Mark Levinson 27.5 strange failure with....

[mara2054]

Hello, my name is Marian and I'm Italian.
For some time I have a ML 27.5 I listen with great satisfaction.
I opened the bottom cover to give a dusting to the monster and I noticed that a circuit trace input power was interrupted and a 1000 ohm resistor interrupted in the middle.
I point that the final working properly and it sounds so divine, respects the ignition delay and without a dump off.
I have several patterns of the monster but I have the schematic on the PCB power. I ask for help figuring out what happened to melt an ice large enough to require a lot of energy (at least 20A. I think).
A circuit diagram of the protection circuit would be preparatory to plan a possible recovery of the track and the replacement of the resistive component damaged.
I know that the way forward is to remove the PCB and proceed to the design of the circuit but now I will not remove or risk running out of the monster.
Thanks in advance friends that I will respond.
Greetings to all ...
marian

T.Y.

 

[piero7]

 

[mara2054]

Added layout of electronic components.
T.Y.

 

[mara2054]

Hello guys,
Yesterday I spent a happy Sunday with my Mark Levinson 27.5.
I took courage and began to remove the PCB (100 Faston)
I repaired the RC circuit which is located in parallel to the power switch,
Need to avoid making contact torched or better undo the arc in the contact phase.
I reset the circuit trace a piece of art and I replaced the resistor of 1000 ohms with a vintage 1200 ohm given by circuit leveling an old Olivetti printer.
I did not understand what kind of short circuit has melted the track!
The important thing now everything is working correctly.
Enjoy these photos ...
Note the diode bridge from 30Amp. which is Italian.
Good vision,

Mariano from Italy

[IMG=jpg]http://win.archimedesys.it/Share/ML27_5/18.jpg[/IMG]

Sorry for the mess in my lab ....

Thanks

 

[trofian]

Congrats & well done Mariano! Thank you for sharing, it was useful info for me.

 

[om2n]

Hi mara2054, you are fabulous!! you repair the amp by yourself , it is incredible!!
I have a question , I got a second hand 27.5 two month before , whatever how long I listen to,
the amp was not hot , I mean I can put my hand on the heatsink, this amp is class A amp, is it suitable (normal) , I had a MF A120 , it hot like a engine................

 

[stifa]

Great work!
What preamp and speakers are you using and could you recommend a preamp for 27.5?

 

[aymcheng]

I once had a No. 27 in 90's . As long as I remember that is not a class-A machine and its only running warm especially when the air conditioner is on.

 

[stifa]

It is class A up to 15ish watts...spec doesnt say that but I think that is the reality when looking at the schematc. I know some people use it with 100+db speakeers with great results...when wanting bit more "controlled" class A.
Correct me if Im wrong.
Still waiting on info what preamp works best with this amp... Im using KEF 107s and Linn Sara

 

[Stereohans]

I run ML No. 27 with ML 38s. Sounds fine, with well defined bass area and contoured mid range. The only problem with No. 27 occurs with higher frequencies and higher gain. Then it may sound a bit harsh and glassy but I will get this corrected by servicing it in the New Year. The preamp is in working order and has no problems at all.

Greetings, Hans

 

[alex66]

ML27.5

Mariano, peccato tu abbia sbagliato il valore della resistenza da sostituire! Essendo una Dale, le prime 3 cifre sono il valore, la quarta è il moltiplicatore. Quindi 100 x 10 elevato alla 0 (quindi 1)=100 ohm!

Un saluto
Alessandro