[sdiy] Wiard/Blacet Miniwave issue - Help please

Richie Burnett rburnett at richieburnett.co.uk
Thu Mar 31 18:52:36 CEST 2016

When you touch the polyfuse with your fingers you are sinking heat from it, so it's temperature will drop and resistance drop too. Unless you wiggled it by poking at it with something plastic...?


Sent from my Xperia SP on O2

---- Thomas White wrote ----

>Just gave a warm chip test. PS1 on the positive rail does get hot. No IC's get hot. When I wiggle the poly fuse on the positive rail operation goes normal then when I let it go the power drift down starts again. No time to solder as I have to go to work. Maybe a cold solder joint? I am thrown off by the wiggle solving things temporarily. 
>Thomas White
>Natural Rhythm Music
>> On Mar 31, 2016, at 8:10 AM, blacet at blacet.com wrote:
>> 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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