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-   -   Marantz CD74 repair advice (http://www.diyaudio.com/forums/digital-source/153383-marantz-cd74-repair-advice.html)

eboy2003 15th October 2009 06:08 AM

Marantz CD74 repair advice
 
I have a Marantz CD74 bought off ebay to repair. It powers up, the laser arm moves, and laser has red light emit and focus action. The display and tray loading mechanism also works, but if I put in a CD, the turntable motor does not spin. I've done basic troubleshooting, checked power supply section voltage and servo MCU clock, and they are all fine. Just got the service manual but seems the turntable amplifier circuit is pretty complicated. Any advice where to start?

amc184 15th October 2009 06:23 AM

Can you tell if the laser has successfully focused? Some CD players won't spin a CD until the laser has been focused.

The CD player might have a service mode that will tell you if the laser can focus or not, but it's a good bet that if the objective lens keeps bobbing up and down a few times instead of less than once, it's not focusing.

oshifis 15th October 2009 09:21 AM

It should spin up before focusing. The motor control board (on the underside of the CDM-1 mechanism) should get +12V supply. If you can identify the motor control wire and apply let's say +1.5V on it from an external source (battery), the motor should rotate. If this is OK, the problem is on the servo board, which is located unfortunately at the bottom of the metal cage, and is not very service-friendly :(

eboy2003 15th October 2009 07:26 PM

Thanks for all the reply. I removed the tray mechanism and check the lens focus action from side during power up with a CD loaded. The lens does move up and down a few times before displaying error on VFD.

When power off, the turn table motor spins briefly, so I guess the motor is OK. The CDM0 servo board is pretty complicated with all discrete components, I don't know where to start. Any advice?

oshifis 16th October 2009 08:53 AM

Check the Brake signal coming from the uCom to the Servo board, pin 8 of J203, see:

http://tube.fw.hu/Marantz5.pdf

You can disconnect this wire temporarily, and see the result.

I had similar problem when I modded my CD-84 by removing the PCB at the back that holds the six RCA sockets. Then I had to short Pin 3 (REMOCON) and pin 4 (GND) of the JT06 connector on the uCom board, that is behind the display. Normally the REMOCON pin should be at 0 volt.

eboy2003 17th October 2009 04:10 AM

I checked pin 8 of J203, it's at 0V, seems normal. :-(

oshifis 17th October 2009 07:15 PM

I think it should be high, but let me check on my player.

eboy2003 19th October 2009 02:33 PM

Quote:

Originally Posted by oshifis (Post 1952606)
I think it should be high, but let me check on my player.

any update? The CD74/84 service manual does not give any reference voltage on testing points, which make it hard to troubleshoot. Many thanks!

oshifis 22nd October 2009 12:08 PM

Sorry for the delay. The player is now in the basement. I try to find out if it still does work at all, then I disassemble and measure some voltages in the weekend.

eboy2003 22nd October 2009 02:46 PM

Many thanks, oshifis!


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