Allen and Heath ZED16FX mixing desk – with a moral of the story.
Like most engineers, when we get a mixing desk in, our hearts sink. Given the nature of most of the budget desks, such as Behringer etc when they come in with a fault, they can be hard to check as all the channels are bussed together on one large PCB. Separating the channels to determine where the fault sits is a nightmare. You end up by searching for duff OP amps etc, wasting time and patience. Tiny SMD components, all sitting under XLR sockets and so on. Forget it. You can replace the whole desk for 4€ plus a sheet of Green shield Stamps.
So, when a better quality desk comes in, you tend to be a bit more enthusiastic. This desk was an Allen and Heath 16 channel. The client said that it was a few months old, but he had no warranty details. When he last powered it up, he saw smoke coming from it and switched it off. He had no outputs, but the LEDs were on. I asked if it had been look at and the answer was NO. Strange how various screws were missing underside?
These desks are nicely made. All the input channels and other parts are all on separate PCBs, bussed together with ribbon cables. This makes fault isolation much easier. Close inspection showed that the Audio MIX PCB had some burn marks. This board is bridged by the FX board and another piggy back PCBs. I noticed the FX board was at an angle and the retaining screw loose. This proves that nobody had been inside before me!
With the Audio MIX board out, I was faced with a burnt hole in the board where a 8 pin SMD device used to be, along with other SMD components. The series resistors that fed the +/- 12V supplies were also toast. Various calls to Allen and heath requesting details and or spares availability were met with a total non response. Now look here. This client (known for years) wanted his desk fixed. This sort of thing is hard to achieve in Southern Spain. He relies on me to keep his equipment working. He had bought 5 of these desks for his various studios. His thinking was that if he cannot get these repaired he would go elsewhere. In frustration, I rang around the phone system at Allen and heath and eventually landed in the lap of a very helpful young lady, Fiona Viney. She put me in touch with a Spanish agent who, was as usual, reluctant to talk to me. Again, Fiona employed her “kick arse” tactics and I got a quote for a replacement PCB. And, I have to say, a reasonable price. The board arrived 6 weeks later and was installed. To my delight, I now had audio and all was well. Or, was it? I noticed the FX channel was dead and the PFL LED was lit. I started to think back to the odd mounted FX PCB, that had never been touched by another person! Close inspection showed that one of the two 10 Ohm resistors feeding the +12/-12 V was burnt. Tracing the circuit told me that if this PCB was not mounted correctly on the piggy back sockets, the +5V, +/-12V supplies were mixed up. Replacing this resistor restored correct operation.
All the locals came out of their houses and shops to rejoice at the wondrous sounds from the mixing desk.
Here is the moral of the story. If it had not been for Allen and Heath’s employee, Fiona, I would have struggled fixing this desk and this client would not have placed an order for another 6 desks here in Spain. Which, he was happy to do when his local repair chap could buy spares.