Help required to repair Yamaha AVR RX-V667

mbhangui

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My Yamaha AVR Model RX-V667 started powering off automatically since few days back. It is very random. Sometimes it lasts for 3 hours and sometimes just for few minutes. The power off is due to some in-build protection based on microprocessor power control. I downloaded the service manual and have been trouble shooting for the last few days. There is a diagnostic mode which you can enter by pressing Info + "tone control" + power button. It displays "PS1 PRT 3L". The cryptic message I'm supposed to decipher is that it is something to do with Power supply 1. PS1 is supposed to monitor ACBH, ACBL, AC_12, AC-5, ±12, ±7, +3.3D, +1.8D.
Now I checked all the above voltages and I find it to be fine. Today while trouble shooting, I found one issue. One IC TOP254PN is getting very hot. In fact it gets too hot to touch. I measured voltages across the pins as per the schematic diagram in service manual. The voltage on pin 3 is way off than what is in the printed manual.

As per datasheet, TOP254PN is a AC/DC Converters Off-Line Switcher IC 26W/64W. Does anyone know where I can get this locally in India. Mouser, digikey, etc are listing this device, but the cost of this IC is just few rupees and shipping of Rs 1500 and unknown custom duty.
I have also inserted the schematic of the offline power supply that most Yamaha AVR use
1635937037482.png
 

OM_2K19

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Edit:- typo
 
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mbhangui

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Edit:- typo
I had seen this earlier. It is out of stock. On element14, it says that this will be in stock around June 2022. There is an SMD version TOP254GN which is rated 20 watts. TOP254PN is rated 25 watts. Worst case, I will order the SMD version and solder it on a 8 pin IC socket.

These last few days have been fun. I have learned to open the entire amp and fit it back. I can sure help someone with Yamaha AVRs to troubleshoot :)
 

spirovious

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Are you getting same audio out @ certain volume? If db level is reduced then perhaps its processor is malfunctioning.
 

KNRAMU

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I had the same problem with my Denon 1912. IC TOP 252MN was faulty in SMPS board. As these were locally not available I bought 2nos of the ICs from Aliexpress at couple of dollars.
 

mbhangui

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Are you getting same audio out @ certain volume? If db level is reduced then perhaps its processor is malfunctioning.
There is absolutely no issue with db level. The power supply for the amps are different (unregulated 37 volts). All yamahas have multiple taps on the main transformer. However the main transformer is never connected to the mains directly. There is a standby power supply which uses 0.022 microfarad caps to bring down the AC voltage (C3701 and C3717) in the diagram. The most common problem with Yamaha AVRs I have come to know in various forums is that this design of using polypropylene caps rated for 630v is bad. They fail a lot and is the most common problem. In my case, the caps are fine. But have ordered better caps rated > 1000v to replace them. I have put the image of the caps below.
1636004550179.png

There is a SMPS circuitry which provides 5.64 volts and 3.3 volts for the digital board and the power on switch to function. The SMPS circuitry is based on TOP254PN IC (IC371 in the schematic diagram posted above). In the standby state, the digital board functions partially. e.g. If you have A/V sources connected to the HDMI ports, and a TV is connected to the HDMI out, you can switch the HDMI ports even when the AVR is in standby state. When you press the power switch button, it activates a relay on the standby power supply board and the main transformer starts getting power. Only when the main transformer gets power, the actual AMP gets activated. The amp boards also have 7812, 7912 and 7905 regulators which provide power for various signal processing boards.

In my case what is happening is that, even in the standby state, the amp switches off. It becomes totally off. The red led also doesn't light up and pressing the power button does nothing. To start the unit, I have to pull out the cable for around 20 seconds and connect it. Once I do that, the standby PS becomes on again and the push button starts functioning and the AVR works perfectly for few minutes till the power protection circuit gets triggered. The IC TOP254PN gets extremely hot.
 
