RCA CDP18S711 VIL Troubleshooting Hints, Other Problems, No Sound, No Display, Signal Tracing

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VIL Troubleshooting Hints

This section is aimed at helping you diagnose and fix hardware problems should they occur. First, check all IC's to make sure they are properly inserted in the PC card. An IC inserted in the wrong direction can be permanently damaged. Check that the +5 V DC supply voltage ripple does not exceed 0.2 volt. Visually inspect the PC card for solder shorts or bad solder joints. Try to avoid zapping your PC card with static electricity charges. Discharge youself, if necessary, by touching a grounded object before touching any IC's or PC card wiring.

Other Problems

Using operating system mode 0, load bytes into RAM using all 16 hex keys. If a key doesn't work or shows the wrong value on the display screen, check the keyboard and U13.

If everything except the cassette interface works, check U14. Review the cassette recording guidelines in Appendix A. Use the cassette phase and data test procedures described in Appendix A to find out what's wrong.

No Sound

If everything works but you don't hear any sound from the speaker you probably have a bad U15, bad speaker, or bad connection. Flip RUN up with key C down. Hold any key down and the Q light should come on. Check the Q line if it doesn't. The Q line should be at +5 V with a key held. If the Q light is on, but with no tone, check U15 and your speaker connections.

If you can run some programs but not others, you may have a bad RAM bit. Load and use the memory test program provided in Appendix A. Try changing RAM chips, one at a time.

If nothing seems to work and you can't run the operating system, check your power supply and PC card wiring for shorts again. If everything still seems OK you will have to start signal tracing.

No Display

If you get no display but do get operating system key tones, check the video output signal. First, select the operating system to make sure video should be present. The video signal should be 0.5 volt peak to peak or higher. You should see negative-going vertical and horizontal sync pulses and positive-going video pulses. The sync pulses should be about 25% of the total swing. Check your display system and interconnections if you have the video signal present. Make sure you are using the correct high-impedance input setting, for example.

Signal Tracing

Check the U3 oscillator output. If not present, replace U3. If the 3.521280-MHz signal is present, check the U4 divider. Replace U4 if it isn't toggling. Make sure you use a 7474 type. With RUN up, you should see TPA and TPB pulses being generated at pins 33 and 34 of U1 If they are not present, check the RUN level to make sure the switch is working, then replace U1.

Check the output of U6B to make sure that the ROM is initially selected when RUN is first flipped