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From: clicliclic on 2 Feb 2010 16:31

Hello!

A ten year old color TV set of mine with vacuum picture tube has
recently lost its horizontal synchronization: the display shows the
corresponding diagonal stripes, slanting from left to right. Vertical
synchronization is functional however.

The entire video processing of the set is done by a Micronas VDP3116B
processor in a 64-pin shrink-DIP package. I have checked those external
voltages and signals that appear to be vital for its proper operation,
and they all looked ok. The only symptom of misbehavior is that, with a
video test signal with a synch-to-synch pulse distance of 63.9 us fed
into the VDP default video input pin 63 (VIN3), the output signal on pin
50 (HOUT) shows the shorter period is 63.1 us, where a duty cycle of 50%
moreover confirms the lack of synchronization, according to the VDP
datasheet. The synch signal output on the unused pin 7 (FSY) has the
wrong period of 63.1 us too, but here the duty cycle is around 7%, which
looks ok.

The VDP3116B is configured by the control processor (an ST92R195) of the
TV set via an I2C-bus interface; disconnecting the interface lines and
using a hardware reset on the VDP3116B didn't restore horizontal
synchronization (I believe the VDP default parameters should suffice for
synch extraction). Nor did a replacement of the VDP3116B chip restore
horizontal synchronization!

A wiring diagram of a closely related TV model is available at
<http://www.eserviceinfo.com/downloadsm/983/Schneider_TV9.html>, almost
everything of significance here is in agreement with my board). A 1998
version of the VDP3116B datasheet can be found at
<http://www.alldatasheet.com/datasheet-pdf/pdf/101251/MICRONAS/VDP3116B.html>.

Any suggestions? How can a working Micronas VDP3116B loose its ability
to extract the horizontal synchronization of the input video signal?

Martin.
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