Yamaha THRc10 (motherboard issue) is it fixable?

[wunschie]

I bought this yamaha THRc10 amp Mabey 3-4 years ago and it has been neglected because it doesn't have any sound output after one day of shredding on it (sparked a little bit). I decided to open it up and diagnose the issue on the motherboard. I have highlighted the areas that look effected/damaged in the photo attached and also one with the board intact (best one I could find). I would love to know if this is easily fixable with solder ect. Thank you very much for your assistance. Kind regards, someone who wants to play electric again...

[tedmich]

yikes, that's likely a MANY layer board and it may be impossible to fix if multiple circuit paths were burned. The visible craters were most likely caused when some associated IC or component failed (effect, not cause) so you'll need to find that as well.

I have a working THRX I'll let you have for cheap, if that version has any appeal. I've decided I like big amp again...

(Enzo can fix most anything while I am more (justifiably) pessimistic of my abilities ; )

[Enzo]

I see no reason it would not be repairable, just depends upon your skill.

Just looking, appears to me some incoming power issue. That looks like the power adaptor jack. Perhaps someone connected the wrong supply.

[Enzo]

And there you go. I suspect the answer is somewhere in that range.

[glebert]

Wonder if there is a schematic available for this, or some way to know what the component values would be? On the plus side the components aren't the smallest SMD size.

[Jon Snell]

Everything is repairable. Looks like the wrong power adaptor was used maybe as the choke and tuning capacitors are gone.
Here is a service manual link but I suspect there will be a free manual somewhere. https://www.service-manual.net/?down...service-manual
One must ask the question, is it worth repairing as it is nothing special and very low power.

[Mick Bailey]

It looks like inductor L10 isn't fitted to your amp. R57 and R60 are zero Ohm bridging links and R512 is a 0.22 Ohm resistor. On the good board C232 is absent, but your board has a burn in this location so maybe had a capacitor fitted on that revision. With heavy damage - especially to the links and a low value resistor - it's likely that one or more components downstream have failed but are not visibly damaged. The track to the right of IC501 and it's through hole are burnt up too. Often power input components use just the outer layers if the board is multi-layered, so damage may just be confined to the top and bottom of the board (and some through holes). Take a look underneath to see if there's damage beneath the burnt components.

Can you confirm exactly which power supply you were using at the time? To fix this you'd need a schematic, otherwise it will be difficult to understand what's going on.

EDIT: Corrected designation - R506 changed to R512

[wunschie]

Thankyou all for your very informative discourse, im very novice but willing to learn although i think it is time to upgrade and begone of the burden of this machine. but i would like to use the speakers as a portable unit, should i just buy a cheap soundboard and drill a hole for input and power?

[wunschie]

also mick, I used the same power source I got with the amp unless I perhaps mixed it up with one of my monitor power supplies, but i very much doubt that. Would it help to say that i was recording via usb to logic?

[Mick Bailey]

Well, it could be that it was just its time to fail and there was nothing untoward with the power supply or connections.

If you want to use the existing speakers you could find where they connect, unplug them and measure the DC resistance. This will give you a figure close to the nominal impedance - 4 or 8 ohm or whatever. A small stereo amp module should fit in there somewhere and you'll need to install some sockets, but it should be straightforward to do. The speakers and enclosure design in these amps are pretty decent.

[dmeek]

Here is the manual for the head version.
Personally, if this was for a customer I wouldn't do it. But since you own it, there's no pressure and it would be a learning experience if nothing else.
There may be many more bad parts that are not visibly burnt.
THR5_THR10 SM.pdf

[tedmich]

well it does look like it could have been just the wrong PS plugged into the 15V input, and several of the SMD components look to be zero value resistors (R60, R57) which often serve as "fusible links" The other burned part (R512) is a beefy power resistor associated with the mosfet (IC501). It looks like Yamaha left out several planned protective components in the circuit (no_use) unfortunately. The zero value resistors can be replicated by creative jumpers, while replacing the other stuff involves some delicate SMD work... good luck!

[J M Fahey]

I´m not sure even Yamaha themselves repair it at component level.

At most, they will swap the whole board (which a machine took 5 minutes to assemble) than pay a Tech 1 hour bench time.

[Mick Bailey]

Their manufacturing cost is in the Far East is probably less than 10 minutes repair time in the west. It's always nice to fix something, though. Especially if it's for yourself. Plus there's the bonus of learning something. I have one customer who insists I repair everything he gives me, whatever the cost in parts and time. He's got an admirable quality that overrides cost with the need to stop discarding electronic equipment.

[J M Fahey]

Oh, I definitely agree with him, on moral/principles grounds.
Plus being OCD/hoarder afflicted, I HATE to junk anything.