Yamaha RX-V373 PS PRT error - Page 1
Forum section: electronics / repair

author: Majorbob
author_rank: Regular Contributor
timestamp: April 22, 2020, 02:42:54 pm
content: 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

author: Majorbob
author_rank: Regular Contributor
timestamp: April 22, 2020, 05:38:16 pm
content: Sorry... probably would have helped to actually put a question. What should I check next? What do people think are possible causes?

author: PKTKS
author_rank: Super Contributor
timestamp: April 23, 2020, 06:39:33 pm
content: You are missing the point:* the code indicates a PS (power supply) PRT (protection) errorYou do have a faulty regulator somewherestart in the manual with this code on spotPaul

author: kawal
author_rank: Frequent Contributor
timestamp: April 23, 2020, 08:33:34 pm
content: What ever the processor is measuring cannot go more than 255 for a 3.3V processor.That should give you a clue.

author: mzacharias
author_rank: Frequent Contributor
timestamp: April 24, 2020, 01:38:37 pm
content: Quote from: kawal on April 23, 2020, 08:33:34 pmThe 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 = 1.16470Which 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: April 30, 2020, 09:48:51 am
content: 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 regulatorS9 9.3 10.25 Through 4 pin regulator+7D 7.8 8.79 Not regulated, just rectifiedAC2 AC31.0 34.4 16.9 and 17 to center tap+5.5 5.8 5.82 Through 3 pin regulator-VP -38.0 -32.6AC40.9 44.8AC40.9 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 RegulatedSo my thinking is that there is possible issues with S9 and -VP?

author: PKTKS
author_rank: Super Contributor
timestamp: April 30, 2020, 12:56:28 pm
content: Quote from: Majorbob on April 30, 2020, 09:48:51 amPossible - actually the protection is activatedif the reading is out of rangeRange is also issued with the code or on the manualUnfortunately a bit criptic values but easy to decipherPaul

author: Majorbob
author_rank: Regular Contributor
timestamp: April 30, 2020, 01:14:31 pm
content: 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 MeasACL 40.9 44.8AC2 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).

author: kawal
author_rank: Frequent Contributor
timestamp: April 30, 2020, 06:28:35 pm
content: 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. .

author: kawal
author_rank: Frequent Contributor
timestamp: April 30, 2020, 06:47:09 pm
content: Re-solder all the higher power stuff as well and the regulators.

author: Majorbob
author_rank: Regular Contributor
timestamp: April 30, 2020, 09:27:44 pm
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: April 30, 2020, 09:30:13 pm
content: And I'm glad I understood the schematics the same way as you.

author: kawal
author_rank: Frequent Contributor
timestamp: May 01, 2020, 11:57:19 am
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 01, 2020, 04:07:41 pm
content: 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.

author: kawal
author_rank: Frequent Contributor
timestamp: May 01, 2020, 06:37:11 pm
content: 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

author: kawal
author_rank: Frequent Contributor
timestamp: May 01, 2020, 06:56:35 pm
content: 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

author: Majorbob
author_rank: Regular Contributor
timestamp: May 01, 2020, 07:00:28 pm
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 04, 2020, 10:05:44 pm
content: 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.

author: SpecialK
author_rank: Regular Contributor
timestamp: May 05, 2020, 02:36:42 am
content: Quote from: Majorbob on May 04, 2020, 10:05:44 pmJust solder another 10ohm across that resistor as a bodge. Or better yet, remove R90 and then solder two new 10ohms in parallel.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 05, 2020, 08:20:45 am
content: 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).

author: kawal
author_rank: Frequent Contributor
timestamp: May 05, 2020, 11:38:06 am
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 05, 2020, 11:50:50 am
content: Thanks! I desoldered 1 leg and checked it in situ. I'm hoping that that is the fault and not just a symptom.

author: kawal
author_rank: Frequent Contributor
timestamp: May 05, 2020, 02:30:14 pm
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 06, 2020, 08:25:07 pm
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 06, 2020, 08:41:12 pm
content: I have removed one of the boards in the way and nothing seems to be damaged in any way...

author: Majorbob
author_rank: Regular Contributor
timestamp: May 06, 2020, 09:33:12 pm
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 07, 2020, 08:30:18 am
content: 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?

author: Majorbob
author_rank: Regular Contributor
timestamp: May 07, 2020, 09:09:01 am
content: 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?

author: Majorbob
author_rank: Regular Contributor
timestamp: May 07, 2020, 09:25:46 am
content: 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?

