Yamaha RX V773 PS2 prt issue

[Frank Wurpel]

Hallo everyone, this will be my first attempt to repair a complicated piece of electronics. I have no electronics background but have taught myself electronics over the last 15 years as a hobby.
Recently my trusty Yamaha RX V773 AVR started to misbehave. For some reason the two front speakers did not produce a sound. Interestingly enough, they did work again after switching the unit off and on again. However, at some point the AVR did not switch on at all, and only a red blinking light appeared after pressing the on button. After reading another thread here on the blog, I downloaded the service manual for the v673. which is fairly similar. I could not find a service manual for the RX V773. In this service manual, it describes the interrogation feature of this AVR, by pressing tone control and info whilst pressing the on button. This is very handy feature, which indicated in the history that PS2 had a problem. It showed the values 60; 33; and 30. From the service manual I understand that this means that the value of power supply PS2 has been too low at a number of occasions. The interesting thing however is that if I have a look at the voltages using the P1 function, it shows ps1, PS2 and ps3 having the correct levels? What I do notie
De is that both ps1 and PS2 are not stable an fluctuate a bit, whilst ps 3 is very stable. Personally I would think this to be a sign of a faulty equalizing capacitor of the ps1 and PS2 power supplies, but I am very much interested in your view and knowledge.
One other thing that puzzles me is where these power supplies are located. I don’t think they are on the small power supply board with the 5.5 volt output on it. This to me seems like a small SMPS used for standby power to switch the mean transformer on and off.

I hope someone can help me and educate me on how to bring my AVR back to life.

Greeting from The Netherlands
Frank Wurpel

[PKTKS]

Intermittent problems are the worst thing to track down.

I would do - just by pure experience of mine - the total
opening of the case.

Disassembling of the boards related or even all possible
as much as to have a clear view - may be microscope needed.

I  WOULD DO AN EXTENSIVELY EYE SEARCH LOOKING FOR BAD
CRACKED AND DRY SOLDER JOINTS (in the very first place)

While doing this as primary - i would check caps about possible
even small leaks

My first guess:  bad cracked solder joints

Paul

 

[Frank Wurpel]

Thanks Paul,

I will have a very close look at the circuit boards. The amplifier is very clean, so no problems there. I have meanwhile read all the Yamaha threads, and notice a lot of problems with the 12 volt and 5 volt voltage regulators. Maybe time to attach my scope and have a look at the output voltages. Do I need to hook the speakers up to test this, in order to add a load?
One thing that keeps puzzling me is that the fact that the two front speakers were off on two occasions. I hope this is not caused by one of the output transistors or anything more complex.....

Frank

[PKTKS]

Thanks Paul,

(..)Do I need to hook the speakers up to test this, in order to add a load?
One thing that keeps puzzling me is that the fact that the two front speakers were off on two occasions. I hope this is not caused by one of the output transistors or anything more complex.....

Frank

Normally you don't need speakers unless you are  troubleshooting the
output stage.  But obviously it will do no harm putting some dummy load.

YAMAHA service codes help a little bit to spot the region.

I always put some dummy meter on the PSUs while doing
tests no matter how silly it may be - you may have one more clue

Paul

[Frank Wurpel]

Hi Paul,

I have had a good look at the schematics this weekend, and removed the video board from the amplifier. No obvious signs of broken components, so I started at the beginning measuring the SMPS providing the 5.5 volt. According to my DMM, this was 5.6 volt, without the video board attached. Using the scope gave me different (much higher value) measurements, which I need to verify (missing load?). Could it be that a smoothing capacitor in the high frequency part of this power supply could lead to PS 1 and PS 2 fluctuating?
On this topic, can you tell me what PS1, PS2 and PS3 are? I can't find this in the schematics. Which is the 5 volt and which is the 12 volt power supply? Once I know this, I can attack the problem a bit better...

Thanks in advance,

Frank

[PKTKS]

Those PSx are labels you will find across the schematics.

All RXV series are very much alike - aside the extra features.

Those PRT PS codes will give you a hint of the location
where the fault is sensed.

