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Old 12th June 2005, 01:55 PM   #1
MaXiZ is offline MaXiZ  Italy
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Default 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...
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Old 12th June 2005, 02:07 PM   #2
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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
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Old 12th June 2005, 03:27 PM   #3
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Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.
I hope that could help...
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Old 12th June 2005, 04:37 PM   #4
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Well, at first glance, it looks like the legs of the LCD are shorted...
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Old 12th June 2005, 05:18 PM   #5
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Led is ok...
I think problem maybe bc546...?
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Old 12th June 2005, 05:32 PM   #6
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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
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Old 12th June 2005, 05:37 PM   #7
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did you also parallel 3 output transistors per rail and not have emmitter resistors connected to each of them?

-Matthew K. Olson
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Old 12th June 2005, 05:54 PM   #8
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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
????????????
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Old 12th June 2005, 06:45 PM   #9
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how about this for clarity....
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File Type: jpg p3a thing.jpg (43.1 KB, 373 views)
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Old 12th June 2005, 06:59 PM   #10
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Q1 VBE = 60V?????

\Jens
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