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Posted by Mark on 12/15/06 16:20
Mark wrote:
> Notes on Accurian ADR 3223 DVR.
>
> This unit is a clone of some popular Lite-on units. My brand new unit
> had a bad video hum associated with the built in NTSC tuner. I took it
> back and got a new unit and the new one had the exact same hum. The
> hum was associated with the video and was worst with white scenes. I
> examined the built in NTSC mono video tuner. It uses a Sanyo LA75676
> video demodulator chip. The data sheet for the chip indicates that Pin
> 2 is the power supply filter bypass pin for the audio FM detector and
> Sanyo recommends a 1uF cap to ground. The tuner had a small chip cap
> connected to pin 2. It may be 1 uF, I could not tell. I added a 68uF
> filter cap to ground and the hum is greatly attenuated. The hum is
> not caused by the 60Hz power line but is crosstalk from the video via
> the internal power supply in the LA75676 demodulator chip.
>
> (Note there can be many causes of hum. This particular hum can be
> identifed because it changes with the video. Very white scenes cause
> more hum, dark scenes cuase less hum. If your hum is not like this,
> then it is a different problem.)
>
> The built in tuner is a small sub assembly that can be easily unplugged
> from the main board by removing the back panel. Note the screws are
> of different types, keep track of where they go when you take it apart.
> The LA75676 can be accessed by removing the shield cover on the bottom
> side of the tuner can. The cover cannot be completely removed but can
> be bent back a little enough to get in and tack solder a small wire to
> pin 2 of the IC. Then a capacitor is added outside the shield can
> attached to the small wire. This is a small 24 pin SOIC. Don't try
> this unless you are good at soldering small SMT type parts.
>
> Fee free to forward/post this info to however needs it.
>
> Mark
Subject line corrected
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