transistor was PNP or NPN or 1st Pin Base or 2nd Pin Base or 3rd Pin base. Because pins are not responding to the Multimeter. My head is all messed up with this problem.

I am also not sure to find an alternative of the transistor now. Now, I have moved to problem phrase 2.

Help me if anyone can. Thanks in advanced.

 

[Blackdragonier]

Hi again.

Posting in the same issue again. I just went through a lots of documentation and found multiple problems with one PCB. Like my my transistor was BR 9012 which blew up and I replaced it. Then I checked with the IC D6282 and replaced both circuits. Still there was no sound output So I studied resistors and saw something different.

My 33k Ohm resistors shows 22k ohm reading in digital multimeter resistor test. Also, some other resistors like 18k ohm shows 11k ohm, 7.2k ohm shows 6.1k ohm, etc.

My problem now is that I am confused whether I should change the resistors or not. Please help me out here.

Thanks in advanced.
Dragon

 

[BradtheRad]

Do you measure the resistors in-circuit? Then likely neighboring components contribute their resistance (in parallel), affecting the reading on your meter.

To do the job properly means snipping one resistor lead, so you can test it out-of-circuit. However it looks as though there are too many resistors for that to be practical.

On a remote chance, I would try the following in hopes I can determine whether the transistor is NPN or PNP. It requires a lot of Sherlock Holmes thinking.

1) Test for positive voltage or negative voltage at each of the 3 pads, relative to 0V ground. (You also need to figure out whether the power supply is single polarity or split bipolar.)

2) It seems to me if two pads are more positive than the third, then the transistor is NPN. If two are more negative, then it's PNP. This is a chancey supposition of course.

3) Follow a trace from every pad, looking for a series resistor with very high ohm value. That is most likely the bias wire.

4) If the high-ohm wire carries positive voltage then it suggests NPN transistor.
Further proof is if it carries an audio signal which can be heard if you feed it to an amplified speaker.

5) If you decide to try a replacement transistor, a wise safeguard is to insert resistors (using jumper wires), in order to limit current in the collector and emitter.

6) If the board works a little, then you're doing okay. This might be a sign you can take the next step and solder the transistor in place.

7) Reduce the supply voltage a few volts, just to play it safe while you're testing the repair. Hold the transistor between your fingers, to see if it heats up alarmingly.

8) If things work okay then restore full power.

 

[BradtheRad]

Doesn't the other channel have a similar transistor? Compare their circuitry. Test volt levels. It should give you a clue to characteristics of the broken transistor.

 

[Blackdragonier]

Hello.

Thank you for all of your support and specific replies. I am attaching a block diagram of my own understanding of the PCB and I worked and learnt through so far.

After you check the diagram here



[found at: imgur. com /a /wxc4eVu]

I have already replaced some of the parts on the PCB.

1. Replaced one swollen 16v 470uf capacitor. Others are okay.
2. Replaced the burnt PNP BR 9012 transistor with the exact model transistor.
3. Replaced the Amplifying circuit D6282 with CD6282CS model (slightly change in the name).
4. Replaced some small capacitors like 100uf 16v, 2.2uf 50v.

After completing the steps. When I power up the PCB and put the duo channel audio input 3.5mm jack I hear some buzz noises on the speaker for like 5 seconds then silent. No sound on touching the PCB at all.

Things that I am unsure about -

There are ceramic capacitors, tantalum capacitors, resistors with variations on ohms, rectifier diodes. I am not sure how to determine if they are good and bad. Also, there is another NPN transistor related to the bass sound effect. Also, I am not sure if I purchased and replaced the correct amplifier circuit, previous one model was CHMC S2702 D6282 and new ones are written CD6282CS. Because after attaching the power cable both the amplifying circuits become real hot. Like I mean it. I checked the small IC UTC4558, it's fine.

Things I am going to do -

1. Change the diodes / rectifier.
2. Give my life fixing this shi**y PCB.

I am hoping to get some quick witty steps after this reply.

Thank you all and waiting for your kind replies.

BD

 

[Audioguru]

The CD6282CS ICs are the power amplifiers that drive the speakers with a few Watts. If you connected their pins backwards or connected the polarity backwards of the power supply then they will get very hot and burn out.

 

[Blackdragonier]

Okay. Audioguru. Can you please post me a pinout of the CD6282CS or my old D6282. I think I need a comparison here.

Waiting for your reply.
BD

 

[ads-ee]

You know you can use an internet search to find datasheets for many ICs...
Type the following into google and the first link is to the datasheet which has the pinout of the part.
"cd6282cs datasheet pdf"

I would use a LMGTFY link but results are an entire page filled with ADs that don't even link to the IC's datasheet. Useless site now.

