Re: [softrock40] SDR40 v6.1 TX/RX stopped working
- Hi Tony, I searched for and found my digital thermometer and took readings on the unit as follows:U1 69.4 FU2 69.2 FU3 72.6 FU4 95 FU5 77 FU6 74.6 FU7 79.3 FU8 86 FU8 pin 7 reads 4.2VIan
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>U8 86 FAt 2:44 am ((PDT)) Thu Aug 2, 2007, in Digest 1865 Tony Parks wrote:
>U8 pin 7 reads 4.2V
>Sure looks like U8 is a problem.Perhaps, but output near the +ve rail could be:
a) inputs driven to output saturation
b) output pulled high externally (i.e. by a pins 7-8 short)
c) device failure which also emulates (a) or (b).
Both (b) and (c) can explain the U8 heating
but only (c) is that device's fault.
(There's no source for the heating current in case (a).)
Meanwhile, none of these explain why:
d) Q9 ran hot and
e) Q9 replacement ran hot
This doesn't seem to be in a related part of the circuit,
so was Ian just unlucky with two rogue 2N3904?
[BTW, my apologies for saying that Q9 collector pad voltage
3.63V with Q9 removed seemed too low. I recalculated as
3.64V - within the DVM last digit uncertainty.
(Vcc-Q8vbe) * R40/(R35+R40) + Q8vbe =
(4.32-0.65) * 22.1/(4.99+22.1) + 0.65 = 3.64V ]
>Let me know what components you need to restore your boardI continue to admire your outstanding support for this project;
>and I will send them right away at no cost.
"May Great Leader Tony live ten thousand years!"