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Technics SU-X920D abnormally hot

Hello everyone.

We recently got this Technics SU-X920D digital amp into our workshop.
The problem is that the top cover becomes extremely hot under normal workload. It does have a working cooling fan, however it only kicks in when the power amp is running at heavy load. (Like when the volume is set to about -30dB or at loud bass kicks)
After about an hour of testing with normal volume settings, the top gets so hot, it almost burns to touch it. We also got an SU-X520D for reference, this one doesn't get nearly as hot as the X920, plus the fan kicks in at much lower loads and temps.
I already refreshed the solder points on the power amp and replaced the thermal paste. Did not help at all.
Also, the customer says that this problem is fairly new. The amp did not get as hot before, so I'm guessing these temperatures are not normal.

Could the temperature sensor be broken? Or what else could be the problem?

Thanks a lot in advance.
Tamerlan



Re: Technics SU-X920D abnormally hot

The trouble with those 1990's Technics is that the cooling fan is triggered on intermittently by speaker audio levels, the louder the level, the more the fan runs.
Additionally, the heatsinking, while being generous, is not well serviced by the fan.
There is simply too much space between the fan's outward air flow and heatsink.
So much of the heat generated flows up and out of the case top vents, instead of being forced out the rear.
The best solution is to re-construct the fan's triggering circuitry to make it on "full time" and at a speed/noise level that isn't noticable or distracting.
Also, adding some aluminum shrowding around the end of the heatsink and up to the fan's shrowd helps to "pull" more air through the cooling fins.
I had to do this on mine, along with some other modifications.
Since then, it runs nice and cool.

Re: Technics SU-X920D abnormally hot

Hi Tamerlan,

have you ever found a solution for this problem?
I have the same issue with the Su-X920 and i also dont know how to handle it.

regards

Re: Technics SU-X920D abnormally hot

What is getting hot? Is it the heat sink or power transformer? If there is a bias adjustment it may be off.

Re: Technics SU-X920D abnormally hot

it‘s the heat sink. it is getting so hot that i cant touch the housing after 1,5 hours of normal radio-usage. a bias-adjustment can only be done by an expert, right?
thanks for your help.

Re: Technics SU-X920D abnormally hot

There is no bias adjustments for those units.
They use the famous Technics "SVI" series integrated output chips.
Read my previous comments.