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Old 11-28-2017, 01:53 PM   #1
rauno45
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Default Question about Yamaha rx-v457 power board

Hello,

I have a Yamaha receiver that does not power up. Does absolutely nothing. I have this far changed the common fault capacitor C405 to another 22nf 650V capacitor but that does not seem to help.

Testing the voltages I have 16 volts on C411, 5v standby is also present(excactly 5v). And AC input 230V is also present.
Only problem I have is that from the transformer leads I do not get 230V output at all. When I measure plus and - on D408 the multimeter shows only 3 Volts(testpointts marked on picture).

What would be the bad component here? What should I look for?
I am not really that familiar with mains voltage rectifying procedures.
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Old 11-28-2017, 10:29 PM   #2
redwire
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Default Re: Question about Yamaha rx-v457 power board

The power board makes a 10VDC standby rail from the small power transformer at conn CB401/S10.
It has no 5V rail; that comes from the main board and to power the reset circuit.

There is a complicated AC power detect and standby switch circuit with IC402 and C405 on the power board. It does many things. Also, it is floating at hazardous live on AC mains, so careful with voltage measurements there.
What voltage do you get across C406, which is power for this section.

If you have voltage on C411 then Q404 is on and hopefully power detect PDET signal is working, which also controls the reset circuit.

I would look at CB401/PDET and PRY (power relay) signals to see if they are doing the right thing.
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Old 11-29-2017, 01:24 AM   #3
diif
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Default Re: Question about Yamaha rx-v457 power board

I think the rx-v also have an issue with the thermal fuse in the transformer failing.
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Old 11-29-2017, 04:12 AM   #4
rauno45
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Default Re: Question about Yamaha rx-v457 power board

Nope, the thermal fuse in the transformer was OK, I measured it. Continuity test between blue and grey wire was OK. There was a youtube video that instructed on fixing this, but on my unit this is fine.

I will measure C406 and other points tonight and report my findings.
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Old 11-29-2017, 11:36 AM   #5
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Default Re: Question about Yamaha rx-v457 power board

After further measurements I can say:
220V also reaches legs of C405
C411 had 17,74 Volts which is a bit high for a 16V capacitor
5M rail had 4,975 Volts
S10 had the same voltage as C411 which is a little odd. It had also the same 17,74V, alltough it should be 10.

I guess the anomaly is in the 10V rail somewhere which sets too high voltage? But where?
C406 has stabile 9Volts
CB401 PDET has 0,61 volts
CB401 PRY has no voltage.
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Old 11-29-2017, 01:14 PM   #6
redwire
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Default Re: Question about Yamaha rx-v457 power board

The 10V rail is unregulated and will go up without no load.
I worry about it at 17.74V, as the +5.5V reg IC452 (sheet 91, E3) rated 14V max. but it's working OK to make +5M. C411 is 50V?
The schematic shows only 69V going into the standby transformer T401 though, I think it's a bad or DC number, not AC? The schematic has seems to have mistakes for voltage readings.

The main relay needs PRY to turn it on, from the MCU IC451. I would see if the MCU is on.
Can you check the voltages for the MCU +5S (+5BU I think is OK if +5M is present). Is reset (CB401/RES) stuck low, or does it go up?

Pressing the main power button takes /PSW low (normally high from +5S), so the MCU turns then everything on.
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Old 11-29-2017, 01:42 PM   #7
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Default Re: Question about Yamaha rx-v457 power board

Yes, 5M rail gives almost exactly 5 Volts so I guess that the regulator somehow handles it(barelyy I guess). As C411 I have 3300uF 16V capacitor(with SMG markings)- it seems to be factory fit.
The +69V seems marked a little low for this kind of mains transformer yes.

Dumb question, but I can not find the IC451 on the power board. Is it located somewhere else where I need to check? I only see IC402 and on the schematic there is also only IC 401 and 402.
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Old 11-29-2017, 01:59 PM   #8
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Default Re: Question about Yamaha rx-v457 power board

Also for information that the guy I got it from said that it got a lightning strike and after that did not power up. I dont know if knowing that helps with my situation or not.
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Old 11-29-2017, 10:30 PM   #9
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Default Re: Question about Yamaha rx-v457 power board

Lightning can get into the AV receiver on mains, or HDMI, or RCA's etc - almost any connection.
The problem might be on another board.

On/off switch is OPERATION board(1) to (2) CB801, to SUBTR(2) board- which has the microcomputer IC451, not on the power board. It has small pins so better to measure on the big parts or connectors.
Again, looking for +5S and /RES to see why MCU does not give out command to relay to power everything up.
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Old 11-30-2017, 12:14 PM   #10
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Default Re: Question about Yamaha rx-v457 power board

I found what you mentioned and here are my findings:
CB458 - 2 pins have 5 volts preset. one slightly higher, one slightly lower - 4,95 and 5,05
CB401 - reset(RES) is 5 volts when I get a good ground point with multimeter. It is kind of hard to measure down there. It did not seem to fluxuate to lower levels at all.

