Need help to diagnose a Hafler DH200 problem...

drosenberg · 20th December 2009, 02:54 AM

I upgraded a DH200 (about one week ago) with new caps on the circuit boards and also the two big power supply caps (upgraded to 18000mf). The amp worked fine for a few days and did sound improved.

However, today the amp developed a strange problem. About 2 seconds after I turn it off there is a strange whistling noise in both channels that decreases in pitch and volume over about 5 seconds, then everything is quiet. It sounds like a capacitor discharging but I have no idea how to isolate this.

I am wondering if it could be the small caps on the input connecters but it seems unlikely that both would fail at the same time. These were not replaced.

Has anyone encountered this problem before?

Thanks in advance for any suggestions you might have.

tauro0221 · 20th December 2009, 04:59 AM

Hi,
Did you check the polarity of the capacitors? Make sure they are installed with the polarity right ?

djk · 20th December 2009, 09:12 AM

Put a pair of 47µF bypass caps on the 18,000µF and see what happens.

eyoung · 20th December 2009, 04:36 PM

Hola Y'all...

Recheck your solder joints on both boards, but if it's in both channels it's more likely in the P/S. I also bypassed my big caps with smaller caps and a 6800 Ohm 2w resistor parallel to my bypass cap.

Regards, Elwood

tauro0221 · 20th December 2009, 05:28 PM

Hi,
Also make sure the large capacitors are 75 volts or higher.

Rafael L · 20th December 2009, 05:32 PM

When the amp on, there is some noise?
Which was the previous capacitance?

drosenberg · 20th December 2009, 11:21 PM

Thanks for advice guys. I will work on this tomorrow night when I have a minute. To answers the questions asked in support of a diagnosis.

- There is mechanical noise which I believe is coming from the transformer. I have a replacement part arrive tomorrow to swap in.

- The new power caps are rated 75volts (18,000mfd). The original caps were 10,000mfd 75V.

- The polarity looks fine to me. The are electrolytic so I assume they would have blow up right away.

My current thinking is that it is the small cap that is solders on top of the rectofier. This could effect both channels if it is not working properly.

Thanks again for all the ideas. I will report back on Tuesday.

-

20th December 2009, 02:54 AM	#1
drosenberg diyAudio Member Join Date: Dec 2009	Need help to diagnose a Hafler DH200 problem... I upgraded a DH200 (about one week ago) with new caps on the circuit boards and also the two big power supply caps (upgraded to 18000mf). The amp worked fine for a few days and did sound improved. However, today the amp developed a strange problem. About 2 seconds after I turn it off there is a strange whistling noise in both channels that decreases in pitch and volume over about 5 seconds, then everything is quiet. It sounds like a capacitor discharging but I have no idea how to isolate this. I am wondering if it could be the small caps on the input connecters but it seems unlikely that both would fail at the same time. These were not replaced. Has anyone encountered this problem before? Thanks in advance for any suggestions you might have.

20th December 2009, 09:12 AM	#3
djk diyAudio Member Join Date: Feb 2001 Location: USA	Put a pair of 47µF bypass caps on the 18,000µF and see what happens. __________________ Candidates for the Darwin Award should not read this author.

20th December 2009, 04:36 PM	#4
eyoung diyAudio Member Join Date: Aug 2007 Location: Sunny SC,USA 15 min south of Charlotte NC	Hola Y'all... Recheck your solder joints on both boards, but if it's in both channels it's more likely in the P/S. I also bypassed my big caps with smaller caps and a 6800 Ohm 2w resistor parallel to my bypass cap. Regards, Elwood __________________ "when you open your mind to the imposible, soon you will find the truth...."

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20th December 2009, 04:59 AM	#2
tauro0221 diyAudio Member Join Date: Nov 2008 Location: Victoria,TX	Hi, Did you check the polarity of the capacitors? Make sure they are installed with the polarity right ?

20th December 2009, 05:28 PM	#5
tauro0221 diyAudio Member Join Date: Nov 2008 Location: Victoria,TX	Hi, Also make sure the large capacitors are 75 volts or higher.

20th December 2009, 05:32 PM	#6
Rafael L diyAudio Member Join Date: Nov 2008 Location: Brazil	When the amp on, there is some noise? Which was the previous capacitance?

20th December 2009, 11:21 PM	#7
drosenberg diyAudio Member Join Date: Dec 2009	Thanks for advice guys. I will work on this tomorrow night when I have a minute. To answers the questions asked in support of a diagnosis. - There is mechanical noise which I believe is coming from the transformer. I have a replacement part arrive tomorrow to swap in. - The new power caps are rated 75volts (18,000mfd). The original caps were 10,000mfd 75V. - The polarity looks fine to me. The are electrolytic so I assume they would have blow up right away. My current thinking is that it is the small cap that is solders on top of the rectofier. This could effect both channels if it is not working properly. Thanks again for all the ideas. I will report back on Tuesday. -

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