Re: RT802 DAC board

Hi,
If you can isolate the +/-15v terminals and inject the 15 +/- voltages
with a good lab supply with current limiting( and monitoring), the
part thats drawing to much current will get warm. Since the DC-DC
convertor is not a high current unit ~60mA), it might not cause the
offending device to get noticably warmer. Like Jon said about the DC-
DC convertor, it may be the offending device internally, so this test
will rule that out too.

Another way is to get a sensitive voltage meter or make up an op-amp
with high DC gain (to drive the vohm) and look for the greatest
millivolt drop along the power rail branches/traces (this isn't as
useful for power planes)

I was bringing up a protoype PCB for a major company product, and a
solder 'splash' was under a bypass cap. I tried these tricks and it
got me within 1" of the part and then manual inspection and
perspiration did the rest.

Hope this is useful.
-Lee

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <jmelson@a...> wrote:
>
>
> wanliker@a... wrote:
>
> > In a message dated 5/23/01 10:39:55 AM Mountain Daylight Time,
> > dengvall@e... writes:
> >
> > << When hot the outputs are about +/- 8v and unstable - which
> > > of course means the dac outputs are unpredictable. >>
> >
> > You might want to take a look for leaky capacitors on the output
line. from
> > the other post this is a +- 15 volt output and running at 8
volts, means
> > leakage somewhere.
>
> Oh, yeah! Of course! Look for those epoxy-dipped Tantalum
capacitors
> that look like a raindrop. I'll bet one has shorted out. This is
a classic
> problem on gear that has been out of service for a year or more.
> If you are still getting 8 V across it, it should be getting plenty
hot
> enough to detect the bad one. (Of course, there could be a bad
tantalum
> INSIDE the DC/DC converter, which will be a problem.)
>
> Jon