Author Topic: Yamaha RX-V373 PS PRT error (Read 13351 times)

Majorbob · « **Reply #25 on:** May 06, 2020, 09:33:12 pm »

I think it might be the transistor Q7. When I measure across its collector and base the amp turns off with a current protect error. If i do the same test on any of the other channels, i get 52.8V.

Edit:

I managed to find the correct spec eventually (Yamaha have used center collector not center base like everyone seems to make for this transistor) and am going to order 10 tomorrow. Once they are ordered I will swap the suspected faulty one for a good one from one of the other channels. If that fixes it then when the new ones arrive I'll replace all 5 of them.

Majorbob · « **Reply #26 on:** May 07, 2020, 08:30:18 am »

So I've checked the hFE of the suspect faulty transistor and one from a good channel, both are reading around 130, which is correct by the datasheet. Swapping the two transistor locations has also not had any effect, the fault is still present in the centre channel. At this point I think it's a faulty power amplifier IC (STK433) which I've already replaced once.

Can anyone shed some more light on this?

Majorbob · « **Reply #27 on:** May 07, 2020, 09:09:01 am »

I added a load (10ohm resistor) across the centre channel speaker terminals and the DC value rose to 016. With this resistor in place I checked voltages across all of the speaker outputs and the fault has appeared in the front right channel (the one that had the original 50V fault when I first changed the IC). Adding a load across this channel as well the DC value has risen to 042 (within tolerance).

This makes me want to change the main power IC and all of the power transistors. Would this be the recommended action?

Majorbob · « **Reply #28 on:** May 07, 2020, 09:25:46 am »

Using the load gave me an idea. I bypassed C35 and R74 (and the Front Right equivalents) and it had the same effect as adding a load, so turning the amp on normally I found it stayed on with no fault code.

Is one of these components going to be a fault or is this a red herring?

Update: I'm able to ground it straight from the power IC and the fault goes. Makes me firmly believe it's a power IC error again?

kawal · « **Reply #29 on:** May 08, 2020, 12:57:12 am »

Wow they started putting Hybrids in the RX-V series? Didnt know that . That they made all amps discrete.

Majorbob · « **Reply #30 on:** May 08, 2020, 06:46:00 am »

Yeah, it's got 2 STK433s. A 130 for the rear L/R and a 330 for the front 3 channels.

mzacharias · « **Reply #31 on:** May 08, 2020, 12:53:45 pm »

Quote from: kawal on May 08, 2020, 12:57:12 am

Wow they started putting Hybrids in the RX-V series? Didnt know that . That they made all amps discrete.

A few of their lower end units did for a while. Back to discrete now.

edit: I have a few original STK's of this type which I inherited when my shop closed, if anyone in the U.S. is interested. We can work something out.

Majorbob · « **Reply #32 on:** May 18, 2020, 07:38:56 pm »

New IC arrived today! Have soldered it in, replaced the thermal compound on everything and have a DCPRT: 000 error... F***. Measuring the voltage across the center channel I get 2.75V (approximately 20V less than before) now I really want to know where this voltage is coming from 😫.

Does anyone think they can work it out?

I have attached an image of the relevant part of the schematics. The red line going from the IC through the channel goes to the speaker out.

Edit:

When the back panel is grounded to the bottom panel, I have DCPRT: 000. When I remove that connection the readings change. PSPRT: ~190 (high) DCPRT: jumps to 255 then settles down to ~110 (high) nominal for DCPRT is 27-88.

Edit 2:

I mis-measured the FL and FR channels, they have the same -2.75V

Majorbob · « **Reply #33 on:** May 18, 2020, 07:48:24 pm »

Quote from: mzacharias on May 08, 2020, 12:53:45 pm

Quote from: kawal on May 08, 2020, 12:57:12 am
Wow they started putting Hybrids in the RX-V series? Didnt know that . That they made all amps discrete.

A few of their lower end units did for a while. Back to discrete now.

edit: I have a few original STK's of this type which I inherited when my shop closed, if anyone in the U.S. is interested. We can work something out.

