Left side distortion, Hitachi hma-7500 mkii

[PeterLov]

Please help! My beloved Hitachi hma-7500 mkii have started to distort heavily in the left side. I've switched speakers: The error remains in the left side.

It may have started a few weeks ago, when I pushed the audio level to the limit – something I do very rarely. In the beginning, the noise was notably worse at specific frequencies, but now, it all over the frequencies.

Could this be due to old capacitors? If yes: Any advice before changing them?

Thank you in advance…

 

[chazix]

Could this be due to old capacitors?

Perhaps, but also be suspicious of the resistors that are noted as "fusible" on the schematic (which I believe is available from hifiengine.com).

Welcome to AK!

 

[grabread]

I would look at the schematic to find the fusible resistors and replace them . They go way off value over time and cause issues.

 

[ivandezande]

Can someone recommend a technician that can work on a Hitachi HMA - 7500 MKii?

I prefer a tech that has worked on these Mosfet Amps before. I had the greatest tech in Des Moines work on mine and he got frustrated and told me to come get it. I have replaced the Mosfets and the Filter Caps and for some reason the right side Mosfets heat up as soon as you power the amp on.

Once again, I want a tech that has worked on these before, they are very basic but obviously very frustrating.

Thank You, Ray

Who in Des Moines.....
You replaced the mosfets? Pray tell with what as they are irreplaceable TO-3's as far as I know?
Did you monkey with it before or after it had issues? Lots of red flags here.

 

[roger2]

@Arkam you should have started, and still should start, your own thread because, IMO, it is unfair to PeterLov to glom onto his. Every post you make, and every response you receive, lessens the chances that PeterLov's first and only post ever on AK will receive any attention.

And I agree with ivandezande...lots of red flags in the information you posted...and he asks the key question regarding when the issue started...

Sorry to come off cranky...it's been that kind of day. But it is always better to open your own thread instead of tacking onto the end of one about the same or a similar model. Better for you, better for the other guy...

 

[roger2]

Please help! My beloved Hitachi hma-7500 mkii have started to distort heavily in the left side. I've switched speakers: The error remains in the left side.

It may have started a few weeks ago, when I pushed the audio level to the limit – something I do very rarely. In the beginning, the noise was notably worse at specific frequencies, but now, it all over the frequencies.

Could this be due to old capacitors? If yes: Any advice before changing them?

Thank you in advance…

Because you have a separate preamp and amplifier you can determine which of those units is the source of the distortion. Swap the RCA inputs going to the amplifier and see which side the distortion goes to. If the distortion stays on the left then source of the problem is the amp, if the distortion moves to the right the problem is in the preamp.

I listened to your video twice but it I have really crappy computer speakers and was not able to hear it clearly. But fusible resistors, as has been suggested, could be causing issues as they are known trouble makers. Another possibility is a bad transistor or perhaps some other semiconductor. IMHO capacitors are lower on the list of possible causes. Sorry I can't be of more help in the troubleshooting department.


...and welcome to AK