Vintage Synth Repair

Hi Frank

 

A point no one has mentioned is that capacitors may not be 'bad' but they
may well have changed value.  This could have a major effect on power
supplies.  My experience has always been to replace all electrolytics and
tantalums on old equipment, especially so if the equipment has rested
unpowered for a year or three.  There have also been problems with plastic
capacitors such as the Wima types where the case cracks allowing the ingress
of moisture.  One very popular plastic capacitor used extensively in the 50s
and 60s is black in colour and these crack seriously, usually around one
end, replace them as well.

 

The other potential problem not mentioned are resistors that change value.
While this is usually associated with valve (tube) gear I have seen it on
transistorized equipment as well.  Those around the power supply would be
worth checking.

 

Regards

Brian G3OYU

 

From: vintagesynthrepair@yahoogroups.com
[mailto:vintagesynthrepair@yahoogroups.com] On Behalf Of Frank Simon
Sent: 10 July 2010 8:11
To: vintagesynthrepair@yahoogroups.com; SequentialCircuits@yahoogroups.com
Subject: [vintagesynthrepair] Prophet 10 rework

 

  

Does anyone have a strong opinion on replacing old parts on Prophet 5 or 10
like capacitors and 4000 series and 74LS series ICs. I definately am
replacing tantalum but are the highly populated .1uF Z5U caps Mica or
ceramic and do they really go bad? I understand mica is obsolete in terms of
current production so I am thinking to replace mica with ceramic if this
across the board rework happens. I have declared war on my P10 and plan to
replace all parts on the PCB3 board (computer board) like caps and logic
ICs. There is a guy with a nice website that states the logic IC technology
was poor in the 70s with a 6 micron fabrication process versus a current 0.7
micron process that the reliability of the old chips were poor. I figure
this is the way to go first before I question the DAC71, which costs a
fortune. The way I look at it is it is a rework that probably is healthy for
longevity. I am not sure how to troubleshoot the DAC.