Marantz CD74 repair advice - Page 2 - diyAudio
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Old 22nd October 2009, 10:57 PM   #11
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Default cd74 problem

Hi all.I have the same problem with my Marantz cd-74.Laser is work but motor not working.I can't find solution.Can anyone help me?Thanx
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Old 24th October 2009, 07:30 PM   #12
oshifis is offline oshifis  Hungary
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Quote:
Originally Posted by oshifis View Post
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.
Well, I measured the BRAKE signal with an oscilloscope: it is 0 normally, and it goes up for a short time when the spin motor has to be stopped, then goes back to zero. This signal can be measured on the uCom PCB "in situ" (grey wire).

The motor is connected to the PCB with two wires. The easiest check of the motor functionality is to disconnect these wires and apply some voltage from a 1.5V battery. The motor should rotate. Check both polarities, it should rotate clockwise and counter-clockwise. If there is too much mechanical friction (due to dry grease, etc.) it can be felt by manually rotating it. There is a plastic screw, adjustable with a Torx key. It supports the rounded end of the spindle. The position of this screw sets the platter height, it is critical.
If the motor is OK, the problem might be in the servo board (lower PCB), or possibly the motor driver IC. I can measure some more voltages, just tell me where and what.
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Old 25th October 2009, 06:43 PM   #13
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Quote:
Originally Posted by jimmyhumuhumu View Post
Hi all.I have the same problem with my Marantz cd-74.Laser is work but motor not working.I can't find solution.Can anyone help me?Thanx
I have another friend with CD84 has the exact same symptom, laser is working but motor is not spinning. It happened after he swapped the CDM0 laser. It seems these CD74/84 has some weak link somewhere in the servo PCB. I will spend some time today to troubleshoot and hopefully we will find a solution.
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Old 25th October 2009, 10:58 PM   #14
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I spent some time to troubleshoot today. The turntable motor circuit is mainly driven by two signal: MCES and FCO. The FCO is the focus on signal and it is at high (4.4V DC). The MCES signal is zero, on scope I only see about 200mV noise signals. But according to the doc, it's supposed to be 88.2KHz square wave at standby, 44.7KHz at run up or play time, while run up time has more duty cycles. MCES signal comes out from SAA7020 pin 4. I checked SAA7020's clock (pin23, 4.2336MHz) and power supply (pin1 at -2.4V, pin21 at +11.85V, pin40 at +4.89V), all these are normal. I suspect the SAA7020 is dead.

Oshifis, I downloaded SAA7020 and related chip's datasheet from your site, thanks for all the info. Can you check your CD84's SAA7020 pin4 MCES signal and all pins voltage during standby and play time? I don't have another SAA7020 to try right now, but if I can confirm it's the SAA7020 problem, I will try to get one.

Last edited by eboy2003; 25th October 2009 at 11:00 PM.
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Old 26th October 2009, 08:04 PM   #15
oshifis is offline oshifis  Hungary
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I measured the MCES signal: it starts from zero, then goes into a square wave with variable duty cycle. But this signal just controls the motor speed once the PLL SAA7011 is locked. The motor should rotate without this control signal until it reaches the PLL's pull range. I think the problem is not here in your machine. I'd check Q233 and Q234, D245, Q401 and Q402, and the Q209 IC. The TM- signal from the SERVO board (P200 PCB) directly supplies the motor with variable voltage. Check this voltage somehow at the common emitters of Q233 and Q234. As I said it is not easy because this PCB is at the bottom. I soldered some colored wires at specific points, then assembled back the metal frame holding the PCBs, so that I can measure some signals during normal operation.
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Old 26th October 2009, 10:00 PM   #16
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But isn't MCES signal is generated by SAA7020? If it does not generate this signal at all, must be SAA7020 and surrounding circuit has problem. I checked TM- voltage before, it's at 0V.
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Old 27th October 2009, 01:20 PM   #17
oshifis is offline oshifis  Hungary
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MCES is generated by the SAA7020 indeed, but as long as the speed of the TT motor is below nominal, this signal is 0. If the motor rotates around its nominal speed, this signal alternates between low/high and the duty cycle controls the motor speed.

A good example is when there is no disc in the tray. The laser focus action takes place and the motor rotates at full speed for a while, because MCES stays low.
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Old 28th October 2009, 04:19 AM   #18
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I thought SAA7020 still outputs MCES signal during standby (no motor spin).

I desoldered Q233, Q234, D245, Q401, Q402 and Q209 IC to test them, but they are all good. :-( All surrounding resistors are fine as well. After I solder them back, the symptom is still the same. I also used a battery to test the motor, and it does spin properly.

Other than generated by SAA7020, it seems the MCES signal also is output from pin2 of Q205, I don't know if it has anything to do with the initial spin up.
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Old 28th October 2009, 10:43 AM   #19
oshifis is offline oshifis  Hungary
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I read somewhere that such problem might be caused by the 5 pcs 33uF capacitors on the laser PCB. The ususal recommendation is to replace them all. In my device they are blue axial electrolytics.
Other than this, the servo PCB gets -12V on the J204 connector pin 6 when the tray is closed, check also this voltage.
The motor is "kicked in" by the FCO signal coming from Q201 through C214 22uF/16V, I would check also this capacitor.
Sorry, it is difficult to point at one component, because everything depends on the proper function of other parts in this player.
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Old 30th October 2009, 06:34 AM   #20
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Desoldered C214 and all 5 33uF caps on laser mechanism PCB and they all tested good. Also replaced Q205 (LM339) and UA741 on laser PCB and still no help. I run out of ideas. :-(
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