Yamaha RX-V393 in protect mode

[Fwrothy]

Just got thru an RX-569 receiver/ amp with a blown fuse; turned out to be a bad bridge rectifier S4VB20 which is incidentally discontinued by Shindengen. Found a nice 600v 6A unit, an easy fix and good confidence booster

Now for much bigger challenge, this receiver is stuck in protect, and due to my lack of experience, not sue what to do next. Downloaded a service manual checked the code by holding tuner& preset no.8 keys and activating power button: PRT-DC 001
I'm thinking I need to get the unit out of protect mode before I can do any thing else...
Any thoughts on the best way to proceed?

[tom66]

Re: Yamaha RX-V393 in protect mode

DC protection: check outputs (before relays) for high voltages - all should measure below about 100mV.

[Fwrothy]

Re: Yamaha RX-V393 in protect mode

The unit only powers on for about 2 seconds couldn't find the info on how get around that.

[tom66]

Re: Yamaha RX-V393 in protect mode

You will have to power it on/off a lot of times and check the outputs individually, it may take a few tries to get right.

[Fwrothy]

Re: Yamaha RX-V393 in protect mode

Really!?
That would explain why I couldn't discover how to disable the protection...
I guess this is where the min/ max function come handy.
Thanks!

[tibimakai]

Re: Yamaha RX-V393 in protect mode

I would go right away to the final transistors and check them for short.
I'm working on a Yamaha too, but different model, RX-V671. Blown finals, pre finals, 5.1V zener diode.

[nilez2006]

Re: Yamaha RX-V393 in protect mode

Check all transistor, if it is dead short. Other related problems can be checked near power area, where you found blown rectifier. Check the diode and fuseable resistors are possible. Most amps are on protection due to output transistors. Check throughly.

[Fwrothy]

Re: Yamaha RX-V393 in protect mode

Thanks guys, suspecting output transistors makes good sense. I haven't really disassembled the unit too much yet, like to do as much trouble shooting as possible first, the main board trace is hard to get at. Found an accessible spot at r151 & r152 and their respective inductors where I can check voltages.
Here are Sch if anyone is interested...

[Fwrothy]

Re: Yamaha RX-V393 in protect mode

Check all transistor, if it is dead short. Other related problems can be checked near power area, where you found blown rectifier. Check the diode and fuseable resistors are possible. Most amps are on protection due to output transistors. Check throughly.

The bad bridge rectifier was on a different unit. This unit uses the some bridge but it seems ok.

Using the min/max feature of my DMM, I'm getting 5+VDC at both outputs before the relay when cycling the power switch.

None of the power transistors are shorted.

[budm]

Re: Yamaha RX-V393 in protect mode

See my notes on PDF.

[Fwrothy]

Re: Yamaha RX-V393 in protect mode

Wow, thanks Bud!
So I think maybe I'm grasping the mechanism here; I have a PRTDC fault, so I think q18 and in turn q19 switch PRTDC to low and RY101(output to speakers) from SP ON is latched through this as well. POW controls RY102 the sub supply relay that supplies power to main transformer. So the fault to switch q18-19 comes through from the centre tap of mains transformer, somewhere?

[tom66]

Re: Yamaha RX-V393 in protect mode

Check you have the ±B voltage - a missing negative rail (blown fuse, shorted bulk cap, etc.) would cause the outputs to have positive bias - also check the sub voltages (often ±15V or ±12V) as a fault there can cause the same on some amplifiers too.

[Fwrothy]

Re: Yamaha RX-V393 in protect mode

Ok it's like somebody stole my tricycle and now I'm trying to ride my big boy bike with no training wheels...
What is the B voltage?

[budm]

Re: Yamaha RX-V393 in protect mode

Yes, that is the idea. Page 55, when Q119 Base pin receives DC from the output of the amplifier, it will turn on which will route the DC voltage (SP ON) that turns on Q115 through D117, E-C of Q119 to ground which cause the speaker relays to turn off and protect the speakers. At the same time the processor will see this LO signal, then the PROTECTION Indicator will light up.
Follow Tom's suggestion.

[budm]

Re: Yamaha RX-V393 in protect mode

"What is the B voltage?" see block diagram page 49.

[Fwrothy]

Re: Yamaha RX-V393 in protect mode

Thank you gentlemen, the validation is appreciated
I figured the POW is controlled by a logic function( I little knowledge is a dangerous thing, contemplated disabling the protect, but deemed that a dangerous/bad idea) cycling the power button is a pain.
I will do some more studying, have the complete service manual but it's 12Mb.

[budm]

Re: Yamaha RX-V393 in protect mode

Does the power relay RY102 turn off when the PROTECTION is activated? if not, then the DC at the output of the bad amp will always be there.

[rievax_60]

Re: Yamaha RX-V393 in protect mode

I find that DC fault readings will remain for some time after the mains relay turns off because the rail capacitors stay charged for a while.
It can be normal to measure some voltage fluctuation at the output at power up.
The controller allows some settling time for this.

[Fwrothy]

Re: Yamaha RX-V393 in protect mode

I hear RY102 clicking after a couple seconds ( with a subsequent high pitch 'squelch' for lack of a better word), when testing the output, since I was using min/max, leaving the test leads connected when the unit cycles off results in a large -V spike. Checking again immediately after the unit is off results in a constantly decreasing voltage( discharging caps).
Same result for both channels.

[budm]

Re: Yamaha RX-V393 in protect mode

You have 5 amplifiers to check, all the outputs are OR together to feed the detection circuit.