Genius SW 5.1 DHT-510 - No sound?

[zynix]

INTRODUCTION
You don't remember me, but I remember you... (nah, it's not the Grease song!)
Okay, not really. Enough digressions! Some of you may remember me from the LCS-8038TX thread. As you might have noticed from my previous thread and this one too, I mostly mess with sub-$100 equipment. Most would say worthless stuff, or at least not worth the time or bothering. Well, the primary reason I'm trying to fix them is to (hopefully) gain some experience whilst not breaking something wildly expensive, but also because it's fun (for me) to see something working neatly again. So, if you don't feel like wasting time on such a thread, for your own sake, stop reading now!

THE ACTUAL ISSUE
Wow, you've decided to read on? Thanks!
On to the issue. As the title says, this subwoofer I'm dealing with is having a problem with being partly mute. Of five terminals where you can connect a speaker, only one output works (plus the core subwoofer speaker). Perhaps I'm doing something wrong, but I get sound output only when plugging an external speaker in the rightmost terminal (take a look at the first picture in the attachments), regardless of being in the AC-3 or 2-ch mode.

I took a photo of the main PCBs in case there's something I've overseen, as well as the service manual (downloaded from here), to clarify at least some of the doubts you might have while reading this post.

Once again, thanks for your time and any provided feedback!

[stj]

Re: Genius SW 5.1 DHT-510 - No sound?

before you fix the speaker, fix the light in the room!

[budm]

Re: Genius SW 5.1 DHT-510 - No sound?

You can muting control pins DC voltage of the ICs.
IC 1 (CENTER): PIN 11
IC2 (SUB WOOFER, probably OK since you are getting sound): PIN 9, 10
IC3 (FRONT LEFT, FRONT RIGHT): PIN 5
IC4 (REAR LEFT, REAR RIGHT): PIN 5

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

I should have added "If you despise people who have basic or no electronics knowledge at all, the same applies." at the end of the introduction part . Anyway, if you don't mind my ignorance, what would be an appropriate (read: the most common way) to do so?

before you fix the speaker, fix the light in the room!

Yeah, sorry mate. Pictures truly turned out crappy. Guess setting everything to auto doesn't always do the justice .

[momaka]

Re: Genius SW 5.1 DHT-510 - No sound?

On the 3rd picture you posted, if you look at the top-center position of the picture, you will see a bit of discoloration. On the reverse side (4th picture, lower-center position), it looks like this corresponds to resistors R11 and the resistor next to it as well as diodes D4 and D5(?). If yes, check them with a multimeter. Color bands on R11 appear to be gray, brown, black, gold - which doesn't return a valid E12/E24 series resistor. So perhaps it's white, brown, black, gold? If so, that would be 91 Ohms. If not, then maybe it is gray, red, black, gold? That would correspond to 82 Ohms. Either way, try measuring the resistance with a multimeter and let us know what results you get. The diodes (D4 and D5(?)) should be checked with diode test function both ways.

I am assuming you know how to use a multimeter. If not, let us know so we can point you to some articles/videos on how to use one.

Finally, there seems to be burn marks close to another resistor. The resistors is located next to the connector next to connector JP4 (4th picture, upper-left corner of the board).

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

Measured resistors R11 and R12. I have got values of about 820 ohms (808 Ω on R11 and 803 Ω on R12), as in the schematic on page 19. Hope I've read it properly. If it doesn't matter if the resistors are soldered on the board (thus measuring overall circuit resistance on these two spots), the values are matching and inside the ±5% tolerance. Seems okay?

However, regarding those two Zener diodes D4 and D5, I've got about -543k ohms in anode-cathode direction when measuring resistance, and some insane (not readable) value in opposite direction, while in the diode test mode it starts with a -500 value and slowly raises to the value of 1000, regardless of the direction. Same applies for both diodes. Should I desolder them and repeat measurement?

The connector next to JP4 is JP23 (CMIIW!). There is a resistor there. It's R89. Again, according to the schematic, it ought to be 180 ohms, and I get a reading of 175. Seems okay too.

[stj]

Re: Genius SW 5.1 DHT-510 - No sound?

if you dont have a zener tester and they could cause a problem then just replace them.
dont go making asumptions with a regular diode tester.

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

Indeed. Is there any way I can tell for sure if they're burned or not prior to seeking a replacement, something like this? I tried to follow the instructions from the linked page, but the DMM picture is way too low-res and I can't tell in which mode it is. It would help me a lot if it was a higher resolution picture as I have an identical DT-830B thingy. It's not the best thing on the world, but most of the time it does the job. Would desoldering make any difference regarding measurement results?

