Hi All,
I just finished recapping all the boards in my 2270.
The receiver sounds and works great - and the FM and the phono
are working really well.
The issue is - I see hardly any bias voltage across the collectors (metal
body) of the driver transistors - with the volume turned down, I
see just about 0.5mV. Adjusting R763 seems to make little difference.
Just to be sure, I also measured it on one of the boards directly across J754 and J760 and
it's the same.
And I see the same thing on both channels! The heat sinks are cool to touch.
Both boards are clean, with no sign of any burnt resistors.
With the volume at a moderate listening level, I can see the voltage
varying to as much as 100mV with the music.
I cannot find the 2SC495/496 or the NTE295 here in India.
So I replaced the cylindrical 2SC984 with a MJE243G which
was posted here earlier. I put a small mica spacer to insulate the metal tab from
the heat sink.
The bias comp diode is in good shape and tested fine with a multimeter.
For the bias transistor H760, I also have a couple of
2SD669 on hand, as it was recommended here, but they
are PNP, unlike the original NPN. Should I try that
instead of the MJE243? Do I need to make any change for the PNP?
FWIW, I was able to adjust the DC offset from about 200mV down to zero.
Across the main filter caps, I have 43V-0-43V and the
J802 on the P800 power board is rock solid at 35V.
Appreciate your help and ideas.
I just finished recapping all the boards in my 2270.
The receiver sounds and works great - and the FM and the phono
are working really well.
The issue is - I see hardly any bias voltage across the collectors (metal
body) of the driver transistors - with the volume turned down, I
see just about 0.5mV. Adjusting R763 seems to make little difference.
Just to be sure, I also measured it on one of the boards directly across J754 and J760 and
it's the same.
And I see the same thing on both channels! The heat sinks are cool to touch.
Both boards are clean, with no sign of any burnt resistors.
With the volume at a moderate listening level, I can see the voltage
varying to as much as 100mV with the music.
I cannot find the 2SC495/496 or the NTE295 here in India.
So I replaced the cylindrical 2SC984 with a MJE243G which
was posted here earlier. I put a small mica spacer to insulate the metal tab from
the heat sink.
The bias comp diode is in good shape and tested fine with a multimeter.
For the bias transistor H760, I also have a couple of
2SD669 on hand, as it was recommended here, but they
are PNP, unlike the original NPN. Should I try that
instead of the MJE243? Do I need to make any change for the PNP?
FWIW, I was able to adjust the DC offset from about 200mV down to zero.
Across the main filter caps, I have 43V-0-43V and the
J802 on the P800 power board is rock solid at 35V.
Appreciate your help and ideas.
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