Crate pa6fx powered mixer, powers on but when I hook speakers up to them, hear loud hissing and pops out of one of the speakers, nothing out of the other. I can hook up a mic and hear myself through the one speaker but not the other. I can hook up the speakers to other units and get sound out, so I know the speakers are ok....

https://www.scribd.com/doc/55465995/Crate-PA-6-Manual
https://www.scribd.com/doc/55465995/Crate-PA-6-Manual

You trying to fix it or sell it ?

I also have this issue. Same crate combo amp. There is a loud buzz emitted only when there is a cable plugged in. Cables and instruments checked good, only possible issue is inside the input of the amp. Popped it open, solders and connections were intact and appeared solid. Anyone have a guess as to why this is happening?

If it buzzes when you have no inputs AND no output leads connected, there is a problem with the power supply... HOWEVER if you have used UNBALANCED output cables instead of the REQUIRED TRS BALANCED output cables, it is possible the noise is being driven backwards and that is what you are hearing. Note that at full gains, there often is a tiny bit of noise, usually hiss. Also make sure the supply is powered from the SAME receptacle as the equipment this drives such as an amp or powered speakers.

Hopefully you were powering ALL interconnected equipment from the SAME receptacle. People can destroy the input circuit of powered speakers by plugging them into a receptacle at the stage and then powering the mixer from another receptacle... Pro's know to power ALL interconnected equipment from the same source, be it a receptacle or a power conditioner to avoid ground bounce damage to equipment. They carry power from the stage back to the mixer on an extension cord. You may have had a static discharge that blew one side of the balanced input of the speaker. The parts are inexpensive, however the labor to get at the amp is usually not fun. I have the dual 10 powered Kustom's and one gets at the POWER amp via removing the speaker after the grille... HOWEVER that is to get at the power amp. The Preamp is probably the failure and it is right at the input plug area and you can get at that by removing the panel with the plugs and power switch and volume control.
I don't have the schematic. Look for shorted RF bypass caps on one side of the balanced input circuit and possibly a damaged input op amp.

All interconnected equipment MUST be powered from the same receptacle or source. The XLR to the speakers should NOT have ground lift. The power for the mixer should come from where the speakers are and be routed alongside the XLR cables. All the other connected items should also be powered by the same source. The ground bounce within a building cannot only cause noise, but can rupture the input circuits of equipment. As an electrical engineer I don't know why manuals supplied with the equipment doesn't go into this more. The professionals at the big venues all know this as they have had to pay to get equipment repaired.

Now to get down to "hiss" once you get the other stuff straightened out, there are two things to know at the start: The first is that due to the statistical nature in electronics "noise and hiss" are among the laws of physics that we can't completely get around. The level of the hiss should NOT be objectionable however. The second thing is that proper level setup is important to minimize the effects of noise and hiss. You should be sending the levels to the powered speakers at near full line level into the line inouts, never mic inputs that some have. Using excess gain at the speakers will amplify any noise pickup on your audio lines. Next, at the mixer, try to keep all the level controls around 10 to 2 0'clock for rotaries and 70% for faders. Excess gain at certain stages will cause hiss to be objectionable.

Cease using the mixer until it is repaired. One or both of the amps have blown. Further use MAY result in power supply damage. 1 to 6 switching power transistors will have blown and often a Zener diode or two. If the metering resistors smoked, there will be two small surface mounted transistors per channel blown wide open as well. These are all in the HCA2400 amplifier module.

These can develop around 500 Wattts or so into speakerss that are 4 ohm.

If your speakers are 8 ohm the max power to each is around 250 Watts.

The efficiency of your speakers may reduce the loudness . The power rating of your speakers really has nothing to do with the loudness, only the power that can safely be sent to the speaker.

You can try Loud Technologies @ 866-858-5832, [email protected].

They hooked me up with parts and schematic for my Crate G212XL.

if they are square cement power resistors they are probably 3-5 watt 300-500 ohm .... are there colored stripes on the resistors? those are probably grounding resistors, they usually are installed too close to the board, get real hot a bunch of times and then crack the solder welds. when you replace them bring up the height and make space under the resistor to keep it off of the board and put a little drop of silcone underneath to hold them in place.