Marantz 2270 dc offset problem- solved !
- Thread starter Scotteboy
- Start date
Scotteboy
Active Member
Didn't see any movement but then again I didn't go through the full 25 turns. I will try that to be sure. Australia ! Man the internet is amazing, the only person I know down there other than you is Rod Elliot, I have enjoyed building a few of his kits and enjoy his approach to electronics>
Scotteboy
Active Member
No But I did also buy these just in case with the last batch of parts so I will replace them next. I have been looking at them with the stink eye anyway with the others giving problems. I buy these and then repair and test to full specification before flipping them. I like tube setups overall and have a bottlehead 2a3 and am about to replace that with Luxman Mb-3045 with the 6lf6 conversion. This marantz supposedly "worked" but the output transistors were very leaky so I doubt it worked too well. I test everything on my bk precision 530 for leakage and matching gain.
Scotteboy
Active Member
Replaced them with 7.5v 1 watt zener as I could not get 7.1v at order time. Still - 0.559vdc at right speaker terminals . I am suspecting the differential pair "screaming" even though I replaced them with matched KSA992's as always but when they oscillate there can be problems. I have not hooked up the "o-scope" yet but am running out of suspects !!
Scotteboy
Active Member
Just put it on the oscilloscope and no signal or voltage output on the right side. Will have to go back and check preamp signal forward. Thats probably it for today ! Checked Preamp in and out and its okay so has to be in the right amp. Still looking will trace the signal loss.
Scotteboy
Active Member
Success ! finally measured all resistors both sides on both amps and compared. The stray voltage was coming from the 30 K resistor at R777. This -14.4 vdc was off the negative rail and went through the 7v zener to the junction of the feedback circuit at R775/c756 and R759/c755. I replaced the resistor with a 33k for test purposes and now no significant dc voltage at the speaker terminal and was able to adjust with R762 to zero. Will replace all "test" parts with proper values to finish and again thanks to all. BTW the signal loss was a broken preamp wire to the right channel.
