Question about Hitachi 50SBX70B 50" Rear Projection Television
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 OSD processor.
Posted on Jan 04, 2008
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