need some technical help with m100.

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frankyboy
Posts: 3
Joined: Sat May 11, 2019 10:53 am

need some technical help with m100.

Post by frankyboy »

i'm doing some servicework on an m100 , but i'm not sure if i'm correct or not. the emitterresistors measure zero mV , shouldn't there be a few mV for bias ? and the outputs measure 88mV and 180mV to earth/ground , isn't this to much ? any suggestions about whats eventually wrong
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Mr. Wild
Posts: 257
Joined: Mon Mar 21, 2011 4:47 am
Location: Finland

Re: need some technical help with m100.

Post by Mr. Wild »

You're right, the bias current should show up as some mV across the resistors. Maybe 5mV, I can't recall exactly. The pots on the PCB are for adjusting bias.

DC offset at speaker connectors should be 30mV or less. Large values indicate the amp has had a hard life and the output transistors are "leaking current".
--
M50, MS275, MPS2500, ZX450, ZPA0.3
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