Help diagnose Sonic Gear 2.1 computer speaker woofer no bass

[mikey5791]

Hi forum friends,
Yesterday when i switched on my pc to play some mp3 on this speaker, i noticed the music is coming from two side speakers but the bass(woofer) speaker no sound. Normally the bass will pump out some vibration. I fed dc3v to woofer speaker red and black wire at sp near cap c23, it had some speaker crackling sound. Fyi, the woofer speaker positive side is traced to 4th leg of Tda2030 audio power amp at the bottom middle of img095833 while negative side is traced to yellow 104 cap at c27.
I opened up the inside and checked pcb(img 095833) on ac input got 12.6v at left side big cap(near J2) but no ac detected from the rightside big cap. They are both 3300uf 25v electrolytic cap. Using my cap meter, the leftside cap measured 3330uf while the rightside cap measured 2780uf.
Using my dmm, i do voltage check at 8 pin amp 4558 (those 2 pcs on heatsink) by positive red probe on pin 8 and negative black probe on pin 4. Got 18.7vdc on both amp.
Another voltage check on tda2030, positive red to pin 5 and black negative to pin3 on all 3 pieces shown 16.3vdc. This should be good?
I did 200ohm resistance test on those tda2030 by pin4 output to pin3 ground, the tda2030 near subwoofer speaker line showed 5.4(is this low?). The other two tda2030 on heatsink showed high resistance(1) and i can feel the heat sink warm to touch during power on voltage test.
Appreciate very much for anyone kind comment and suggestion on making the bass to come back again. Thank you in advance.

 

[mikey5791]

Hi forum friends,

Anyone can help with the no bass signal? I can't find any schematic for this unit.
Just an update. I used the center tap black wire of transformer as circuit ground.
Using my dmm on dc scale, i checked all the 3 tda2030, positive probe to pin 5 vcc gives reading 15.7vdc. While power on with audio input signal, dmm on 2vac scale, positive probe to pin 4 output gives reading of 0.053 ~0.060 which i think is fluctuate with my audio signal.
I also checked on the 2 op amp 4558 on dc scale, positive probe to pin 8 vcc gives reading 9.1vdc
The woofer ic is tda2030 near c23 while vr3 on the control board is the bass feeding to pin 1 input of woofer tda ic. While power on, and vr3 turn to maximum, me touching the white leg of vr3 gives a loud hum on the woofer. But the strange thing is i can't figure out why there is no bass output when audio signal is pump in?
Has anyone come across similar issue? I highly appreciate any kind comment and advice on where and how to check where is the fault. Not sure how to diagnose with a digital multimeter and soldering iron but no oscilloscope.

 

[Harald Kapp]

Get the datasheet of the TDA2030 for reference.
Put your multimeter in AC. Check for an AC input signal on pin 1 of the TDA2030 to ensure the signal reaches the input.

• If present, chances are the TDA2030 is defect or simply a solder joint has come lose. Re-solder all pins of the TDA to make sure this is not the case.
• If not present, follow the signal chain backwards to the input until you find an input signal. You will then have located the point where the signal is lost. Inspect that area closely.

 

[mikey5791]

Harald Kapp,

Thanks for reply.
As per your guide, with external audio input mp3 and main power on, dmm set to ac 2v scale, probe on pin 1 of tda2030 (the one near to c23) produces some buzzing noise where i also can hear light audio input. I will replace this defect tda unit. I had performed the same probe on the other 2 tda on the big heat sink but no buzzing or audio at all. I will report back the result after replacing the defect unit.

 

[mikey5791]

Hi Harald Kapp,

Done the tda 2030 replacement but i still do not get sound from bass speaker.
Referring to your quote, "Check for an AC input signal on pin 1 of the TDA2030 to ensure the signal reaches the input." maybe i done it wrong. Is it correct to put the dmm red positive on pin 1 tda while negative probe on circuit ground (black center tap of transformer), dmm set to ac scale 2v, mains power on and mp3 music as audio input. If signal present does it mean the woofer will make some hissing or is it referrring to dmm ac reading fluctuate up and down?
I am working backward tracing on pin 1 tda (the one near c23), it leads back to a 22k ohm resistor, then to positive leg of c21 (0.47uf50v cap), the negative leg of c21 leads to JK1 jumper wire, finally reaching vr2 connector white wire being the last point. May i know how to test the signal if it is reaching up to here? Sorry being a noob, i m really not too sure how to procced. I am attaching img 070012 on the top part of the board.

 

[mikey5791]

Reference on tda 2030 datasheet and schematic example but i have to confess that i do not understand fully. Hope it helps in our further diagnosing. Appreciate your guidance.