Help diagnose Sonic Gear 2.1 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.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

The unit uses bi-polar power supply to supply + with ref to circuit ground, and it also has - supply with ref to circuit ground.
The ground ref you want to use for circuit ground is where the - leg of the filter cap is connected to the + leg of the other filter cap, so basically the circuit ground is where the black wire (center tap of the power transformer) of the transformer is soldered too, so recheck the Voltage on the TDA and the op amps (Pin 4 is -VCC, pin 8 IS +VCC) with ref. to the circuit ground.

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

Thanks for reply and explaining on bipolar power supply wiring.
I hope i understand your explanation and using the black wire(center tap
of transformer) as circuit ground in my below voltage testing.

On tda2030, on dmm +pos probe to pin 5, while - to circuit grd, all three pieces showed 15.7vdc.
On op amp 4558, +pos probe to pin 8, while - to circuit ground, all two pieces showed 9.1vdc. Looks like the dc voltage reaching the op amp drop significantly as compared to my first post measurement of 18.7vdc (using pin 4 as ground).
Hoping to hear from your further advice and guide. Appreciate very much.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

The 4558 and the TDA run on bi-polar power supplies.
So pin 8 of the 4558 has +9.1VDC (it runs on lower Voltage) with ref to circuit ground, how about pin 4 of the 4558, does it show as - 9.1 VDC?

The TDA2030 pin 5 (+Vs) has +15.7 VDC with ref to circuit ground. What do you have on pin 3 (-Vs) with ref to circuit ground?
What do you have on pin 4 (Output) of TDA2030 with ref t circuit ground?

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

Thanks for reply.
Using black wire(center tap of transformer) as circuit ground(c.grd), on op amp 4558 while pos.+ on pin 4, neg.- on c.grd reads neg. -9.1vdc on dmm.
On tda2030 pdf i noticed max rating vs suppy pin 5 is + -18v. Sorry to say i do not understand much on the rest of those remaining ratings.
As you requested on tda2030 while pos.+ on pin 3, neg.- on c.grd reads neg.-15.7vdc on dmm.
But if i put pos.+ on pin 4 output, neg.- on c.grd reads 0 zero nothing on all the 3 pieces tda2030. Is this consider normal no voltage on output since i have not pump in any input signal?
Looking forward to your kind guidance.

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,
Just for curiosity i plugged in a tablet playing mp3 song and send as input signal thru the audio input. Switched on ac main power and using dmm i put pos.probe on pin 4 output of tda2030 while negative probe on circuit ground. But dmm still show zero volt, nothing.
Now it is a bit strange. Can it be all the 3 units of tda2030 audio power amp gone faulty now?
Kindly advice and if possible to continue helping on the diagnose. Thank you.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

So the IC's are getting correct Voltages.
Pin 4 is the Output pin of the TDA so the offset Voltage should be 0V, so the output section is OK. If you feed the audio signal to the unit while having the AC V meter at 2VAC scale, Red probe on pin 4 and Black probe on circuit ground, you should see the meter display jumps around in sync with the audio.
At this point you need to find out if the audio input signal is getting all the way from Op amp input all the way to the TDA input or not.
Do you have Oscilloscope or Audio Tracer?

You may want to make Audio Tracer like the one in this thread: https://www.badcaps.net/forum/showth...ht=audio+probe

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

While setting my dmm on 2vac scale, then probe red pos.on pin4 output of tda2030, while neg. probe on circuit ground and with the audio signal in, the dmm display jumps around in figures in sync with the signal.
Sorry i do not have an oscilloscope or audio tracer. I will see if i can build that audio tracer as per your link.
Thank you for reply.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

While setting my dmm on 2vac scale, then probe red pos.on pin4 output of tda2030, while neg. probe on circuit ground and with the audio signal in, the dmm display jumps around in figures in sync with the signal.
Sorry i do not have an oscilloscope or audio tracer. I will see if i can build that audio tracer as per your link.
Thank you for reply.

So if you do not have audio feeding the unit, will the AC meter show any activity? How high does the AC V number jump up to?

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

https://www.badcaps.net/forum/attach...2&d=1604289264
BTW, can you provide straight shots of the bottom side of the board for me? not in an angle as shown.

https://www.badcaps.net/forum/attach...0&d=1604289191
The red and the black wires go to the speaker, correct? Did you already check the resistance between the Red and Black wires to see if it shows the speaker DCR (DC Resistance)? No power applied to the unit when testing resistance.

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

Refer to your suggestion on making an audio tracer, can i use an electrolytic cap of 4.7uf 50v as i do not have any film cap .
Also, can i connect in series 3 pieces 4.7k ohm resistor (yellow,purple,red, gold) to replace a 10k resistor .
I attached an image of all materials on hand including a used working left side speaker, the electrolytic cap and resistors as mentioned above.

