Yamaha RX-V373 PS PRT error

[Majorbob]

I have a Yamaha RX-V373 and it is failing with a PS-PRT 160H error.

I have the service manual.

All of the voltages from the regulators are reading correctly.

In service mode I have PS:160-165 and DC:255.  The nominal values, from what I can determine looking at the stated voltages in the schematics are PS:131 and DC:124 (3.3v=255) and I am reading PS:2.03V DC:3.4V.  I can't find anywhere anything telling me what the tolerance for these values is but the initial error is the PS-PRT.  The unit is not hugely old and has recieved fairly light use.  The 3ch power amp has been replaced for new (STK433-330N-E) with a direct replacement.  The old unit was sending DC 50V to one of the speaker channels.  Using a multimeter I no longer detect any DC voltages on any of the speaker channels.

None of the capacitors look like they are dead.

I'm starting to lose my will with this one a bit.


Thanks in advance

[Majorbob]

Sorry... probably would have helped to actually put a question.  What should I check next? What do people think are possible causes?

[PKTKS]

You are missing the point:

* the code indicates a PS (power supply) PRT (protection) error

You do have a faulty regulator somewhere
start in the manual with this code on spot

Paul

[kawal]

What ever the processor is measuring cannot go more than 255 for a 3.3V processor.
That should give you a clue.

[mzacharias]

What ever the processor is measuring cannot go more than 255 for a 3.3V processor.
That should give you a clue.

The way Yamaha does it is the error code given represents the voltage expected for that protection line, according to formula.

example:  If the "OK" range given is 125 to 170, but the error value shown is 90:

3.3 / 255 x 90 = 1.16470

Which is the approximate wrong voltage that would generally be seen at the output of the resistor summing network, and at the microprocessor itself.

Why they do not have the micro report the voltage directly I do not know - this is how Yamaha has done it for a long time.

[Majorbob]

I have checked all voltages that feed on to PSPRT and these are my results:

source   Value        Measured         
+5         4.9             5.02   Through 3 pin regulator      
S9           9.3             10.25   Through 4 pin regulator      
+7D          7.8           8.79      Not regulated, just rectified   
AC2      AC31.0           34.4    16.9 and   17 to center tap
+5.5           5.8           5.82       Through 3 pin regulator
-VP         -38.0           -32.6         
AC40.9                   44.8         
AC40.9                     44.8         
+7A           6.9             6.9      Not regulated - voltage divider   
-7A          -6.9           -6.9      Not regulated - voltage divider   
+3.3D   3.3            3.2      Regulated   

So my thinking is that there is possible issues with S9 and -VP?

[PKTKS]

So my thinking is that there is possible issues with S9 and -VP?

Possible - actually the protection is activated
if the reading is out of range

Range is also issued with the code or on the manual
Unfortunately  a bit criptic values but easy to decipher

Paul

[Majorbob]

OK... I found on page 40 of  the manual it tells me what the PSPRT is taking voltages from (A/D Data Check section, so not where I expected to find it) and it tells me to check:

          Spec    Meas
ACL     40.9    44.8
AC2     31.0    34.4
+12A  12.0    11.92
-12A  -12.2  -11.75
+7D     7.8      8.6
+5A     5.0      5.07
+5U     5.8      5.82
-VP    37.9     39.8 (on main board where it appears the supply is coming from, however on the operation 2 board, where PSPRT takes its measurement, i have spec: -38.0 meas: -32.5)

The manual says range is 101 to 155 for PSPRT (1.31V to 2.01V)  I have 165 (2.14V).

[kawal]

Figure out why -Vp is Low. Fixing it should bring the reading down.  -Vp should be -38V or about based on schematic. Maybe transistor has degraded beta or zener diod is damaged Its a very simple circuit.  That voltage is only used on the VFD display. But based on your measurements the cables or connectors could be an issue. Resolder the connectors there could be cracks in the solder and the load is making the voltage low. This happens a lot with the eco solder due to thermal cycling. .

[kawal]

Re-solder all the higher power stuff as well and the regulators.

[Majorbob]

Ok thanks! I'll get my kit out when I next have time!  Got some new kit arriving in the next few days that should make this task a bit easier.  I'll post again when it's done and I have the results.

[Majorbob]

And I'm glad I understood the schematics the same way as you.

