Harman Kardon AVR Not Retaining Settings During Power Outage

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Old 07-27-13, 01:49 PM
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Harman Kardon AVR Not Retaining Settings During Power Outage

I have a Harman Kardon AVR 635 audio/video receiver and it does not retain certain settings during a power outage (and never has since it was brand new). According to Harman, there is a backup capacitor (not a battery) that needs to be replaced. I was curious if anyone can vouch for this and whether anyone has had this supposed capacitor replaced (or better yet, done it on their own and can tell me which one it is). I find it hard to believe that a capacitor would go bad, but apparently that's what the problem is. I've been searching some forums online and several others are having this same problem, and apparently not just any 47 uF cap will work, for some reason. HK supposedly has the part, but some have had problems getting it due to limited availability. One person said they measured the voltage on the cap while powered on (4.4V) and when they unplugged the power cable, the voltage dropped to 2V then discharged to 0V within a few minutes.

Update: I found a reference to a replacement part number (called a "Supercap") and ordered a few from Digikey. It has worked for some, but not for others. I'm going to give it a shot.
 

Last edited by mossman; 07-27-13 at 02:25 PM.
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Old 07-27-13, 02:09 PM
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It's not just a capacitor. It's a supercapacitor. Almost equivalent to a battery in an ultra low drain situation. They are not terribly reliable. I've changed many in small electronic items. They go leaky and don't hold the charge.

Open your unit up. It shouldn't be too hard to find. It's on the second board ......the DSP board.
You may see a value of .047F at 5.5 volts.

In the link is a thread on another site that deals with this issue.

AVR 635 Not Saving Settings Any More
 
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Old 07-27-13, 02:15 PM
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Can't tell you where it is....but caps go bad all the time. When I was in the Navy...caps were probably one of the highest failure items, esp electrolytic (cans). Ask our HVAC guys about bad caps...lol.


You might be able to find something just by visual inspection...normally pretty apparent when they go. Bulged where they should be flat, leaking a black oil type stuff, etc.
 
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Old 07-27-13, 02:26 PM
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Update: I found a reference to a replacement part number for the "Supercap" and ordered a few from Digikey. It has worked for some, but not for others. I'm going to give it a shot.
 
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Old 07-27-13, 02:49 PM
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It's not 47 mfd. It's .047F It's like 470,000 mfd. or more.
 
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Old 07-27-13, 03:45 PM
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Service manual says "0.047 F" = 47 mF = 47,000 F.
 
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Old 08-20-13, 07:41 AM
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I got the part in this week, have the receiver apart, and located the super capacitor. I'll be replacing it this evening. At the same time, I'll be wiring the cooling ran to run continuously since it never seems to come on and the unit gets pretty hot (especially with it being inside a cabinet).
 
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