[vdr] Re: burned DVB-s

[Thomas Breuer <tb@tb-electronic.de>]

Hi Roberto,

I have some hardware info + questions on the AV7x. I already asked
around for the technical data sheet of the chip. Do you know if this is
available? I only have the PDF with the "Functional Specifications".
Actually, I am only interested in the schematic of the output stages.
Any info on the outputs only would be great as well.

On 18/10/2002 11:14 Roberto Deza wrote:

> I'm sorry by your card but I don't have any hope that this problem can
> have any recovery, if your card is really damaged :-( ; the Composite
> Video goes out directly from the AV711x and any semiconductor is very
> easy to broken.

Some time ago I had a rev 1.3 card here which had been killed by
applying 12 volts to the composite output. The result was a short
between the supply pins of the AV7111, so the card was useless.
However, by applying a current of several amps into the dead output, I
was able to remove the short. The output is still dead, of course, but
the DSP is functional again and the card can still be used as a
secondary card now.

Most likely there are clamping diodes from each output to the supply
rails, one of which had been molten when the 12 volts had been applied.

I can not understand why even the original composite cinch output goes
directly to the chip (well, there are some caps plus one coil in
between, but there is *no* DC discoupling). I made some scope
measurements and found that all four outputs are actually constant
*current* outputs rather than voltage outputs. There is a constant DC
current of approx. 5.5mA to ground even if you add additional series
resistors of up to 70...80 ohms between the output pins and the 75 ohms
load of the TV inputs. Also, all video signal levels will stay constant
at the 75 ohms load independent of the series resistors! Therefore, I
run my primary card with additional resistors (47 ohms) now, this will
at least help to limit currents into the output pins in case of any
external voltages being applied ...

As I plan to add a video multiplexer (with MAXIM chips) to my box, this
problem will be solved anyway.

>> There  are  the  connectors J3,J4 (for CD-audio) and J8. Is it
>> possible to connect the tv set via J8? (I'm afraid, no. right?)
>
> You are right, is not possible. Nor in a revision <2.1, with J2, could
> have much hope, as there is only *one* Composite Video output coming
> out of AV711x, wich is also need on the RGB (for the TV Syncs) and
> S-VIDEO modes.

I read the postings of you and some others regarding the attempts of
identifying the RGB outputs pins for rev 2.1 cards back at the beginning
of this year. Well, the pins *are* available! There was a request in the
German newsgroup de.science.electronics back in July which triggered me
to take a close look at my rev 1.3 card. The outputs are located
as follows at the outside of the thin PCB which carries the chip
(take the wide gold track at one of the edges as a reference as seen
here: http://www.christoph-roell.de/dvb/vergl.html)

O = via, | = track without via

O||O|||O||O|||O  O| GOLD
R    G    B

So R and B are available at vias, while G is only available at a track
between two other tracks. Soldering connections for R and B should
be possible, but a making a connection for G will be very difficult.
I don't know if this is of any practical use, but if I had a rev 2.1
card only I would give it a try ...

Thomas










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