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-   -   p3a problem (http://www.diyaudio.com/forums/solid-state/58977-p3a-problem.html)

MaXiZ 12th June 2005 01:55 PM

p3a problem
 
I've built some p3a board but some of them don't run correctly...
Without output transistor i've negative rail at the output...
ANy ideas?
If i connect positive and negative i've negative rail at output..
If i connect only positive i've a small positive at output...
If i connect only negative i've full negative at output...

Andypairo 12th June 2005 02:07 PM

It seems that you could have a short somewhere or a transistor inserted the wrong way.... if you don't show us a pic I'm afraid we can't help much.
A pic of the board might do, even better to check the node voltages and send a pic of the schematic with the values written on the nodes.

Did you draw the boards yourself?

BTW it is better, to avoid damages, to provide supply voltages through a 100 Ohm 3-5W resistor per rail when testing amplifiers the first time.

Ciao

Andrea

MaXiZ 12th June 2005 03:27 PM

http://utenti.lycos.it/Maxiz80/DSC00028.JPG
http://utenti.lycos.it/Maxiz80/DSC00029.JPG
http://utenti.lycos.it/Maxiz80/voltage.gif
I hope that could help...

pinkmouse 12th June 2005 04:37 PM

Well, at first glance, it looks like the legs of the LCD are shorted...

MaXiZ 12th June 2005 05:18 PM

Led is ok...
I think problem maybe bc546...?

Mattyo5 12th June 2005 05:32 PM

According to that schematic, you've got +30v AND -30V in the SAME PLACE on BC546. Two different voltages can't exist at the same time in the same place. I'm not great w/ terminology but it looks like thats the base of bc546 thats got both +30v and -30v at the same time...so which is it?

-Matthew K. Olson

Mattyo5 12th June 2005 05:37 PM

did you also parallel 3 output transistors per rail and not have emmitter resistors connected to each of them?

-Matthew K. Olson

MaXiZ 12th June 2005 05:54 PM

According to that schematic, you've got +30v AND -30V in the SAME PLACE on BC546. Two different voltages can't exist at the same time in the same place. I'm not great w/ terminology but it looks like thats the base of bc546 thats got both +30v and -30v at the same time...so which is it?

-Matthew K. Olson
[/QUOTE]


NOOO! :) One reffer to base and the other reffer emitter.

Quote:

did you also parallel 3 output transistors per
????????????

Mattyo5 12th June 2005 06:45 PM

2 Attachment(s)
how about this for clarity....

JensRasmussen 12th June 2005 06:59 PM

Q1 VBE = 60V?????

\Jens


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