[stj]

Re: Genius SW 5.1 DHT-510 - No sound?

i just posted a tester for ya.
https://www.badcaps.net/forum/showthread.php?t=38843

[budm]

Re: Genius SW 5.1 DHT-510 - No sound?

"However, regarding those two Zener diodes D4 and D5, I've got about -543k ohms in anode-cathode direction when measuring resistance, and some insane (not readable) value in opposite direction," So what dc voltage do you read across those two Zeners? They are 12V Zener so the voltage across them should be around 12VDC. Thses +/-12V are for the OPAMP's (4558's), and since one of the channel (Center Channel) and the SUB Woofer are working OK, then the OPAMP's must be getting the correct +/-12VDC feeding them.

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

i just posted a tester for ya.
https://www.badcaps.net/forum/showthread.php?t=38843

Aw, thanks mate! You shouldn't have bothered for such a newb like me .

@budm, forgot to measure the voltage. Will check and report back.

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

Okay, measured voltage on Zeners. D4 reads 12.24V, and D5 12.57V.

P.S. I know it's kinda late, but congrats on the Badcaps.net 12th anniversary! Live long and prosper !

[budm]

Re: Genius SW 5.1 DHT-510 - No sound?

Those Zener diodes are fine. You still need to check those voltages on my post #3.

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

There's no reason why wouldn't I do that, but how? By desoldering leads?

[budm]

Re: Genius SW 5.1 DHT-510 - No sound?

"There's no reason why wouldn't I do that, but how? By desoldering leads?" I do not understand?

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

Oh, pardon my ignorance. I was just wildly speculating. What I wanted to know was how can I mute those control pins?

[budm]

Re: Genius SW 5.1 DHT-510 - No sound?

If you look up the spec of those IC, there is the control pin (which I have listed) the spec will tell you if HIGH = mute or LOW = MUTE. But I do not understand by you will want to mute the circuit, right now I have you check the voltages on those pin to see if the ICs are stuck in mute mode or not which may explain why you are not getting the sound form some of the channel.

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

It's my fault. You said "You can muting control pins DC voltage of the ICs." I thought I was to mute stuff somehow. Sorry. Will check.

[budm]

Re: Genius SW 5.1 DHT-510 - No sound?

Sorry, It is my fault too, it should be "You CAN CHECK muting control pins DC Voltages of the ICs", sorry about that.

[zynix]

Re: Genius SW 5.1 DHT-510 - No sound?

Long time no see! I was occupied by other stuff, projects, day-to-day obligations, etc. This absence was not a manifestation of a loss of interest, just lack of time at the moment ... and ... I made a boo-boo. There were some perceived deviations in IC1 values below so I wanted to redo the measurement, but I burned the TDA7360 chip by accidentally shorting pins 8 and 10 during runtime. It just went mute. Damnit!

Prior to that stupid mistake this were the results of my measurements. I have measured the voltages using my generic DT-830B multimeter. Labels (test points) on the left were connected with the positive (red) test lead, while ones on the right side with black (negative) lead.

IC1 - ST TDA7360 (datasheet here)
STAND-BY (pin 11) > +Vs (pin 9) = -0.57 V
STAND-BY > chassis = 15.50 V
STAND-BY > P-GND (pin 6) = 15.50 V
STAND-BY > S-GND (pin 3) = 15.50 V

IC2 - ST TDA7296 (datasheet here)
MUTE (pin 10) > chassis = 11.65 V
MUTE > -Vs (POWER) (pin 15) = 39.80 V
MUTE > -Vs (SIGNAL) (pin 8) = -3.71 V
STAND-BY (pin 9) > chassis = 13.15 V
STAND-BY > STAND-BY GND (pin 1) = 13.15 V
STAND-BY > -Vs (POWER) (pin 15) = 41.70 V
STAND-BY > -Vs (SIGNAL) (pin 8) = 41.70 V

IC3 - ST TDA7269A (datasheet here)
MUTE (pin 5) > chassis = 3.93 V
MUTE > GND (pin 9) = 3.93 V
MUTE > +Vs (pin 3) = 1.42 V

IC4 - another ST TDA7269A
MUTE > chassis = 3.75 V
MUTE > GND = 3.75 V
MUTE > +Vs = 1.22 V

So, if such a malpractice caused such results, could it be that ICs 3 and 4 faced the same fate by someone other, perhaps by shorting output cables by mistake? Also, could something die along with the TDA7360? What should I check?