Static, left channel from B&K EX-4420

Is it possible that it is related to something as simple as a slo blow fuse?

Otherwise, is it worth repairing. I paid $400 a few years ago for it. 



hi, re: Output relay; Thanks for the suggestion- can you point me in the right direction for where I might find one? Thx, Frank

Omron makes lots of relays.  If you are unfamiliar with what they look like on the circuit board just look for a little rectangular plastic box component near the output jacks.  It will have a number on it that you can easily google and find a cross-reference number for.  Sometimes the number is on the side, the top or the bottom, in which case you won't see it until you remove the relay.  The average price is around $12.  I have purchased many on Amazon and eBay.  They are easy to replace without the need of expensive tools.  Just a cheap soldering gun and some solder (lead free) will work, but a desoldering tool with vacuum will speed up the process.  The relay is going to be a double pole double throw.  Just make sure the voltage is the same (usually 12 or 24V.  Relays have contacts inside.  Often these contacts wear out or get damaged and no longer close the circuit properly, or do it intermittently, thus the static. Without testing the unit, it is very difficult to be 100% certain that the relay is your problem but based on what you described and the fact that there are no pods (knobs) on that amp and my past experience the relay is likely the culprit.  After all it's a cheap part.  What have you got to loose!


Page 3 is the schematic, the difference lies in the number of output devices between models.

ST1400 2 Pair/Ch 105 W 8 ohms
ST1400M 4 Pair MONO 150 W 8 ohms
ST2020 3 Pair/Ch 150 W 8 ohms
ST3030 3 Pair/Ch 200 W 8 ohms
EX4420 5 Pair/Ch 200 W 8 ohms
EX4420M 10 Pair MONO 250 W 8 ohms
EX4430 4 Pair/Ch 200 W 8 ohms
REF7450 5 Pair/Ch 200 W 8 ohms
REF7420B 5 Pair/Ch 800 W 8 ohms
REF7420M 10 Pair MONO 1000W 8 ohms