hi everyone
a few minutes ago i tried powering my green mic pre that i have just finished. and within seconds i hear a loud noise, high pitched. i'm a noob but my guess from the sound of it would a component blew

any help ?


Mbira

Re: help please ? problem powering my green for the first time
« Reply #1 on: July 07, 2011, 05:22:49 PM »
maybe a bacward cap?  Unplug it and look around-you'll probably see the problem.

I'm assuming you were not trying to pass a signal at the same time?
Joel Laviolette

Rattletree   |  https://www.rattletree.com
The Rattletree School of Marimba | https://www.learnmarimba.com

Re: help please ? problem powering my green for the first time
« Reply #2 on: July 07, 2011, 05:23:38 PM »
i tried again after making there was no short cut, and the condensers of the PSU started smoking .... may i have made mistake in wiring the transformer ? i did the series wiring with the central bridge for 2x15vac ...

http://fr.mouser.com/ProductDetail/Triad-Magnetics/VPT30-830/?qs=wkKrz7WmEgNXIHrxEqIP6Q%3d%3d

that's my transformer

is it likely i've blown any component ?

Re: help please ? problem powering my green for the first time
« Reply #3 on: July 07, 2011, 05:25:08 PM »
Quote
maybe a bacward cap?  Unplug it and look around-you'll probably see the problem.

I'm assuming you were not trying to pass a signal at the same time?

i already check but i'll see that again

the integrated circuits wre not mounted on their supports and nothing was plugged at all

thanks

Mbira

Re: help please ? problem powering my green for the first time
« Reply #4 on: July 08, 2011, 12:43:28 AM »
Well it sounds like you are only needing to worry about the power supply at this point.  Disconnect the main board and just test the voltage coming out of the PS.  Are you getting +-15, 0, and 48v?

But yes-if you are smoking something, then you have a problem.  You'll need to replace whatever smoked.
Joel Laviolette

Rattletree   |  https://www.rattletree.com
The Rattletree School of Marimba | https://www.learnmarimba.com

peterc

Re: help please ? problem powering my green for the first time
« Reply #5 on: July 08, 2011, 01:55:25 AM »
As Joel says, test the PSU first and make sure the voltages are correct.

Smoke sounds like a short circuit.

Unplug everything including the transformer on the PSU, & make sure all the PSU caps are discharged (the voltage should get close to zero). Then measure the resistance across Gnd & +V, then Gnd & -V. The readings will fluctuate, that is good. If they read as a short circuit, then there is a problem. Re-check everything, all solder joints, component polarity.

Do the same on the Mic Pre board as well.

If opportunity doesn't knock, build a door.

Re: help please ? problem powering my green for the first time
« Reply #6 on: July 08, 2011, 04:10:44 AM »
okay i will see about all this. althought i can hardly imagine where there could be a short circuit

i just hope i won't have to replace too many components
 thanks

Re: help please ? problem powering my green for the first time
« Reply #7 on: July 08, 2011, 05:28:26 AM »
so, so far :

i haven't test the transformer yet

but on psu i get 5kohm (well it's my first time using a multimeter, but i don't think i could be wrong it's the 1k p osition and the needle reads 5) for both 15v and ground, and 15v and grand

BUT on the pre, i get 2K for +15 and 0, while i get +infinite for -15 and 0v .... so that's a short circuit right ...

and i noticed that the only capacitor which shows signs of damage is a 1000uf - it's kind of as if the top "opened up"

peterc

Re: help please ? problem powering my green for the first time
« Reply #8 on: July 08, 2011, 06:17:15 AM »
Short cct is 0 (zero) ohms, infinite is open circuit.

If one of the electrolytics has blown its top, the it was probably inserted the wrong way round.

In my projects, generally, all the electrolytic caps are polarised in the same direction on each PC board.

Peter
If opportunity doesn't knock, build a door.

Re: help please ? problem powering my green for the first time
« Reply #9 on: July 08, 2011, 06:27:04 AM »
well it's definitely the right way !
maybe a stupid question but i used electrocytics for those which which are not polarized ... does the way i mounted them still count ?

the voltages on the transformer seem ok, but it's more 18-19v ... i measured from 15 to 0v, and from 0v to the other 15v

PS i mean for the 0.1uf on the psu i used electrolytic ... but i have a few 0.1 polypropylene caps, should i use these instead ?
« Last Edit: July 08, 2011, 06:35:46 AM by amaurythewarrior »


peterc

Re: help please ? problem powering my green for the first time
« Reply #10 on: July 08, 2011, 06:41:10 AM »
Quote
does the way i mounted them still count ?

Yes. Rather use the poly caps.

Quote
the voltages on the transformer seem ok, but it's more 18-19v

Yes, they are right. Unloaded transformers will be higher in voltage, output voltage will drop when a load is connected. The less it drops, the better the transformer. Can be up to a couple of volts depending how close you load the transformer to its' rating.

Peter
If opportunity doesn't knock, build a door.

Re: help please ? problem powering my green for the first time
« Reply #11 on: July 08, 2011, 06:52:58 AM »
i'll put them on right away and i'll see ...

peterc

Re: help please ? problem powering my green for the first time
« Reply #12 on: July 08, 2011, 07:07:11 AM »
What was the voltage rating on the electrolytic that blew?

If you are getting 18v AC, that will translate to (18 x 1.414)v DC = 25.4v DC.

So if the cap was a 25v cap, it might just not have been good enough & blew up.

I would use 35v caps in this application.

Peter
If opportunity doesn't knock, build a door.

Re: help please ? problem powering my green for the first time
« Reply #13 on: July 08, 2011, 07:18:30 AM »
if that's so it explains a lot of thing ... because the 1000uf is only 10v - but i actually took the one from the mouser link on the BOM ... i paid extra attention to using 100v and 63 where needed, but i wasn't worried about these because it said nothing about special rating ...

Re: help please ? problem powering my green for the first time
« Reply #14 on: July 08, 2011, 08:38:10 AM »
i've had some great help from someone on audiofanzine, i guess once i'll have changed a few components the power supply should be ok ... only then i will see about the preamp itself

- it seems there were two problems
- i had the electrolytic caps where plastic films were recommended (so my caps were probably the wrong way)

and the 1000uf caps were 10v so obviously not enough

so it confirms what peter said

but that also tells me i have a few more things to change on the pre aswell

but it's likely the bridge rectifier has suffered too ...


 

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