My Yamaha C-65 pre-amplifier blew up!

[Logistics]

Well, I got my pre down to the shop, and opened her up. Wow, does this thing smell bad! It has two obvious issues: the burned up portion of the PCB, which now appears cracked and one if not both of the mains caps look bloated. One main cap is much more bloated looking than the other. And I've seen main caps that just have a little bulge, but this one looks extreme compared to every one I have seen.

This was my headphone amplification. Any idea if I can bring her back? I don't have an issue making jumpers in the area the PCB cracked, but aside from aging components, I don't know what would have caused such a failure in such a low power device.

[budm]

Re: My Yamaha C-65 pre-amplifier blew up!

Service manual:
https://www.hifiengine.com/manual_li...aha/c-65.shtml

[R_J]

Re: My Yamaha C-65 pre-amplifier blew up!

Looks like R145 & R147 burnt in the MC HEAD AMP circuit, tr117/119 are likely bad and maybe others in that circuit.
I would press down on the plastic on those caps, if they press down the caps are likely ok, if it seems they don't press down then the caps are bad.
Manual is also here:

[Logistics]

Re: My Yamaha C-65 pre-amplifier blew up!

Those two transistors are completely cracked in half. But what would have caused this? Just age? I don't want to replace the components, and rework the traces to have them blow, again.

Matthew

[Sparkey55]

Re: My Yamaha C-65 pre-amplifier blew up!

Those two transistors are completely cracked in half. But what would have caused this? Just age? I don't want to replace the components, and rework the traces to have them blow, again.

Matthew

First find the original fault that caused the burnt components before blindly replacing parts. Start with the power supply section, but first remove any short circuits to isolate from the power supply.

If you do rebuild the the burnt section I suggest obtaining either some phenolic perfboard or copperclad board and rebuild onto that. You can move all the affected wiring to the new board when completed. May or may not look ghetto but should work.

[R_J]

Re: My Yamaha C-65 pre-amplifier blew up!

Hard to say what caused it, could have been as simple as a poor solder connection that upset the ballance and once one transistor shorts away they go, up in smoke.
The good news is there is an identical circuit in the other channel that you can compare to.
If C147 is ok and did'nt short it is likely the problem is limited to that mc head amp area only.
Remove the bad parts then check the other transistors and diodes, also check the resistors, they can sometimes look ok but be open or changed in value, again compare to the other channel.
That seems to be just for the phone input, with the blowen parts removed you should be able to check the rest of the amp, just not the Left phone input.
make sure the + and - voltage for that circuit is ok, looks like it should be around + & - 19 volts. it should be ok or the other channel would have smoked also.
check the resistors that supply the + & - voltage R275 and R276 (2.2ohm) if they are ok likely the power supply is ok

[Logistics]

Re: My Yamaha C-65 pre-amplifier blew up!

I assume that it must have something to do with the power supply stage as well because the unit powered down, and will not power back up.