The machine boot image and sound normal, 10 minutes after the first random black horizontal bar on the screen, after 3 minutes into black, but the sound has been normal; black by remote control or on the machine panel button, there is no character display.
The failure reasons: 1. Black screen failure is generally depending on the cut-off, video channel circuit with damage to the components; 2. Blanking pulse signal is not added to the DG (digital) box; 3. The filament voltage without CRT projection tube.
Because the black screen is not getting dark, and the first black stripes, so not the filament voltage problem.
The DG box is the core of video signal processing, maintenance should be black, from the DG box socket measure hand. The output video signal DG socket box the a44 26, 27, 28 pin is r, G, B trichromatic video output pin, the normal should be 3.5Vp-p, measured only is 1.5V DC voltage, there is no video signal.
The 11 pin and 59 pin of the socket DG is the input of the main video signal of the A44 box, and the 69 foot is the sub video signal input terminal of the DG box, and the measured data are normal video input signal (2.3Vp-p). Now the DG box has a video input and no output, apparently in the DG box.
Video signal output IC is IC1309 DG box, RGB video signals from IC 13, 15, 17 foot input (pictured above), and IC 3, 4, 5 feet input tricolor character mixed signal, from IC 7, 9, 11 feet output. The 13, 15, 17 feet have normal 0.5Vp-p video input waveform, but the 9, 7, 11 feet only 1.5V DC voltage, no video output. It is clearly that the IC1309 interrupt the video signal pathway. Because IC1309 itself caused by damage to the video signal interruption, the control voltage or IC1309 input does not normally cause no video output Nick?
This will be a full test of the voltage and the waveform of the foot of the IC1309 to determine the fault location.
IC1309 19 foot line blanking pulse input pin, normal should be 3.3Vp-p pulse (pulse base is 0V, pulse top is a 3.3V, the cycle is 32 Mu s), measured in black screen when the signal into 2.8V DC voltage, 2.8V DC voltage is superimposed on a 0.5Vp-p of small amplitude pulses. Obviously, the control circuit of the 19 foot has a failure. The high level of IC1309 (19) foot from the D1304, along the circuit to look forward, it is found that Q1310 is bad, will replace Q1310, troubleshooting