Static, left channel from B&K EX-4420

Schematics

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

I looked at the schematic. Looks like the relay you need is twT9as 24VDC.

Your amp takes two since they are single pole relays. One for the left and one for the right channel. I would replace both while you are at it, since they are electromechanical devices and have a life cycle. The good one is likely not far from giving out also. They are very cheap, and you can find them all over the internet by typing twT9as. Check eBay. Would love to know the outcome! Best regards.

There also a relay RL3, looks like it's a 12V DPDT relay with a coil resistance about 900Ω.

It was a slo-blow fuse, All fixed!