XR8600, connected to 115xt bass bins and crossover out to Pro 15s (all 4 ohms). Left side muffled then died. Later, right side cut out several times. Then power lost. What might the fault be?

Check that all the eqs are set not to cut bass, check there are no effects on and that the XPQ is off. If you still have the problem how sure are you there is no bass coming from the mixer? Have you tried it with another amp? We had one hire customer who had the same problem you describe and his amp had a crossover and it was set to act as a mid/top amp and wasn't giving him any bass, unsurprisingly, switching it back to full range sorted it.

Could be the crossover has died or the main speaker winding has failed. Open her up and connect on side of the main speaker direct to a 9v battery and then wipe the other wire over the other terminal. If you get a crackling from the speaker then it's likely the crossover, if there is no response at all from the speaker then it is dead and possibly the crossover too.

What kind of problem are you having with this, I assume impedance matching. 2 speakers in parallel cut impedance in half. ex. 2 x 8ohm in parallel equal 4 ohm. IF the same speakers are in series, they double impedance, ex. 2 x 8ohm in series equal 16 ohm. Now matching 2sp and 2 sp, both pairs SHOULD be wired the same and the removal of 2 (dep on config) usually would be treated as 1 ?ohm circuit that equal the other ?ohm circuit. AFTER the removal of 1 leg, the impedance could double or half, depending on configuration.

No, the ATV50 head is rated for 4 ohms total. Using both 4 ohm cabinets at once will fry your amp. Your only option would be to rewire your cabs internally to 16 ohms each by connecting the speakers in parallel, but that would cut your amp's power in half.

The Peavey CS4080HZ is intended to place 2,040 watts
per channel into four-Ohm-rated speaker
impedances. The "HZ" suffix is intended
to state the amplifier has a relatively high
impedance output and is optimized for no
lower than four-Ohm loads. Are you strapping in Bridged or Stereo Mode? Bridged Mono Operation
Both amplifier channels can be bridged together to make a very powerful single-channel monaural amplifier. Use
extreme caution when operating in the bridged mode; potentially lethal voltage may be present at the output
terminals. To bridge the amplifier, depress the rear panel Bridge switch to the IN position. Direct the signal to channel
A's input and connect the speakers across the hot outputs (the "+" binding posts) of channels A and B. Only channel
A's input attenuator is active while in Bridge Mono mode. Both connectors are strapped together, so either connector
can be used with a patch cable to drive the input of another amplifier.
Unlike the stereo mode, in which one side of each output is at ground, both sides are hot in bridged mode. Channel A's
side is the same polarity as its input with the minimum nominal load impedance being 4 ohms (equivalent to driving
both channels at 2 ohms) in bridged mode. Driving bridged loads of less than 4 ohms will activate the DDT
circuitry, resulting in a loss of power, and may also cause a thermal (overheating) overload.
Therefore, check the impedance of the cabs for each mode. Remember, if you connect two individual speakers in Parallel (+ to + and - to -) you cut the impedance in half. Two 8 ohm speakers in parallel now have a load of 4 ohms. Series connection + to - to + to -, will double the impedance. Two 8 ohm speakers will have a load of 16 ohms.
I have actually taken a two speaker cab with a 4 ohm impedance and opened up the back to re-do the wiring. I rechecked the impedance with a ohm meter. So yes, be careful. Whatever you do, keep the speaker lengths as short as possible. Buy really good speaker wire or if you make your own, go with 10 gauge wire.

Sorry, those speakers are rated at 250 Watts RMS continuous, NOT 600. The speakers are nominally 8 ohms. The PMP6000 will deliver about 250 watts RMS to an 8 ohm load so the speakers should be able to take this as long as you had one per side and NOT using bridged mode of the PMP6000. It is possible that you fried the amp, although the PMP amps have a speaker protection network that shorts the output should the amp hard over. It is strange that you could draw smoke with the setup. Hopefully you were not generating very low frequencies that were below what the speaker could handle OR that you did not crank up the bass with the EQ such that frequencies below the speakers rating were sent at high levels. Your speakers are rated for a low end at 55 HZ. You should have the eq cut the gain below that. The leftmost EQ (50 Hz) should NOT be higher than center... if you boost that one, you likely will be buying new speakers. If you need power below that, then you need to be using subwoofers. Hopefully you haven't damaged the PMP6000... I assume that was the amp you were using, although you haven't stated that. At this point, unless the stuff is under warranty, you nee to open the speakers and see what has blown... could be the woofers or the crossover network...Use an ohmmeter to check the woofer DC resistance... should be between 7 and 9 ohms. If it is open circuit, the voice coil is blown.

