Ross Powered Mixer PC-4110MT transformer wiring

[ronthesoundguy]

First of all let me start by saying that I am new to forums and postings.

Having said that, I am an A/V installer, doing a bit of service work for a local music store and this one's a bit out of my league.

I am looking at a powered mixer, Ross PC-4110, and the customer brought it in because it keeps blowing the 3amp fuse, when powering up.

I tore into this item and can see that the transformer has been replaced, since the wires are cut and soldered together with shrink wrap covering. (there's also obvious marks from removing the old transformer.

Since I don't know the wiring diagram of the transformer leads, I was hoping someone out there knew the correct AC side of the wiring to the switch and the circuit breaker.

The transformer has the number PC4110MT, obviously standing for the Ross PC-4110 Mixer Transformer.

Thanks,
Ron

[Enzo]

Hi Ron, I am up in Lansing. I own a pro audio repair facility, Shiawassee Technical. If you find yourself in need of backup professionally, feel free to contact me.

On to your problem.

First, unless I am just unaware, the Ross stuff is pretty old. I don't know what you charge, but at our shop the rate is $60 an hour. Amps that blow fuses may or may not be complicated to repair, but they will require some parts, so just for reference, in my shop, that repair would cost the customer at least $75-100. Oh if it were just a wire off the AC cord, maybe less. SO consider that cost within your own rates, and compare with replacing the unit. COnsidering that pretty nice powered mixers can be had these days for not much money and likely ones with more performance at the price.

On to your problem.

With this present transformer in it and wired the way it sits, did it used to work? I mean it may have been repaired in the past, but was it working until it failed for thecustomer? If so, then the transformer wiring is not likely incorrect. Or has the wiring been ripped apart?

When power amps blow fuses, the most common reason is shorted output devices in the amp section. Check the powr transistors for shorts. And even in the absence of schematics, you can usually identify the driver transistors that push the outputs. Check them for shorts too. Obviously more complex things could be wrong in the amp circuit.

After output transistors, shorted rectifiers in the power supply are next on the list.

Less likely still, but it happens - shorted or VERY leaky filter caps.

Transformers do fail, but they are about the last thing on the list most of the time.

You should be able to identify the rectifiers, and if so, the transformer wires that feed them. You can disconnect those wires and apply 120VAC to the transformer sitting alone. If that blows fuses, then yes the transformer is shot.

There is a thread in this forum about the model, has some photos.
http://www.diyaudio.com/forums/music...cuit-help.html

[ronthesoundguy]

Thanks Enzo!

I'll check out the tread pics.

The powered mixer came into the store not working, blowing fuses. I opened it up (it had already been opened, the screws were missing) and discovered the neutral wire (white) from the AC cable wasn't connected to anything, just cut clean and stripped back.

There is evidence of replacement of the transformer, but I'm not sure which leads are the proper ones for connecting to the switch (hot) and the neutral (white)

The wires to the switch have been soldered and bby the looks of the insulator, way too much heat.

Is there any way to establish the leads that need to connected and the ones that do not?

I made note of the connections, as they are, but without knowledge of the proper wiring of the transformer, it may keep blowing fuses.

Ron

[ronthesoundguy]

Thanks, I'll check out the thread and pics.

Ron

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