Marantz 4220 Toshiba ta7109p ta7109ap

Discussion in 'Marantz Audio' started by Fatkid138, Feb 20, 2018.

  1. Fatkid138

    Fatkid138 New Member

    Messages:
    3
    97AE33F7-8A72-486F-8322-8F7CFADC570E.jpeg 2FFE07ED-CD23-4367-A9CE-D973620AF614.jpeg 2AF94694-31A7-47B5-ABED-A60DD5B8BA50.jpeg I repaired a dead channel and some distortion in a Marantz 4220. After a recap of all the boards except for the ones relevant to the fm/am boards. Replaced the output transistors which were originally 2sc790 for new tip41 transistors. Also replaced the ic originally they were toshiba ta7109p in the right and left front channels. In the left and right rear channels there were toshiba ta7109ap. All four for were replaced with unused toshiba ta7109ap ic. The dead channel was in the right rear. Now the all channels are alive and working after the recap and new semiconductors and toshiba ic.


    My question is. Before I do my audio adjustments. I have read on some posts that using the new ta7109ap there has to be a 2k trim pot put in the r755-r758 positions on the amp board, for bias. Originally my amp board had no resistor or did it have markings for r755-r758. The schematic I aquired said that those should be a 15k. I found a place to install them, which would connect pins
    5 and 6 by way of a 2k trim pot. But since this receiver a marantz 4220 already had the ta7109ap installed with no resistor or trim pot. Should I not even install the 2k trim pot. I just didn’t want to go into all this work and waste it by not putting this trim pots in, and ruining the work i have done. The pictures are of the original board before the recap and new ic. Also a picture of the schematic and amp board from the service manual. I hi-lighted the location of where the trim pot is supposed to go. Is it needed when switching from the toshiba ta7109p to the toshiba ta7109ap?
     

     

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  2. catrafter

    catrafter Marantz Specialist Subscriber

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    I had to add the pot when I replaced a TA7109P with an AP, the bias was too high without the 2K pot.
    YMMV

    Tom
     
  3. Fatkid138

    Fatkid138 New Member

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    Thank you for the reply.
     
  4. Fatkid138

    Fatkid138 New Member

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    I received this reply from the seller “great-estate-items” on evay. Thanks to everyone for taking the time to help me.

    Yes, you are correct as Marantz has nothing listed in the parts list for these Bias resistors due to Toshiba was having issues with these chips during the time Marantz was in full production with the 4220 receiver amplifier. My experience working with this TA7109xx chip in a few makes/models of stereo gear has taught me some good lessons.
    Early 1st run of 4220 P700 pcbs used the TA7109 which the chip itself had some bias issues, then Mfgrs of this chip changed to TA7109P which still had bias issues. Marantz had already run many of the P700 pcbs at the time of these changes and left out some info in service manual with no TSB (Technical Service Bulletin) updates/changes but kept the unmarked component locations and copper tracks on the P700 pcbs between pins 5 & 6. Then Toshiba came out with a new replacement TA7109AP which had all bias issues resolved but required a 2k 1/2w bias resistor X4 to keep the bias to the output transistors at a safe level.
    Using the TA7109AP chip will require the 2k resistor installed in all four channels to keep the output transistors from running to hot. Usually the outputs will sound fine at low volume levels without the bias resistors but when set at a higher volume level will quickly heat up the output transistors and will most likely go into (thermal runaway) if kept on for a long period of time.
     
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  5. catrafter

    catrafter Marantz Specialist Subscriber

    Messages:
    6,127
    Location:
    Montana
    This is good to know, thanks for sharing!

    Tom
     
  6. Eagle72

    Eagle72 New Member

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  7. Eagle72

    Eagle72 New Member

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    May I ask the OP, where did you get the TA7109AP ICs?
    Thank you in advance.
     

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