Vintage Synth Repair

Hi Alan, Duncan and Group!
 
Yes, my master keyboard is transmitting to several other rackmounts in the group 
- looks like a Pink Floyd laser show. ;-)  In my initial checking of things, I 
(carefully) resoldered the optoisolator and all the MIDI jacks - obviously to no 
avail.  However, you've given me plenty to check out, what with the optoisolator 
and 220R resistor.  HAS to be something rather simple, as I was using the thing 
without problems up until it upped and quit (Remember, if you're gonna' quit, 
it's a good idea to "up" first - that makes it more final).  

 
So, I have a replacement opto on order now.  Lookin' forward to solving this 
little mystery - and I'll let you know.  And of course, Thank You for your help 
and suggestions!
 
Best Regards,
Dave Garfield - in Microville, Coloraddy, USA...

________________________________
From: Alan Probandt <alan_probandt@...>
To: vintagesynthrepair@yahoogroups.com
Sent: Tue, April 5, 2011 6:33:23 PM
Subject: Re: [vintagesynthrepair] Re: E-Mu Vintage Keys Plus - No MIDI Reception

  
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.