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mbhangui

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I had the same problem with my Denon 1912. IC TOP 252MN was faulty in SMPS board. As these were locally not available I bought 2nos of the ICs from Aliexpress at couple of dollars.
You are a god saver. Does aliexpress deliver to India? I thought they had stopped delivering last year.
 

mbhangui

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Bad news. The shop in Pune in which google search showed having TOP254PN has emailed me that minimum order quantity is 20 with each costing Rs 200. If any FM in Mumbai/Bangalore who is visiting for any spare parts, can you check if this IC is available? Or do you know any shop in Mumbai who stocks difficult to find IC and can accept online payment and order?

I don't have electronics background. But can anyone who knows electronics, can you tell me if TOP258PN can replace TOP254PN. They both have the same pins but wattage ratings are higher for TOP258PN. Here is the data sheet for these TOP25X family. TOP258PN is easily available and so I can buy that and revive my AVR which has been down for almost 10 days.
 

mbhangui

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I just thought of an idea of modding the Yamaha AVR PS. The PS is just for standby function. It serves two purposes

1. Enough power so that when you press the power button (soft touch) or the power on button on remote, the unit powers on.
2. Provides 5v power supply to the HDMI board so that the HDMI inputs can be switched even if the AVR is just in standby and not on.

The Yamaha power supply is way too complicated. Primarily because it a SMPS based supply. This PS is not used for any critical function like powering the AMP. The AMP has its own power supply that uses bridge rectifiers and a big capacitor bank. This power supply is turned on by a Relay RY371.

Disabling the in-built Yamaha Power supply

1. Remove L3701
2. Remove L3702
3. Remove R3712
4. Remove R3710
5. Remove C3710
6. The capacitors C3701, C3717 (.022 uF) will continue to power optocoupler EL816(M) IC375. This is required to provide the AC PWR Detect line.
7. Connect an auxiliary power supply 5.6v on CB379 or I can use an existing mobile phone charger

My guess is that this should work. Just have to try this out. Tomorrow I will be busy visiting in-laws. I will try this on Sunday. Will post if this results in a success or failure.

~
 

mbhangui

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Work in progress. By removing these 4 components, the in-build Yamaha SMPS will get completely disabled. Post that I should be able to put my own 5.6v supply

EDIT: I realize now that removing C3710 is not at all necessary if one is removing L3702


IMG_20211105_212049339.jpg

IMG_20211105_212026724.jpeg
 

Deepak123

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Kudos to your DIY efforts.
How do you want to have in future, completely disable the SMPS functionality ?
If you want to restore your AVR back to original state, you will have to put double the efforts since you are tampering multiple components. That will become another and bigger DIY. But again, I understand that your AVR is currently not in a usable condition.


I just thought of an idea of modding the Yamaha AVR PS. The PS is just for standby function. It serves two purposes

1. Enough power so that when you press the power button (soft touch) or the power on button on remote, the unit powers on.
2. Provides 5v power supply to the HDMI board so that the HDMI inputs can be switched even if the AVR is just in standby and not on.

The Yamaha power supply is way too complicated. Primarily because it a SMPS based supply. This PS is not used for any critical function like powering the AMP. The AMP has its own power supply that uses bridge rectifiers and a big capacitor bank. This power supply is turned on by a Relay RY371.

If you remove this PS1,
1. how HDMI board gets power, from main transformer ? Is it safe for HDMI board to get power directly , as these circuits are already very fragile (you see HDMI boards getting fryed for small reasons in this forum itself)
2. When you switch on main power, AVR gets ON. Any other circuits/components powered thru PS1 now gets power. Are they rated correctly .. etc etc. Just make doubly sure
 

mbhangui

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Kudos to your DIY efforts.
How do you want to have in future, completely disable the SMPS functionality ?
This SMPS is actually not required. Most manufacturers are doing this to get past Euro regulation norms to have very low standby power consumption. All this this SMPS does is to provide power for the standby circuit that can be switched on by pressing a button on the front panel or remote. The board also has some other use.