Nevertheless the main power schema should be checked
just after you have dead sure the solder joints are not "cracked"

Some typical figures of the RXV777 below
they are reasonable alike

Paul

[Frank Wurpel]

Hello all,

As I could not find any dry solder joints or hairline fractures in boards, I have now reflowed all the solder joints that even looked slightly suspect, together with all the joints that are on known high thermal stress locations. Good to see that after putting the complete amplifier back together again, it still worked, although it did need some help. After clearing the fault memory, I ran through all the menus, and everything appeared to be OK. The values for DC, PS1, PS2 and PS3 were all perfect. I only observed that PS1 and PS2 were not exactly stilling that the last digit changed sometimes.
Anyway, I thought I had won the battle after a weekend or resoldering, but today, the amplifier did not start up again. Only the little red light was flashing after pressing the on button. Holding the tone control and info key whilst pressing the on button started up the amplifier in non protect mode (I have to keep them pressed, otherwise the amplifier does not start up). In the fault log, I found that PS2 had been low again. (3rd PS2 30L). Obviously, there is something wrong with the PS2 power supply. The strange thing however is that if I clear the history, I can switch the amplifier on without any problems. It will also stay on for a long time (albeit without speakers attached, as it is on my desk at the moment).
The thing that puzzles me is that the fault seems to occur after it has been switched off, i.e. in standby mode. This leads me to believe the fault lies in the section that is not energised by the relay on the power supply board. This again is strange as PS 2 needs the relay to be energised to provide the PRT function and the PS2 power supply. Another possible cause could be a bad capacitor allowing a low voltage dip on the PS2 circuit when I with the amplifier on or off.
Can anyone help me with this problem?

Thanks in advance,

Greetings from The Netherlands,

Frank

[mzacharias]

If the PS2 is low that should indicate that one of the 5V lines is low, therefore not pulling the PS2 line up.

You may have a bad solder connection but really,  5V regulators are cheap and plentiful. Replace them.

[Frank Wurpel]

Hi Mark,

Thanks for your quick reply. I am currently running a test, whereby I am deliberately not switching on the amplifier for two days, to se what happens if I switch it on the third day. As I mentioned above, it is very strange that he the low PS2 prt occurs after the amplifier has been off. Coincidence?? I don't know. It feels like a stabiliser capacitor not functioning properly. When I had the whole amplifier apart, I actually tested all the electrolytic capacitors with an ESR meter. All of them proved to be within they range, although the two capacitors around 5 Volt regulator IC333 (C3311 & C3312) both differed a lot. One had an ESR value of 0.2, whereas the other had an ESR value of 5 ohm. Since an ESR of 5 ohm should be OK for a 1 microfarad 50 volt capacitor, I have left it as it was.

I could change out both IC333 and IC334 (I think these are the only two 5V regulators right?), but still find it strange that the amplifier works without any problems if I clear the fault memory. Can you explain this Mark?

By the way, I have watched your repair videos on the Yamaha RX amplifiers on you tube, and they hare really ace! Amazing you can resolver the processor IC on the bottom board with a magnifying glass.

Now that I have your help, I won't give up yet and hand it over to the Yamaha repair centre...... Let's see what we can do first

Thanks in advance for your help,

Greetings from a windy Netherlands,

Frank

[ambrosia heart]

 For some reason the two front speakers did not produce a sound. Interestingly enough, they did work again after switching the unit off and on again. This is a very typical faulty symptom of all av-amp after using 5 to 6 years.


However, at some point the AVR did not switch on at all, and only a red blinking light appeared after pressing the on button.  Use DIAG mode to pinpoint the faulty part of your amp including over-current, DC offset, temperature and
voltage problem.

[Frank Wurpel]

Gentlemen, New developments:
As mentioned in my previous comments, I have left the amplifier off (on stand-by) for two days to see if it reproduced the fault. Well, when I tried to with on the amplifier yesterday, only the red flashing light came on. This therefore means that the fault is generated with the amplifier in standby, i.e. without anything attached downstream the main transformer. This time, I was also not able to normally switch on  the amplifier after clearing he fault log, indicating that the fault had worsened. The only way I could start up the amplifier was by holding tone control and info depressed whilst turning the amplifier on. Interestingly enough, the fault log showed a low PS2 history (1st, 2nd, 3rd, and 4th) after I had cleared the log. I have repeated clearing the fault log, and trying to start up, but was unsuccessful in starting up normally as before. The fault log once showed a low PS1 as well. The low PS2 value was below 30 (12, 23, etc) for all cases, indicating a very low PS2 (or PS1) line.
However, with respect to the fact that this all happens when the machine is on stand-by, I now strongly suspect the SMPS, as this produces a 5.5 Volt DC supply. This standby power supply, has obviously been in operation far more than the actual amplifier, for which components in this circuit will / may be more used. On the schematics, I could not deduct if the 5.5 volt power supply is used as a reference voltage for the other power supplies which are downstream the main transformer. If this is the case, it all makes sense that the PS1 and PS2 fault codes appear, as the reference voltage will be incorrect. This weekend, I will have a closer look at the SMPS board using my oscilloscope. I actually suspect a capacitor in this circuit to have lost it. Unfortunately the SMPS board of my V773 is not the same as the one Dave repaired in his EEV blog video. However, maybe an identical capacitor could be the culprit.
As always, all hints and suggestions are welcome. I will keep you all posted on the progress.

Greetings from a sunny Netherlands,

Frank