[sdiy] Wiard/Blacet Miniwave issue - Help please

blacet at blacet.com blacet at blacet.com
Thu Mar 31 17:10:02 CEST 2016

Check the 5v supply also!

> Just a friendly reminder: Any time you have even the slightest suspicion
> that there might be a power issue with your electronics, always put on eye
> protection before powering up the device. You don't want capacitors
> exploding and damaging your eye!
> Ok, now, back to your regularly scheduled circuit diagnostics...
> Brian
> On Mar 30, 2016, at 8:55 PM, m brandenberg <mcbinc at panix.com> wrote:
>> 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.
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