Yamaha XP7000 Crackling in left channel

[xfreakx]

Hi guys,

I have a problem with the power amplifier Yamaha XP700, I hope someone can help or point me in a direction.

The amp started occasionally to crackle in the left channel which in a short time period got more frequent and after a while the crackling occurred instantly on power on.
While checking for loose connections the amp's protection kicked in and turned the amp off. From then the protection turned the amp off in between 1 - 5 seconds after power on.

I switched the mono blocks for a test to make sure the error is in the block itself and not maybe in the input module or power supply.
Removed the heatsink and found some burnt out components (Q207, R216 and R224. Replaced them. Protection doesn't kick in anymore but the crackling is still there.
Replaced for a test the 3 audio caps (C225, C211, C213), Q205 and also the op-amp IC201 without any result.

Can someone help?

* (Besides a digital multimeter I don't own any equipment so my possibilities are quite limited.)

[petehall347]

Re: Yamaha XP7000 Crackling in left channel

you could try heating and cooling different areas .

[xfreakx]

Re: Yamaha XP7000 Crackling in left channel

you could try heating and cooling different areas .

Yeah I was also thinking on that but I'm a bit worried I might burn again the protection circuit components if I turn the amp on for longer than a few seconds and since the crackling occurs instantly, it doesn't look to me like a thermal related issue.
I have also removed the heatsink to be able to access the board from the bottom and I don't know how long I can run the block without to destroy the output transistors.

[petehall347]

Re: Yamaha XP7000 Crackling in left channel

you cant run it even for less than a second without the heatsinks as it will destroy the transistors

[petehall347]

Re: Yamaha XP7000 Crackling in left channel

check the transistor numbers against lists of known noisy ones