1. Has a relay RY371 that gets powered to a transistor Q3802 in the schematic diagram that I posted in the first post. This transistor is on a totally different board. The connection to this relay is through connector CB379. I'm not going to disable this
2. Has a power provided to an optocoupler IC375 via two 0.022 uF caps (C3701, C3717). I'm not going to disable this. See the bottom of the schematic that I posted in the first post. This also provides AC power detect to another board. This is how the microprocessor detects that the board has AC power coming in and switched on. When it detects this power, the red led on the front panel lights on.

If you want to restore your AVR back to original state, you will have to put double the efforts since you are tampering multiple components. That will become another and bigger DIY. But again, I understand that your AVR is currently not in a usable condition.
It will never be required to put the AVR to original state. By doing this, I will not lose a single functionality. But in fact, I will gain the functionality to replace the SMPS whenever it goes bad. This is like replacing your laptop power supply when the adaptor goes bad. Just because the adaptor goes bad, we don't have to throw away the laptop. So by doing this, it will be like Aug 15th 1947 for the AVR. It will get freed from the cruel clutches of a evil SMPS.
If you remove this PS1,
1. how HDMI board gets power, from main transformer ? Is it safe for HDMI board to get power directly , as these circuits are already very fragile (you see HDMI boards getting fryed for small reasons in this forum itself)
2. When you switch on main power, AVR gets ON. Any other circuits/components powered thru PS1 now gets power. Are they rated correctly .. etc etc. Just make doubly sure
The HDMI board doesn't get power from main transformer. It gets powered by 5.6 volts from this SMPS via connection board CB379. There is another board which has transistor Q3802 and which gets triggered when you press the power on button. This transistor then switches on relay RY101. RY101 relay finally switches on the main transformer which then starts supplying power to the AMP and other boards. There are multiple bridge rectifiers, regulated power supplies using 7812, 7912 and around 3 dc-dc convertors on totally different boards. The main amp gets powered via unregulated capacitor bank (+- 37 volts from the transformer and bridge rectifier). So I'm not going to fry the HDMI boards as long as I give a steady 5.64 volts (this is what this in-built SMPS is doing).

Basically I'm going to discard this complicated SMPS which provides 5.6v to the HDMI board. I have seen repair shops having charged around Rs 9000 for changing this board. I contacted the Yamaha service centre. These guys will cleverly tell you that they don't sell spare parts. They do this just because they want to fleece the customer by charging exorbitantly. In my case this SMPS has gone bad because of just one IC TOP254PN which is no longer available. The cost of this IC is less than Rs 100. Now I find that even Denon uses this TOP2xxx IC for SMPS. In most of the case where Yamaha AVRs don't switch on or give protection fault, it is because of two problems with this SMPS board.

1. This board uses 0.022 polypropylene capacitors to drop the AC voltages. They should have used resistors. But resistors reduce the voltage/current by wasting energy in the form of heat. So Yamaha is making some kind of GREEN smps by using caps. But these caps fail often. This is the most common fault found in Yamaha AVRs.

2. The SMPS itself. SMPS are always complicated because they have to switch the mains frequency and be safe enough. Over these years I have had to throw away equipment because the on-board SMPS went bad and the IC/MOSFET is no longer available. Today Yamaha/Denon/Marantz etc designs an AVR and puts in a SMPS with a chip that will no longer be available in few years. So what do you do after 10 years? Throw away the AVR? Lot of carbon, effort went into making this AVR. I just don't want to throw it away and also not give money to these authorized service centers. I would rather have drinks with my friends or donate money for some cause. How many times have your phone charger gone bad? These mosfets and switching IC fail like anything. So I'm going to replace this 5.64 volts with a LM318 regulator.
 
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mbhangui

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Update. After lot of reading and review of spec sheets and also folks from eevblog.com forum, I pulled the trigger to buy TOP258PN from here. This IC is the same as TOP254PN but with higher wattage rating. The output voltage is anyway decided by R3712 and R3713, which I will not change.