author: kawal
author_rank: Frequent Contributor
timestamp: May 08, 2020, 12:57:12 am
content: Wow they started putting Hybrids in the RX-V series? Didnt know that . That they made all amps discrete.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 08, 2020, 06:46:00 am
content: Yeah, it's got 2 STK433s. A 130 for the rear L/R and a 330 for the front 3 channels.

author: mzacharias
author_rank: Frequent Contributor
timestamp: May 08, 2020, 12:53:45 pm
content: Quote from: kawal on May 08, 2020, 12:57:12 amA 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: May 18, 2020, 07:38:56 pm
content: 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

author: Majorbob
author_rank: Regular Contributor
timestamp: May 18, 2020, 07:48:24 pm
content: Quote from: mzacharias on May 08, 2020, 12:53:45 pmUnfortunately I'm across the pond.

author: Majorbob
author_rank: Regular Contributor
timestamp: June 24, 2020, 07:10:23 pm
content: 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!

author: electronicjunky1
author_rank: Newbie
timestamp: June 28, 2020, 01:02:12 am
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: June 28, 2020, 06:59:52 am
content: 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.

author: electronicjunky1
author_rank: Newbie
timestamp: June 28, 2020, 07:55:54 am
content: 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 correctCB136 - have 5.5 V and -40v for -VPCB134 - 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.

author: electronicjunky1
author_rank: Newbie
timestamp: June 28, 2020, 08:07:43 am
content: 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?

author: Majorbob
author_rank: Regular Contributor
timestamp: June 28, 2020, 08:33:38 am
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: June 29, 2020, 06:33:43 pm
content: 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).

author: electronicjunky1
author_rank: Newbie
timestamp: June 29, 2020, 09:04:13 pm
content: 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: June 29, 2020, 09:41:32 pm
content: 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).

author: electronicjunky1
author_rank: Newbie
timestamp: July 02, 2020, 05:58:18 am
content: 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 2.8VTrace 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.

author: Majorbob
author_rank: Regular Contributor
timestamp: July 02, 2020, 07:56:03 am
content: 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).

author: electronicjunky1
author_rank: Newbie
timestamp: July 04, 2020, 06:58:19 am
content: 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.

author: zwarder1
author_rank: Newbie
timestamp: April 19, 2021, 08:05:45 am
content: I know this is an old thread but I am currently working on one of these unitsThe 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 55vTransistors etc seem fine & the 10 ohm resistors in the power supply are also fine.Any ideas would be appreciated.

author: Majorbob
author_rank: Regular Contributor
timestamp: April 20, 2021, 08:26:28 pm
content: 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.

author: zwarder1
author_rank: Newbie
timestamp: April 22, 2021, 02:51:30 pm
content: I bought a new stk433-330 I believeAnyway with ch3 out disconnected I havePre - 54.34vPre + 54.96vVcc- 55.53vVcc+ 55.44vStand-by 2.79vThese seem high if I connect the stk ch3 output pre- fluctuates & of course amp cuts out with 20v on Front right channel

author: Majorbob
author_rank: Regular Contributor
timestamp: April 22, 2021, 03:38:24 pm
content: 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?

author: zwarder1
author_rank: Newbie
timestamp: April 22, 2021, 05:07:36 pm
content: 20 V DC on the actual speaker output FR when the STK is totally connected.With STK ch3 disconnected the amp will work as normal.Took out Q11 & tests fine I have also measured resistors & they all seem ok.

author: Majorbob
author_rank: Regular Contributor
timestamp: April 22, 2021, 05:59:59 pm
content: Sounds like the STK is kicking out the 20V, confirm this by measuring CH3 when it is disconnected from the circuit (CH3 only). If it is follow the voltage back through the amplifier and see where it's coming from.

author: zwarder1
author_rank: Newbie
timestamp: April 22, 2021, 07:04:10 pm
content: I think there was 2 volts across CH3 on the stk when it was disconnected from the rest of the circuit.Not entirely sure, when compared to chassis ground they were around 53 to 54 volts.Then it was closing time

author: Majorbob
author_rank: Regular Contributor
timestamp: April 22, 2021, 08:36:14 pm
content: 2V from CH3OUT to GND when it's not connected? Should be 0V so you've likely got voltage on CH3IN from somewhere. Possible that it's from the extra voltage on PRE but unlikely, the STK has quite a large input voltage range IIRC, and if it was the increased voltage I'd expect to see the fault on all channels.

author: zwarder1
author_rank: Newbie
timestamp: April 29, 2021, 12:37:10 pm
content: Finally got back to this today.Yes I have 0.6v on ch3 input ( ch3in & Ch3NF )I will have a hunt round this lineCH 1 & 2 measure 0v