Hi everybody!
I have an amp that I have to fix. The problem with the amp is 1,2V offset at the input and at the output.
The offset at the input appears at the junction between R322 and R310. On the other sides of both the resistor and the cap, its 0V, so the offset isnt produced by the offset-trimpot or the preamp. the strange thing is that the same offset appears on the output, at the same level, so its not amplified (gain is set to 23.5 by R343/R344)
what should i look at first?
shematic:
http://lorbas321.square7.ch/dlf/E-800.pdf
I have an amp that I have to fix. The problem with the amp is 1,2V offset at the input and at the output.
The offset at the input appears at the junction between R322 and R310. On the other sides of both the resistor and the cap, its 0V, so the offset isnt produced by the offset-trimpot or the preamp. the strange thing is that the same offset appears on the output, at the same level, so its not amplified (gain is set to 23.5 by R343/R344)
what should i look at first?
shematic:
http://lorbas321.square7.ch/dlf/E-800.pdf
The capacitor (C318) in series with R344 means the gain is unity at DC, so it makes sense that the output offset is the same as the input offset.
Maybe the input offset is caused by a bit of leakage current from somewhere. Any sign of spilled coffee/beer/whatever on the PCB?
Maybe the input offset is caused by a bit of leakage current from somewhere. Any sign of spilled coffee/beer/whatever on the PCB?
From the voltages around the emitters of T301 and T302, it looks like they're not conducting any current. That suggests T303 or it's emitter resistor (R327) may be dead.
To confirm there's no current through T301 and T302, you could check the voltages across their collector resistors (R323 and R324).
btw: There's a trimpot to the right of R322. Does fiddling with that change the offset? It should allow about +- half a volt adjustment
To confirm there's no current through T301 and T302, you could check the voltages across their collector resistors (R323 and R324).
btw: There's a trimpot to the right of R322. Does fiddling with that change the offset? It should allow about +- half a volt adjustment
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T301 & 302 have 0Vbe
No other T Vbe have been posted.
R322 has 1.2V across it.
No.everything measures just as it should...
What you have measured so far shows that roughly half your readings are wrong.
No.
What you have measured so far shows that roughly half your readings are wrong.
but when measuring the parts unsoldered, they measure as they should, dont they?
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