[sdiy] yamaha o1v

[WeAreAs1 at aol.com]

In a message dated 5/25/05 5:45:20 PM, dustin.sedlacek at gmail.com writes:

<< while not a synth question , i am sure that someone here can help.

plugged a juno 60 into a o1v and now the channel does not work , this has 

happened on 2 channels ...is it the pre ? what maybe going on ? anyone have 

some tips or advice ?  >>

I have seen those transistors in the 01V mic preamps blow on several 
occasions.  I've also seen the opamp that those transistors connect to go bad on a few 
channels from time to time.  It's kind of a hassle to open the thing up and 
get to the mic pre board, but once you're in there, you can swap some 
transistors (and/or the opamp) from a good channel into the bad channel to see if 
that's the problem.  If you need new transistors or an exact replacement opamp, you 
can order them directly from Yamaha USA (714-522-9011).  Just call and ask 
for Pro Audio parts.  If you don't have a service manual, the parts order person 
can probably help you find the part number.  Before you call, first get the 
part designation number from the PC board, i.e.  "Q42". "IC38", etc.  Also give 
them the name of the board in question -- it should be marked somewhere on 
the board.

If swapping out the transistors or the opamp doesn't help, then you have a 
bad A/D converter chip.  These are stereo converter chips, and each one handles 
two input channels.  Therefore, if you lost two channels at the same time, 
there's a good possibility that the ADC chip is where your problem lies.  It's a 
surface-mount chip, so hone up your SMT soldering skills (or ask for help from 
us -- we'll walk you through the process).  You'll just have to get a new 
chip to find out for sure, because you can't reliably desolder one from a good 
channel to try it in the bad channel (trust me, I've tried.  Several times.  It 
only kills the good chip....)

Michael Bacich

P.S.  -- It's probably just an odd coincidence that this happened when you 
plugged in the Juno 60.  Those 01V channels seem to go bad with very little 
provocation, but they normally seem to be OK with most synth outputs.  
nevertheless, it's probably a good idea to check and make sure your Juno isn't putting 
out any large DC voltage at its output (it shouldn't be).  If you see any DC at 
the Juno output, then it needs some attention, too.