This update covers to the following Hitachi
models and chassis
46UX50B/51K, 50UX52B/53K, 60UX54B/55K, 50SBX70B, 60SBX72B, 70SBX74B. All projection
televisions using the AP73 & 74 chassis's From Dennis Viereck
Intermittent loss of Raster, On Screen Display,
sometimes sound. BUT ALWAYS HAS HIGH VOLTAGE! Also removing power and
reapplying it again restores operation.
THE PROBLEM: There is a lack of a secondary
ground for the CRT Dag connected to each CRT board. You can identify this missing ground
on the CRT board by locating two vacant pins on each CRT driver board near the CRT socket.
The connector is named P801, P831, and P861 relative to each board. The pin nearest the
socket is the ground pin in question. The pin furthest from the socket is connected to the
cathode of the CRT.
OBJECTIVE: Run a separate ground wire from the
"GROUND" pin on each CRT board to the chassis ground. You can use the circuit
board mounting screw on the frame under the green CRT. See drawing below.
DIRECTIONS: Obtain 3 wires 10, 14, and 18
inches long. The wire is 18 gauge stranded with an insulated jacket. Attach one wire to
each ground pin on the CRT socket. Choose the correct length of wire so that all wires
will connect to the circuit board mounting screw near the center of the chassis frame.
EXPLANATION: The extra ground is needed if an
internal arc occurs in the CRT. This energy must find a path to ground. Before, the only
path to ground is through the signal ground wire on the RGB drive connector. This thin
wire does not go directly to chassis ground and is inadequate ground for the CRT dag. If
the energy level of the discharge is high enough it may corrupt the data flow on the data
& clock lines or negatively effect the OSD microprocessor. Since electricity takes the
shortest path to ground, the additional ground wire will route the majority of that static
pulse to chassis ground quicker and reduce the possibility of corrupting operation of the
Nov 12, 2007 |
Hitachi 50SBX70B 50" Rear Projection...