Help repair Krell KSA-50S

[Wizard]

My friend's Krell KSA-50S need to repair,Who can help me?Who can send me the schematic of Krell KSA-50S,Thank you very much!
My e-mail: paco.mok@hotmail.com

[AndrewT]

is this a genuine repair help request?
or
could this be a Faker looking for ???

[Mark Allen]

Lets get him to reverse engineer it for us so we can build the dang thing! It's high time for a new Krell to construct... KSA-50S or hows about the KSA-80B??? The data on the latter one already exists...

Mark

[john65b]

Yeah!! Show us some pics of the amp!!

[Mark Allen]

Here is the thread... I did save all the pictures and schematics and so on and I will work to post em on my flickr site in the next week or so... they are on another computer from another time... but I do have them. BTW: The KMA-160 is a bridged mono version of the KSA-80 and more or less the same.

Mark

Reverse engineering Krell KMA 160

[Wizard]

Originally Posted by john65b

Yeah!! Show us some pics of the amp!!

As the New Year holiday because, I am sorry such a late reply to you.

[Wizard]

Originally Posted by Wizard

My friend's Krell KSA-50S need to repair,Who can help me?Who can send me the schematic of Krell KSA-50S,Thank you very much!
My e-mail: paco.mok@hotmail.com

Will someone can tell me, shown in red marker the four regulator diodes' model?Thank you very much!

[singa]

Originally Posted by Wizard

Will someone can tell me, shown in red marker the four regulator diodes' model?Thank you very much!

Ni Hao Wizard,
It would be more helpful if you tell us what happen to this
Krell amp.As far as I can see,the pcbs you show don't have burnt or
exploded parts.You have also desoldered quite a few components.So what
do you suspect is wrong with the Krell.In one photo you have taken out a 3 pin device connected to a optoisolator (white colour) and in another photo,
some transistors.What really happened?

As for your question in this post about the diode, the
part number that I can see is 4749A which is 1N4749A, a 24V 1W zener.As there is a corresponding diode pair opposite this negative 7918 regulator that is 7818 ,I guess the diode pair could be the preregulator for the +18V and - 18V rail.I do not think that it is bad but there is a discoloured patch under the positive 18V side (diodes).You have to take it out to confirm the
part number whether I am correct or not or measure across them.

You may be too quick to remove parts ,have you check with your
multimeter and have you found anything that lead you to suspect them as
bad?
We can only help if you give us details of what really happened
in the first place that led to the failure of this Krell amp.

Ps you can confirm the diodes if you can still power up the amp and measure across
1N4749A and will get + or - 24Vdc respectively.

The 2 pcbs are the power supply am I right? regards .

[Wizard]

Originally Posted by singa

Ni Hao Wizard,
It would be more helpful if you tell us what happen to this
Krell amp.As far as I can see,the pcbs you show don't have burnt or
exploded parts.You have also desoldered quite a few components.So what
do you suspect is wrong with the Krell.In one photo you have taken out a 3 pin device connected to a optoisolator (white colour) and in another photo,
some transistors.What really happened?

As for your question in this post about the diode, the
part number that I can see is 4749A which is 1N4749A, a 24V 1W zener.As there is a corresponding diode pair opposite this negative 7918 regulator that is 7818 ,I guess the diode pair could be the preregulator for the +18V and - 18V rail.I do not think that it is bad but there is a discoloured patch under the positive 18V side (diodes).You have to take it out to confirm the
part number whether I am correct or not or measure across them.

You may be too quick to remove parts ,have you check with your
multimeter and have you found anything that lead you to suspect them as
bad?
We can only help if you give us details of what really happened
in the first place that led to the failure of this Krell amp.

Ps you can confirm the diodes if you can still power up the amp and measure across
1N4749A and will get + or - 24Vdc respectively.

The 2 pcbs are the power supply am I right? regards .

Hello Dear Singa!
Thank you for your reply!

This Krell amplifier that has been repaired once someone else, So I'm not sure those components are original.
Now the fault is the current very large, machines can’t boot.
A light bulb in the AC power supply series, the light is very bright.
In the figure,the 1N4749A is I changed up, not the original components!

So I must now determine whether the components to be replaced the same as the original!

Because that group power is the power supply to the BAIS part, I think the current very large part of the problem may be due to the BAIS!

So I very need the Original circuit diagram!

[singa]

Originally Posted by Wizard

Hello Dear Singa!
Thank you for your reply!

This Krell amplifier that has been repaired once someone else, So I'm not sure those components are original.
Now the fault is the current very large, machines can’t boot.
A light bulb in the AC power supply series, the light is very bright.
In the figure,the 1N4749A is I changed up, not the original components!

So I must now determine whether the components to be replaced the same as the original!

Because that group power is the power supply to the BAIS part, I think the current very large part of the problem may be due to the BAIS!

So I very need the Original circuit diagram!

Hi Wizard,
Oh I see,But at first when you open it what can you see like
burnt (shao chiao) parts or can you detect shorted parts with meter?
Because this is the area that is easy to trace.Troubleshoot logically
step by step ( yi pu,yi pu lai) ,it is not difficult.Is the original diodes(1N4749A) shorted?

Sorry I can not find original Krell KSA50S schematic but here
is a drawing of the old one maybe? At least it will give you some idea.

Here is a page where you can see the servo circuit on page 14.

http://www.diyaudio.com/forums/solid...-160-a-14.html

Good luck Singa