Marantz Model 250 smoked resistor R529

[tubeblue]

I just replaced all capacitors in my Marantz Model 250 .. fired it up and worked great till it didn't. Resistor R529 .. 39 ohm 1watt went up in a smoking blaze. So I replaced it with a 3 watt and smoked again. I guess I was hoping that being an old carbon resistor it would have gave in. Well now I am trouble shooting. The schematic shows the resistor tying the base of a pair of the output transistors to ground. I am new to this type of amp as I have mainly worked on tube amplifiers. But I am ready to learn. So any help from someone who is familiar with the Marantz model 250 and could lend some advise would be most appreciated.

 

[petehall347]

best check the transistors first for being shorted . most times they short c to e . but not always .

 

[mbz]

best check the transistors first for being shorted . most times they short c to e . but not always .

+1
Check Q510, Q511 and maybe R531 and R532 for stress.
As for cause, check Q507

 

[tubeblue]

Thanks for the replies.. I am schooling myself on transistor testing. thnx

 

[rBuckner]

Check this out: https://audiokarma.org/forums/threads/bipolar-junction-transistor-testing-basics.43186/

 

[tubeblue]

Check this out: https://audiokarma.org/forums/threads/bipolar-junction-transistor-testing-basics.43186/

Very helpful. thank u

 

[mbz]

I like this from mtf, concise, simple, in a nutshell...

 

[Jose Jimenez]

I just replaced all capacitors in my Marantz Model 250 .. fired it up and worked great till it didn't. Resistor R529 .. 39 ohm 1watt went up in a smoking blaze. So I replaced it with a 3 watt and smoked again. I guess I was hoping that being an old carbon resistor it would have gave in. Well now I am trouble shooting. The schematic shows the resistor tying the base of a pair of the output transistors to ground. I am new to this type of amp as I have mainly worked on tube amplifiers. But I am ready to learn. So any help from someone who is familiar with the Marantz model 250 and could lend some advise would be most appreciated.

You may be busy, but I'm interested in what you found out with the amplifier. Did the amplifier perform well before the cap replacement, and I presume this is in only one channel?

This is a great amp and easy to work on. A side note, the bias circuit needs to have good connections to minimize component failure. We are here to help.

 

[tubeblue]

Hi thanks for all the replies. I'm awaiting parts and have been a little turned around on the placement of the power transistors I've included a drawing of the power board and below it I show the transistors as they should appear on the back does this look correct thank you for your replies

 

[Jose Jimenez]

Look at post 36. There is lots of good information.

audiokarma.org/forums/threads/marantz-250m.960339/page-2#post-16947349