Electronics > Repair
Yamaha RX-V473 repair. PS3 PRT: 094L [SOLVED]
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David_AVD:
Correct, it measured as expected at the time of the measurement. There are various Yamaha models that have issues with the sense resistors varying in value over time / intermittently. Mostly the ones that use 0603 size SMD resistors, but I have seen it (although rarely) with through hole resistors as well.

The other thing to check is the SMPS. I've had units come in where the SMPS controller chip goes intermittent (but not fail completely). I've also seen bad resistors / corrosion in the feedback path around the transistor side of the opto isolator. Lastly, the small electro capacitor next to the SMPS controller chip can go marginal, causing issues.
perieanuo:

--- Quote from: Comp_Sci_hater on September 05, 2024, 01:17:01 pm ---Re: perieanuo
I unfortunately dont have a power supply and i also dont have proper gear to solder/desolder smd parts like the resistors in the voltage divider. The thing i hate the most is that i cant really trace where the 5v5 is coming from on the microprocessor board, the board is double sided so tracing gets tricky relaly quick. I checked all the 5v5 inputs coming in to the microprocessor board and they seem fine with 100mVpp ripple at max.
 I can chcek the power up voltage, although i think i checked it a couple times with single trigger enabled at (-500mV) - (-300mV) and it didnt trigger once. At this point tho its either that or the microprocessor is damaged so i guess im gonna try again.

--- End quote ---
put 3 AA batteries in series, that's your 5V, you won't reach the error threshold you calculated before.
if you don't have desoldering tools, how do you want to repair this????
another users are saying you may have a rogue 5v supply, i'm not alone :)
Comp_Sci_hater:
Re: perieanuo
So i should check if there are really 5.5V coming in to the voltage divider? Im not trying to sound ignorant (im a total noob), but why would i check that, if according to calulcations the voltage out of the divider is spot on? Is there something i am missing?
Thanks for replying.
Comp_Sci_hater:
UPDATE: I just found something big, (i think?) the OPERATION_2 board supplies 5.5V to MAIN_4 board which then supplies 3.3V to the DIGITAL_2 board, where the CPU is located. I dont know how i didnt notice this before, but none of the 3.3V connectors actually supply 3.3V. Here are the measurments:

  PIN           EXPECTED     MEASURED
+3.3M               3.3V            5.44V
DGND                0V              54mV
ACPWR-DET       3.3V            5.44V
CPU-N-RST        3.3V            5.44V
PRY                   3.2V            4.69V
DEST                 0.3V            4.49V

This seems all messed up, am i reading the schematics correctly? What could cause this if it is in fact right? I dont know if i should even care about this, the manual says that the 3.3M rail is responsible for the standby led, the remote and the buttons on the front panel and all of these seem to work okay. Attached pictures of all 3 boards. Measurments were taken at the DIGITAL_2 side of the connector with the amp powered up (it was the same with it powered down tho).
The 5.5V coming out of MAIN_4 is correct (Measured 5.6V). The PS3 error is really strange considering the PS3_PRT is responsible ONLY for detecting voltage abnormalities on the +5.5V rail.

Comp_Sci_hater:
UPDATE: The reference voltage given on the manual is wrong (?), it says that 3.3V = 255, but i did a little test that proved this to be wrong. I measured all PS3_PRT, PS2_PRT and PS1_PRT. The values i measured with my scope, and the values being shown on the display are as follows:

PSx_PRT    DISPLAY [A/D]      DISPLAY (USING 3.3V = 255)  [V]        MEASURED [V]
   PS1                 030                                         0.388V                                 0.639V
   PS2                 041                                         0.530V                                 0.876V
   PS3                 094                                         1.216V                                    2V

So after doing some calculations:
 30 * x = 0.639 => x = 0.0213000
 41 * x = 0.876 => x = 0.0213659
 94 * x = 2       => x = 0.0212766

It all lines up perfectly, is it possible that the A/D conversion is wrong?
Guys am i going insane or does this make sense? Until now i used the conversion 255=3.3V =~ 1 = 0.013V, is this wrong?
Does this mean that the cpu is getting (255*0.0213=) 5.431V instead of 3.3V as the reference voltage? If that was the case the PS1_PRT and the PS2_PRT voltage would be still within bounds, going from our 255 = 5.43V system back to the 255= 3.3V system we would get:

  PSx_PRT    3.3V = 255 [A/D]      BOUNDS       
   PS1                 049                      12 to 100                           
   PS2                 068                      34 to 106                             
   PS3                 155                      132 to 168

I really hope all this is making sense. Please reply with your thoughts.   

UPDATE: A/D conversion reference voltage is input at pin 2 of IC21, it should be 3.3V, the 3.3V comes from +3.3M rail. Its surely a coincidence, that +3.3M is the same rail that i measured 5.44V on (almost exactly the reference voltage that lines up with the A/D values being displayed on screen), instead of 3.3V  8) ;D ;D 8). Guys, i think this is it.     

UPDATE: Everything liens up. The voltage at pin 2 is 5.2V. I need to find out why the 3.3M rail is at 5.43V, and get it back to 3.3V.
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