Question about Sony CDX-M800 CD Player
Thanks for the reply re the Sony cdx m800 with no displays. As I say the ribbon cable has been fitted correctly & has not cured the problem, like you suggest I think it has a problem on the front panel as everything else works fine. Yes I am an electronics engineer & have all the necessary tools & power supply. So if you can give me any help or suggestions that would be great. I don't think it is the lcd as both displays are out, I assume it is a missing supply problem.
I think you are going to need the service manual to properly troubleshoot this. You can try to follow these instructions without one, but having one makes it so much easier. You will need to have the radio on a work bench with the CD mech out and the harness out of the car as well so you can turn on the radio and check some voltages. Since you are an electronics engineer, I should not need to point out any safety precautions, after all, I am just a technician.
For starters, check the voltages at pins 7,8,15,16,17 on connector CNP909 the 24 pin connector for the display on the main board. Pin 1 should be the one closest to the corner of the board that connector is near. Pins 7 and 8 should have 10 volts each, pin 15 should have 5 volts and 16 and 17 should both have a much higher voltage. I suspect you may be missing the 10 volts from pins 7 and 8. If so, check the voltage at the emitter of Q914 on the main board. It is a digital transistor (surface mounted) and when the power is on it should have 10 volts there and 10 volts on the collector and zero volts on the base. If any of those voltages are not there, check Q915. It should have 10 volts on the collector, 5 volts on the emitter and 5.6 volts on the base. It is not a digital transistor but is surface mounted and much bigger than Q914. If you are missing the 5.6 volts on the base, check the zener diode D905. It should have 5.6 volts on the cathode and ground on the anode. The cathode goes directly to the base of Q915. Use your multimeter on the diode check mode and see if it looks normal. Could be that zener diode is shorted. There is also 2 capacitors in parallel with that zener, C928 and C930, check those as well. If one of them shorts out it will look like the zener is shorted.
You can also check CNP805 for the 10 volts, it is supposed to be there as well. I don't know what pin number but I think that connector is on the top of the board. The 10 volts should be either pin 5 or pin 7, depending on which side you start at. CNP805 is the connector for the sub-board with the reset switch on it. After you know what these voltages are on CNP909 we should be able to narrow down the problem.
I hope this helps, I really do not have a lot of time right now. I have a power supply to fix and a big stack of car amplifiers to repair. Let me know if you need more help, I just may not be able to answer as quick as you may like, but I will answer when I have time.
Posted on Jan 27, 2009
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