Dell Harman Kardon Dead Left Speaker

[dorfman]

Working on an early 2000s dell / harman kardon computer speakers.

Suddenly only the right speaker works. No sound is coming out of the left. Also, the right is much louder than when both speakers were working. The minimum volume setting sounds much louder than where I previously set it (half way). And the loudness difference between minimum and maximum position on the knob is small compared to when both were working.

I checked the signal wire for continuity from the board to the jack. Both channels and the ground are continuous with low resistance and not shorted together. I am suspecting the amplifier ICs. TDA1517P and LM324N

Is there anyway to rule out the other components like the volume potentiometer or a bad cap? Or maybe dianose if only one IC is bad and which one it is? There is nothing obvious on the board.

[прямо]

Re: Dell Harman Kardon Dead Left Speaker

Have you tried connecting the speakers to another audio source? Like your cellphone perhaps? just to check if the same problem persists.

Have you also checked if the supply voltage for both ICs is at the correct value?

I wouldn't be so quick to put a verdict that they need to be replaced. LM324N is VERY cheap. As for TDA1517P I have no idea what it costs over there, it was long discontinued and I never used it myself.

Having said that, I checked the datasheet, and TDA1517P is a 2X6W amplifier. If you still want to re-use the speakers including its casing, you can ditch the amplifier board and replaced it with something else, say a PAM8406 module (2x5W) which probably cost the same as a single TDA1517P, provided if you can find and buy one.

[stj]

Re: Dell Harman Kardon Dead Left Speaker

resolder the phono socket.

[dorfman]

Re: Dell Harman Kardon Dead Left Speaker

I thought about reflowing the brown connector to the left speaker too but I wiggled it and the sound didnt come back at all. Not even a crackle. So I figured that probably wasnt it.

Plus given the strange increase in volume of the right speaker and lack of volume control I wouldnt suspect a bad phono jack to the left speaker could cause that.

While measuring the voltages at the tda1517p just now the sound starting coming out of the left speaker again. The pin 7 voltage was 15V. That seems high considering the power supply is only rated for 12V. Checking the power supply output at the barrel connector is over 16V. But the data sheet says Vpmax 18V.

Its working, but for how long? Who knows. Im pretty sure that amplifier ic was the problem. I found the tda1517p on ebay for $3 shipped. Says new but who knows. Ill look into the PAM8406 just in case.

[lti]

Re: Dell Harman Kardon Dead Left Speaker

Maybe it was a bad solder joint if it started working again while probing it.

If I remember right, the TPA1517 was in production longer, but it has two extra pins on one end. You might have room to just cut those pins off (they're just extra ground pins).

Also, there's another big thread about these speakers where those Fujicon caps blew up. It looks like C104 on yours is 47uF instead of 100uF.

[dorfman]

Re: Dell Harman Kardon Dead Left Speaker

I saw the thread you authored about replacing the caps to fix the bad sound from 2011. Are you still using the speakers?

The sticker on the bottom of mine says Rev. A00. So the values may be different from yours. It seemed like the big caps in the corners were problematic. Mine aren't showing visual defects. Yet...

I think I slipped with the probe and jumped some pins while measuring voltages and that woke the amplifier up. There was some popping sounds from the speakers and when I played something it was back to normal. All the joints looked good. Its been working ever since. Id rather not reflow it unless necessary. I'd probably just make it worse.

I prefer to get identical parts to avoid modifications. Its likely there are still new old stock parts available. If it doesn't work out, Ill look into new speakers. I feel Ive gotten my moneys worth out of these. But at this point it works so Im not touching it.

[lti]

Re: Dell Harman Kardon Dead Left Speaker

My parents are using them as TV speakers. They still work, but the volume potentiometer needs cleaned again. One channel will cut out sometimes, and turning the volume knob will bring it back.

The big caps were the only ones that showed any visible signs of failure, but the 100uF caps tested bad. I wonder if Fujicon had some QC problems back then because other people don't have any problems with them. I've even seen people recommend them.

It's a lot easier to find caps in these smaller case sizes than it was back then. I'm starting to use Rubycon PX for 100uF 25V because they're 5mm diameter instead of 6.3mm.

I didn't look at the circuit much back then, but I now see that the switch on the volume control just switches the TDA1517 out of standby mode. Everything is constantly powered. The volume potentiometer is connected between the LM324 and TDA1517 instead of being directly on the audio input. It looks like the LM324 is doing some kind of non-adjustable EQ, but the circuit is a little too complex to trace out through pictures.

[dorfman]

Re: Dell Harman Kardon Dead Left Speaker

Update:

The left speaker died again and I replaced the TDA1517 and the same problem persists. So for anyone who has the same symptoms. Replacing this chip wont fix it.

[lti]

Re: Dell Harman Kardon Dead Left Speaker

I do see that the left speaker jack has a cracked solder joint, but that wouldn't cause those symptoms. I wonder if you're losing the ground connection to the volume potentiometer.

Also, it looks like the ground connection to the left speaker is made through the heatsink.