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5-Minute Repair 003 - Behringer UB1832FX-Pro Mixing Desk

Having retired from active duties as main soundman for Souled Asylum and from playing guitar in bands, I still from time to time pick a few licks with my friends for fun. The PA we use includes a Behringer UB1832FX-PRO 18ch mixing desk which I bought via Ebay 2nd hand just for the job.

However, not long after getting it the desk developed a problem whereby the right channel (RHS) of the MAIN outputs stopped working. The symptoms being no output on the RHS main output XLR, and no RHS LED's showing on the fader.
So, until I got a permanent fix in place I temporarily configured the SUB outputs as mains to the external amp, the only downside being SUB's don't go via the desks 9-band graphic EQ and so it was parametric EQ on each channel only for a while.

So, time for an IanJ 5-minute repair job then.


Here's the desk on the workbench:-


Here's the L-R mains output led's in action which as you can see RHS isn't working despite both faders being at the same level:-


Pulling the desk apart the first port of call was to scope the output from the final drive op-amps (MC3371 type SMD dual channel) that output the MAIN L-R signals onto the bus. RHS confirmed completely dead:-


Looking at the input side of the op-amps (pre-faders) I saw that both LHS & RHS were fine, and indeed powering down and measuring the resistance across the RHS fader it was open circuit (should be at least 10k). I by-passed it with a temporary link and the RHS started working. Problem found.

Taking the fader apart after de-soldering it from the Pcb the problem was obvious. Looks like it has taken a fair dunt at some time in its life, enough to crack the pcb and the plastic casing:-


With no time or patience to purchase a new fader I glued it up and used some conductive paint to repair the carbon track. This sort of repair can be a bit hit-or-miss, but heck it's not a desk in a mission critical install so well worth a try!
Here's the underside glued up with 2-part epoxy which will have to be solid as any flex or movement could break the conductive paint trace:-


Conductive paint is available at any diy electronics store, or online. The stuff I use contains pure silver in the formulation to give pretty good conductive properties and a hard resilient surface film.


Here's the carbon track repaired with the conductive paint. Importantly the fader control doesn't actually run that far along so the paint should stay intact without being worn away, and luckily also the break is at the full-volume end which isn't often used:


Back in the desk and proved to be working, both LHS & RHS led's are showing the faders are doing what they are meant to......Job done.