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uedat125

M9 no sound hardware repair experience

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I thought I’d share my experience with a non-working M9 which I successfully repaired myself.


I auctioned off a M9 described as faulty, no sound,. The owner used it for a long time and when he powered it on for the first time in about a year, it failed to produce any sound.

Uppn receiving I pluged in and confirmed the condition where the LCD and switch indicators light up normally and function as expected but no sound. However the sound would come through when the effect was bypassed via tru-bypass, but not a humming noise when it’s on, so I figured the input/output and their relays are okay, and on an assumption that the trouble was somewhere around the DSP, I began probing the test points for voltage. I found +12V power was not there in the analog amp section and spotted the DC regulator “2SC1623-L4” (D23) was faulty. However it’s an old transistor rather hard to find. Eventually it was found at a Chinese parts shop Aitendo in Akihabara where I’d been a few times, but they only had “2SC1623-L6.” Crossing my fingers that the circuit design wasn’t so strict I bought a strip of them and managed to replace the faulty one with a new one which is smaller than a grain of rice. Having seen the correct voltage at the test point,  I connected the guitar and amp to hear colorful sound fly out of the box. It was worth the perseverance in the research and craft. 

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Nice work I had the same problem on my m9 and got the transistor L6 and replaced it and it work now I have a question I have the same problem on my m13 the very same tried to look for the d 23 transistor but on this unit d23 is a diode is the analog amp section under the ic chip 2374 A ? Any help would be awosome thx 

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Hi pepethebull,

 

Congrats on successfully repairing your M9. I have an M13 which is a working unit, I haven't gone far as to opening it up,  but I'd examine voltage around the audio section by checking out all the test points, as the circuit design may vary. While you have the power on, check the test points, then if all check out okay,  check the semi-conductors visually for any indication of burnout. Also make sure that the tru bypass is working to eliminate possibility of relay or coil burnout. I've had a faulty inductor in a Tonecore, FWIW.

 

Best of luck!

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Hi uedat125,

i have the same problem with my m9,so i check the pcb,i see there is 2 ic jrc2374 burnt,so i replace them with good one,but problem still, no effect sound,blank light screen.

L4 seems good , and +12/-12 test  normal,i dont kown what to do next,would you help ?thank you.

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Hi Wtfusay

 

I would try to separate issues.

First check the connectors between PCBs.They can come loose over time and quite often the problem.

 

If the sound is there but no display, make sure the display driver has the right voltage. 

 

If there’s no sound, check the input/output for potential disconnect, or any indication of small piece of metal/solder  bridging input and the ground. 

Chances are that the IC/transistor you’ve replaced had fault in itself or  not in good contact.

 

Check all test points for correct voltage. 

 

Check any indication of dead IC/transistors. It could be resistors or caps, by the way.

 

If there’s a faint sound coming from the output, check the op amps and power amps.

 

All these things will require patience, but remember that the circuit once worked well and there’s probably one disconnect in the path of the guitar signal. 

 

Good luck!

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Wow, thank you very much, that's very nice of you, i'll try.

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