Yamaha RX-V671 wont turn on - Page 1
Forum section: electronics / repair

author: bjornhallberg
author_rank: Contributor
timestamp: December 08, 2018, 09:41:46 am
content: Stop me if you've heard this before but I have a Yamaha receiver that just went belly up. Pushing the power button turns the unit on and then it turns itself off again within a second or so. Starting in diagnostic mode gives error "PS2 PRT: 40L". The exact number (voltage?) seems to fluctuate. I gather from previous posts about the capacitor issue here and from reading the service manual that is something to do with the power supply and the pcb where mains power first connects.I have not removed and measured any components yet ... There is only 5.5V coming off the board and those pins measure 5.5V.I noticed that the glass fuse was blown and inserting a new fuse will just cause it to blow again and quite spectacularly as soon as the on button is pressed. This is something I didn't see on previous posts about the capacitor issue which combined with a slightly different PCB makes me uncertain. Not that great with electronics and replacing a cap is about as much troubleshooting as I'm comfortable with. So I thought I'd ask here before doing something dumb, or wasting my time in case the unit is just rubbish.

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 08, 2018, 11:54:40 am
content: That "capacitor issue" would not cause the main fuse to blow. More likely you have a shorted main filter capacitor or bridge rectifier, or a blown output IC. More likely involving the cap and rectifier, I would think.

author: PKTKS
author_rank: Super Contributor
timestamp: December 08, 2018, 12:46:01 pm
content: This particular chassi is far from trivial.It uses a plethora of secondary regulators all tied to thesame transformerSanely they have made separate windings and even thesymmetrical centered tap power amp stage is isolatedBut there are SMPS and several regulators.I would start by disconnecting the transformer secondary targetsand gradually power each in turn using a VARIAC..with luck just one more fuse will blow on the bad branch.FAULT ISOLATED seems a good start pointPaul

author: Rasz
author_rank: Super Contributor
timestamp: December 08, 2018, 07:03:24 pm
content: Quote from: mzacharias on December 08, 2018, 11:54:40 amyep, would start there

author: Armadillo
author_rank: Super Contributor
timestamp: December 08, 2018, 08:29:33 pm
content: The circuit clouded in Red is responsible for producing the 5.7v, so you don't need to bother with it.The one clouded in Blue is the circuit that blew the fuse.The single lines circuit there is not very clear, but what seems like a crowbar circuit there to purposely blow the fuse.If you have a better clearer schematic on that portion, maybe someone can advise you better.

author: Armadillo
author_rank: Super Contributor
timestamp: December 08, 2018, 09:31:01 pm
content: I suggest you begin to look from the circuit here;The shortcut is to measure ohms across those big caps and quickly see which part of the circuit is shorted.BUT REMEMBER TO OFF POWER, DISCHARGE ALL CAP before you measure the ohms across it.There is no crowbar.

author: bjornhallberg
author_rank: Contributor
timestamp: December 10, 2018, 11:10:18 am
content: Thanks for all your input! I'll see what I can do but to be honest I'm not that skilled.One other known issue I found on Youtube was the thermal fuse presumably buried along with the transformer. Could this be worth looking into?

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 10, 2018, 11:16:54 am
content: Quote from: bjornhallberg on December 10, 2018, 11:10:18 amNo it's not the transformer. Frankly it seems like you may be in over your head on this one.

author: bjornhallberg
author_rank: Contributor
timestamp: December 10, 2018, 12:35:20 pm
content: Quote from: mzacharias on December 10, 2018, 11:16:54 amYeah, that would be an understatement :-) It would take a small miracle in troubleshooting and then another in sourcing to pull this off.

author: Armadillo
author_rank: Super Contributor
timestamp: December 10, 2018, 01:21:04 pm
content: Seems like you only have ONE part of the boards, because you will never miss those BIG huge 6800uF cylindrical capacitors.

author: bjornhallberg
author_rank: Contributor
timestamp: December 26, 2018, 09:11:38 am
content: I've taken the receiver apart completely (good god what a jigsaw puzzle of boards and cables) to expose the bottom board (marked as "Main 1") and measure resistance across the 6800uF caps. C1084 reads ~0.6 Ohm. C1085 reads as ~25 MOhm (!).I've looked at the boards as I've taken them apart and seen no visual damage, scorch marks or funny looking caps.

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 26, 2018, 09:56:17 am
content: So you mentioned that the glass fuse (F3702) blows as soon as the unit is turned on.It looks like that fuse supplies the transformer on board 'video 6'or'video 9' via the voltage selector board 'video 8' depending on your specific model.You'll notice that there is a relay (RY371) and a capacitor (C3707). The way this is set up, it appears that the capacitor can be switched in and out of circuit, looking almost as an inrush limiting system (Usually it's a PTC instead of a capacitor for inrush current limiting though).It's a common way to limit inrush current into transformers, I have seen it a lot in welders etc. Not with a capacitor as it appears here, but with the PTC.This setup may not even be for inrush current limiting, but I would check if that capacitor is ok, and that the relay contacts aren't shorted as a first check. It's an easy check to do with a multimeter before you dive deeper.Also, double check that your voltage selector switch is set correctly too...After that, I'd look at the 'Video 7' and 'Main 2' boards. Do you have schematics for them?

