Posted by
Don Wilhelm-4 on
Sep 12, 2007; 10:48pm
URL: http://elecraft.85.s1.nabble.com/voltage-display-problem-tp452774p452778.html
Joe,
These symptoms are possibly (but only indirectly) caused by a defective
U6. The firmware is the major element in the power control system, but
from your other conditions, it is difficult to pinpoint - if indeed the
power control circuits were the cause for low power, that would not
cause a high current draw - in fact the current draw would be low rather
than high.
Your D6/Q1 statement is a bit confusing. Check the 8T and 8R voltages
at D6 and D7 anodes as well as the collector of Control Board Q1 and Q2
for both the receive and transmit conditions. The voltage at the anode
of D6 is 8R (through RFC12) and CB Q1 is the 8T control transistor. 8T
is at a high voltage (8 volts nominal) during transmit and 8R is at a
high voltage during receive - they should never be on at the same time.
High Current is usually a problem associated with the low pass filters
or T4, but resolve the 8T/8R situation first because if both are active
at the same time, high current could result.
73,
Don W3FPR
MARY HAYS CARNEY wrote:
> Don:
> Thanks for the quick reply. Indeed the voltage at pin 5 of U6 is as expected (2.31 for 11.9 v in).
>
> To be sure: the firmware chip is U6, on the control board?? I'll replace that and see what happens.
>
> If I may continue with my litany of problems since they may well arise from U6(ctrl brd):
> The receiver works well but problems show up on transmit. On initial test, it indicated excess current even at lowest power setting. After several trials, it would no longer switch to transmit. (The voltage at D6 anode rises to about 4 v then drops in spite of having 7.9 v at the emitter of Q1 (ctrl brd)). Pin 2 of U8 (ctrl brd) remains at 0 v though there is 0 v at the rf det on the rf brd. Right now I'm not ruling out a problem from Q5 through Q8 on the rf brd, which may have fried U6 (ctrl brd), so I'm still looking.
>
> Are these problems compatible with a faulty U6 or do I need to continue looking?
>
> joe carney KB3FBR
>
>
> If you find the voltage going into U6 pin 5 is the same as at U3 pin 7
> and your voltage display still says 23.3, the only cause can be a bad
> input on U6 (in that case, you need to replace the firmware chip).
>
> 73,
> Don W3FPR
>
>
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