[kawal]

Keep us posted.
I  broken solder is hard to see without a microscope and proper lighting or maybe good eyes (I dont have these anymore). I just repaired a monitor that did not show any signs of life. I figured the caps where the issue, but all it was is  broken solder joints on the connector going to the CPU board.  After re soldering all came back to life and its been working every since.   Its like magic but  I have a scope now and i could see the broken solder  with it.  Without the microscope it looked ok.

[Majorbob]

I've been planning to get one of those digital microscopes but since the pandemic hit other priorities have arisen so the best I can do is 10X, not really enough so see solder cracks.  I've  removed the boards I need to resolder today so now it has to sit until next week when I have a few hours set aside for working on it.

[kawal]

Optical ones are much better because you see in 3D and no delay .
I think 5x is good  enough ( i use only 5X as 10x is too much and narrows the field of view too much) . A zoom from 2x..10X would be perfect.  Working distance is most important  min 20...30cm is needed.

I bought one of these locally  but even new prices are pretty good.  Well worth the $230 they are asking for it.


https://www.amscope.com/stereo-microscopes/5x-10x-binocular-boom-arm-stereo-microscope-with-led-gooseneck-light.html

[kawal]

Its hard to take a picture because you get a different view from the camera .  But more or less this is what you will see wtih a 5x lens. With 10x you can only see 4..5 legs on the IC

[Majorbob]

My magnification is just a desk lamp type (similar to this: https://oypla.com/sports-leisure/arts-crafts-hobbies/desk-clamp-magnifier-magnifying-lamp-with-5x-magnification?gclid=EAIaIQobChMI5P-gsayT6QIVRLTtCh3hgAgAEAkYASABEgJJpPD_BwE) so the illumination is fantastic but its clumsy to work with.

[Majorbob]

I have done the resoldering this evening and checked the errors to find no change.  When the unit was powered up I accidentally knocked it and found the PSPRT drop to 145 and DCPRT drop to 000.  I changed the unit so I could work on the main board and simulated what I had done when I knocked it with a croc clip wire and got the DCPRT to 045 (within its tolerance) by shorting the speaker terminals to ground momentarily.  (I have no idea why this worked) that effect was permanent after I removed the wire.  I now have PSPRT 165 and DCPRT 045.  I was checking the voltages around the -VP source and found a couple of odd ones.  Resoldering one side of R90 I checked its resistance and it has 10ohm (it's a 4.7ohm resistor 5%).  Left it soldered and am going to order some new ones... lowest i have in stock is 10ohm.

[SpecialK]

R90 I checked its resistance and it has 10ohm (it's a 4.7ohm resistor 5%).  Left it soldered and am going to order some new ones... lowest i have in stock is 10ohm.

Just solder another 10ohm across that resistor as a bodge.  Or better yet, remove R90 and then solder two new 10ohms in parallel.

[Majorbob]

I don't want to just add another 10ohm as the existing one is likely to continue degrading.  Replacing with 2 10ohms is an option I was considering, however I will want to get it to within the specs of the original to confirm the fault.  (Even if it's not necessary it will give me peace of mind).

[kawal]

Good find with the resistor. Resistors are the least likely failure points usually so that is strange.  Did you check that resistor in circuit or out of circuit as it make a difference usually.  That resistor is under a lot of stress and it is a fusible resistor which is supposed to fail open.  I guess its somewhat doing its job.

[Majorbob]

Thanks!  I desoldered 1 leg and checked it in situ.  I'm hoping that that is the fault and not just a symptom. 

[kawal]

sounds like at least some part of the issue. Hopefully all of it. Earlier you mentioned that when you measured the voltage on the output of the power supply you got good voltage  close to the regulator but lower voltage by the processor. So might have been multiple issues including bad solder joints. The last explains better the lower voltage closer to processor.

[Majorbob]

Resistors arrived today and I replaced R90, PSPRT in service mode now reads 133 (within tolerance!) Wahoo!

The DCPRT is no longer reading 255 thanks to the weird grounding thing, however I now 000.  There is a voltage across the centre channel of ~ –22V.  There is no voltage visible across the emitter resistor (R64) however I have 13V across R24 (which feeds back in to the power IC).  Ch2 in has 0V (as expected) and there is no voltage coming from the volume IC (as expected).  R24 is reading the correct resistance.

Across the transistor I have –22 on B and E and about the right voltage on C.

I feel like I'm looking in the wrong places though.

Finally managed to upload a picture! Sorry for not being able to before.

[Majorbob]

I have removed one of the boards in the way and nothing seems to be damaged in any way...