when using amps,, you can't go by the number of the amp to determine what wattage the unit puts out, after checking on this amp,, the white marks that your seeing on the cable, is probably just some of the thermal paste that you apply to any heatsink or CPU ,, nothing to worry about, now as far as the wattage,, here is what they say about that amp, so there is a difference between the 4 and 8 ohm set ups
The Markbass Little Mark 250 bass amp head is a high-quality bass amplifier with a solid-state preamp and an analog power amp. The Little Mark 250 delivers 250W of power into a 4 ohm cabinet, or 150W into an 8 ohm cabinet. This Little Mark has a 4-band EQ, Markbass' VLE (Vintage Loudspeaker Emulator) and VPF (Variable Pre-shape Filter) filters, as well as both Gain and Master volume controls. The front panel accepts both a passive or active bass 1/4" input, as well as a balanced XLR input for acoustic bass pickup systems or a microphone. On the rear panel you'll find a Neutrik Speakon combo jack output that accepts both Speakon or 1/4" speaker cable as well as a second 1/4" speaker out jack. You'll also find a balanced XLR out, unbalanced tuner out so you can tune as you play without passing your signal through pedals, and a Send and Return Effect loop which saves you from losing your signal if one of your pedals dies or a cable in the chain gives out.

Hi. The mixer puts out a full range mix, the solution is in your speaker setup.

Many subs have a built in crossover that splits the signal for the tops. Check your sub specs or manual. If your subs have this, run your output signal to them first and then link them to the tops from the special daisychain socket.

If they don't have one, you can install a passive crossover to your subs or buy an external crossover unit.

The last (and not very good) option is to fake a crossover with the desk's stereo EQ. Connect the subs to the left or right channel and the tops to the other and use the EQ to remove the bass from the tops and vice versa, pan everything dead center. Obviously this sacrifices your stereo sound and isn't brilliant.

You CANNOT power 4 total 4 ohm speakers from this unit without special configuration. The lowest you can go is 4 ohms per side, which would be one 4 ohm cabinet per side. You would have to do a series parallel arrangement with the resources you have... two Peavey's in series and that combination in parallel with two 15's in series...
This is a VERY unsafe configuration with this mixer. ALSO please read my tip on here in regard to PMP mixer grounding hazard of the A channel when using Speakon to 1/4 inch cables.

Frankly, forget about maximum performance unless you want to risk blowing your mixer...

If I were you, I would put the two 15's in SERIES as 8 ohms on one of the channels and the Peavey's in SERIES as 8 ohms on the other channel.

You would be well to heed this warning as I have repaired a bunch of these units. Be careful of any poor speaker connections as there is an insulation breakdown problem in the power amp circuit board if a speaker becomes intermittent. If something fails DO NOT replace the pwer fuse as you will do more damage.

Here is a link to the manual:http://www.peavey.com/assets/literature/manuals/00513220_7.pdf I didn't look at the manual for the crossover but this is probably the way I would do it. Look at page 13 in the manual : Come out of the Main out (31 in the diagram) into the main in of your crossover. Go out of your crossover Hi and Mid out setting back into Power amp In 1 (labelled 32 in the diagram). Hook your speakers that you normally use to the output jacks on the back of the Peavey. Make sure you match the output impedances. Go out of your crossover low output into the Pyle power amp and out of the Pyle into your subs. Make sure the impedance ratings of all your speakers match the output impedances of your amps. You will only be running in Mono mode as that is the signal output of the Peavey mixer. You can run faux stereo by using the Main monitor Out as 1/2 the pair and the Main Out as the other 1/2 to both channels of the crossover but you won't be getting a true stereo pan mode.