Vintage Synth Repair

hi, i have a omni 2 with nothing powering exept the power on light. 
was wondering if i replace the tantulum 10uf caps on the power board 
can i use electrolytic caps of same value. does it matter if they are 
non-polarized. Would ceramic disk caps work or do i just need to keep 
looking for tantulum. i searched all previous posts but didn't find 
anything too specific. I am new to electronics and would appreciate 
any help. thanks
Ps should i go ahead and replace all the 10uf caps on all boards or 
start with the power supply board and hope that gets me somewhere.

Trevor

>hi, i have a omni 2 with nothing powering exept the power on light.
>was wondering if i replace the tantulum 10uf caps on the power board
>can i use electrolytic caps of same value. does it matter if they are
>non-polarized. Would ceramic disk caps work or do i just need to keep
>looking for tantulum. i searched all previous posts but didn't find
>anything too specific. I am new to electronics and would appreciate
>any help. thanks
>Ps should i go ahead and replace all the 10uf caps on all boards or
>start with the power supply board and hope that gets me somewhere.

If the board has tantalum caps now it's probably a good idea to replace them 
with electrolytic (of equal or greater working voltage).  You can replace a 
polarized cap with a non-polarized one (but you should be  careful if you 
want to replace a non-polarized capacitor with a polarized one).

Other capacitors may need replacement but the ones on the power supply are 
generally the best candidates (though if you haven't yet diagnosed the 
problem with the power board, replacing the caps might not do much).

issues w/tantalum caps in the omni are more relevant to the upper and lower voicing boards 
than the power supply...i would check the big electrolytic caps on the power supply 
(w/appropriate precautions taken), the voltage regulator, and other components on the 
power supply first...it's also a good idea to disconnect (if you haven't already) the 
power supply from the rest of the synth until it is putting out the correct voltages

see my pages at http://people.umass.edu/brownp/arp for schematics & other info...

fwiw, i replaced the tantalum caps on the voicing boards in my Omni w/aluminum 
electrolytics, mostly because they are cheaper than tantalums

thanks, PB>>

Scott Nordlund wrote:
>> hi, i have a omni 2 with nothing powering exept the power on light.
>> was wondering if i replace the tantulum 10uf caps on the power board
>> can i use electrolytic caps of same value. does it matter if they are
>> non-polarized. Would ceramic disk caps work or do i just need to keep
>> looking for tantulum. i searched all previous posts but didn't find
>> anything too specific. I am new to electronics and would appreciate
>> any help. thanks
>> Ps should i go ahead and replace all the 10uf caps on all boards or
>> start with the power supply board and hope that gets me somewhere.
> 
> If the board has tantalum caps now it's probably a good idea to replace them 
> with electrolytic (of equal or greater working voltage).  You can replace a 
> polarized cap with a non-polarized one (but you should be  careful if you 
> want to replace a non-polarized capacitor with a polarized one).
> 
> Other capacitors may need replacement but the ones on the power supply are 
> generally the best candidates (though if you haven't yet diagnosed the 
> problem with the power board, replacing the caps might not do much).
> 
> 
> 
> 
>  
> Yahoo! Groups Links
> 
> 
> 
>  
> 
> 

-- 
Peter Brown, Ph.D.         Dept. of Microbiology
IT Coordinator/Lovley Lab  422F Morrill Science Center IVN
(413) 577-2747             University of Massachusetts
http://geobacter.org       Amherst, MA 01003-9298

thanks for the quick responses.  I just noticed that the bracket that
bolts the board down gets extremely hot when turned on. Guess thats
the reason when i got it it had duct tape on the bottom screws. are
the original tantum caps polarized? also could you point me to
somewhere i could learn simple diagnosis. i have a multimeter will i
need anything more specialized.sorry about the easy questions, just
trying to learn, all help appreciated.

Trevor

On Monday 01 May 2006 04:34 pm, tdb1274 wrote:
> hi, i have a omni 2 with nothing powering exept the power on light.
> was wondering if i replace the tantulum 10uf caps on the power board
> can i use electrolytic caps of same value. 

I wouldn't.  The characteristics of those two kinds of parts are NOT the same. 
I forget in which datasheet it was,  but one of the datasheets I have around 
here for one of the common 3-terminal regulators (7805,  etc.) talks about 
the need for a cap right at the output of the device,  and they specify 
either a 1uF tantalum or a 25 uF (!) aluminum electrolytic...

> does it matter if they are non-polarized.

Dunno why you'd want to go there.

> Would ceramic disk caps work or do i just need to keep looking for tantulum.

Where are you going to find a 10uF ceramic disk?  I've never seen one that 
big,  ever.  10pF,  maybe,  but that's not at all the same thing.

> i searched all previous posts but didn't find anything too specific. I am
> new to electronics and would appreciate any help. thanks
> Ps should i go ahead and replace all the 10uf caps on all boards or
> start with the power supply board and hope that gets me somewhere.

If you're relatively inexperienced you might end up doing more damage than 
what you have now.  Troubleshoot the thing first!  You seem to suspect the 
power supply has a problem.  That's easy to deal with -- measure the output 
voltages.  ARP color-coded the output wiring,  red is +15,  purple is -15,  
and orange is +5,  with black being ground.

Do you have a meter?

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

On Monday 01 May 2006 04:52 pm, Scott Nordlund wrote:
> If the board has tantalum caps now it's probably a good idea to replace
> them with electrolytic (of equal or greater working voltage).

