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Marantz 1150D No bias after new outputs/drivers

Raccoon1400

Raccoon1400

Super Member
I replaced the outputs and drivers in a marantz 1150D. I used Onsemi MJ21195/96 and MJE15032/33. After rebuild there was no bias in either channel. Before, one channel was blown and the other biased fine. So I guess this is one of those situations where I need to tweak a resistor to compensate for something different about the new parts. The question is which one?
 
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Here's a clipping of the schematic.

Everything works except bias, so I'm thinking it must just need compensation. And the good channel biased fine before I changed the parts.
Everything seems to be in the right place.
 

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The pre drivers were what transistors stock? If you still have them, look at them and provide the numbers , including the suffex at the end.

Marantz sometimes used lettered suffexs (like other manufactures) and that provided a greater degree of beta selection.... That may give you a hint as to why you no longer can bias the unit.

You may have replacement parts with too low beta compared to the "letter" selected stock parts.

Jk
 
Is the bias current changing with the manipulation of R742? If it can't be dial down low or high enough, a modification of the resistors will address this; but if there is no bias at all (i.e., 0 mV) , the problem is elsewhere.
 
Oh, please measure all voltages as indicated in the schedmatic.... My bet you may find some voltages of spec.

Jk
 
Well it looks like I didn't solder the drivers in. I bet that would do it. No idea how I managed to do that in both channels... Must have worked too late.

I did solder one side but then I had to desolder because they were backwards (that I at least noticed before powerup)
 
You want to change resistor values or check the beta ranges via the suffex...?

More different value parts or more original value parts....?
 
I don't recommend changing resistors.... May be you will get some one to guide you on that... I recommend correct beta transistors, but that's just me.

Jk
 
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