Unfortunately I'm across the pond.

Majorbob · « **Reply #34 on:** June 24, 2020, 07:10:23 pm »

I have managed to work on it again. Using the removed IC I made a test bench to play around and understand what is changing what. I found that the +/- Pre voltages were very important in setting the DC offset on the output. (Pins 1 and

. Checking these in the amplifier I found -pre to be -2.1V and +pre to be 0V when these should be +-53.3V. Following them back I found them to have their own power circuits starting with 10Ohm resistors which were reading a very high resistance. Replaced these and it works.

Thanks to everyone who has helped me with this, I've learnt a massive amount!

electronicjunky1 · « **Reply #35 on:** June 28, 2020, 01:02:12 am »

Hi, i have yamaha 373 and appears to have similar simptoms as yours. It was not coming on, i replaced a cap on the stdby board, now it comes on and shuts down after few seconds, your post is very helpful. i removed both STK and unit is showing PRT089H now, would you mind sharing which resistors you changed, the numbers would be helpful. I can only find one R113 with 100ohm value. Appreciate the help.
I will start checking the voltages next.

Majorbob · « **Reply #36 on:** June 28, 2020, 06:59:52 am »

Do you have the service manual? If you enter self diagnostic function it will help you greatly in finding the actual fault. When you are checking voltages you must ground it as shown in the manual (rear panel, heatsink and "G3" on the main board all connected to the base with leads, I used crocodile clips on both ends). If you don't it will give you false readings on the PSPRT.

A PSPRT fault will cause it to turn off instantly, a DCPRT fault will cause it to turn off after ~5 seconds.

electronicjunky1 · « **Reply #37 on:** June 28, 2020, 07:55:54 am »

A quick update - I had some chance to work on the unit and check all power transistors (Q7 - Q11) for channels with DMM, all seems to be fine. The respective collector resistors are ok as well. I decided to re-solder one of the SDK CHIP (for surround sound), the other one is still out and i am in diagnostic mode. I also checked voltages on the connectors, compare with service manual and seems to be correct
CB136 - have 5.5 V and -40v for -VP
CB134 - has + and - 12v as well -40v for -VP, PS-pRT is 1.02 as oppose to 1.6 but i think it is within tolerance.
CB132- has correct/close engouh voltages - 8.6V, 2.2V, 6.5V, 0V - not sure about pin 2, it should be 3.3V i am getting 2.2.

I need to figure out to connect all boards outside of the unit so i can measure voltages on the power transistors, may be deal with it tomorrow.

Any help and suggestions would be appreciated.

Majorbob, would appreciate any help regarding the resistor numbersl. SO far i checked few resistors, R93, R112, R113, R114, R67, R69,R65,R75,R63,R62,R70,R73,R76R80,

Saga continue for another day.

electronicjunky1 · « **Reply #38 on:** June 28, 2020, 08:07:43 am »

Majorbob, Thanks for reply. I am getting DC PRT 089H error and it is taking about 5 seconds to shut down. I have the service manual and I have used the alegator clip and use the correct ground. You mentioned that you changed few resistors to fix your issue, what was the resistor numbers?

Majorbob · « **Reply #39 on:** June 28, 2020, 08:33:38 am »

If you look in self diagnostic section 9 in the service manual it tells you the ranges for PSPRT and DCPRT. I had incorrect values on + - PRE values for the STKs. Tracing this back I found that R18, R22 were gone. It wasn't complete failure though, they should be 10 Ohm and I had 1 reading ~100kOhm and one 10kOhm.

Majorbob · « **Reply #40 on:** June 29, 2020, 06:33:43 pm »

If you have DCPRT 089, then I'd expect the PRE voltages to have a slight imbalance. Check the voltages on pins 1 and 8 of the STK433-330 you should have the same on both (just one +ve and one -ve).

electronicjunky1 · « **Reply #41 on:** June 29, 2020, 09:04:13 pm »

Thanks.
R18 and R22 checked out fine.I will check STK433-330 in next few days and report back. Getting bit frustrated with the unit, want to take a break for few days.

