Grundig Vision 9 37 9880 T USB (Chassis SR) TV Repair Help - Distorted Subwoofer Sound and overall weird sound waveforms

[Diah]

the speaker sound look like No any Base.. let hear the same music from the TV system to compare

[LEECH666]

Sure here are two clips of Music with / without sound bar. In the second clip I am disconnecting the power lines of the L/R channel amplifier boards to shut up the sound bar.

The sound at the subwoofer is obviously distorted and as mentioned previously all waveforms I have measured are total garbage quality on all devices (soundbar speakers, subwoofer module, headphone out). They sound vaguely fine (i.e. over the headphones) but a smooth crispy sine looks different the last time I checked. Now a difference between the bench setup I used to test the subwoofer module and the audio path into the TV obviously is that the former setup uses analog audio fed from a smartphone into the Sure amp that drives the subwoofer and the TV is purely digitally fed via a PC via HDMI2 (also tried HDMI3) because I can't get the analog inputs to work. Maybe the PC AV channel (VGA + 3.5mm jack) needs to have the VGA connected to even consider reading in the audio from the 3.5mm jack and putting it out to the speakers?

[Diah]

you need to disconnect the subwoofer V supply. not the wave input... so this crack will remain or out

EDIT; also after disconnect the Supply on subwoofer , take out audio out from TV to test it with your external amplifier

[LEECH666]

You mean I should disable the voltage supply of the subwoofer amplifier IC U53? To check if the sub amp ic is causing the problems?

[Diah]

You mean I should disable the voltage supply of the subwoofer amplifier IC U53? To check if the sub amp ic is causing the problems?

on the ic pin or complete on the boards socket rail.... in my post #3 i mentioned Filter leak... on subwoofer boards you have filter standing Caps.. need to take them out check the legs if they are leaking and measure the ESR

[LEECH666]

I can measure the capacity and ESR with the transistor tester but I don't know how to measure leakage. Hmm ...

EDIT: Never mind, you meant checking for leaking electrolyte. Yeah sure. I can do that

[Diah]

if you don't have tools to measure ESR. i encourage you to replace them. with now days almost 12 years old

[LEECH666]

Can't see any leaking electrolyte on any of the caps and I won't have much time to work on the logic board this week. Maybe on Friday or Sunday. As mentioned these little transistor (or component) tester modules from AliE can measure ESR though probably not as accurate as a dedicated professional ESR meter.

[nomoresonys]

Usually those testers are pretty accurate but you can not get decent readings with the component in circuit.

[LEECH666]

Ah that is good to know. I will at least lift one of the legs of the capacitors or even desolder them completely with my desoldering station.