[Ronja] nebulus test points don't match

[Gullik Webjörn]

On Sun, 2009-08-02 at 01:17 +0300, mohamad al-jamal wrote:
> come on guys , i need help here
> 
> 
> On Sat, Aug 1, 2009 at 2:28 AM, mohamad al-jamal
> <mohammadaj at gmail.com> wrote:
>         Hi 
>         
>         I've just finished building my nebulus Tx , following the
>         exact instructions in the guide to the last detail , except
>         for the zener , where i used a 7.3V instead of 7.5
>         as i couldn't find one  . but the "DC - no signal" test points
>         didn't  match , i rechecked the connections , and tested the
>         parts before placing them , and afterwords, 
>         but there are differences , 1.3 V for P7 for example !! here
>         are my results : 
>         P1   1mV
>         P2    5.55 V
>         P3    4.88
>         P4    5.58
>         P5    9.88
>         P6    4.21
>         P7    5.00
>         P8    0
>         P9    1mV
>         any help is highly appreciated 
>         
>         

	P1 = 1 mV ?? Do you have a proper AUI connected at coax input?
	P2 = 5.55 V, well, 7.3 - 0.7 = 6.6V, do you have 7.3 at D2?
	P3 = 4.88 V, well 5.55 - one VBE 0.7 V, seems OK
	P4 = 5.58 V, derived from P2, higher than P2 ???? with or without
signal ??
	P5 = 9.88 V, reasonable, 9.88n - 4.88 = 5 V over Q2 VCE
	P6 = 4.21 V, I should have expected same as P7, something taking
current, broken IC U1, U2 or U3??? 
	P7 = 5.00 V, 7.3 - 1.4 ( 2 * VBE) = 5.9, a little low, how much current
does nebulus take?
	P8 = 0, very reasonable with P6 at 4.21 V
	P9 = 1mV, well, if P8 is at 0, then P9 should also be 0 V, 
		since P9 is voltage drop over R17, and with no voltage 
		out of the driver ICs you do not get any current, thus 
		no voltage drop.

In all, your circuit looks good, BUT, it looks like your U1-U3 are
taking input current, which they should not, (P6=4.21 V) so maybee you
broke one of them. I would have expected P6 = P7 (+/-) 50 mV, with no
signal. IF you have a signal, the difference might be OK, depending
on signal duty cycle....

So, with input signal disconnected P6 = (almost) P7, WITH signal
lower, i.e. 4.21 V might be OK.

Hope this helps

Gullik
>         
> 
> 
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