Yamaha RX-V771 won't power on - Page 1
Forum section: electronics / repair

author: viggen
author_rank: Newbie
timestamp: August 15, 2024, 07:16:48 am
content: Unfortunately my Yamaha RX-V771 won't power-on anymore.It won't even power-on when trying the self diagnostic function via "While pressing the “TONE CONTROL” and “INFO” keys, press the “MAIN ZONE ” key to turn on the power."This is what happened, it all started with my Jamo 660 Sub not powering on anymore.I checked the fuse and it was brown/burned. (worked for over 15 years)By accident I ordered the wrong fuse, I ordered the T4.0AL/250V instead of the T2.0AL/250V.In addition, as I was not looking properly I put the cable that connects the Yamaha RX-V771 into the Jamo 660 Line Out instead of Line In via RCA cable.Then when I powered on the Jamo 660 with the wrong T4.0AL/250V fuse and the new wrong fuse in the Jamo 660 shattered.And from that point the Yamaha RX-V771 won't power-on anymore either.My priority is fixing the Yamaha RX-V771, does anyone have any ideas of what might be wrong please?

author: Xena E
author_rank: Frequent Contributor
timestamp: August 15, 2024, 12:18:39 pm
content: Unfortunately there are a lot of people who think that if a fuse blows that it's somehow the fuse that's faulty and they just go ahead and replace it (with one twice the size in this case), without first investigating the cause.Fuses are basically included into equipment for the sole reason of preventing fire, and/or further damage.Those who are so inclined, do not have the skill level to do repairs on their equipment themselves, and it would be irresponsible to encourage them to do so.Normally these kinds of posts get ignored for that reason.I'm sorry to be so blunt, but for your personal safety I'd suggest taking your equipment to a professional electronics repair shop to have them assess the damage.Best Regards,Xena.

author: MathWizard
author_rank: Super Contributor
timestamp: August 15, 2024, 03:00:35 pm
content: Well if you have a multimeter, and are familiar with some electronics and safety concerns...with the Yamaha unplugged, check some resistances on the outputs, and the voltage rails. Maybe some cap or op-amp in the Yamaha output, got fried by the Sub, and some voltage rail went short, and the current goes way up and cooked the fuse?So exactly which Yam output, did you connect to the Sub's output, by mistake ? And what mode was the Yam on at the time ? Trace back from the Yam output, and you should find some capacitor, op-amp, transistor, voltage regulator, something like that would get fried. Hopefully not much else got damaged before the fuse went.As long as no hard-to-find IC got damaged, or the transformer, most problems in a stereo should pretty fixable.Here's the service manual link, it's too big to upload.https://www.manualslib.com/manual/1307355/Yamaha-Rx-V771.html#product-RX-V771

author: Xena E
author_rank: Frequent Contributor
timestamp: August 15, 2024, 04:35:26 pm
content: Quote from: MathWizard on August 15, 2024, 03:00:35 pmAnd remember, 8Amp fuses are available!Edit: just be bloody careful if you do try and don't burn your home down..

author: viggen
author_rank: Newbie
timestamp: August 15, 2024, 08:24:43 pm
content: Thanks, the RCA cable was in the Subwoofer 1 Out on the Yamaha RX-V771.By accident I plugged the other end of the RCA cable on the Line Out on the Jamo 660 (instead of Line In).The Yamaha RX-V771 was switched off at the time when I switched on the Jamo 660 with the wrong T4.0AL/250V fuse (instead of the T2.0AL/250V).Sorry, let me clarify, I'm trying to establish if the potential repairs are that significant that it is not worth me taking it to a professional electronics repair shop.

