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

[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.

[nomoresonys]

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

[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.

[Diah]

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

[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]

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]

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 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]

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]

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

[LEECH666]

The audio signal looks in very bad shape on the scope on all outputs and I tested the subwoofer speaker module on the bench with a little Sure Electronics AA-AS32157 15W class D amplifier since it was the easiest to hook up to the module and the subwoofer speakers work fine when driven this way.


Ignore the German talking in the video it's not important (just me explaining to my non-technical friend for whom I am trying to repair the TV). I recorded this before I started this post and it just shows the setup and that the music sounds how it is supposed to sound when the subwoofer speaker module is driven externally.

[Diah]

long time ago a friend asking me his TV sound was innormal , first things i took the audio output to my amplifier and the sound was good.. mean no issuer at signal .. could be amplifier IC or caps or speaker...i went first to check the speaker and i found one was broken from the frame..LOL... what i do mean such issue need to suspect every small things after you are sure the signal in good shape

[LEECH666]

Hi Diah, sorry no I didn't notice your instructions. As mentioned I find your post hard to understand sometimes. It's probably a language barrier.

I did what you asked now and reverted everything and I can now confirm that the PSU coil buzzing is only happening when the +24V backlight connector (P201 as named in the BEKO PSU manual attached to one of my posts above) is connected. If the connector is disconnected the CFLs are off, no buzzing but also no change in audio behavior. It also looks like the audio PSU (YDK 192 in the schematics attached above) does not only power the sound bar but also has some influence on the subwoofer out. If I disconnect the audio PSU all audio except the headphones stop working. Maybe the STV8537FSX is communicating with the processing board (ANT192) in the sound bar. I haven't fully figured out how they work together. Might be related to the MONITOR_OUT_L/SUBW signal from that board. I need to do more measurements on the various signals and amplifier circuits.

[Diah]

did you read my Post #15.
yours PSU working fine.. so remove the stand alone mode.. put every things back as it should.. now we need to REMOVE LOAD .. until the buzzing on the PSU Stop.
for example the BL connector the yellow one on the left side.. disconnect and turn on... just use your ears ti check the buzzing remain or not... if it remain... mean this circuit not the issue turn off and put back the socket...

[LEECH666]

So I made a video with some more information on how this is currently wired up and the various loading options I have available.

Grundig 37 9880 T USB Some More Information and Loading Options

"Too long - no time to watch" Video Summary:
1) I think I connected the PSU PCB according to the previously provided description (provided by @Diah) but I could be wrong. The Logic Board is not connected to the PSU PCB but the Back Light inverter board is.
2) I have the following loading options: a programmable (Chinese) electric dummy load, some 100W power resistors + passive cooling, sadly no car 1157 (BAY15D) car light bulbs

[Diah]

BTW yes you were right... its not LED.. CFL and the the overload could come from it... remove yours mode which you did... bring it as Original and try to disconnect the BK circuit to check if the buzzing noise remain or not.... you can also try disconnect the screen / t-con to

[Diah]

Oh "here goes nothing" is just a saying like "alright let's try this!" or "wish me luck". I wasn't refering to the function of the TV at all.

I measured the voltages with the +5VS connected to the 1K and BL, STBY and DIM pin connected the other leg. Everything connected but the logic board. All voltages (12V, 24V) are presents but no loud buzzing from the PSU. Just very very faint clicking every 1.5 seconds or so and I can observe my external, totally unrelated LED desktop lamp flicker at the same interval. Also the 12V seems more noisy to me now on the scope. I will update this post with screenshots in a moment.

Video of the clicking and +12V pin on scope (AC Coupling / Ripple).
Grundig 37 9880 T USB Faint Clicking
https://www.youtube.com/watch?v=bY16snmayIY

what are you doing??? we said the socket to MB should disconnected... in yours video its is connected ..

[lotas]

Your power supply is running idle, you need to provide a load (put it at the output +5v, +12V, +24V of the car lamp power supply).

[LEECH666]

Oh "here goes nothing" is just a saying like "alright let's try this!" or "wish me luck". I wasn't refering to the function of the TV at all.

I measured the voltages with the +5VS connected to the 1K and BL, STBY and DIM pin connected the other leg. Everything connected but the logic board. All voltages (12V, 24V) are presents but no loud buzzing from the PSU. Just very very faint clicking every 1.5 seconds or so and I can observe my external, totally unrelated LED desktop lamp flicker at the same interval. Also the 12V seems more noisy to me now on the scope. I will update this post with screenshots in a moment.

Video of the clicking and +12V pin on scope (AC Coupling / Ripple).
Grundig 37 9880 T USB Faint Clicking

[Diah]

I couldn't find any mention of it being LED based anywhere so I assumed it's still CFL based which may be incorrect. Anyway I connected the 1K between +5VS and STBY+BL pins. Here goes nothing.

what do you mean goes nothings?
do you have 12V & 24V on the socket ? do you still have buzzing noise?