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biggsd  
#1 Posted : Saturday, March 23, 2019 11:13:50 AM(UTC)
biggsd

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Hi Everyone

So a few years ago I was having lots of problems with Placied BPs Rectifiers blowing up - as i have oversized transformer (160w) means inrush current is a lot. I Solved the problem with large oversized rectifiers - and the system has been working perfectly for around 2 years.

As a note its a DUAL STEREO dac (two separate dacs on one case with shared power for the digital, separate power for the analog)

Last weekend at an event we had a LOT of white smoke when DAC was turned on. It was in case so couldn't see what failed.

I tried replacing rectifiers but still lost the fuse. Now i have isolated the issue to one of the Placid BP Power supplies.

Back on the bench with lab power supplies limited at 300ma when there is NO load on it measures 15v on the outputs. As soon as theres a load (legato in this case) the voltage on the dodgy side drops to around 8-9v. Strangely enough, when just the positive side is powered that side sticks at 15v and shunts normally. Its when both pos and neg load is connected that it does this strange behaviour.

Is it worth trying to fix it? Is there any other tests i can run to see what has failed? its clearly had a bit of an incident, and i am wondering if it isnt just things getting tired over time with the caps filling up fast. ALSO R1A and R2A are blackened.

I am happy to send the board somewhere to understand the problem so can make it more robust.

Thanks - this is the one thing i keep having problems with - but it sounds so much better for electronic music with oversized trannies.

Thanks!

-Dave

Edited by user Saturday, March 23, 2019 11:20:58 AM(UTC)  | Reason: Not specified

akras  
#2 Posted : Sunday, March 24, 2019 4:27:00 PM(UTC)
akras

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If you insist on using a large transformer (which doesn't make much sense to me in this case), I suggest you use something like this in parallel to the primary to limit the inrush current:

https://www.mouser.com/P...Y9IKjMoVXHnXGq73Sw%3D%3D . In fact, it wouldn't hurt to use it even with the regular size transformers.
Brian Donegan  
#3 Posted : Monday, April 1, 2019 3:43:50 PM(UTC)
Brian Donegan

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The issue you are describing is not caused by inrush current. That is not how current works...

Generally speaking, current must be drawn, not pushed. Something on the Placid must be drawing an excessive amount of current to cause the rectifiers to smoke.

Inrush current issues are usually caused by large transformers building initial magnetic flux, or large banks of capacitors building initial charge, causing fuses to fail.

The attached photo is a 650VA Plitron transformer feeding a Placid BP. Rectifiers don't even get warm.

IMG_20190323_074811.jpg (122kb) downloaded 5 time(s).

Edited by user Monday, April 1, 2019 3:53:30 PM(UTC)  | Reason: Not specified

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