author: Xena E
author_rank: Frequent Contributor
timestamp: August 15, 2024, 09:37:24 pm
content: So.All I can say is that your cable misconnected would have not been likely to have caused any damage had the subnotbeen faulty.I can only assume that there was a catastrophic failure in the sub and that the fault somehow propagated through the ground line of the Yamaha RX-V771 and destroyed something in its power supply, at the very minimum, (again assuming that there is no sign of life whatsoever).It's something that would need to be inspected to confirm a diagnosis, but it is a very complex piece of kit and won't be a cheap fix, if at all.It's just whether you want to pay a fee to find out or put that money towards a replacement.I did wonder if the Yamaha was still functional after the sub failed before the fuse was replaced?I hope you get sorted and I'm sorry to disappoint.Regards,Xena

author: viggen
author_rank: Newbie
timestamp: August 15, 2024, 11:39:36 pm
content: Hi, yes the Yamaha RX-V771 was fully functional before the wrong fuse was put into the Jamo 660 Sub and was connected wrongly to the Yamaha RX-V771.

author: RayRay
author_rank: Frequent Contributor
timestamp: August 16, 2024, 12:12:57 am
content: I'd say your description is lacking some details.Does it show a standby light? And if so, what exactly happens when you try to turn it on?

author: viggen
author_rank: Newbie
timestamp: August 16, 2024, 02:06:52 am
content: Hi, the Yamaha RX-V771 does not have a standby light. (or I have not noticed it in 15 years that it was working)Absolutely nothing happens when I try and turn it on. Not even the relay clicking noise.

author: MathWizard
author_rank: Super Contributor
timestamp: August 16, 2024, 04:08:48 pm
content: I'm in rush ATM so I didn't check the sch, but a lot of these types of things, will have lots of powered voltage rails, when plugged in. And when you hit the power button, maybe another rail gets turned on to power all the control chips. I think on my Denon AVR, the power switch only turns on/off the 5V rail.I'd guess the max voltage out of the JAMO would be pretty low, only a few volts, so most stuff should be safe. But it can drive a lot of current (if it's an output meant for another sub-speaker). And then things overheat and fry if something goes short or near short, as in very little resistance to that current flow.But here's a link to Jamo SUB660 repair with some schematic's in the 1st post, I'll have a look at it more tonight.https://www.eevblog.com/forum/repair/jamo-sub660-repair/

author: wasedadoc
author_rank: Super Contributor
timestamp: August 16, 2024, 09:33:23 pm
content: Quote from: MathWizard on August 16, 2024, 04:08:48 pmUsually it is the opposite. One low power rail is on all the time the unit is plugged in to AC mains. Pushing the on button (front panel or IR remote) activates all the other rails.

author: David_AVD
author_rank: Super Contributor
timestamp: August 16, 2024, 11:04:13 pm
content: Check that you have the 5.5V standby voltage on the output of the SMPS (power supply) board. You can measure it on connector CB377 on the video board. The PCB is marked with the 0V and 5.5V pins.Be very careful around the SMPS as it has 240V AC and 340V DC on it ready to bite you. Also be careful around the mains input connector on that video board.

author: shakalnokturn
author_rank: Super Contributor
timestamp: August 17, 2024, 01:03:32 am
content: It could also be a half coincidence if the power to the Yamaha was completely cut when the 4A fuse blew (circuit breaker or common fuse in socket opening).A lot of Yamaha amplifiers use a capacitive dropper in the standby supply, the capacitor ages and eventually leads to the symptoms you have, it may have aged to the point where it was able to only just keep the standby going up to that point but not enough to reach sufficient voltage from a cold start.As said above check standby 5V.

author: MathWizard
author_rank: Super Contributor
timestamp: August 17, 2024, 05:53:49 pm
content: So if it was just connected to line out from the Jamo, I don't see it on the schematics Raff had, but it should be just a low-power signal, from the op-amp section. And even if the Jamo had some input signal, a line level output, shouldn't damage much of anything. Maybe some IC would not like any negative voltage from a line-out.In the Yamaha the SW-opamps are on page 115, and their mute circuits are on p117. Those mute circuits are run from +/-12V, where as I think the op-amps in the Jamo are +/-15V rails. In the Yam I see the caps around there are 50V, but they are electrolyics, and could get reverse biased, and fry. Or can some base junction in the muting circuit see too much voltage ?As for the Jamo, well I wish I had it here, I'd start with it unplugged, and probably find a few problems right away just with a DMM.