author: Armadillo
author_rank: Super Contributor
timestamp: December 26, 2018, 09:57:57 am
content: Before you reorder, take out the 6800uF cap and measure again to re-confirm that it is the problem [0.6 ohms] and not any other things else.[Remember, I mentioned measuring across it is just a shortcut to identify the "sides" of the problem].So this could be the "Left" side or the "Right" side amplifier;If it is not the capacitor causing the shorts, then it will be the output transistors [mounted on heatsink]. Dead shorts are easy to check. With the cap removed, is more easy to identify the shorted transistors.

author: TERRA Operative
author_rank: Super Contributor
timestamp: December 26, 2018, 10:03:59 am
content: Another thought to narrow it down, If you can unplug the output of the transformer, then plug one output plug in at a time, you'll soon see which one to trace for the problem.

author: bjornhallberg
author_rank: Contributor
timestamp: December 26, 2018, 03:46:09 pm
content: I removed C1084 but can't quite figure out what to make of it. My DMM takes forever to get a capacitance reading and it usually lands around ~1200 uF then after a while it goes to 0L and then back to ~1200uF. Resistance is ~10 MOhm.

author: Armadillo
author_rank: Super Contributor
timestamp: December 26, 2018, 04:07:16 pm
content: That means your capacitor is OK, not the fault. Your DMM cannot be relied on to charge so big the capacitor.If you measure the OHMS from the pads of the removed cap, you will see the short circuit [0.6 ohms], telling you that the output transistor is shorted.If you have a problem locating it, just post up pictures so that other readers can participate in advising you how to locate it.But ultimately, enjoy the troubleshooting. cheers.Quote from: bjornhallberg on December 26, 2018, 03:46:09 pm

author: bjornhallberg
author_rank: Contributor
timestamp: December 26, 2018, 06:39:14 pm
content: Yeah some pointers as to where to look next would be greatly appreciated. Here are some photos of the MAIN 1 board.

author: Armadillo
author_rank: Super Contributor
timestamp: December 26, 2018, 08:58:33 pm
content: I was waiting for others to join in.Anyway, First to check is D1040 before we go any deeper. For simplicity, take it out from the board. Take your phone to capture a picture first before you unsolder it. Note washer, insulator ring, mica sheets if any. Don't need to take out the heatsink [if you can take out the diode bridge].Diode Mode check the Diode Bridge.For hint; [ don't know if you need it]Red on B, Black on A = ?Red on C, Black on A = ?Black on B, Red on D = ?Black on C, Red on D = ?

author: bjornhallberg
author_rank: Contributor
timestamp: December 27, 2018, 05:48:54 pm
content: Got the component off finally, was also able to get a screwdriver past and unscrew the heatsink thankfully. Anyhow, here is what I have:Red on B, Black on A = 0.1 OhmRed on C, Black on A = 0.57 MOhmBlack on B, Red on D = 0.57 MOhmBlack on C, Red on D = 0.57 MOhm

author: Armadillo
author_rank: Super Contributor
timestamp: December 27, 2018, 07:13:45 pm
content: So you found the faulty component.With it removed, now the short on the PCB disappeared.Measure the from the empty capacitor pads to confirm.Reorder and replace the bridge. Edit: And reinstall the capacitor and any blown fuse and you are all done.

author: bjornhallberg
author_rank: Contributor
timestamp: December 28, 2018, 07:32:59 am
content: Wow, thanks! Yeah, the resistance between the capacitor pads is now high, my DMM can't quite seem to catch it but is well over 30MOhm. DMM keep counting up.Are there any other components that I should consider ordering "just in case"? I mean it looks like I'll have to turn to Mouser to get a replacement and I'd rather save on shipping and such. Anything else that could have taken a beating?Also, how critical is it to get the same exact manufacturer and model of diode? Aside from the form/packaging and 200V/6A rating that has to match of course.

author: Armadillo
author_rank: Super Contributor
timestamp: December 28, 2018, 07:50:59 am
content: As long as the package size is the same, higher rating should be fine, best would be those modern ones with less forward voltage drop.But don't confuse with too much parameters or just get exactly the same to have a peace of mind.The rule in eevblog is, "if is not spoilt don't touch it".Probably cable ties, those that beautify and neat it a bit.Or add things to your tools for saving on shipping.

author: Armadillo
author_rank: Super Contributor
timestamp: December 28, 2018, 08:18:06 am
content: Oh don't forget,the white paste thermal compound and fuse/s...

author: bjornhallberg
author_rank: Contributor
timestamp: December 28, 2018, 09:02:32 am
content: Right! Good point. The thermal grease feels about the same as the stuff you'd put on any CPU heatsink so I assume that stuff will do? It has pretty much the same thermal limits as the diode bridge.

author: bjornhallberg
author_rank: Contributor
timestamp: January 06, 2019, 11:35:33 am
content: Success! I got a new rectifier (Mouser, 6A but 400V) from some guy on another forum. Put it all back together again and the receiver seems to be as good as new! Doesn't seem to be any other issues.Thanks everyone! And in particular Armdillo that had the patience to deal with a noob. Learned a great many things from this!

author: Armadillo
author_rank: Super Contributor
timestamp: January 06, 2019, 12:00:26 pm
content: Congratulation!Repair is great but mostly it's the small little spark that will definitely brings much more interesting electronics knowledge to you for many many years to come.