Disclaimer: I do not advise you to try repairing any equipment connected
to mains power on your own if you have no clue. Especially, while it is
connected to the mains power. Proceed at your own risk. Remember: I told you
do not even think of opening up that receiver case!
I have my Onkyo TX-SR313 since a few years now and it is a very nice piece
of amplifier equipment. The sound quality is really superb and it has all
the connections and functionalities I need. Unfortunately, when watching
some of my favourite series, in the midst of an action scene, suddenly, the
receiver shut off. First, I suspected some overheating issue or similar,
so I continued watching with my crappy built-in TV speakers, but then after
a while the amplifier would not turn on. This is when I started worrying
(in reality, I already worried before, since it had never overheated before, even
on high volumes and there is nothing blocking the airflow above it, so this
should not be an issue).
Even on the next day (because a lot of guides on the net suggest letting
it cool down and decharge all the caps and such), the thing would not work.
The only indication of life it was giving was a constant glowing "HDMI Thru".
When I pressed the power button, nothing would happen, except the "HDMI Thru"
led would start blinking. No satisfyingly clicking relais inside, nothing.
Apparently, the most common fault in receiver amplifiers with dedicated
transistors in the amp is such a transistor shorting out. This can be due
to overheating or more likely due to a faulty bias current resistor. These
resistors are the white blocks in front of each transistor pair. Therefore,
I went ahead and checked every resistor if it has the correct value and
every transistor if it was shortened out from collector to emitter. For further
details, I would like to refer to the many excellent youtube videos out there.
Every resistor and every transistor checked out positively and by visual
inspection of the rest of the device, I could not find any obvious broken
components (for example bulged up capacitors or something like that). At first,
I was tempted to give up, since a quick research could not bring up any
other obvious things to check or obvious faults in similar devices, that
would exhibit the same behaviour.
But then taken by my ambition I decided to repair that sucker. I downloaded
the schematics and started looking through it. Especially through the
amplifier section, since I still suspected some protective circuit to shut
down the device immediately. After a while of studying and more youtube
videos about receiver repairs, I encountered one specific video by the
excellet EEVBlog, where a broken Yamaha receiver gets fixed, which has
a fault in the standby power supply circuit. This gave me the idea to look
more specifically at this section and check out the voltages there.
If you look at this part of the schematic, it is clear that a 12V support
voltage is generated which is supplied to the main IC and then two more
interesting lines come back, which are those which trigger the main supply
relais. Especially, POWERD.
Schematic for the power supply section.
So it ocurred to me to check out the relais in the first place, since if
there is still some protective circuit engaged, the relais should be triggered
at least once and then immediately release again when the power button is
pressed (which it did not!).
So supplying 12V to the lines +12VD_ST and GND to POWERD did not
produce any clicking sound. Very odd. Could it be the relais itself is broken?
A quick bridging of the relais ...
Dangerously bridged relais makes it work.
revealed, that indeed the relais is broken. The reveiver turned on and did
it's job flawlessly. So now we know who is to blame.
A quick search brought up that the type of relais Tyco is more or less not
available to the end user for buying. Therefore, a suitable replacement had
to be found. The datasheet of the Tyco SDT-S-109LMR2 relais revealed,
that it is a relais designed for 9V operation and the coil is supposed to
have 540 Ohms with a max coil power of 150 mW. Good luck finding exactly
a matching piece.
Digging around further in the schematics, reveals that the relais is driven
by a KRC105S transistor, which is rated up to 100 mA, so we should aim
for maximum coil current of 50 mA, just to be safe.
Fortunately, I could find in an old stack of discarded PC power supplies one
which not only has 230 V input but also a switched 230 V output for a monitor
or such (thumbs up for that old things lying around). It had a relais in,
which pretty much matched the requirements.
5 amps of switching at the 230 V side and a coil resistance of around 330 ohms.
Almost perfect. Almost, because desoldering the old relais
Desolder the old relais.
revealed, that the new one was too short to perfectly fit in there.
The new one is too short, bummer.
But a electronical engineer approved solution, helped to get the new component
There - I fixed it!
No one will find out that is not original.
After testing the new relais, the machine was working perfectly again.