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Marantz 4300

Discussion in 'Troubleshooting and Repair' started by mrmodify, Dec 26, 2010.

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  1. mrmodify

    mrmodify

    157
    32
    Feb 13, 2010
    Back to working on Marantz 4300. Thanks to this site I have been greatly helped in getting the power supply, FM and AM sections up and running. I Installed amplifier boards with new outputs this morning. Thought I had thoroughly check everything but missed something. Powered it up and it smoked R745, R757. on the front right channel board. Burnt R745 on Left front board. Opened H713 on right board, Found both front channel R & L PNP outputs shorted and Both front R & L NPN outputs opened.
    Can I power up reciever with outputs removed to make some checks? I would hate to quit on reciever now, to much money and time invested. Can anyone give some directions on what I should do next.
    Thanks JC Guzzardo
     

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    Last edited: Dec 27, 2010
  2. shrtrnd

    shrtrnd

    3,785
    501
    Jan 15, 2010
    I'm wondering what you were trying to drive when you installed the amp boards.
    Yes, I'd disconnect the outputs, and start checking your voltages.
    Also, I haven't seen a Marantz in a lot of years. The ones I've seen had switchable
    power input 120VAC/220VAC (and switchable 50/60Hz). Are you sure your unit is
    accepting the correct input voltage to your amp?
    Just one other thing to verify while you're troubleshooting.
     
  3. mrmodify

    mrmodify

    157
    32
    Feb 13, 2010
    Thanks will check for switches tonight but don't think this unit has the 110/220 or 50/60 htz switchs. I had two known to be good but dinky 2 way 8 ohm speakers connecect to the main front speaker terminals. Had the main speaker button depressed with fader to front. Protection relays never came in to my knowledge. So it should be ok to install amp boards and remove all 8 output transistor and check voltages.
    Thanks shrtrnd for replying
     
  4. shrtrnd

    shrtrnd

    3,785
    501
    Jan 15, 2010
    Was just wondering if maybe you bought it from some foreign seller.
    You need to watch out for those speakers you're using.
    If you're overdriving the 'dinky' 8-Ohm speakers you're using, THAT WILL blow your
    output transistors.
     
  5. mrmodify

    mrmodify

    157
    32
    Feb 13, 2010
    Got these speakers with a old Monkey Wards stereo system I got when I was a teenager many years ago. I use the speakers in my hobby room and are usually powered by a old sansui 6060 receiver. I sometimes use them to test a amplifier im not to sure of. Thanks for the info about overdriving.
     
  6. shrtrnd

    shrtrnd

    3,785
    501
    Jan 15, 2010
    The problem would be if the speakers are very low power, and even the low volume setting
    on your Marantz is a fair amount of wattage.
    Just something to think about, next time you repair that circuit, and consider outputting
    the power to the speakers. Good luck with it. I was just thinking your speakers might
    be what caused your amp transistors to fry. You might consider using fuses in-line with
    your speaker output, just to be on the safe (safer) side, if that's all you've got to work with.
     
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