Yamaha Emx series mixer design issue

[Tubetec]

A buddy dropped me out a Yamaha mixer today , It  took a little fall while powered up at a gig.
It instantly popped its mains fuse when it took the impact.
So I opened her up , heavy duty switchmode inside ,lots of big heavy components on the board ,secured along two sides with six screws . I lifted out the power board and sure enough the force of the bump had caused the board to flex and one of the primary pins of the switcher transformer had made direct contact with the chassis. It was like a spot weld  and the board in that area had layer of evaporated metal from the arc. The crazy thing was under the board they had gone to the trouble of putting a strong insulating plastic layer down ,but this only covered less than half the area of the underside of the board . I also noticed the trimming of the component legs wasnt very uniform ,some protruded about 5 mm below the board , The mountings were about 8mm high ,Just gently pressing the board down by hand I could feel she was hitting the deck . For the sake of a few cents worth of polycarbonate sheet,  a small plastic standoff in the middle of the board or even just better quality control on the trimming of the components, this would never have been an issue .  Anyway switcher transformer primary winding intact , but still no show after swabbing off the vapourised metal residue, Bridge rect and caps all fine too , so I guess my issue is with the switcher transistors .  I wonder should I document the fault and the cure and buzz Yamahaahahahah sevice the details . Its my experience that you get no thanks for telling the giant he has egg on his face ,maybe the best thing to do is document it all up nice so that owners of this model can either diy a fix or get someone technical to do the nessesary preventative mods .If you happen to own an Emx5000-12 or know someone who does best take remedial action to stop your mixer turning into a fireworks display at some point down the line .

 

[JohnRoberts]

The EMX series of powered mixers has been around for years with a reasonable reliability reputation (AFAIK but I have been out of the trenches for some time).

I have not looked inside one this century but did look at a top box when they were brand new... IIRC the switching supply is for a tracking amplifier PS rail that saves on heat sink and improves amplifier efficiency.

Good luck trying to embarrass Yamaha. It might be a little late in that products life cycle for design advice feedback, if it is no longer being made and sold.  :

Maybe tell your friend to get help lifting it, or be more careful placing it. It would have been even heavier and done more damage from a fall with a heavier conventional amp/PS, but I still wouldn't want to drop that one on my foot.  8)

JR

 

[Tubetec]

Thanks for the reply John ,
yeah your right, a little late in the day for recriminations ,still no harm to document it though ,
a stitch in time saves.........

 

[iampoor1]

Might just be on that unit too. I have worked on the max series and the lead length on all components was nothj g out of the ordinary. Maybe a new employee on the line that day?  ;D

 

[JohnRoberts]

Might just be on that unit too. I have worked on the max series and the lead length on all components was nothj g out of the ordinary. Maybe a new employee on the line that day?  ;D

I took apart a cheap low power class AB amp that I was using in my surround system, that kept blowing fuses. I found a 3/4" long clipped component lead sitting on top of the through hole PCB causing the power short (another problem avoided by SMD).  These amps were probably hand assembled in some low tech dirt floor factory in nowhere mainland china.

Yamaha has been in the game long enough to only use competent contract manufacturers, but stuff can always happen, and hard drops can stress even decent designs (its not the fall but the sudden stop, so what it lands on matters).

JR 

 

[Tubetec]

Apparently it wasnt the owner that dropped it but a drunken punter who stumbled ,knocked the desk ,and promtly hightailed out the door 

 

[iampoor1]

I took apart a cheap low power class AB amp that I was using in my surround system, that kept blowing fuses. I found a 3/4" long clipped component lead sitting on top of the through hole PCB causing the power short (another problem avoided by SMD).  These amps were probably hand assembled in some low tech dirt floor factory in nowhere mainland china.

Yamaha has been in the game long enough to only use competent contract manufacturers, but stuff can always happen, and hard drops can stress even decent designs (its not the fall but the sudden stop, so what it lands on matters).

JR

Definitely. I have seen my fair share of "oopsies" in otherwise well built gear. I once came across a board missing some soldering joints that low and behold, stopped working after a jolt one day. I was amazed that it worked the few years the owner had it in the first place!

 

[JohnRoberts]

Definitely. I have seen my fair share of "oopsies" in otherwise well built gear. I once came across a board missing some soldering joints that low and behold, stopped working after a jolt one day. I was amazed that it worked the few years the owner had it in the first place!

When I was managing an engineering group at Peavey I would meet with the service department technicians once a month to let them beat on me..(the customers beat on them the rest of the time). They were my "not so early" warning system to help me identify manufacturing/design issues, but even then if they knew how to fix the fault, or it was a low volume SKU, they may still not complain loudly enough.

Back last century when we (Peavey) extended our warranty to 5 years, I did a study of service repair work across all electronic SKUs to figure out what to expect. Unexpectedly I found one (low selling volume) amplifier with a disproportionate number of service repairs.  I referred that amp to the analog engineering group to find and fix the design flaw, which they did.  8) I did not find any significant increase in field failures from another couple years, so the longer warranty period was painless and good marketing.

JR