Yamaha rx-v757 av reciever keeps turning off  - Page 1
Forum section: electronics / repair

author: Sneaky1
author_rank: Newbie
timestamp: March 14, 2021, 10:22:14 am
content: Hello everyoneSo i've got this "old" av reciever that's keep turning off.It has been sitting on my attic for about 3 years, since i got a newer model. And it worked perfectly when i put it there.So far i've cleaned it for dust inside and checked for any loose wiring and everything looks fine.I've also gotten the service manual. Found it here:https://www.manualslib.com/manual/1053815/Yamaha-Rx-V757.html(Dont know if its okay i link it here?)And when i start the reciever in diagnostics it says: ps prt 034KIt has also saved the error code: psprt 035As far as i can tell it's a power supply protection code, but where to go next, i've got no idea.I got a background as car mechanic so i've got no issues using a multimeter or soldering.Hope anyone can help.

author: Rasz
author_rank: Super Contributor
timestamp: March 15, 2021, 12:08:33 am
content: when is it turning off? when you want to play something?supply protection will kick in if for example amp output mosfets are blown and shorted - you can check those by measuring in diode mode across legs (unit turned off), it can also trigger if power supply itself is wounded in some way - check voltagesDave fixed similar unit by replacing small cap in the 5V power supply sectionit seems to be a common fault mode on those units, here 757 with same problem

author: Sneaky1
author_rank: Newbie
timestamp: March 17, 2021, 05:41:47 pm
content: It's turning off after 1 second on.I've trying replacing the cap in the videos with this one:https://elektronik-lavpris.dk/p102769/mkp10n022k630-10-mkp-capacitor-22nf-630v-10-p10/But it still turns off after 1 sec. :/Dunno if the fault codes point in any direction?

author: KevinA
author_rank: Regular Contributor
timestamp: March 17, 2021, 09:46:20 pm
content: Page 16 of your service manual states that PSPRT (Power Supply Protection) voltage must lie between 36-49V; outside of these, the protection shuts down.Your line is low at 34V

author: Kerlin
author_rank: Regular Contributor
timestamp: March 17, 2021, 10:53:44 pm
content: I have one of these same AV receivers that I got as faulty years ago and repaired it. Didn't need a circuit, used a repair technique know as Milking the front panel.I am finding it a brilliant bit of gear certainly sounds better than most.I almost blew it up once by connecting a bad load to it, but the protection worked well and kicked in then shut it down and prevented the smoke getting out.For me its proved to be like only very few things,a real keeper, like my sports car.My problem was with the stand by power supply and the symptoms were the same as yours, this is an example of how it could be many things.Eliminate the guess work and allow for proper diagnosis instead of using it "might be this or that" by providing some measurements.]Replacing components one at a time by using guess work is a technique I see used by many car mechanics who try to fault find electronics in cars they don't understand electronics. If you ever get the chance its great fun to listen to them talking to a customer after one of these repairs. Using this method they have often replaced half or more of the electronics, very expensive.Measure before and after voltages. It will be easier to measure the start up before voltages if you lock an auto ranging multimeter onto the correct range as it can then provide measurements more quickly.

author: mzacharias
author_rank: Frequent Contributor
timestamp: March 18, 2021, 01:39:13 pm
content: Quote from: KevinA on March 17, 2021, 09:46:20 pmThe values given do not represent the voltage directly. For some reason Yamaha does not report the voltage errors directly.It goes something like this:The sum at the output of a resistor summing network is normally approximately zero volts.Take the source voltage, usually 5 volts on the older ones, divide by 255.multiply the error code by this remaining decimal value to see the actual voltage the microprocessor is reporting.5V/ 255 = .0196078431.0196078431 x let's say 45 = .88VSo the sum of the resistor network is approximately .9 volts HIGH, suggesting a negative voltage source may be LOW.

author: mbz
author_rank: Contributor
timestamp: August 27, 2024, 11:31:23 pm
content: Quote from: mzacharias on March 18, 2021, 01:39:13 pm

author: wasedadoc
author_rank: Super Contributor
timestamp: August 27, 2024, 11:47:47 pm
content: Quote from: mbz on August 27, 2024, 11:31:23 pm

author: mbz
author_rank: Contributor
timestamp: August 28, 2024, 10:41:19 pm
content: Thanks for chiming in, voltage regs and rail caps were the first thing checked, all regs outputting spec voltages. The clue is the small departure from spec 52 versus 49, a failed regulator would(?) cause a larger departure from spec, eg, 90. I need to work through the math to work out for different failure scenarios and PST diagnostic. Spent a fair bit of time troubleshooting, isolating boards/pulling out connectors etc...