Mark Levinson 380s PreAmp Schematic needed

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#2
mgkman said:
Hello, I am trying to troubleshoot a startup problem on my ML 380s Preamp. Can anyone provide a service manual and/or schematic?
Click to expand...

I don´t have a factory circuit diagram, but one made by myself of the audio section.
What is the nature of your problem?

380S.jpg

The Buffer of the 380S is equipped with dual transistors, Mat01 and Mat02.

buffer.jpg

Hans
 
#3
Hans,
Do you have any more details on the buffer such as resistor values, the number of the op-amps used and which transistors in your schematic are MAT01 and which are MAT02?

Also, do you know the V+ and V- voltages?

Thanks...
 
#4
ammel68 said:
Hans,
Do you have any more details on the buffer such as resistor values, the number of the op-amps used and which transistors in your schematic are MAT01 and which are MAT02?

Also, do you know the V+ and V- voltages?

Thanks...
Click to expand...

Transistors are Mat02 and mat03, resp dual NPN and dual PNP making the 4 transistors in the buffer.
Opamp is the current feedback amp EL2020
Power supply +/-15V.
I will make a diagram with all details, but have no time for it today.

Hans
 
#10
Thanks Folks, Also been conversing with willcycle offline on this. Im unlikely to tackle the repair myself since I have no electronics experience. The schematic was requested by a local electronics repair shop in Charlottesville, VA but I dont think the guy wants to take this on. The preamp still powers up with seemingly random rapid relay clicks and varying odd characters on the display which seem to have no regular pattern. Its non functional so I have pulled it out of my system until I can get it fixed by a reputable shop. Not crazy about shipping the unit. Trying to choose a shop now. Closest recommended in Springfiled VA 2hrs away. Looking for recommended shop but all have mixed reviews.
 
#12
mgkman said:
seemingly random rapid relay clicks and varying odd characters on the display
Click to expand...


There is a pretty good chance the processor/rom are cooked and only ML can fix that. Instead of having random technicians poke inside why don't you send it to the factory?

A good technician can reach a diagnosis quickly but a poor one can do plenty of damage. Worth taking the risk?
 
#15
Unfortunately, there was a 15K resistor missing between the two darlingtons.
I have put the model in LTSpice, and here are the results, Bode diagram and distortion figures at 1k, 3k, 10k and 20 kHz.

Bode.jpg

Distortion.jpg

Notice that the 100pF in the previous diagram was adjusted here to 860pF for the best results.
However, components differ a bit, but in the final build version, you will have to twiddle with this cap with the help of a 10kHz square wave to get the best results.

Hans
 
#18
Mark Levinson 380 NO audio on the left channel

Hi, I am a new member and I need any one can help me out. I had a Mark Levinson 380 and no audio on the left channel. Please any one out there have the schematic 380, 380s or any ideas can help me out. I really appreciated.

Thanks,
Bruce
 
#19
The schematic for the 38 is easily available. Just search google and you will find it. The 380 is built on the same circuit board. There are a few parts changes — some documented above. I have heard of a similar problem with a 38. In that case one of the 74HC4094 shift registers that control the dac volume control had failed and thus no signal through the dac. I would first verify rail voltage. Have the electrolytic caps been replaced? Next I would follow the signal path from input to output and see where it stops.
 
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