[hpsdr] Anyone help with a-12v problem with LPU?

[Scott Cowling]

Hi Domenic,

Make sure that jumper JP1 is NOT installed. The jumper disables the 
-12V supply.

If the jumper is not there and you still get no -12V, make sure R1 is 
installed and you have input voltage (+12) on U4 pin 5.

Next I would check the resistance of F4 to make sure that it is not 
open (or high-resistance, since you do get some output). Also check 
to make sure that D1 polarity is correct (which it probably is, since 
you do get some negative output).

Check the feedback circuit (R2/R3) and make sure you have a negative 
voltage on U4 pin 3. It should be about -1.3V if things are working correctly.

No HPSDR modules use the -12V bus except Janus.

Good luck!

73,
Scotty WA2DFI

At 10:58 PM 3/27/2010 +0000, you wrote:
>***** High Performance Software Defined Radio Discussion List *****
>
>I've clearly made a mistake building my LPU, but I can't spot where. 
>I've checked all the obvious things - polarity etc.
>
>It's with the -12v supply from U4 - the others are fine.
>
>When I plug the LPU into my bench supply and slowly turn up the 
>voltage from 0v, I see -5v on the -12v output when the input voltage 
>of the LPU is less than around 7v.
>
>Above 7v into the LPU, the -5v I see above starts to fall back, 
>until it drops to completely nothing at an input of 10v plus.
>
>Any help as to the likely source of the problem would be much 
>appreciated - it's so frustrating not being able to put it into use yet!
>
>Thanks all,
>
>Dominic G6NQO.
>
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