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Subject: Re: Another CS-80 on the overhaul bench


Hi all.

I'm getting into refurbishing/fixing my CS-80 and thought some people
would be interested in seeing what's involved. I created an album in
the Photos page called CS80 renovation.

There's a picture labeled "Here's where it's happening!", which shows
a corner of my TV room, converted to a repair shop. I picked up a
Weller desoldering station and Beckman Oscilloscope very cheap on
eBay. On the floor, you can see the box from Digikey where I got all
the CMOS chips, IC sockets, and capacitors.

There are also three pics of the TSB boards. These are the first I'm
upgrading. They multiplex the aftertouch voltages from the keyboard.
I desoldered the five 4051 chips and installed machined sockets. One
semi-problem: the holes between the rows of pins are supposed to be
exactly 0.3" apart. Well, they're slightly wider. This isn't a
problem with the chips, since the leads are flexible. However, it
made putting in the sockets a pain. Also, since the socket pins were
forces into a slight angle, it made getting the new 4051s in
difficult. For the last few, I cut the sockets in half and inserted
each row separately. This made everything much easier.

In the pic "Back of upgraded TSB board", you can see the little bypass
caps I put on the 4051s. The 4051s are different than most digital
CMOS parts since they're analog switches. They have a negative supply
(-6.5v), and two positive supplies, one for digital and one for
analog. They are both tied to +8.5v. The minimal bypassing was
between these two supplies. I added caps from each to ground. The
ones that reached a longer distance are covered in red heat-shrink tubing.

In pic "TSB board after upgrade" you can see the 4051s in their
sockets. In the top, left corner you can also see two bigger, blue
capacitors I added to bypass the +8.5 and -6.5 supplied where they
enter the board (the red and green wires in the corners).

One last weird thing: the two TSB boards in my CS80 are slightly
different versions! I think they're electronically identical, but the
PC boards are a bit different. After I put the caps on the first
board I was just going to put them in the same places on the second
board. When I tried to do that, I couldn't find some of the reference
points I was looking for. I thought I was going blind, but then
realized the differences.

The good part is that everything still works after all the soldering
(which is really good since it was all working before I started)!

Now I'm on to the other boards.

David