Why?

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

On Monday 01 May 2006 05:21 pm, tdb1274 wrote:
> are the original tantum caps polarized?

Yup.  And you don't want to put them in backwards...

> also could you point me to somewhere i could learn simple diagnosis. i have
> a multimeter will i need anything more specialized.

That's a good start.  See my earlier post...

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

Generally, bog standard electrolytics are cheaper and have a greater
tolerance to ripple current, so they are happier to live in power supplies
than Tantalum.  Tantalum capacitors are great when you need to pack a lot of
capacitance into a very small space.
JohnB
----- Original Message -----

From: "Roy J. Tellason" <rtellason@...>
To: <vintagesynthrepair@yahoogroups.com>
Sent: Tuesday, May 02, 2006 6:39 AM
Subject: Re: [vintagesynthrepair] arp omni problem


> On Monday 01 May 2006 04:52 pm, Scott Nordlund wrote:
> > If the board has tantalum caps now it's probably a good idea to replace
> > them with electrolytic (of equal or greater working voltage).
>
> Why?
>

>On Monday 01 May 2006 04:52 pm, Scott Nordlund wrote:
> > If the board has tantalum caps now it's probably a good idea to replace
> > them with electrolytic (of equal or greater working voltage).
>
>Why?

Tantalum capacitors are more sensitive to overvoltage conditions and can do 
much more evil things when misused (see Oldcrow's synth repair tips that 
were referenced here a little while back).

In some cases tantalum capacitors will be more desireable due to tighter 
tolerances and better high frequency response but it really depends on the 
circuit.  For critital power supply decoupling it might be better to use 
(for example) a 10 uF electrolytic with a 0.1 uF of a different type in 
parallel.

On Tuesday 02 May 2006 09:43 am, Scott Nordlund wrote:
> >On Monday 01 May 2006 04:52 pm, Scott Nordlund wrote:
> > > If the board has tantalum caps now it's probably a good idea to replace
> > > them with electrolytic (of equal or greater working voltage).
> >
> >Why?
>
> Tantalum capacitors are more sensitive to overvoltage conditions and can do
> much more evil things when misused (see Oldcrow's synth repair tips that
> were referenced here a little while back).
>
> In some cases tantalum capacitors will be more desireable due to tighter
> tolerances and better high frequency response but it really depends on the
> circuit.  For critital power supply decoupling it might be better to use
> (for example) a 10 uF electrolytic with a 0.1 uF of a different type in
> parallel.

Might be.  But OTOH I'm not about to second-guess the guy that designed the 
thing in the first place.  Yeah,  tantalum caps have some issues,  but as 
long as you go with the right value for them,  and make darn sure that you 
don't put them in backwards,  I see no reason to replace them wholesale with 
aluminum electrolytics...

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

That is right up to a point. I don't change them just for the sake of it but
over the years I have had more Tantalum failures in PSUs than any other
type.  If the power supply has been 'designed' with very little reserve in
capacity then there can be a fair bit of ripple on the supply rails.  Tants
just don't like this, and while they will not fail immediately, they will
not outlive the more robust ally can type.  As for getting one in backwards,
you would never believe so much smoke could come from such a tiny bead.
JohnB
----- Original Message -----
From: "Roy J. Tellason" <rtellason@...>
To: <vintagesynthrepair@yahoogroups.com>
Sent: Tuesday, May 02, 2006 6:37 PM
Subject: Re: [vintagesynthrepair] arp omni problem


> Might be.  But OTOH I'm not about to second-guess the guy that designed
the
> thing in the first place.  Yeah,  tantalum caps have some issues,  but as
> long as you go with the right value for them,  and make darn sure that you
> don't put them in backwards,  I see no reason to replace them wholesale
with
> aluminum electrolytics...
>
> Information is more dangerous than cannon to a society ruled by
lies. --James

> M Dakin
>
>
>
>
>
>

On Tuesday 02 May 2006 04:14 pm, John Brewer wrote:
> That is right up to a point. I don't change them just for the sake of it
> but over the years I have had more Tantalum failures in PSUs than any other
> type.  If the power supply has been 'designed' with very little reserve in
> capacity then there can be a fair bit of ripple on the supply rails.  Tants
> just don't like this, and while they will not fail immediately, they will
> not outlive the more robust ally can type.

Ok,  that makes sense...

> As for getting one in backwards, you would never believe so much smoke could
> come from such a tiny bead.

Or such a loud noise,  on occasion.  :-)

> JohnB
> ----- Original Message -----
> From: "Roy J. Tellason" <rtellason@...>
> To: <vintagesynthrepair@yahoogroups.com>
> Sent: Tuesday, May 02, 2006 6:37 PM
> Subject: Re: [vintagesynthrepair] arp omni problem
>
> > Might be.  But OTOH I'm not about to second-guess the guy that designed
>
> the
>
> > thing in the first place.  Yeah,  tantalum caps have some issues,  but as
> > long as you go with the right value for them,  and make darn sure that
> > you don't put them in backwards,  I see no reason to replace them
> > wholesale
>
> with
>
> > aluminum electrolytics...
> >
> > Information is more dangerous than cannon to a society ruled by
>
> lies. --James
>
> > M Dakin
>
> Yahoo! Groups Links
>
>
>

-- 
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space,  a critter that can
be killed but can't be tamed.  --Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James 
M Dakin

>As for getting one in backwards, you would never believe so much smoke 
>could come >from such a tiny bead.

I know :)