MCU IC451 power: schematic shows pin 14 and 64 for Vss:
pin 14 had 5,13V
pin 64 at C462 had no voltage.
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Old 12-01-2017, 11:32 AM   #11
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Default Re: Question about Yamaha rx-v457 power board

VSS is ground, if there is 5 volts on pin 14 check for an open trace between it and ground, Pin 8 should also be ground
and maybe check c463 to make sure its not shorted.
On page 68 of the manual I have shows the board layout, J584 & J563 should be ground also the can of the crystal should be connected to ground in that area

Last edited by R_J; 12-01-2017 at 11:48 AM..
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Old 12-01-2017, 12:19 PM   #12
redwire
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Default Re: Question about Yamaha rx-v457 power board

Yes, MCU pin 14 is VSS or GND, so you might check where your multimeter was connected.

You can also find +5S on Q451; maybe easier to probe.

The power management for sleep and standby is always tough to figure out.

On the power board, it's weird the 10V standby transformer primary is controlled by MOSFET Q404, as if a voltage regulator circuit with IC402/403. That would mean Q404 may be shorted, which lightning on mains would do. Check Q404.

PDET seems to turn on +5S then the MCU keeps it on with P5V.
This is why asking to see if +5S is up.
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Old 12-03-2017, 06:13 AM   #13
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Default Re: Question about Yamaha rx-v457 power board

Quote:
Originally Posted by rauno45 View Post
I found what you mentioned and here are my findings:
CB458 - 2 pins have 5 volts preset. one slightly higher, one slightly lower - 4,95 and 5,05
CB401 - reset(RES) is 5 volts when I get a good ground point with multimeter. It is kind of hard to measure down there. It did not seem to fluxuate to lower levels at all.

MCU IC451 power: schematic shows pin 14 and 64 for Vss:
pin 14 had 5,13V
pin 64 at C462 had no voltage.
Hi, can you please check the value of R419(2.2kohm) with mulitmeter . i had the same issue with my Rx-e410 the power supply circuit is similar to this , the problem was this resistor shows higher value than 2.2kohm, i replaced with another resistor then it receiver came alive- just check that resistor
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Old 12-03-2017, 03:21 PM   #14
rauno45
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Default Re: Question about Yamaha rx-v457 power board

OK, thanks for the suggestions. I got 5v on pin 14 by having ground point on one screw connected to the metal frame of the receiver.

I will try what you have suggested(also the +5S signal) and let you know what I find out.
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Old 12-05-2017, 11:18 AM   #15
rauno45
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Default Re: Question about Yamaha rx-v457 power board

Ok, I found the +5S now from the schema. Measured after r475 from pin 55 it showed 4,8 volts
Also found out that the ground is OK. The 5V I measured was from pin 13, not 14. Was quite tricky to count the pins there.
R419 has 2,168 kiloohms.
Q404 however after I unplugged the receiver measured IN CIRCUIT that all the pins were shorted with each other. Is this something how mosfets measure in circuit or should I solder it out and properly test it? When I unplugged the power board then only the 2 side positioned terminals remained shorted - I guess gate and source?

Last edited by rauno45; 12-05-2017 at 11:24 AM..
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Old 12-05-2017, 03:11 PM   #16
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Default Re: Question about Yamaha rx-v457 power board

I would pull MOSFET Q404 and test it. With a jumper from G-S (to ensure it's off), D-S should read open. If it is shorted, that explains the high +10V rail.
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Old 12-06-2017, 03:19 PM   #17
rauno45
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Default Re: Question about Yamaha rx-v457 power board

I tested Q404 by turning it off with a G-S jumper. After that d - s reads 0,52kohms. When I activate it again with multimeter by having leads on gate and source the resistance between d and s does not change, it always remains at 0,52kohms so I guess this MOSFET is broken?
The multimeter was in diode testing mode so it should have activated the mosfet and give a different D-S reading after activation.

Last edited by rauno45; 12-06-2017 at 03:21 PM..
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Old 12-07-2017, 10:49 AM   #18
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Default Re: Question about Yamaha rx-v457 power board

OK, I changed the mosfet Q404 to NEC K3114 mosfet that should be eqvivalent, but this did not solve the problem, however now instead of 3V on D408 it is now about 150ish, so I guess it got better somehow, however it still does not power on and 230V do not reach big transformer.

Power on C411 also dropped to 10V which is better.

Any ideas?

Last edited by rauno45; 12-07-2017 at 11:01 AM..
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Old 12-07-2017, 03:09 PM   #19
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Default Re: Question about Yamaha rx-v457 power board

Quote:
Originally Posted by redwire View Post
The 10V rail is unregulated
This is wrong, Q404 and IC402 regulate the 10V standby; 2SK3850 looks like good substitute.
Ok, so the 10V standby supply is regulating now, 2SK3850 looks like good substitute for Q404.


The MCU sends the command to the relay to turn on, after remote control or push button. We'll have to see why it stays sleeping or what.
+5M and +5BU and +5S should all be on.
What do you get on Q452, MCU power supply SUBTR(2) board. Is +5S up? RESET is still 5V?
If so, then scope on the crystal oscillator MCU pin 13 to see if it oscillating.

I'm running out of ideas why the MCU is doing nothing.
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Old 12-08-2017, 01:02 PM   #20
rauno45
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Default Re: Question about Yamaha rx-v457 power board

I measured all 5V rails just in case and yes, where I tested(specified before) all three 5v rails were up.
5M = 4,973V
5BU= about 5V
5S = 4,778V
Res = 4,926V

I found Q452 on Ic board(Small SMD transistor) and it only had 0,654V on the middle pin.

Unfortunately I do not have a scope so I can not probe pin13.

I have also measured all other capacitors on the main power supply board and they were in spec.
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