krell ksa 300s right channel dead maybe transistor problem?? - diyAudio
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Old 7th November 2008, 02:19 PM   #1
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Default krell ksa 300s right channel dead maybe transistor problem??

I have ksa 300s , one day i unplug all the input and output, when reconnect everything back the right channel was keep "booming" every second and the four of the bias led was light won't go down, so i try disconnect the speaker cable at this time i got shock by electricity at the speaker output. after i turn it off and than turn it back on, the protection circuit keep kicking in and turn the amp off. so i took off the whole right channel from the amp, and turn it back on and the left channel is in full operation. i assume some of output transistors were burn. anyone know what is my situation here? please help me out! i can provide some picture if necessary. thanks
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Old 7th November 2008, 06:22 PM   #2
jotape is offline jotape  Europe
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I'll try to help.More info needed.
Keep booming... can you be more precise?
Low freq. sound from the speaker?
Did you smell something? Smoke?
Any visible fired part?
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Old 7th November 2008, 10:05 PM   #3
AVWERK is offline AVWERK  United States
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You did this un/repluging of the input with the amp off, right?
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Old 8th November 2008, 12:14 AM   #4
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the booming was from the speakers it "boom" every other second, and i use this amp to drive bottom, so i just can heard the low frequence, At first i can smell a bit somthing from the right channel of the amp, but not like "wire burning smell" it's kinda like "fish??" after i took the right channel apart, i try to find where was the smell from, and the smell was gone. and i don't see any smoke, either any burning part. I did the un/replug with the amp on. thanks for all the reply!!
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Old 8th November 2008, 05:50 PM   #5
jotape is offline jotape  Europe
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Next step: (if I were you)
- CAREFULLY dissassemble ONLY the top board.
Then you'll be able to do some basic measurements on the power
transistors.
If all TRTs are without damage(hope so), measurements should be very similar.
I don't know your electronic equipment and experience.
Here's a photo of the more accessible power section with top board removed (It's a KSA200S, very similar to 300S).
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File Type: jpg pow__.jpg (50.1 KB, 517 views)
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Old 8th November 2008, 06:15 PM   #6
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Quote:
Originally posted by yipyip55

At first i can smell a bit somthing from the right channel of the amp, but not like "wire burning smell" it's kinda like "fish??" after i took the right channel apart, i try to find where was the smell from, and the smell was gone. and i don't see any smoke, either any burning part. I did the un/replug with the amp on. thanks for all the reply!!

boy that sure sounds like a leaking power supply capacitor!!! the fish smell is the key. i would carefully check for wetness or signs of leaking around all the caps.
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Old 9th November 2008, 01:30 AM   #7
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I have a DMM, I know some basic electrionic skill, but i don't know how to measure a transistor in a circuit. for the top board dissassemble, do you know how to uninstall the XLR female socket? do i need to unsolder it fist? i spend half hours on it and still can't get it out without unsolder, the picture you just attach looks almosts the same with the 300s, the 300s just have more transistors. i can't find any puffy capacitor in the board.
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Old 10th November 2008, 09:47 AM   #8
jotape is offline jotape  Europe
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XLR: Doesn't need to be unsoldered:
Use a suitable small flat screwdriver (min. 40mm long). Insert into the quasi-center hole (the one without contacts), and rotate clockwise some degrees to unlock.

Suggestions:

There are NPN type TRT's on one rail and PNP in the other.
Arrangement (see figure):
200S: 2+8 NPN & 2+8 PNP
300S: Check if 2+12 NPN & 2+12 PNP

Possible basic measurements: DMM in "diode mode". Measure as if the bipolar TRT were a two diodes arrangement: one between C-B and the other B-E.
Check that measurements are similar for each each 4 transistor groups, and none is a Short or open circuit.

Be EXTREMELLY careful NOT to mechanically force the two 16 pins connectors between PCBs. They are low quality ones and prone to bad contacts. PCB traces below screws are also of concern.

Remember to check that big capacitors are discharged.
If not, softly discharge them.
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Old 11th November 2008, 02:04 AM   #9
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yes you are right there are 2+12 NPN & 2+12 PNP, i Check all the transistors within the circuit, the measurements are similar eachother, and none is a Short or open circuit. i really have on idea right now.
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Old 11th November 2008, 09:42 AM   #10
jotape is offline jotape  Europe
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As Zero Cool suggested, inspect all electrolytic capacitors.
Aluminium body comes with small grooves on top.
This grooves allow the case to "open" (and not explode) in case of failure (pressure).
Sometimes a bad capacitor only shows little distortion of his cylindrical shape.
Check all caps on both boards (compare with left ones).
I'm supposing that you don't have more sophisticated equipment than DMM.

Board's top pictures perhaps could help now, before going further.
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