Pioneer KEX-M900 troubleshooting

vincegironda · 20th November 2020, 09:48 AM

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

Perry Babin · 20th November 2020, 02:28 PM

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?

vincegironda · 20th November 2020, 11:09 PM

Hi Perry I've emailed you the SM.

Perry Babin · 21st November 2020, 12:00 AM

On connector CN751, are pins 104 the points where you had only one clean channel?

vincegironda · 21st November 2020, 05:55 PM

On CN751 there's audio on the FL pin only

vincegironda · 21st November 2020, 06:11 PM

I FL is Pin 1 on CN751

Perry Babin · 21st November 2020, 06:58 PM

That should have been 1-4 not 104.

How do the input and output signals of IC761, 762, 763 and 764 compare?

vincegironda · 23rd November 2020, 12:57 PM

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?

vincegironda · 23rd November 2020, 01:35 PM

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

vincegironda · 23rd November 2020, 02:43 PM

IC 762 no audio in or out

IC 763 no audio in or out

20th November 2020, 09:48 AM	#1
vincegironda diyAudio Member Join Date: Sep 2013	Pioneer KEX-M900 troubleshooting 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

20th November 2020, 02:28 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	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? __________________ Anyone who purchased the repair tutorial, email me (babin_perry@yahoo.com) if you want to download the latest version.

21st November 2020, 12:00 AM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	On connector CN751, are pins 104 the points where you had only one clean channel? __________________ Anyone who purchased the repair tutorial, email me (babin_perry@yahoo.com) if you want to download the latest version.

21st November 2020, 06:58 PM	#7
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	That should have been 1-4 not 104. How do the input and output signals of IC761, 762, 763 and 764 compare? __________________ Anyone who purchased the repair tutorial, email me (babin_perry@yahoo.com) if you want to download the latest version.

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20th November 2020, 11:09 PM	#3
vincegironda diyAudio Member Join Date: Sep 2013	Hi Perry I've emailed you the SM.

21st November 2020, 05:55 PM	#5
vincegironda diyAudio Member Join Date: Sep 2013	On CN751 there's audio on the FL pin only

21st November 2020, 06:11 PM	#6
vincegironda diyAudio Member Join Date: Sep 2013	I FL is Pin 1 on CN751

23rd November 2020, 12:57 PM	#8
vincegironda diyAudio Member Join Date: Sep 2013	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?

23rd November 2020, 01:35 PM	#9
vincegironda diyAudio Member Join Date: Sep 2013	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

23rd November 2020, 02:43 PM	#10
vincegironda diyAudio Member Join Date: Sep 2013	IC 762 no audio in or out IC 763 no audio in or out

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