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HK990 right channel runs hotter
HK990 right channel runs hotter
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Old 22nd October 2016, 03:11 PM   #1
jkasch is offline jkasch  United States
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Default HK990 right channel runs hotter

I have an HK990 that functions properly but the right channel runs 10 degrees F hotter than the left when measured at the heat sinks. Is this enough to be concerned about? (I'm a novice at circuit level electronics, so it's something I don't feel qualified to chase down and repair if it is.)

Also, if anyone knows of a good technician within 75 miles or so of Lansng, MI that would be good at servicing this unit, I would appreciate the referral. (Blackies in Grand Rapids, MI is the closest authorized HK service center, but I wasn't overly impressed with them.)

Thanks for your thoughts.
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Old 22nd October 2016, 03:17 PM   #2
Mooly is offline Mooly  United Kingdom
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HK990 right channel runs hotter
10F difference sounds pretty small tbh if you say that the heatsink on one side may for example be 120F and the other 130F.

A very small difference in bias current between the channels would account for something like that, as would any asymmetry in the physical layout internally.

Based on just a 10 degree difference I don't think you have anything to worry over. You could check and compare bias currents for interest though.
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Old 23rd October 2016, 12:32 AM   #3
jkasch is offline jkasch  United States
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Thanks, Mooly. I pulled the cover and noticed a couple caps on the left channel (the cooler side) seem to have a brown substance around their base that's messy in contrast to the same caps on the right channel which have a neatly applied cream color there. So, it would seem that a sloppy adhesive was used on the left channel or they're leaking?

Looks like I may have it checked out by an authorized HK service center, but the closest one that I might trust is 115 miles away in Toledo.

Anybody know of a good independent shop?
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Old 23rd October 2016, 08:10 AM   #4
Mooly is offline Mooly  United Kingdom
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HK990 right channel runs hotter
That sounds like glue tbh. The difference in colour could be attributable to differences in airflow within the amp (brown side seeing more atmospheric pollution sticking to the glue).

You may not have any problem at all. Post some pictures of the caps if you like showing the glue.
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Old 23rd October 2016, 07:49 PM   #5
jkasch is offline jkasch  United States
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HK990 right channel runs hotter-fullsizerender2-jpg

Right Channel (hotter side)

HK990 right channel runs hotter-fullsizerender-jpg

Left Channel (cooler side)

Thanks again, for the replies.
Attached Images
File Type: jpg FullSizeRender2.jpg (77.1 KB, 141 views)
File Type: jpg FullSizeRender.jpg (101.7 KB, 141 views)
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Old 23rd October 2016, 08:35 PM   #6
Mooly is offline Mooly  United Kingdom
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HK990 right channel runs hotter
Both of those are glue.

In the first picture, the plastic sleeve of the cap suddenly goes very dark at the base. Is that just an effect of the camera ? The second picture has the sleeving as a uniform colour all the way down (as it should be).

The slits cut into the top of the cap are the safety vent. Often when there is a problem with a cap the vent pushes out due to excess pressure internally. These look fine.
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Old 23rd October 2016, 09:22 PM   #7
jkasch is offline jkasch  United States
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Yeah, it's just lighting. Thanks for the education and saving me from taking it in.
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Old 9th December 2016, 11:59 PM   #8
jkasch is offline jkasch  United States
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Just a bump to this thread. Today, I finally dug into the 990 and was able to check and adjust the bias. The TP's are difficult to reach and the service manual is hard to interpret, but I found the cooler side to be running at half the spec (19mV). I adjusted both to the 38mV spec and both channels are within 1 degree of one another.

Can I hear the difference? Maybe I sense a little more smoothness and depth to the image. Can't say for sure, it's helped my audio OCD.

Thanks for the replies, Mooly.
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Old 10th December 2016, 07:58 AM   #9
Mooly is offline Mooly  United Kingdom
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HK990 right channel runs hotter
Thanks for the update good to hear you were able to sort it out.
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Old 18th December 2017, 10:11 PM   #10
dude2010 is offline dude2010  Denmark
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Quote:
Originally Posted by jkasch View Post
Just a bump to this thread. Today, I finally dug into the 990 and was able to check and adjust the bias. The TP's are difficult to reach and the service manual is hard to interpret, but I found the cooler side to be running at half the spec (19mV). I adjusted both to the 38mV spec and both channels are within 1 degree of one another.

Can I hear the difference? Maybe I sense a little more smoothness and depth to the image. Can't say for sure, it's helped my audio OCD.

Thanks for the replies, Mooly.
Did it continue to sync temp? Exactly this has been tried out in another post, 1 were 119mv other 38mv - both adjusted to 38mv and left. Just to fire it up the next day, and the bias was down to 18mv and second still 38mv.

Just wondering how yours were doing.

Could you perhaps do a video of how to adjust it?
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