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Prophet 10 rework

Prophet 10 rework

2010-07-10 by Frank Simon

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 I understand mica is obsolete in terms of current production so I am thinking to replace mica with ceramic if this across the board rework happens.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.

Re: Prophet 10 rework

2010-07-10 by Doug

Mica and ceramic caps are extremely stable, so you shouldn't need to mess with them.  Micas are still in limited production, so I wouldn't worry about them.  Ceramics are in HUGE production and are typically used for power bypass, so I wouldn't worry too much about those either.

Electrolytics are the real 'bad-boys'.  I'm not sure how tantalums age.  Anyone?

I've heard strong stories about 4000 series parts "aging" (may be lot/manufacturer related), but never about 7400 series.  The 4000 stuff may have gotten a bad rap due to impurities in the manufacturing processes in use at the time.  I just can't speak to that though.

Hope that helps, just a little.

--- In vintagesynthrepair@yahoogroups.com, "Frank Simon" <fsimon001@...> wrote:
Show quoted textHide quoted text
>
> 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 I understand mica is obsolete in terms of current production so I am thinking to replace mica with ceramic if this across the board rework happens.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.
>

Re: Prophet 10 rework

2010-07-10 by Alexis V. Rogers

I could go either way on replacing the ICs. Yes, definitely get those tantalums out of there. I'd leave the mica and ceramic caps alone though. Mica caps have a 60-70 year lifespan, but are prone to DC leakage. I haven't seen this in a Prophet 10, but have in antique radios and tube amps so I'm guess that it takes a long time for leakage problems to show up. And I've never seen a ceramic cap fail.

--- In vintagesynthrepair@yahoogroups.com, "Frank Simon" <fsimon001@...> wrote:
Show quoted textHide quoted text
>
> 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.
>

Re: Prophet 10 rework

2010-07-10 by Alexis V. Rogers

Tantalums dry up, develop internal shorts, and then light up like burnt marshmallows. I always replace them with electrolytics when I see them.

--- In vintagesynthrepair@yahoogroups.com, "Doug" <dougslocum@...> wrote:
> I'm not sure how tantalums age.  Anyone?
>

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.
----- Original Message -----
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From: jammie
Sent: Saturday, July 10, 2010 6:44 AM
Subject: Re: [SequentialCircuits] Prophet 10 rework

its 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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RE: [vintagesynthrepair] Prophet 10 rework

2010-07-11 by Brian

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
Show quoted textHide quoted text
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.

Re: Prophet 10 rework

2010-07-12 by Monie

Not necessarily.  You never know when a cap is ready to blow.
Someone correct me if I'm wrong, but it's not a good idea to replace tantalums with other kinds of caps.  

Replacing the electrolytics is a good idea, 'cause they're old enough to merit it.

I'm not a tech, but I'd check the boards for cracked solder connections & other stuff like that before shelling out the dough for the CEM's.

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