Majorbob · « **Reply #42 on:** June 29, 2020, 09:41:32 pm »

The voltages should be there regardless but if the 2 ICs are not in place you won't have an accurate DCPRT reading anyway, its measuring the voltage at each of the speaker outputs.
With your multimeter take a look at all of the voltages around the ICs and compare them with the values stated on page 90 (Main 1/3 schematic).

electronicjunky1 · « **Reply #43 on:** July 02, 2020, 05:58:18 am »

i was able to take voltage measurements on both STK IC, and yes they are off.
-pre is -46.46V, it is suppose to be 52.6
+Pre is 44.3v, it is suppose to be 52.6.
St-By (pin 13) is 5V, it is suppose to 2.8V

Trace back to the to its power source, all resistors, capacitor and transistors are checking out good. I am getting the correct -B and +B voltages Q2 and Q6. -pre supply is good till R22 on Q6, the voltage drops to 46.46 ( same as -Pre) after the R22, the resistor is checking out good in and out of the board. I am also seeing the same behavior on B+, it is correct till R18 and then drops to 44.3 (same as +Pre), the resistor tested good and correct value. I will try to replace these resistors anyways to see it that fixes it, need to order resistors now.

Majorbob · « **Reply #44 on:** July 02, 2020, 07:56:03 am »

That definitely says to me R18 and R22 need replacing. Don't worry too much about the standby voltage, the pin needs 2.5-5.5V to set the IC as ON so your 5V is within spec for the IC. However as it has increased I'd check R32 (22K).

electronicjunky1 · « **Reply #45 on:** July 04, 2020, 06:58:19 am »

I replaced the resistor today and unfortunately it still goes in DC protect mode. I used the dignostic mode and check all the voltages again, all good except the important one
-pre is -46.46V, it is suppose to be 52.6
+Pre is 44.3v, it is suppose to be 52.6.

I checked all the channel resistors, transistors and capacitors and they all look good. I have the once IC1(STK433 330) out during all this process, decided to put that back in. Now it immediately shuts down, nothing on display either. It will not even go in diagnostic mode, i think the IC is bad, even though it does not explain the low voltages for PRE. I will order one from China and it will take about 3 weeks, if that does not fix it i will recycle the sucker or use for parts. One way or other i learned a lot in the process and there is no price for that.

Thanks for all the help.

zwarder1 · « **Reply #46 on:** April 19, 2021, 08:05:45 am »

I know this is an old thread but I am currently working on one of these units
The STK was dead short pre + to centre channel.
I have replaced this but am now getting the PRT error 000 & there is 20 volts at the Front right channel.
Pre voltages measure 55v
Transistors etc seem fine & the 10 ohm resistors in the power supply are also fine.
Any ideas would be appreciated.

Majorbob · « **Reply #47 on:** April 20, 2021, 08:26:28 pm »

You will have 2 PRT readings, PS and DC. Before worrying about the PSPRT you want to fix that DCPRT. Do you have the service manual?

You'll want to follow that DC voltage back and find out how it's getting through. Check all voltages around the STK and if you can get a scope on there to see what voltage is coming from where.

zwarder1 · « **Reply #48 on:** April 22, 2021, 02:51:30 pm »

I bought a new stk433-330 I believe
Anyway with ch3 out disconnected I have

Pre - 54.34v
Pre + 54.96v

Vcc- 55.53v
Vcc+ 55.44v
Stand-by 2.79v
These seem high if I connect the stk ch3 output pre- fluctuates & of course amp cuts out with 20v on Front right channel

Majorbob · « **Reply #49 on:** April 22, 2021, 03:38:24 pm »

PRE+- and VCC+- are a little high but not enough to be concerning, Standby voltage is fine. Do you have 20VDC coming from CH3 of the STK? Or is it appearing on the output with CH3 not connected?


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Author Topic: Yamaha RX-V373 PS PRT error (Read 13351 times)

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