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ma 400 worked once now dead

M

MPinLV

New Member
OK total newb here. Was given a MA 400 with the 350 tuner along with Polkaudio monitor 30 speakers. Turned n once, sounded great next time nothing. Tunerstill works but no output from amp. just want it for a bedroom/headphone listening and was stoked with the sound...when it worked. Is this an amp I can restore resonably? I dont care about resell, but man it sounded great in my bedroom. Any thoughts, and where to start?? BTW...I consider myself a clever guy, have a Weller pro iron and have successfully swapped burnt IC board components before, and have only basic knowledge of electronics...retired plumber, tinkerer at heart and really like to DIY if its not so far above pay grade
 
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Welcome to AK!!
This is a pretty rare console amp, not much information available online. You're in the right place as one of the Marantz gurus should pop up soon to assist.
 
MPinLV said:
Tunerstill works but no output from amp.
Click to expand...
When you say "no output from amp" do you mean it turns on but no audio on both channels, or when you turn it on no lights go on and no audio?
  • Check the fuse on the back panel for a blown fuse. (green arrow) Check continuity of the fuse with an Ohm meter (DMM).
  • Check to see if your model has internal fuses, US versions usually did not (red box)
  • Are you sure it does not work. Sometimes lamps burn out but the amp still works.
  • Check the capacitors for leakage or bulging, especially the main power supply caps (yellow arrows)
  • I can't find the service manual or schematic online.
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Ok update n the MA 400. Fuse checked ok on multimeter continuity test. I then removed the top and found very little dust very clean like someone kept it in a ziploc bag. Main caps are normal looking no swelling or shrinkage. All the circuit traces looked clean nothing burnt or overheated looking. So I went ahead and plugged it back in and lo and behold the LED VU lit up and we got power. I then noticed that there wa6 no FM station locking in and thought "hey dumbass wire up an antenna 1st" .old school 300 ohm and solid lock to stereo. I have these old beat but working KOSS M80 plus test speakers - hooked one up and...no sound. That is until I got past halfway on volume (loudness off EQ set flat) and suddenly I get VU bars and what can be described best a bunch of angry gnats buzzing in a 3lb coffee can for sound. Is thata volume knobs issue or maybe that and ...something else?
 
Thank you. One of my invaluable buddies manages an industrial electronics supply house near me he's got tht stuff for sure. I will give it a thorough spray clean tommorow and let you know. Sure is kinda strange it went from sounding ok to hardly at all on the very next power up. But then I could have very easily missed something as well.
 
The amplifier was the PM-350 in other markets. Definitely clean the bowden-cable linked ALPs selector. Be very careful when removing the actuator cap to gain access for contact cleaner. There are small nylon tabs that are very easy to damage- especially after 44+ years.

It was the baby in the 1982-3 "gold" series. 38wpc.

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