[linux-dvb] Re: distortions on P4 systems (12V hungry?)

[Ragnar Sundblad <ragge@nada.kth.se>]

--On den 28 augusti 2003 17:44 +0100 Edward Wildgoose <Ed@Wildgooses.com> 
wrote:

> I think the
> 12v issue was more one of the ARM chip crashing and hence no more signal
> at all from that point?
In my case, I believe it was the tuner that had problems with
a flaky 12V, I got lots of bit errors and such. I actually
fed the 12V with an external power supply in parallel with
the ordinary feed (do NOT try this if you are not sure what
you are doing, and do NOT blame me if anything bad happens! :-)
and could see the bit errors go down as I cranked up the
voltage and the ripple went down in amplitude.

Sure the ARM crashed too every know and then, whether that
was related to the bit errors introduced or not I don't know.
I think the ARM is only fed with 2,5 V and 3,3 V, so
I doubt that it had any problems with a bad 12V itself.

The SP8870, which has it's own firmware, crashed or hang or
at least stop doing its' thing from time to time too, maybe
more often with a worse signal.

In the DVB-T ALPS-TDLB7 + SP8870 card case, I suspect the
tuner varactor voltage doubler or the tuner 9V feed being
the sensitive parts for the basd 12V.
I am not sure about this though.

(And I still suspect the SP8870 A/D input impedance being
much to low for the ALPS-TDLB7 output impedance, since you
see large dips with the sample-and-hold-A/D frequency on
the signal from the tuner to the demodulator.
I don't know enough about those thing, but I suspect that
an amp on that line would make the reception way better.)

/ragge



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