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yamaha rx-v870 help fixit

alex4bass

alex4bass

Member
Hi,

I have a very nice rx-v870 Yamaha receiver unit sitting beside me.

Issue:
Turns on just fine, but powers off after 3 or so seconds. Consistently.

Observations:
Basically its on for the initial "boot up" i guess. Normally after this time the speakers receive power, but instead the unit turns off.
Found 3 fuses, all ok. No evident burn/explosions/popped caps.

Now my questions:
1. Has anyone experienced and overcome this issue before?
2. Does anyone have or know where to acquire a service manual/ circuit diagram for this unit?

Thanks,
Alex
 
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One of the power amps probably has a shorted output device.
 
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I have that same amp I'm the original owner so I looked in my user manual trouble shooting section but not much help. Have you tried turning it on with the vol off and no spkrs ? Mine had an issue with the top of the case causing the readout not to light and shutting the amp down. Let me know if theres any info you want off the user manual
 
I'm plugging it in without anything connected to it.
It seems that the problem is relatively common from a google search. But most solutions end up with a trip to the service centre.

I'm hoping someone here managed to fix it themselves and could shed some light.
 
Measure for any DC voltages on each speaker output connector pair..Should read close to zero millivolts.. You may have to keep powering unit on then off measurement needs to be taken in that 3 sec. window before the protection relay resets. ie. Front left and right ,Rear left and right, Center channel.
 
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Measuring directly from the speaker terminals didn't help. The speaker output relay isn't activated unless the self test passes (after the initial 3 seconds).
From what i gather, to measure the voltage for each speaker I would need to get the signal before the relay.
? is there another way to see if any of the power amps are shorted? I would be difficult to remove the board and power the unit up.
 
:banana::music::banana:

Success!

The final output at each channel can be easily measured by reading the voltage at the emitter leg of the final power transistor per channel.
That quickly showed that the both R channel transistors are shorted. I cut the emitter legs on those and it powers on and plays fine now. Obviously no R channel though.

I only need stereo, so ill run a few more tests to make sure the shorts are the cause and not a symptom then ill just use the center amp compoents as replacement.

THANKS all for the help.
Alex
 
The RX-V870 is a really nice receiver. I owned one for years and wish that I had it still. I wouldn't hesitate to have mine serviced. Here's hoping that you get yours fixed soon!
 
One more dead rx-v870

Well One more dead 870 turned up @ my door.
What power transistor does it have, mine is also shutting off in 3 seconds.
Thanks.
Srinath.
 
OK I opened it up, the thing has 3 power transistors that are like c3658 (not exact numner) and 3 a2556 (again not exact) I presume the C's are one type (npn say) and the A's are pnp's.

Now how does this supply 8 channels of audio with these ?

Now it also has a stereo amplifier chip - one of those 14-16 pin deals - Oh that one handles the 2 front ones like old school stereo ... does it ?

Thanks.
Srinath.
 
All the power transistors were fine, desoldering them all did nothing for the 3 second cut off.
Disconnecting the board with the stk 4151 power amp chip made the thing stop shutting down.
Then I reconnected one plug at a time, and there is a thin 3 wire plug, 3 wires the size of strands of hair which go to the board on the bottom not to the power supply or the outputs ... that being unplugged makes it come on and stay on, all teh rest is plugged in.

I cant get any sound out the headphones though all of this.
I guess I need to find a schematic and figure it out. But can someone who has been here before let me know what that may go to.

Thanks.
Srinath.
 
Rear amp.

OK its in the rear amp section, so I should get audio in the headphones - but I am not.
Is anything related to the rear amp being disconnected. Anyway got the schematic I am troubleshooting tommorow a bit more.
Thanks.
Srinath.
 
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K got sound.

OK I got sound from the headphones, its sending test tones to center just fine too, so I guess that's the best it can do.
I have a rear amp board that seems to trigger it into shut down.
There is an stk4151v on that board, can I just ignore it and use it as a 2 channel amp.
And is it possible the shutdown which seems to be triggered by an input signal wire - super thin = input signal - my assumption - co can the problem be somewhere before the stk, or even after the stk.
Thanks.
Srinath.
 
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