Yamaha A-S301 help

Hi,

Did you try different sources - especially optical vs. analog (OPTICAL vs. CD, TUNER)?
What about the sound using headphones?
Press PURE DIRECT ... any changes?

Are you experienced in repairing equipment like this? Multimeter, soldering station?

Yes, I tried, but the sound at the left output also produces a distorted tone. I tried tuner, phone, optic etc. all of them, while the right side gives good sound, the left side gives a crackling sound. Yes, I have a soldering station. I work in the technical department at Apple service, but I wanted to consult you because I have not repaired an amplifier before. Could one of the output transistors be faulty? Could it cause sound distortion?

"Could one of the output transistors be faulty? Could it cause sound distortion? "

In most cases the protection would be active. Therefore I don't believe so.
The service manual is available for download here:
https://www.manualsl....html?page=18#manual

Page 18 describes the way to use the self diagnostic function.

If it detects no problems, it will be necessary to make some measurements (we'll see later).

Thank you, I will try this tonight.

I would recommend to check the block diagram first to help you identify where the problem could be and which parts to exclude.
Note that many preamp functions of these amps are implemented within one big "Volume IC" (IC402). Yamaha is re-using their AV Receiver IC which originally supports many more channels than just stereo. So here they are using it to support functions like symmetrical input (CD), tone control, loudness, etc.




To support further troubleshooting in case of power amp damage, please find here the left power amp schematic with colorized stages.




- Johannes

Hello again. Last night, I made the troubleshooting combinations recommended by Yamaha. The sound was distorted on the left side. After this combination yesterday, there is no sound coming out from the left side, there is only sound on the right output.
Thank you for the schematic. Which transistor should I look at before Q123A - Q123C transistors?
My device's problem was the same as in the video.
https://www.youtube.com/watch?v=qBceQLDwjvE&list=LL&index=1

As I read this, all your checks so far point in the direction of a damage in the left power amp section.
The firmware self test you started did NOT give you an indication but may have completed the damage to a part in the power amp.

But we already know a lot now.

Since protection does not recognize the damage (does not trigger the relay to cut off loudspeaker terminals from the amp),
---> the damage is not likely to be in the last two current amplifying stages 4 "Driver" and 5 "Final".

And generally, the amp works, it amplifies. Only just distorting somewhat, like an overdriven or limited signal. This means that
---> the damage is not likely to be in stage 1 "Differential input stage", the signal can be recognized as such.

This leaves you with stages 2 and 3 which both belong to the VAS (Voltage Amplifying Stages).

Interestingly, with Yamaha receivers and amps, we recently had multiple cases where single parts (resistors, diodes) in these stages failed due to overload of parts too weak by design.

I would check the two SMD diodes D103 and D104 whether one of them has a fault, like a disconnect. SMD parts are usually placed on solder side of the PCB.
Next I would check the resistor R124 which is in line with them. R124 is implemented as an oldschool through-hole resistor.

Hope this helps.

- Johannes

Thank you for your answer. I will check the D103 and D104 diodes you mentioned and then check the R124 resistance. I will leave you feedback again. I want it to be useful to people who have the same problem.

Poetry2me (Beitrag #8) schrieb:

As I read this, all your checks so far point in the direction of a damage in the left power amp section. The firmware self test you started did NOT give you an indication but may have completed the damage to a part in the power amp. But we already know a lot now. Since protection does not recognize the damage (does not trigger the relay to cut off loudspeaker terminals from the amp), ---> the damage is not likely to be in the last two current amplifying stages 4 "Driver" and 5 "Final". And generally, the amp works, it amplifies. Only just distorting somewhat, like an overdriven or limited signal. This means that ---> the damage is not likely to be in stage 1 "Differential input stage", the signal can be recognized as such. This leaves you with stages 2 and 3 which both belong to the VAS (Voltage Amplifying Stages). Interestingly, with Yamaha receivers and amps, we recently had multiple cases where single parts (resistors, diodes) in these stages failed due to overload of parts too weak by design. I would check the two SMD diodes D103 and D104 whether one of them has a fault, like a disconnect. SMD parts are usually placed on solder side of the PCB. Next I would check the resistor R124 which is in line with them. R124 is implemented as an oldschool through-hole resistor. Hope this helps. - Johannes

Hello Brother. I made the diode and resistor measurements you mentioned and found that the 100k resistor values ​​were low and I replaced it with an upper case and a 100k resistor. My problem was solved. Thank you for your help. The resistor had also lost its value since there was no burn or blackening. Yamaha may have used the 100k resistor cover at this input in a small way. I think it would last longer if a top cover was placed, so I did that.

Better delete your email reference! You may receive a lot of SPAM otherwise as this forum is public.
Use tab "private communication" ("Private Nachrichten" ) instead.

Valenzband (Beitrag #11) schrieb:

Better delete your email reference! You may receive a lot of SPAM otherwise as this forum is public. Use tab "private communication" ("Private Nachrichten" ) instead.

I will correct it, thank you for the information.

____CONGRATULATIONS____ for you successful repair

Glad it worked out well. One more device saved for the planet's sake.

And yes, I think that Yamaha does have an issue with dimensioning their parts.
Maybe the impulse load of the components mentioned may be greater than expected. The components used should be able to handle impuls load better.

- Johannes