Hafler DH-500, Problems of thermal sensors..

fossil8836 · 01:47 AM

Hi Folks,

I have a Hafler DH-500 Power amplifier. It is, of course, secondhanded, but sounds very good.
As you know, it has an AC cooling fan to be operated in the case of the heat sink overheated. But the cooling fan is operating immediately after pushing on the power switch. What would be the problem?
I think this cooling fan has 3 stage of operation from the schematic diagram. Is that right?
So, there may be a problem in the thermal sensor(thermostats, TS401 and TS402 in the schematic diagram), I think.
I want the specifications of the thermal sensor(normally-open type? setting temperatures?) for the replacement. Recommended parts?
Or any possible problems?

Appreciate any help.

djk · 12th April 2010, 10:50 AM

You have described a normal functioning amplifier.

The fan is supposed to rotate as soon as the power switch is turned on. As it heats up it will switch to medium speed, and then high speed.

If you test it at 4 ohms it will move quickly through all three speeds, and then go into thermal shut-off (and the power switch will blink).

The fan switches are about 55°C, the shut-off is about 85ºC.

fossil8836 · 12th April 2010, 02:32 PM

Thanks for your notice about my misunderstandings.
I think I have to be patient with the fan noise.
Is there any tweak for reducing fan noise of this amplifier?

12th April 2010, 10:50 AM	#2
djk diyAudio Member Join Date: Feb 2001 Location: USA	You have described a normal functioning amplifier. The fan is supposed to rotate as soon as the power switch is turned on. As it heats up it will switch to medium speed, and then high speed. If you test it at 4 ohms it will move quickly through all three speeds, and then go into thermal shut-off (and the power switch will blink). The fan switches are about 55°C, the shut-off is about 85ºC. __________________ Candidates for the Darwin Award should not read this author.

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12th April 2010, 02:32 PM	#3
fossil8836 diyAudio Member Join Date: Nov 2009 Location: Daejon City	Thanks for your notice about my misunderstandings. I think I have to be patient with the fan noise. Is there any tweak for reducing fan noise of this amplifier?

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