From what i read on your link, i need to connect positive leg of elect.cap to resistor leg.
What do i do and where to connect the speaker wire? How do i use this as audio tracer?
Hope you can guide me every step. Thank you so much.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Did you check the speaker as suggested since there is activity shown on AC V meter when you check the output pin of the TDA?
BTW, your picture shows the speaker, that is not what you will use for tracer, you need to use the powered speaker of the PC speaker for tracing, it is the one with Volume control and audio input plug.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Powered PC speaker used as Audio Tracer:
https://www.badcaps.net/forum/showpo...7&postcount=18

<------ resistor -------- cap ------- PC powered speaker Left or Right input. Gnd to the chassis/circuit Ground.

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

Refer to your questions earlier, if no audio feeding the unit, dmm meter on 2vac scale (red + on pin 4 output and black neg on c. Grd) will show zero nothing on tda2030.
However, if there is audio feeding as per above set up, dmm will display from 0.053 to 0.060 max.
Fyi, i am attaching image 072945 being straight shot of bottom side of board (i tried as straight as possible) at which you can see the red and red black wires (this goes to connect to the external left /right speakers) Without power on, the dc resistance of either left/right speaker is 42.2 ohm. While in the middle portion, i measured the two soldered points which connect to woofer speaker, the dc resistance is also 42.2 ohm.
I am attaching img 073909 being one of the pc powered speaker either left or right which i have not shown before. Is this the speaker you are mentioning and using this speaker plus the volume control and audio input on the unit as audio tracer?

Looking forward for your continue guidance and kind assistance in making the bass working again. Thank you.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

You know I forget that you have three TDA power amplifiers IC's. So the Left speaker and right speaker are working, but the woofer is not working, correct?
I cannot tell from the pictures which pair of wires go to the woofer.
And also when you check the ACV at pin 4 of the TDA, were you checking all three TDA outputs?

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

Thanks for reply.
Yes, both the left and right speakers are working (their red and red black wires are soldered on bottom of pcb) but the woofer speaker is not working as in output bass.
If you refer to my first post img 095833, looking from the top of pcb, the woofer speaker red and black wire is at the middle part of board at silk screen label sp near brown ceramic cap c23.
On another note, yes, i had checked all 3 pieces tda2030 at pin 4 output on 2vac scale. The dmm reading varies from 0.053 to 0.060 from my audio input.

Up to now we haven't detected any part which is out of spec yet but i still appreciate your patience to guide me through all the testing process. Btw, how do i make the audio tracer?
Do i need to solder either my Sonic Gear left or right speaker positive wire to the 4.7uf 50v cap positive leg and then in series to positive leg of 3 pieces 4.7k ohm resistors? Sounds like an audio test probe.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

OK, my assumption is correct about the RED/BLACK wires by the C23, that IC mounted on the back plate using it as heatsink is the woofer amplifier IC.
Are you sure about the resistance reading of the woofer, it shows as 42 Ohms? I expect it to be < 10 Ohms.

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

Fyi, without power on, dmm set at ohm test 200 scale, i rechecked dc resistance on the woofer red and black wires at sp near c23 which reads 5.1ohm. Sorry for my wrong reading of 42.2 ohm in my earlier post.

Looking forward to your further assistance and guidance. Thank you.

[budm]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

Fyi, without power on, dmm set at ohm test 200 scale, i rechecked dc resistance on the woofer red and black wires at sp near c23 which reads 5.1ohm. Sorry for my wrong reading of 42.2 ohm in my earlier post.

Looking forward to your further assistance and guidance. Thank you.

At this point we do know that the audio input L and R get all the way to the L and R TDA amplifier IC's to drive the L an R speakers OK, the woofer IC gets the low pass audio signal from filter circuit to feed its input, so you need to find out if you are getting the audio signal at the input of the woofer TDA IC or not.
But what gets me is that you do see the activity at the output of woofer TDA, you may want to put your ear real close to the woofer to see if you can hear a faint audio from woofer or not. You can also try using that speaker you show in the picture that you were going to use for Audio tracer by removing the red/black wires from woofer and connect them to that speaker instead and see if you can hear anything.
BTW, there is no bass level adjustment pot for the woofer, correct?

[mikey5791]

Re: Help diagnose Sonic Gear 2.1 woofer no bass

Hi budm,

It is glad to hear the tda woofer ic is working as intended for its purpose so far.

Upon your comment, i switched on main ac power, insert audio signal but this time i put my ear very close to the woofer speaker, then jack up the volume knob and i can hear a faint audio which is hardly noticeable. Fyi, i did not remove the red and black woofer wires and replace with other external speaker as i believe the external speaker will also output a faint audio (i did touched briefly the external speaker wires to the pcb woofer wires just for curiousity but hear no audible sound).

Refering to your question, i am reattaching img 100735 the speaker whole unit side view showing three knobs which are for volume,treble, bass, respectively from top to bottom.
I am also reattaching img 101406 showing the inside view of the above 3 knobs vr1 for volume, vr2 for treble and vr3 for bass. I think vr3 is the bass level adjustment pot for the woofer which you were asking. Now the pot doesn' t seem to work at all, thats why there is no bass effect. I checked for any cold solder but noticed none.
Hope that you can continue to guide and point out comment to fix the missing bass.