Question about Marantz PM-68 Amplifier

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Heat in operation of marantz pm 74d

Would you please show me if this is normal. Should it be equipped with a fan?
Sometimes the left speaker is noisy and nearly mute after playing appx. an hour. In the meantime, I restart the amp. and it is OK again.

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Sounds like your left channel output transistors are getting weak.

Posted on Jan 17, 2009

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Marantz pm 7200 loudspeakers do not cut off when headphones pugged in


Some amps have a button which you press to mute the speakers when the headphones are plugged in. Sometimes marked "Speakers on off". If it hasn't then a new headphone socket would not be expensive to fit. As long as the amp producers sound I don't see any future problems. The previous owner may have used the headphone socket a lot, and simply wore it out!

Jul 19, 2012 | Marantz Amplifiers & Preamps

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RIGHT HAND SPEAKER WONT WORK


If you get scratchy sounds while doing so, the potentiometer needs replacing. If not you could check the solder joints for it and see if its loose. You could just resolder it if that's the case.

Nov 15, 2011 | Marantz PM-68 Amplifier

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I have a Marantz AV Receiver SR 3053 with Pure Acoustics speakers purchased as one. Just today, when the unit is power on and pressed the button for power ON, there is no display and the stand-by indicator...


Generally speaking, an amp attempts to protect itself from heat, shorts, overloads and operator exuberance by refusing to turn on or stay on.

Overloads can be from excessive periods of high output or marginally low impedance loading by the speakers; and shorts would be wiring issues or a speaker blowing up.

You should be able to feel if it's hot. WHY is it overheating? Make sure it has sufficient ventilation on all sides and that vent holes are not blocked by dust balls. Ensure the fan (if equipped) is running as designed (some only operate on demand). Clean dust and debris from it.

If the amp comes back on after cooling, you're lucky. They only have so many self-protection cycles in their lives so continuously resetting or cycling their power without addressing the cause can do more harm than good.

If it protects immediately on a cool power up you should disconnect the speaker connections and try it 'nekkid'. If it comes up then diagnose which lead(s) are shorted. If it does not come up the problem is internal and should be left to an experienced and competent hands-on tech.

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Hello I have Marantz PM673 and it turns and function fine but suddenly it volumes down and finally no sound, if stays turned on soun come back. If any one may guess what is the problem it will be of great...


I'd guess something heat-related.

Generally speaking, an amp attempts to protect itself from heat, shorts, overloads and operator exuberance by refusing to turn on or stay on.

Overloads can be from excessive periods of high output or marginally low impedance loading by the speakers; and shorts would be wiring issues or a speaker blowing up.

You should be able to feel if it's hot. WHY is it overheating? Make sure it has sufficient ventilation on all sides and that vent holes are not blocked by dust balls. Ensure the fan (if equipped) is running as designed (some only operate on demand). Clean dust and debris from it.

If the amp comes back on after cooling, you're lucky. They only have so many self-protection cycles in their lives so continuously resetting or cycling their power without addressing the cause can do more harm than good.

If it protects immediately on a cool power up you should disconnect the speaker connections and try it 'naked'. If it comes up then diagnose which lead(s) are shorted. If it does not come up the problem is internal and should be left to an experienced and competent hands-on tech.

Check for loose speaker connections at the speaker as a root cause for intermittent shutdown.

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The symptom sounds like a feeback loop. As long as that indicator is showing near maximum output on one channel AVOID ATTACHING ANY SPEAKERS TO IT!!!! You'll cook the tweeters.


Turn it off and manually operate every control, knob and pushbutton throughout its range many times to wipe oxides away from their conductors.

Set all EQ controls to their midpoints and re-evaluate.

We don't know if it's an input or output problem yet. Does it do that with all inputs?

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Marantz Pm-7200 left channel weak compared to the right


hmmm. Let's start by swapping the wires you are using for your speakers. Double check the wire connections first, then take the left and place iton the right and vice versa.

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1 Answer

Sound from left channel is small and distorted.


The distortion might be caused by a resistor. The loss of volume could be the capacitors, but you could try injecting signals into the transistors to see if any has gone. They can cause the distortion and loss of signal. If you apply a soldering iron to any part it will heat up quicker, or you could also use a hairdryer for the whole thing. You can also get a freeze spray that cools things that have heat sensitive faults (available from electronic parts shops).

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HI...
You need an 8 ohm stereo "L-pad"
Try partsexpress.com
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OOPS-forgot to mention if your bias turns out ok after replacing any blown outputs, turn it off and resolder the collectors (center) pins of all 4 output transistors and turn it back on-should work but you'll need to recheck bias and dc offset. They appear to both be adjustable on the board sticking up on the top side-it's right in the middle and has 4 trim pots on it......

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1 Answer

Marantz PM-74D


Your no doubt finding the speaker safety/turn on surge protect relay NOT engaging a few seconds after turning it on-right? Check the output transistors. These are the big green and black ones screwed to the heatsink. You gain access to them by taking off the bottom cover. There's 4 per channel--2 green and 2 black. You'll probably find one or more of them shorted. If you find replacements, put them in exactly as the originals with new thermal grease/heatsink compound. Unsolder and lift the center pin (collector) on each of the four transistors of the effected channel. Power it up and check across the outside pins of each device for proper bias-about a half a volt or so on each one. If the voltage is much higher, or not there you've got other problems that will require more diagnostic/troubleshooting. Do all the lights on the front panel work-or just the tape monitor indicators? If just the tape monitors light up, check resistors RN83 and RN84 on main board under the speaker connector board-remove the speaker connector board to get at them. These are bad on mine and I've yet to replace them. I believe these to be 920 ohm 1% precision resistors....

May 17, 2008 | Marantz PM-68 Amplifier

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