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Mark Levinson No.27 amplifier,,,NEED HELP
Mark Levinson No.27 amplifier,,,NEED HELP
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Old 7th February 2019, 02:32 AM   #1
jc9394 is offline jc9394  United States
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Join Date: Oct 2010
Default Mark Levinson No.27 amplifier,,,NEED HELP

i have the Mark Levinson No.27, for some reason it keeps going into protection mode . As soon as it turns on, after few seconds, it turns itself off.
When I removed the right channel, it works perfectly, but when I removed the left channel ,switched on the right channel, , it was shutting down quickly when the power. I think the right channel is bad.
anyone know how to repair it? thanks!
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Old 7th February 2019, 06:31 PM   #2
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
Location: Blaricum
Here is the 27.5 service manual.
May be that can help you.


Hans
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Old 7th February 2019, 06:41 PM   #3
RM is offline RM  Norway
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Join Date: Apr 2005
Location: Buskerud
I have two 27 boards. I will check if they are of use to you. Ok?

Both 23 and 27 suffers from lack of engineering acuity. Sad really, when you consider the exorbitantly pricing of ML.

Regards
Roar
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Old 7th February 2019, 10:40 PM   #4
jc9394 is offline jc9394  United States
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Join Date: Oct 2010
Quote:
Originally Posted by RM View Post
I have two 27 boards. I will check if they are of use to you. Ok?

Both 23 and 27 suffers from lack of engineering acuity. Sad really, when you consider the exorbitantly pricing of ML.

Regards
Roar
ok, thank you very much@
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Old 7th February 2019, 11:21 PM   #5
jc9394 is offline jc9394  United States
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Join Date: Oct 2010
Quote:
Originally Posted by Hans Polak View Post
Here is the 27.5 service manual.
May be that can help you.


Hans
thank you!
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Old 9th October 2020, 08:29 PM   #6
bakedAlaska is offline bakedAlaska  Germany
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Join Date: Jun 2017
Hi,
does anyone have biasing information and voltages for the 27.5? The sm doesn't seem to have those. There seem to be 2+2 pots on AC-8 + 8.5 per channel.

Thanks!

PS: mine is outputting audible noise (around 25mVpp) on both channels when idle (shortened inputs). Will start looking into this.
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Old 10th October 2020, 06:37 PM   #7
bakedAlaska is offline bakedAlaska  Germany
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Join Date: Jun 2017
Found it in another thread! For idle current I found only a guess for ML 27, if anyboy has the official figure, please post :-)
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Old 11th October 2020, 10:07 AM   #8
bakedAlaska is offline bakedAlaska  Germany
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What I posted earlier ( 2+2 pots on AC-8 + 8.5 ) is wrong.
There are 2 pots on AC-8 for +-VREG, and 1 pot for setting bias of current gain stage.
There is one pot on AC-8.5 for bias for 'buffer stage one' if I see correctly. Does anyone have values / measure points on how to set this?

BR
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Old 11th October 2020, 10:38 AM   #9
bakedAlaska is offline bakedAlaska  Germany
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Join Date: Jun 2017
After correcting bias, checked Vreg and Vunreg, which show significant ripple. VREG should have less than 3mVpp afaik, one side has 50 in my case. For Vunreg mine (27.5) has 300mV ripple.
I understand the 45000uF 75V 95C and 1900uF 150V 85C are custom made and not available on the market. Has anybody figured out alternatives yet?

Thanks
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Old 11th October 2020, 12:40 PM   #10
Hans Polak is offline Hans Polak  Netherlands
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Join Date: Mar 2005
Location: Blaricum
The large caps for Vreg, C21 and C22 , are 680uF nothing special and should be replaced to start with.
The other thing that’s very important is that Vreg+ and Vreg- are within 0.1V of each other, to be set with one of the two pots.
The third pot is for the bias, 4x30mA.

Hans

Last edited by Hans Polak; 11th October 2020 at 12:47 PM.
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