[linux-dvb] Twinhan VP-1030C Diseq problem

Manu Abraham abraham.manu at gmail.com
Wed Jul 25 01:58:15 CEST 2007


On 7/25/07, Manuel Kampert <manuel.kampert at online.de> wrote:
> As my original explanations with detailed findings have not been allowed
> to post to the list I will just put some letters and say that I have
> found the root cause of this issue .. It seems that the diseqc signals
> especially on the 17V transponders are such bad that the diseq did not
> recognize them anymore. This became even more problematic with my new
> machine and new PSU...

Normally, for a LNB polarization control you use a 13/18v control
voltage. In _all_ cases a DC-DC converter is used to generate the
polarizer control voltage aka H/V control

With a normal PC SMPS (with regards to PCI DVB-S cards, power is drawn
from the PCI bus) there is usually 2 voltage rails that can be used to
power the DC-DC converter.

Usually the 5V rail is used normally on almost all cards, since it can
source more current.
To obtain a reliable 18v in most of the cases the voltage is pumped up
to say 24v or 30v
the conversion amounts to say around 5 - 6x. Now if your SMPS delivers
a voltage lower than 5v, then the voltage to the polarizer also will
drop.

This is not the case with cards that have a SEC chip, ie they use an
internal PWM regulator where say an additional higher voltage maybe
generated to compensate for the loss. With this said, we have issues
in other cases where we have aging capacitors, where the multiplier
fails due to the aged capacitors.

The best thing to do is check what voltage you have on the 5v rail on
the SMPS of your new computer. Also check whether there is a
significant difference between the old SMPS to verify this thought.

If there is a difference, simply replacing the SMPS would probably help.

Some wandering thoughts that flew by.



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