Spent a fun weekend repairing this Crown CTs 3000 power amplifier!

I bought a set of two of these (well, a 2000 and a 3000; mostly the same) for cheap at auction to be the main power amp for the venue I’m running.
I trust Crown’s designs from the 2000s/2010s very well, and they actually made schematics and service manuals available!

So I was pretty confident when I got them that if something went wrong, I’d have a good chance of repairing.

Well, that happened! I got a text to say that the amp at the theatre just wouldn’t turn on. I came and confirmed this. I swapped over the spare 2000 unit which worked, and took this one home to test.

It was clear that the protection/inrush control relay was never clicking at all, which hugely narrowed the potential faults.

A few test points from the schematic later, I found that the unregulated 28VAC that makes the 24VDC aux power rail was not coming out of the aux transformer.
Desoldered that, and bingo! One of the mains windings is open circuit.

I soldered some wires in to feed 28VDC externally, to simulate replacing it, so I could check if there was a downstream fault that caused the transformer to fail.

Nope! The whole thing powered up and worked great.

(Some minor cleaning of connectors, switches and pots was required on the input board to cure a scratchy right channel.)

So now I’ve ordered two replacements of the aux transformer — happily a drop in replacement is still made, and a few fresh new 24V fans because these have had 20 good years of service and the bearings aren’t what they used to be.

Electronics repair is such fun!

#s0Projects #Tinkering