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 Post subject: Harman Kardon HK3480
PostPosted: 21 Aug 2015, 21:03 
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Joined: 21 Aug 2015, 20:50
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Location: Central VA
Harman Kardon HK3480
see PDF schematic below

Seem to be missing something here on this beast. HK3480 came in dead, fuses blown, Right off the bat, the 2 main filter caps C601 & C602 were obviously done for just from looking at them. On 1 side, 2 output transistors (Q320 & Q322) were shorted and R350 (across Q320) was open, so replaced those as well, over by the regulators C612 was looking swollen and went ahead and replaced it.
I power up and I get both channels playing correctly, but only on Speaker set "B", I only get one channel on Speaker set "A", then after about 5 minutes filter cap C601 gets hot as hell, too hot. But yet it functions, I of course didn't allow it to stay on in this condition
Thing didn't make a sound when it got here so feel like I'm some what ahead right now...lol, double checked to make sure I didn't drop caps in backwards, they were not.
Anybody have a suggestion or idea, I would greatly appreciate it, Thanks


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 Post subject: Re: Harman Kardon HK3480
PostPosted: 24 Aug 2015, 09:10 
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Location: Central VA
Got some time to get on this again, the bias on channel i replaced goes crazy varying from 4 to 30 mV, no matter where the variable is set, other channel I sett @ 21 mV no problem. Now I'm suspecting Q318 (KTC3114A)...am I even close??...lol

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 Post subject: Re: Harman Kardon HK3480
PostPosted: 24 Aug 2015, 21:47 
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Joined: 04 Jun 2008, 20:59
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Location: Arizona, USA
Hi, I am not familiar with that model but it seems like more than one issue. The cap getting hot is probably because it is dissipating AC. So I would check the rectifiers and see if one is blown. One damaged in a bridge (don't know if your amp uses this) will often seem to provide the right voltages, but the AC content is quite high and will cook filter caps. On the bias issue, I would first try to use something like Deoxit on the control. It might just be gunked up. If not then you will need to trouble shoot the stages working either forward or backward until you can find the last stage that is OK. It will help pinpoint the problem. The is some possibility that the faulty side is oscillating. This can cause all sort of symptoms. Only a scope will tell there though.

Good listening
Bruce

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 Post subject: Re: Harman Kardon HK3480
PostPosted: 24 Aug 2015, 22:45 
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Joined: 08 Aug 2009, 03:11
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Location: Chilliwack, BC
Replace Q318 and 318 as well as C315 and 316. Use Simic-II type for audio.

Though a new unit, could be the old problem a lot of Technics had - transformer primaries designed for 117V plugged into today's 125V lines. Check your DC voltages on the "beer can" caps, I bet they're pretty close if not over 63V. Probably why C601 is hot - it's leaking current!

Like a redplated tube - they're gone. Replace them. Use 100V units. Don't mess around.

How's D601? A nice 600V, 35A bridge is like $4. Replace it.

Replace C611 and 612 in pairs. Use 35V rated or if you have room, 50V.

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 Post subject: Re: Harman Kardon HK3480
PostPosted: 24 Aug 2015, 23:36 
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Joined: 21 Aug 2015, 20:50
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Thank you so much gofar99 & Geek, back at it tomorrow...errr....today now I guess ;)
much appreciated

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