Sony STR-DE675 problem..

[El3kTriK]

Greetings,

So i have Sony STR-DE675.
The problems were: No sound in headphones, Radio static/hum, not all buttons working properly(you clicked something but system understood some other button), front left side and surround right played always better than the surround left and front right(balance issue), center relay sometimes failed(especially when system was cold).

Problems with headphones- No audio to headphones but system recognized that the headphones jack was inserted and cuts the audio to speakers.

So i took it apart and discovered that there were some loose connections..
Resoldered some points to.. And check´d voltages.. (5.5v was sometimes 6.6v for some reason couldn't identify why)..

Anyways, put it all back together and tested.. Results are as follows: Headphones work fine, buttons work fine, tuner still the same, NO AUDIO IN SPEAKERS But in headphones and sub woofer there is..

So again took it all apart and found nothing wrong visually.. So I thought maybe headphones jack was behind it.. Took all the fixed connections appart.. Nothing.. So I started looking the schematics.. And found that headphones audio is connected to front L and R, after few resistors. So the amp is fine cause it amplified headphones audio..
After looking around and measuring lots of things i found that the 3 relays(Surrond, Center, Front) aren't working..
If you hot wire the relay contacts then there is audio to speakers, so the fault must be in the relay system..
Started measuring voltages.. Found that center and front relays dont get any volts, and after a while found that only logical thing is that resistors R734 and R534 are dead cause before there is 12.5V and after 0V. Resistors themselves are 4.7ohm.
It seemed that surround resistor was fine(R634), but then i started having question, why doesn't the relay work then? At that point i have made sure that voltage is getting to the relay, but what about negative.. It seems that the negative is controlled by transistor.. Q610 for surround, Q550 for center and Q710 for front. Found that if i trip surround transistors emitter and collector for a sec the relay closes and stays closed. I cant figure out why it stays closed if i let go of emitter and collector..
So at that point it seemed that transistors were dead or base voltage is bad..
Luckily the sub woofer relay worked fine so i had something to compare others with.. I measured base voltages in surround sound mode(where all relays should be on). Got that base voltage for sub woofer transistor was 0.7V, surround 0.57V, center 0.66V, front 0.66V..
So it seemed that surround transistor was getting the same amount of voltage that others were but still didn't work.. Dead maybe?

So to take long story short.. I think i should change R634, R534, R734 resistors and Q610, Q550 and Q710 transistors..
Only problem is finding the correct transistor.. Maybe "BC107B Si-N 50V 0.2A 0.3W 250MHz" should work fine?

What you guys think, am i doing/seeing something wrong?
Any suggestions?
Tomorrow i try to change out the "dead" parts and i will write back if it helped..

I made a picture for showing the schematic.. Red is +12V, Brown is negative and Blue is transistors base rails.
Full schematics: UPLOAD.EE - sony_str-de675_ver1..pdf - Download

Srry for the bad english..

 

[rayma]

Luckily the sub woofer relay worked fine so i had something to compare others with..
I measured base voltages in surround sound mode(where all relays should be on).
Got that base voltage for sub woofer transistor was 0.7V, surround 0.57V, center 0.66V, front 0.66V..

The resistors are probably ok if the base voltages are around 0.6V when on.
The transistors, pcb, and relays are where to look. The relays are normally open,
so they need the coil to be grounded by the transistors to be energized and close.

 

[JonSnell Electronic]

It is a Sony, so anything that has got hot or is heavy, check for dry joints on them.

 

[El3kTriK]

The resistors are probably ok if the base voltages are around 0.6V when on.
The transistors, pcb, and relays are where to look. The relays are normally open,
so they need the coil to be grounded by the transistors to be energized and close.

Those resistors i mentioned are for transporting +12v to relay..
Even if i connect transistors emitter and collector(ie leave transistor out from circuit) for center and front i get no action in relays.. In sum it seems that no +12V reaches relay, so i assume the resistors are dead..
Anyway, i will change them, they are pretty cheap anyways.. Then i can be sure that resistors are not the problem

Pcb seems fine too..
Its hard to believe i have blown relays coils.. But ill measure them tomorrow.. But you will never know.. I normally work with 230V to 110kV.. New to electronics

 

[rayma]

Those resistors i mentioned are for transporting +12v to relay..
Even if i connect transistors emitter and collector(ie leave transistor out from circuit)
for center and front i get no action in relays.. In sum it seems that no +12V reaches relay,
so i assume the resistors are dead..

The resistors likely go to the transistor bases, and not directly to the relays.
It's not likely to be several relays/resistors/transistors all with the same problem.
If measuring directly across the relay terminals gives no voltage when energized,
the power supply connection (either 12V or ground) is likely to be bad, since this
is what is common to all of the circuits.