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Mark Levinson No.27 amplifier,,,NEED HELP
Mark Levinson No.27 amplifier,,,NEED HELP
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Old 12th October 2020, 06:11 PM   #21
Mark levinson is offline Mark levinson
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Old 12th October 2020, 06:17 PM   #22
Mark levinson is offline Mark levinson
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Quote:
Originally Posted by Hans Polak View Post
Before you take things apart, which is indeed very inconvenient, I strongly advise to first replace the two 680uF caps on the upper board and to make Vreg+ equal to Vreg-.

When these two voltages are not equal in magnitude, the start up circuit interferes with the signal chain, that's why.

Hans
Quote:
Originally Posted by Hans Polak View Post
I did say that the regulated voltages have to be of exact the same magnitude for each channel, not at all the currents of both channels.
What do you mean with “there is no start mode ....” ?
What model do you have to 27 or 27.5 ?

Hans
Previously, when you turn on the amplifier in the first second, my speakers moved on the speakers.
As I learned this is a soft start mode due to the absence of a relay in the circuit. So after replacing the worn parts, 27.5 turns on, but this soft start mode is not. The amplifier works, but there is no sound.
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Old 12th October 2020, 07:27 PM   #23
Hans Polak is offline Hans Polak  Netherlands
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So in fact the amp does not work because you get no sound.
At what point did you measure those 4 voltages ?
What are the voltages of P6 and P7 with respect to gnd and what current flows when connecting your multimeter set in the DC current mode directly between P6 and P7 ?

Hans
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Old 12th October 2020, 11:02 PM   #24
Mark levinson is offline Mark levinson
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Hans, I measured these four voltages for about 10 minutes of the amplifier's operation.
It was possible to measure napryadenie p6-earth p7-earth
One channel 0.71 0.68 the second channel 0.7 0.68.
Between p6 p7 could not measure, I can not crawl, tomorrow I will try to measure
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Old 13th October 2020, 07:14 AM   #25
Hans Polak is offline Hans Polak  Netherlands
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The voltages on P6 and P7 are telling that your soft start circuit stays locked in the soft start state and does not release P6 and P7 which should become resp +1.9 and -1.9Volt after the soft start has ended.

Hans
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Old 13th October 2020, 07:28 AM   #26
Mark levinson is offline Mark levinson
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Quote:
Originally Posted by Hans Polak View Post
The voltages on P6 and P7 are telling that your soft start circuit stays locked in the soft start state and does not release P6 and P7 which should become resp +1.9 and -1.9Volt after the soft start has ended.

Hans
What do you think might interfere with unlocking the soft start? What should I check?
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Old 13th October 2020, 08:40 AM   #27
Hans Polak is offline Hans Polak  Netherlands
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It will be close to impossible to measure anything unless you remove the top board.
It is Q216 that's doing the soft start, and either this mosfet is broken, or the cap C213 on it's gate is shorted or something in that range.
C213 should be slowly charged positive after powering up, thereby letting the mosfet transfer from an open into a low ohmic position, thereby releasing P6 and P7.


Hans
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Old 13th October 2020, 10:54 AM   #28
bakedAlaska is offline bakedAlaska  Germany
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Quote:
Originally Posted by Hans Polak View Post
...P6 and P7 which should become resp +1.9 and -1.9Volt after the soft start has ended...
Interesting. P6 P7 are 1,76 / 1,73 in my amp.
Still waiting for the 680uF 100V (Nippon LXV were on offer). I took out C21, C22, they seem to measure ok, but will still replace them. If ripple is still there afterwards, will check C23 C25 .. and 1900uF, just to be sure, before I start taking boards apart.

BR

PS: "..mosfet transfer from an open into a low ohmic position.." so, if it closes not fully, it drains partial current from the driveline?

Last edited by bakedAlaska; 13th October 2020 at 11:02 AM.
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Old 13th October 2020, 11:01 AM   #29
Hans Polak is offline Hans Polak  Netherlands
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Those voltages depend a bit on the Bias current and on Vbe variations, but it clearly is outside the ca. 0.7V at soft start.

Hans
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Old 13th October 2020, 01:09 PM   #30
Mark levinson is offline Mark levinson
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Quote:
Originally Posted by Hans Polak View Post
It will be close to impossible to measure anything unless you remove the top board.
It is Q216 that's doing the soft start, and either this mosfet is broken, or the cap C213 on it's gate is shorted or something in that range.
C213 should be slowly charged positive after powering up, thereby letting the mosfet transfer from an open into a low ohmic position, thereby releasing P6 and P7.


Hans

Hans, thank you very much for the information! Will the channel work without a higher fee? Or will I have to increase the space by extending the jumpers(wires)?
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