[sdiy] best repair screw-ups - was Christmas Projects

[Dave Brown]

The owner found a set of schematics after I had reverse-engineered the power
supply and got it working again.  The schematics are good for figuring out
which cable connects where as they have multiple identical size connectors.
I can't access any of the boards as they are in a card cage and they used
multiple connectors so one would have to have three different extenders!
I've figured out a process that has been highly successful - look for
modifications and remove them all.  Some make no sense and obviously never
worked.  Some are comical.  Someone spliced 28 gauge wire into the 20 gauge
ribbon connector and then insulated them with what look like bandage tape.
They soldered the other end directly to the 0.1" square pin connector but
melted a lot of the plastic so they must have had a huge soldering iron tip.
On a few they just wrapped the wire around the pin and then used Scotch tape
to hold the wires to the header.  They seemed to wire together the data
storage cassette interface with the audio outputs for some reason.  My
favorite was replacing a 7815 with a LM317 and then bridging various
resistors around it in hopes it would do something.  But, 11 hours into it I
have full drums and partial accompaniment!  It is colorful to watch and look
like it would be a great machine to have.  There is a YouTube video on it
http://www.youtube.com/watch?v=KNoEWhGZ0tE

So who here has repaired something that somebody else really screwed up?  I
have a good car story...

Dave

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Adrian Corston
Sent: Sunday, December 16, 2012 5:59 PM
To: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] Christmas Projects

On 17/12/12 10:43 AM, Dave Brown wrote:
> I'm trying to restore up a 1984 Wersimatic CX-2 Digital Drum machine.
> Someone else had worked on this previously and replaced bad parts with 
> wrong parts and then tried to modify the circuit to make them work!  
> Interconnect cables and connectors have melted so obviously the current
limit didn't do
> much.   I've now got the power supply up and running and powered on all
the
> logic.  No shorts and the 7 segment display changes!  Everything's in 
> German and there is no interconnect diagram.  It is a plug-in card 
> cage so I can't access any boards and it appears there were many 
> different options and configurations with differing plug-ins.  Should be
loads of fun.
> http://m.matrixsynth.com/2011/11/wersi-wersimatic-cx2-digital-1984.htm

No schematics, incorrect parts, melted cables and connectors, inaccessible
boards in a relatively obscure 27-year old device with instructions in a
different language.  Heck, why not try repairing something complicated and
difficult next time? :-)

Cheers,
A.