[sdiy] OB8 assistance needed

[Roy J. Tellason]

On Tuesday 01 February 2005 05:07 am, WeAreAs1 at aol.com wrote:
> In a message dated 2/1/05 12:30:22 AM, synth-diy at retrosynth.com writes:
>
> << The symptom is that the unit would latch up after being on for only a
> few minutes.  I found a severe amount of ripple in the 5v line on the
> front panel pot board  >>
>
> My guess is that there is probably a failing bridge rectifier in the 5volt
> supply.  This is a very common occurance on OB8's.  The ripple on the 5volt
> line would indicate that the rectifier is going bad.  Replace it with a new
> one of an equal or greater current rating, and the latchup problem will be
> forever banished to the land of smoke and ghosts.

I don't know about that particular item of equipment,  or whether the problem 
is the bridge rectifier or not,  but my first thought on reading the symptoms 
was -- "Check the power supply!"

I've gotten bit by this one over and over through the years,  not checking 
that something was getting proper power to begin with,  and ending up chasing 
my tail for hours until it finally occurred to me to do so.

It could be a bad bridge,  or it could be bad filtering,  or it could be a 
problem with regulation (if this is a regulated supply),  or it could be a 
bad connection somewhere that might produce any of these symptoms.

This is where it's nice to have a scope in addition to a meter,  but in some 
cases (depending on the meter),  you can switch to "ac volts" and measure 
ripple directly.

Whenever working on anything that's flaky like this,  _always check the power 
supplies first!_

:-)