 

[Blackdragonier]

I see, I found some Chinese documents on the circuit CD6282CS but not on my previous D6282. I am trying to translate the document now but still unsure about the comparison, whether that's the exact circuit replacement or not.

I am still searching for more documentation and highlights. Thanks for giving proper support.

 

[Blackdragonier]

Update:

Things I have tried so far:

1) I checked the IC getting hot and checkout the pins of the IC. And then I checked again with the datasheet and I came to conclusion that I misplaced the IC backwards. So, I desoldered the IC and changed the sides again.

2) I checked with voltage power supply on the PCB. It seems normal.

Result: Still no sound output.

I don't know what to do next. And waiting for the Diodes to arrive from online shop.

Thanks
Dragon

 

[ads-ee]

1) I checked the IC getting hot and checkout the pins of the IC. And then I checked again with the datasheet and I came to conclusion that I misplaced the IC backwards. So, I desoldered the IC and changed the sides again.

Depending on how the chip pins were connect when in circuit backwards, it is highly likely the IC is now damaged and will never work. You probably need to get a new IC and install it.

 

[Blackdragonier]

Hello.

Update:

As ads-ee said that the IC may have been damaged, I quickly replaced the damaged IC with new ones. But still there are no audio output.

Now I am really going blank on this PCB design. I don't know what to do next.

Thanks for the help.
Dragon

 

[Audioguru]

When the IC was damaged by being connected backwards then maybe it damaged a part of the power supply. Measure the power supply voltage to see if it is normal or bad.

 

[Blackdragonier]

Okay.

Let's start from 0 again. Can anyone please explain the power supply part here? I mean what is a power supply for an audio PCB stand for. What are the requirements to make one? What are the parts of this power supply?

With details, like images or video would be great.

Thanks for the help.
Dragon

 

[BradtheRad]

The power supply appears to be at the left edge of your photograph:

4 diodes D1 D2 D3 D4

Two labels 'AC' where wires may be soldered

Largest capacitor on the board

Measure DC voltage on the capacitor leads. A reasonable value is 10-15V.

 

[Blackdragonier]

Hello to all.

And thank you all for your kind replies. I have some update and a hypothesis about the problem. I also attached link of some pictures if that might give a clear understanding.

1. I replaced both IC CD6282CS with the new ones. And still no audio output.

2. I checked with the Power supply output and capacitor lead shows 18.22 DC voltage.

3. I also checked the transistor and capacitors on board, they are working fine. But I am confused about their DC voltage output as there are both PNP and NPN transistor on the board and I don't know how to test or verify the DC output voltage on transistors.

4. I have a hypothesis conclusion about no sound output:

The circuit that was on board before the issue was CHMC S2702 D6282 and I replaced this IC with the CD6282CS. I tried to find the CHMC S2702 D6282 pinout charts and datasheets (if available) but I could not find the exact. Rather, I found YD6282 and similar IC pinouts and datasheets. The CD6282CS has some datasheets and pinout charts available. But they may be company based specific. My hypothesis is that the IC CHMC S2702 D6282 is not the same IC as CD6282CS or doesn't have the same pinouts or is not replaceable with.

Reason 1: CHMC S2702 D6282 was positioned backwards (model written side was faced to the PSU side) and I put the CD6282CS in the same direction of the PSU. But it didn't work (no sound output from any of the two ICs') that way and rather the ICs' become really hottest thing on the PCB. Then I changed replaced it with the new ICs' but on the opposite direction (positioning opposite of PSU by reading the pinout chart of the CD6282CS confirmed) and still it didn't work or become hot at all.

Reason 2: The PCB pin diagram is somewhat different than other audio amplifiers. May be a little too much complex (for me though as I am new to this). It could be built for only the exact types of ICs' and Capacitors. I mean, they are not replaceable or cannot be interchanged anyhow.

Reason 3: If it was the replacement IC, then why didn't it work in the first place? If it wasn't then, why didn't it work even after re positioning? Both time output is 0. If the only replacement for the IC CHMC S2702 D6282 is CHMC S2702 D6282, then I have nothing else to do. Because these circuits are not available in my country or even abroad. That means I am unable to purchase it from anyway.

I have given my hypothesis based on the logical explanations that I got from working through the whole PCB.

I have attached images here: https://imgur.com/a/LjTK9a4

Waiting for your opinions.

Thank you again.
Dragon