But I will anyway go ahead with disabling the PS and use my own 5.6 supply.
 

spirovious

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One doubt .Is this smps handy/necessary when any of component is malfunctioning and need avr to shutdown to avoid further damage? I guess it checks all sections of avr before powering on all relays.
 

mbhangui

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One doubt .Is this smps handy/necessary when any of component is malfunctioning and need avr to shutdown to avoid further damage? I guess it checks all sections of avr before powering on all relays.
No. The only protection this board has is the fuse and that provided by the IC TOP254N (overvoltage, thermal heat) protection. But this basic protection is present in all SMPS boards due to the danger of mains voltage coming directly to the circuit board. There is nothing extra safety feature on this board that even a basic cell phone charger has. 240 volts coming to the main board is the main reason, i have a strong dislike for SMPS. Because it is 240 volts, sometimes even a fuse will be too late to prevent a mini fire. This kind of catastrophic failure has happened to me in a iphone charger also. The charger was completely burnt inside.

The sophisticated protection features are all on the Digital board (the board with HDMI in and out sockets). It is microprocessor controlled. The voltages and currents are measured by SN74LV4051APWR IC - 8 channel analog multiplexer. Basically the pins of this two IC are fed voltages through various resistor divider network from various important portions of the boards. By removing the SMPS, I will not be sacrificing any of the protection features like high/low voltages, speaker short, over current, DC in speaker output.

To repeat, the only functions of the in-built SMPS that I'm disabling is the 5.6 volts out. The SMPS board does the following.
  1. To provide 5.6 volts to the digital board (HDMI board). This is what I'm disabling by removing L3701, L3702, R3712, R3710, By removing L3701, I'm cutting out the power to the SMPS portion. By removing the removing the remaining 3 components i'm disabling any extra load on the DC output.
  2. To provide ac detect feature through an optocoupler (I'm not disabling this)
  3. To provide a return path through a transistor on another board to switch on one relay. This relay when switched on, provides power to the huge main transformer. This is the transform that provides all the useful power to the AMP. I'm not disabling this connection.
 
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Silencer

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I have seen guys at avs do this kinda 'invasive' diy. I am glad to see it here. Do post all the updates even if it's not a major one.

I really admire the passion and confidence. This can really motivate a lot of folks here venture into diy. Well, I am motivated :)

We are in dire need of some expert technicians who knows what they do and doesn't fleece the gullible owners of these sensitive gear.


 

mbhangui

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So finally my Yamaha RX-V667 started singing today. Just hooked up a quick DIY LM317 regulated 5.62 volts to the existing Yamaha Power supply board. Removed L3701. The only thing is that I have an ad-hoc arrangement. To operate the AVR, I have to connect two plugs. The original Yamaha plug and a new plug which goes to a transformer supplying power to LM317 regulator. The output of LM317 has been soldered to the Yamaha power supply board through two wires going inside along with the power cable. You can see the white and blue wire going inside the AVR along with the power cable. This cable is just 5.6 volts and that is all that is required to power the AVR in standby mode and run the entire Digital board. But it took me many hours and few nights to understand this damn power supply.

Tomorrow I should be getting a replacement IC TOP258PN too. I have ordered two of them so that I have enough longevity of my AVR.

Any Yamaha AVR owner here should make sure to download the service manual and buy the SMPS IC pertaining to their model. They are very cheap and but get obsolete very fast. In my case the original IC TOP254PN is no longer available. But lucky for me, TOP258PN should also work.
 

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mbhangui

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Update: Since TOP254PN is no longer available easily, I had ordered TOP258PN. The IC arrived today. This IC has the same specs as IC TOP254PN except that this supports higher wattage and has lower Rds on (resistance of drain and source) of the inbuilt MOSFET. TOP254PN has Rds of 5.4 ohms while TOP258PN has Rds of 1.7 ohm. Which actually means that this IC will run cooler for the same power output. Luckily I ordered two nos. When I connected the first IC, it gave me zero volts and I thought that this IC will not work. Then I connected the 2nd IC and lo behold, the AVR turns on. No more PS1 PRT 3L error. Also the earlier TOP254PN would run very hot. Too hot to touch.

I will order 2 more so that I'm stocked for the future. Couldn't have solved this on my own. I got lot of help from eevblog forum. Link to the thread here.

I can now run the AVR without two supplies powering the unit.
 
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