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Unless the person that analyzed this problem used an oscilloscope and did detailed troubleshooting, I would NOT jump to the conclusion that aan op amp was blown BASED upon my looking at the schematic of the unit. There are MANY components involved with the overdrive channel, including relays and other transistors and components. The most probable caause would be that 1/2 of the V2 vacuum tube is burnt out. Test by swapping V1 with V2. If NOTHING works, then replace the tube that is NOW in V1 as the second section of it has a burnt out heater. Also a bad potentiometer for the OD channel would be a suspect. A VERY common problem is broken solder at pot terminals. Try plugging a set of headphones into the preamp output. See if you can hear sounds in bothe OD and clean channels. Note you will only hear sound in the LEFT headphone as the preamp out is MONO. MOST of the three op amp chips would NOT kill the OD signal if they were bad.
Make sure you are using BALANCED cables from this... eithe XLR or TRS cables. Using TS unbalnced cables MAY ground out the signal which is sent as balanced. Here is a schematic for the 24 channel unit... yours just has eight more channels. http://elektrotanya.com/behringer_ub2442fx-pro_sm.pdf/download.html
Scroll down to "get manual" and click to download. Ignore other download links.
By looking at the signal paths, you can OFTEN do a lot of testing from the available jacks. If the contacts on the right main INSERT jack go bad, that would cause your problem,,, NEVER use other than an insert cable in these jacks.
Try headphones... do you get sound both sides (assuming your PAN controls are centered.???
Now do same with the main output cables discoonected... do you get headphones both sides???
Next solo or PFL a channel... do you get sound both sides???
Answer me these as they are tests that I can do some isolation using the circuit schematics. Make sure to answer all three conditions.
I assume you swapped thee output leads as well as the inputs which you di mention, to verify you amps and cables...
The Vestax schematic I have is NOT your same model, but the companies often re-use circuitry. In the schematic I have it appears that the two channels go through two levels of NJM2068L op amps.
In these two levels there is both a master gain control. It is important to know whether the gain control varies the output level of the right, even if it is low. Also in this gain control area is a master balance pot which varies the ratio of the left and right and is CAPABLE of taking either channel to near zero output... IF you have that control check it for sure !!! The pot is a dual employing both an A taper and C taper which is a reverse of the A.
The right tool for troubleshooting this is an oscilloscope, but first an inspection looking for board cracks around the output and pot area is in order.
Make sure the appropriate channel rotary knob MON1 knob is turned up for the channels you want into MON1. ALSO test other channels if they can be sent to MON1. The MON jacks are TRS with the tip as the hot and the sleeve as resistor to ground.
Hopefully you have used good practice and have ALWAYS powered whatever you are driving from the MON1 out from the same receptacle as the PMP5000. If not, ground bounce MAY have destroyed the driver in thee PMP5000. They USUALLY don't tell you these things in the user manuals, so it is up to us electricaal engineers to educate.
FIRST plug in a set of headphones and see if sound comes out (it will only be one side and fairly low volume, usually the left). If it does, then cabling and whatever amp you have for the MON1 has a problem. I have schematics and can help you troubleshoot a bit.
Also PLEASE read the tip I have posted on here about a grounding hazard of the A channel when using Speakon to 1/4 inch cables.
Always check your cables and connectors on them to make sure the cable is good and the connectors are not loose. This sounds like a bad cable or connection between the line output of your mixer and input to your stereo.