Krell KSA-80B Startup Woes

jhebass

Member
2009-07-13 9:27 pm
Hey,

Trying to rehabilitate a KSA-80B.

Basic problem is that when turned-on, I hear a relay click a few times, with increasing weakness, then nothing, like it's not getting sufficient energy to trip.

I know the Krell has a soft-start/protection scheme. Before I start tackling the problem, wondering if anyone had any tips as to where to begin my diagnoses.

I've attached the schematic/service manual.

THANK YOU!
 

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jhebass

Member
2009-07-13 9:27 pm
Hey ... can't tell if amp works otherwise because of the relay issue. There's no audio at the outputs if the relays don't trip.

But progress was made: removed the rear panel to get at the relays and noticed two totally blown-out electrolytics. They are 0.1uF (400V)paired with some fairly chunky resistors measuring approx. 5ohms. They are soldered between the speaker terminals' ground and hot connection.

Can't locate these on the schematic, and the fact that they're both blown makes me think something is wrong upstream. Any thoughts? Where might I find on schematic?

Thanks!!
 

passive420

Member
2013-06-11 3:39 pm
There is a relay 'K1' on the slow start circuit, maybe if you can get to it check the diodes and caps as suggested. Possibly the relay coil has failed and needs replacing. This amp has some sophisticated features.

The caps and resistors across the speaker terms sound like a zobel frequency filter rather than protection? Someone possibly wanted to create a filter knee to cut some high freq's to suit a certain speaker / cable arrangement. The 'lytics likely got old any leaky, better to use film caps. If you get it to start certainly check bias and if there is any DC on the speaker output.
 
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Hey ... can't tell if amp works otherwise because of the relay issue. There's no audio at the outputs if the relays don't trip.

But progress was made: removed the rear panel to get at the relays and noticed two totally blown-out electrolytics. They are 0.1uF (400V)paired with some fairly chunky resistors measuring approx. 5ohms. They are soldered between the speaker terminals' ground and hot connection.

Can't locate these on the schematic, and the fact that they're both blown makes me think something is wrong upstream. Any thoughts? Where might I find on schematic?

Thanks!!

The relay only bypasses the soft start resistor, look at the schematic again. You may be looking at the protection/speaker relays
Sounds like you have some shorted outputs and drivers
Post some pictures
What are the values of resistors?