Hi all,
I'm currently restoring a KEX-M900 which came to me as a dead unit.
So far I recapped the DC to DC converter
Recapped the main board, ASL board and DSP board
The unit now powers up, display is good, all menu's working too.
The problem is the unit has 4 pre outs and I have only one channel with good clean audio.
I would like some pointers on tracing the audio path to see if I can find where it's losing audio signal to the dead channels.
What I know so far-
I've tested 2 audio sources
Cassette working fine
Aux input working fine
Both with the same result - audio on one channel only
The dsp board is labelled FR FL RR RL where it outputs to the main board and into the ASL board, I intercepted the signal off all 4 channels and it's only outputting audio on one channel so I think the problem lies within the DSP board or maybe just before it?
I've come this far so would really like to troubleshoot and find the problem, any help or suggestions appreciated
I have a service manual pdf if required
Thanks in advance
I'm currently restoring a KEX-M900 which came to me as a dead unit.
So far I recapped the DC to DC converter
Recapped the main board, ASL board and DSP board
The unit now powers up, display is good, all menu's working too.
The problem is the unit has 4 pre outs and I have only one channel with good clean audio.
I would like some pointers on tracing the audio path to see if I can find where it's losing audio signal to the dead channels.
What I know so far-
I've tested 2 audio sources
Cassette working fine
Aux input working fine
Both with the same result - audio on one channel only
The dsp board is labelled FR FL RR RL where it outputs to the main board and into the ASL board, I intercepted the signal off all 4 channels and it's only outputting audio on one channel so I think the problem lies within the DSP board or maybe just before it?
I've come this far so would really like to troubleshoot and find the problem, any help or suggestions appreciated
I have a service manual pdf if required
Thanks in advance
I don't have the SM. Have you tried heating/cooling the various components in the circuit to see if it made a difference with any of them?
That should have been 1-4 not 104.
How do the input and output signals of IC761, 762, 763 and 764 compare?
How do the input and output signals of IC761, 762, 763 and 764 compare?
Hi Perry so before running the tests you suggested I tried tracing the signal further back to IC703 according to the schematic there should be audio on pins 19 and 27
Pin 19 has audio
Pin 27 has no audio
Would it be safe to assume the issue lies with IC703?
Pin 19 has audio
Pin 27 has no audio
Would it be safe to assume the issue lies with IC703?
IC 764 has audio on pins 1 and 7 out
and in on pin 5 no signal in on pin 3
IC 761 has no audio in or out
and in on pin 5 no signal in on pin 3
IC 761 has no audio in or out
I also tested the outputs on IC760 and IC765
IC760 has clean audio on pin 25, and low distorted audio on pin 19
IC765 has no audio on pin 25 or pin 19
IC760 has clean audio on pin 25, and low distorted audio on pin 19
IC765 has no audio on pin 25 or pin 19
What page is IC703 on?
If you have audio on the output terminals of 764, that's what's important. If the op-amp is working properly, you won't see signal on the inverting input unless you go back to the resistor in series with that input.
Does heating/cooling any of the DACs make a difference?
If you have audio on the output terminals of 764, that's what's important. If the op-amp is working properly, you won't see signal on the inverting input unless you go back to the resistor in series with that input.
Does heating/cooling any of the DACs make a difference?
thanks Perry IC703 is on page marked 19, fig 13
I'll try heating and cooling the DACs and let you know if it helps
I'll try heating and cooling the DACs and let you know if it helps
So is it safe to assume if IC 764 has audio on the output terminals then the problem lies further along the circuit after IC764?
You have one good channel, correct? Isn't the one good channel?
I'd think the problem is before the op-amps.
You might try injecting signal into pin 5 of the other 3 op-amps to see if it passes cleanly.
I'd think the problem is before the op-amps.
You might try injecting signal into pin 5 of the other 3 op-amps to see if it passes cleanly.
Correct, I have clean signal in one channel only
Can I pick up the signal from IC 764 and inject into the other ic's?
If yes do I pic up the 764 input signal or output signal?
Can I pick up the signal from IC 764 and inject into the other ic's?
If yes do I pic up the 764 input signal or output signal?
So Perry I did as you suggested and injected signal from 764 to the other 3 DACs and found
761 produced clean audio
762 produced clean audio
763 no audio and it muted the signal from 764.
Looks like 762 is defective, shall I remove it from the circuit and see what happens?
761 produced clean audio
762 produced clean audio
763 no audio and it muted the signal from 764.
Looks like 762 is defective, shall I remove it from the circuit and see what happens?