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
My e-mail: paco.mok@hotmail.com
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
http://www.diyaudio.com/forums/solid-state/42357-reverse-engineering-krell-kma-160-a.html
Mark
http://www.diyaudio.com/forums/solid-state/42357-reverse-engineering-krell-kma-160-a.html
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Will someone can tell me, shown in red marker the four regulator diodes' model?Thank you very much!
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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 .
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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-state/42357-reverse-engineer-krell-kma-160-a-14.html
Good luck Singa
Hi all!
For completeness, the four zeners feeding the two 18V regulators:
D3 and D17 are 13V zener diodes. I use 1N4743
D4 and D12 are 10V zener diodes. I use 1N4740
They just sit in series, so order is unimportant. However, once one breaks it's nice to know which type from where it sits.
Each side has a 23V drop (let's call it a drop even on the negative side) before the 18V regulators.
My negative side 13V zener keeps shorting, and taking out the 10V one too eventually. Possibly it's the 18V regulator that fails and takes out the zeners.
It's tricky troubleshooting with the input PCB sitting on top, with all its connectors. Desoldering all 6 output transistors just to get access to the driver PCB underside doesn't help at all.
My next step might be to replace all optocouplers (and broken zener and regulator of course), and keep my fingers crossed. Also replacing the last 3 caps (near the speaker relay) that haven't been replaced on the driver board (apart from the beer can ones). There are orange/yellow drop shaped caps around the regulator. Tantalum, presumably: 10uF 35V.
If any expert on the DC servo would like to chime in, that would be very kind!
Symptom: I get about 3V DC on the speaker after warming up. Once the neg 13V zener is shorted this happens consistently (no surprise). The way the same (or very nearly the same) symptom goes from intermittent to consistent is a bit puzzling.
Cheers
For completeness, the four zeners feeding the two 18V regulators:
D3 and D17 are 13V zener diodes. I use 1N4743
D4 and D12 are 10V zener diodes. I use 1N4740
They just sit in series, so order is unimportant. However, once one breaks it's nice to know which type from where it sits.
Each side has a 23V drop (let's call it a drop even on the negative side) before the 18V regulators.
My negative side 13V zener keeps shorting, and taking out the 10V one too eventually. Possibly it's the 18V regulator that fails and takes out the zeners.
It's tricky troubleshooting with the input PCB sitting on top, with all its connectors. Desoldering all 6 output transistors just to get access to the driver PCB underside doesn't help at all.
My next step might be to replace all optocouplers (and broken zener and regulator of course), and keep my fingers crossed. Also replacing the last 3 caps (near the speaker relay) that haven't been replaced on the driver board (apart from the beer can ones). There are orange/yellow drop shaped caps around the regulator. Tantalum, presumably: 10uF 35V.
If any expert on the DC servo would like to chime in, that would be very kind!
Symptom: I get about 3V DC on the speaker after warming up. Once the neg 13V zener is shorted this happens consistently (no surprise). The way the same (or very nearly the same) symptom goes from intermittent to consistent is a bit puzzling.
Cheers
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I'd say those zeners are dissipating too much power and they eventually fail from that. I never had any of the zeners fail on any of my ksa50 builds. Do the calculations based on your rail voltage and see if you need to increase your series resistor or if you need to install higher wattage zeners. I always used 5 watt zeners in my builds. That's a part that should never fail!
Mark
Mark
KSA50 and KSA50S are two different amplifiers, totally different circuits... They are not even close.
Thanks for your remark!
I think the originals are 1W only, and they have lasted since 1993 in the other channel. And the zener that just went was replaced, along with the regulator, about a week ago. I suspect some other active device is causing the issue.
I'll order some 5W zeners anyway.
Thanks!