Hello,
I was hoping I could get some help with repairing my Marantz.
A few weeks ago I decided to "tweak" the bias current on this amp (Why didn't I leave it alone?) and in the process blew the two power transistors on the left channel.
I have replaced all transistors on the left channel (I am waiting for the 2SC3419 to turn up). I also replaced three low-value resistors that had blown. I got a copy of the service manual and checked all resistors as well. BUT I came to check the B-E resistance on the transistors to compare them with the good channel and some are way off (The A1303's are nearest the HDAMs):
Tran. L R (kOhms)
1303 3.14 3.53
1837 3.77 3.74
3419 2.01 2.01
4793 5.24 5.26
3284 3.03 3.73
I set the left trimmer to the same value as the right channel (about 1.3k)
Here is a picture of the boards:
http://img137.imageshack.us/img137/645/dsc037438hj.jpg
Any ideas what I need to do to get the resistances for the two main power trannies correct? Any other advice about my problem?
If I have changed the transistors on one side only will it affect the sound of the amp? Or is it best to just get another board altogether? Marantz quoted £240 to replace the board but apparently its £90 just for the part.
I was hoping I could get some help with repairing my Marantz.
A few weeks ago I decided to "tweak" the bias current on this amp (Why didn't I leave it alone?) and in the process blew the two power transistors on the left channel.
I have replaced all transistors on the left channel (I am waiting for the 2SC3419 to turn up). I also replaced three low-value resistors that had blown. I got a copy of the service manual and checked all resistors as well. BUT I came to check the B-E resistance on the transistors to compare them with the good channel and some are way off (The A1303's are nearest the HDAMs):
Tran. L R (kOhms)
1303 3.14 3.53
1837 3.77 3.74
3419 2.01 2.01
4793 5.24 5.26
3284 3.03 3.73
I set the left trimmer to the same value as the right channel (about 1.3k)
Here is a picture of the boards:
http://img137.imageshack.us/img137/645/dsc037438hj.jpg
Any ideas what I need to do to get the resistances for the two main power trannies correct? Any other advice about my problem?
If I have changed the transistors on one side only will it affect the sound of the amp? Or is it best to just get another board altogether? Marantz quoted £240 to replace the board but apparently its £90 just for the part.
pm17 fault
Hello, if you change the output transistors with a good type (sanken!) I think will be the right way (pay attenction to the counterfeits transistors labelled like originals...). You have to make a bias correction, so I think that maybe dangerous.
Often when you turn the bias trimmer a little, the bias current increase much much more, you must pay attenction, you must have a digital multimeter (two are better) for checking the incoming currents.
I don't know if Marantz on pm 17 kis select output devices strongly. You can try to change the defective couple only and (after the regulations and few hours of works) make a listening check.
Can you send me a copy of service manual at my e-mail address (I'm waiting for a defective pm 17) ?
Thanks
walter
Hello, if you change the output transistors with a good type (sanken!) I think will be the right way (pay attenction to the counterfeits transistors labelled like originals...). You have to make a bias correction, so I think that maybe dangerous.
Often when you turn the bias trimmer a little, the bias current increase much much more, you must pay attenction, you must have a digital multimeter (two are better) for checking the incoming currents.
I don't know if Marantz on pm 17 kis select output devices strongly. You can try to change the defective couple only and (after the regulations and few hours of works) make a listening check.
Can you send me a copy of service manual at my e-mail address (I'm waiting for a defective pm 17) ?
Thanks
walter
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