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CE2000 bias -- error in service manual ?


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#1 lingcod

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Posted 01 July 2013 - 08:11 PM

CE series reference manual, p2-5, "bias", suggests that channel 1 bias be set relative to ch1 output and tp38.

Schematic and examination of board traces indicate that tp39 corresonds to ch1, tp38 corresponds to ch2.

Can anybody confirm ?

thanks in advance,
  PA

#2 joust

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Posted 09 July 2013 - 03:54 PM

It is possible. Though, if you try to bias CH1, measure the voltage between the TP closest to the bias trim pot and the Ch1 output rail. For Ch2, measure the voltage between the TP near the level controls and Ch2 output rail. Basically, what you're trying to do is evaluate the voltage that is on the HS (high side) 5R6 resistor. This resistor is in parallel to the output device B-E voltage (+ emitter resistor). The other side of the TP to measure is the output rail, before the relay.

Alain

#3 lingcod

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Posted 10 July 2013 - 11:13 AM

Agreed, thanks, that's why I asked. Bias is developed across BE junction - below cutin for outputs.
Same measurement in the DC300 series. Schematics and board layouts for CE contradict the service manual.

With no load/no signal, if DC offsets are small enough (~0 mV) then which output is used should not really matter, provided
that measurement causes no appreciable current flow (which should be the case with high impedance DVM) - because there
is no current flow through the emitter leg to output (ie., outputs are not on, no IR drop across 0.2ohm).

PA

#4 joust

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Posted 11 July 2013 - 01:24 PM

Correct! :)
Sometimes I even use the ground reference as reference to the output rail because of this low offet voltage; Though, it shouldn't be used as standard practice.

#5 joust

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Posted 12 July 2013 - 02:02 PM

Just to let you know, I can confirm your observation of switched around tp. There is an error in the service manual or else, the silkscreen template on all those modules is wrong! :-)