----- Original Message -----From: jammieSent: Saturday, July 10, 2010 6:44 AMSubject: Re: [SequentialCircuits] Prophet 10 reworkits mostly the tantalum beads and electrolitic caps that fail the ceramics and mica caps are just bypass caps if you disconnected them you would not see much difference there there for noise from asociated
dc circuits and interference
i change the 4051 sample and hold ic in my synths notably my dss1 ensoniq mirage sq80 as the 4051 has a very low slew rate and does not handle fast transients well this makes things like filter frequency be choppy or zippery
i change mine to smp08 from analog devices which is a direct pin for pin relacement and these have a very fast slew rate the envelopes are more snappy
most 4000 series can be upgraded to the 74hc seriesas in 74hc4051 sample and hold and others like it most of these upgrade chips use a lower power rating of ampage so produce less strain on the psu
----- Original Message -----
From: Frank Simon
To: vintagesynthrepair@yahoogroups.com ; SequentialCircuits@yahoogroups.com
Sent: Saturday, July 10, 2010 8:10 AM
Subject: [SequentialCircuits] 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 I understand mica is obsolete in terms of current production so I am thinking to replace mica with ceramic if this across the board rework happens.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.
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Message
Re: Prophet 10 rework
2010-07-10 by Frank Simon
Wouldn't it be fair to say if all my power supplies
are up I don't have any type of capacitor problem, large or small caps, Tantalum
or mica? Even though I plan to replace the Tantalum anyway. I feel I have a
logic related failure. I know the processor is good and can read the EEPROMs but
if the unit simply does not funtion. Only a couple LEDs light up but does not
function. Can anyone offer where they would start trouble shooting
priorities and key pieces of information to isolate at least to a single
board.