Vintage Synth Repair

I agree.  It's rare for the optoisolator to go bad, but it can happen.  The 
first series of Yamaha TX81-Z (very popular) tone modules did not have the 220 
ohm resistor between the MIDI In jack and the opto-isolator.  So the first time 
that I made a MIDI hardware controller device I also forgot the 220 ohm resistor 
on the output side of my device.  The high current zapped the LED of the 
optoisolator immediately and I had to replace it with a simular but not exact 
one.  


  Since the MIDI IN is where a big cable plugs in and as this module is almost 
20 years old, it is also possible that the solder connection between the MIDI IN 
jack and the circuit board has broken.  The MIDI signal might not be getting to 
the opto-isolator's LED section at all.  This is a little more likely than the 
O-I having gone bad.

  Does the keyboard or PC that is generating the MIDI in signal still work OK 
with another piece of MIDI equipment?  A simple LED and resistor can be used to 
check it.


----- Original Message ----
From: duncan <ferrograph@...>
To: vintagesynthrepair@yahoogroups.com
Sent: Tue, April 5, 2011 2:26:08 PM
Subject: [vintagesynthrepair] Re: E-Mu Vintage Keys Plus - No MIDI Reception

I replied to this on the p2k board; suspect the opto-isolator, a tiny six-legged 
IC right close to the midi in socket. never had one fail on an emu, but I've 
seen the same device type fail on other gear. could've been static, or just age. 


they're usually an LED & a phototransistor; the idea is (ironically, depending 
on your sense of irony...) to protect & isolate the delicate innards of y'r 
synth from whatever's coming down the cable. I'd go there first. google the 
device for its pinout, then see if data is making it across the airgap inside 
it. if not, time for a new one. they are not expensive.

hth-
duncan. 

--- In vintagesynthrepair@yahoogroups.com, Dave Garfield <daveogarf@...> wrote:
>
> Hi, group!
> 
> My VK+ will not play from the MIDI In anymore.  A diagnostic sez that the 
> problem's in the MIDI section, and a check of the MASTER settings shows that it 
>
> *should* be receiving - everything's enabled, in OMNI mode, etc.
> 
> Am I missing something?  Does anyone know if this is a recurrant problem w/ 
>E-Mu 
>
> rackmount modules?  Have I looked in the wrong place?  Any suggestions as to 
> where to look now?
> 
> THANKS in advance for your help.  I'd love to be able to sort this out myself, 

> but if needs be, it'll go to a tech.  (Any good techs in the Denver area?)
> 
> Gratefully,
> Dave Garfield
>




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