[sdiy] Wiard/Blacet Miniwave issue - Help please

m brandenberg mcbinc at panix.com
Thu Mar 31 05:55:45 CEST 2016

On Wed, 30 Mar 2016, Thomas White wrote:

> My Wiard/Blacet Miniwave is doing something strange now. It is a Rev.0 board. When I power it on, all is well. 30-40 seconds into power on the right most LED's fade to off. Then the rest start fading and "dancing" a bit before all of them turn off. The longer the power is on, the fade out to non-functioning gets faster. Does anyone know what causes this? When looking at the power rails, my supply is solid. The power component PS1 (unique to my Blacet modules), right after the power jack, loses voltage the longer the unit is on. Think it is shorting the voltage to ground? Seems like my likely issue is to replace this part. Thoughts?

"Loses voltage"...  measured between where and where?  The
PS devices are polyfuses, they are near shorts when functioning
and open up under increased current.  So there should be
near zero volts across one when all is well, rising when
there is a problem.  The usual circuit follows the PS with
a diode to ground so that if you reverse the power supply
voltages, the fuses open up quickly saving everything.

If you are seeing this (voltage across the fuse increasing)
and the nearby diode is cool, you could have a bad fuse.  But
the slow path to failure smells like passives more than
actives.  Poke around looking for a hot component.  And
give the electrolytics a very good eyeball.

To test the fuse, swap it with the other and see if the
problem moves to the other rail.


Monty Brandenberg

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