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Krell KSA 50 pcb
Krell KSA 50 pcb
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Old 15th March 2019, 02:44 PM   #9071
Dave murrey is offline Dave murrey  England
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Location: Ongar uk
Quote:
Originally Posted by Dave murrey View Post
Looking for some more help please.
Replaced blown components
MJE15030 transistors
MJE15031 transistors
4148 diodes
25R5 resistors
2SC2240 transistors
2SA970 transistors.

My problem is without To3 output boards conected when I plug amp in my 100R resistors start to smoke.
Powered down streight away within a second so hope I done no other damage.
These 100R resistors come from pin 1 of A968B PNP transitor then go to +48v
Pin 1. C2238B NPN transistor go to -48v.
Removed and tested all 4 diodes they are ok.
Sorry I feel so stupid but did say it was my first amp build.
Where I substituted parts got my part numbers muddled up so had my pnp and npn in each others places.
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Old 16th March 2019, 09:59 AM   #9072
Dave murrey is offline Dave murrey  England
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Hi amp is playing music but I am still getting 0.8v dc at speaker.
Without speaker conected I get 1.5v dc still.
Any idea's please.
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Old 16th March 2019, 10:36 AM   #9073
Dave murrey is offline Dave murrey  England
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Originally Posted by Itsmee View Post
What voltage do you have at the anode of D1 and cathode of D3?
Hi sorry I missed this post about diodes.
At D1 and D2 I get 26.7v one way nothing the other.
Thought I would check 4148 diodes I get 0.5v both ways the +48v.
On -48v side I get 36v both ways round.
I have tried changing these diodes with same results any idea or is this correct.
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Old 16th March 2019, 11:35 AM   #9074
Itsmee is offline Itsmee  England
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Krell KSA 50 pcb
Quote:
Originally Posted by Dave murrey View Post
...At D1 and D2 I get 26.7v one way nothing the other.
Thought I would check 4148 diodes I get 0.5v both ways the +48v.
On -48v side I get 36v both ways round...
This is a little confusing, D1 & D3 are 1N4148, D2 & D4 are 27v zenners.
Can you measure the voltage at D1 anode, pot wiper and D3 cathode as shown,
and could you also measure the D4 zenner voltage, (all measurements wrt 0V).

PS, sorry about the crappy schematic, it's the only copy I have.
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File Type: jpg Krell KSA 50Mk2 offset V.jpg (7.5 KB, 76 views)
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Old 16th March 2019, 01:05 PM   #9075
Dave murrey is offline Dave murrey  England
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Originally Posted by Itsmee View Post
This is a little confusing, D1 & D3 are 1N4148, D2 & D4 are 27v zenners.
Can you measure the voltage at D1 anode, pot wiper and D3 cathode as shown,
and could you also measure the D4 zenner voltage, (all measurements wrt 0V).

PS, sorry about the crappy schematic, it's the only copy I have.
My circuit is different from one you have shown me its after 1983 version krell ksa 50 mk2 simular as early krell ksa 100 I believe.
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Old 16th March 2019, 01:10 PM   #9076
Dave murrey is offline Dave murrey  England
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Join Date: Apr 2014
Location: Ongar uk
Quote:
Originally Posted by Itsmee View Post
This is a little confusing, D1 & D3 are 1N4148, D2 & D4 are 27v zenners.
Can you measure the voltage at D1 anode, pot wiper and D3 cathode as shown,
and could you also measure the D4 zenner voltage, (all measurements wrt 0V).

PS, sorry about the crappy schematic, it's the only copy I have.
Thank you I will measure them when I get back home I am out at moment
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Old 16th March 2019, 01:19 PM   #9077
Dave murrey is offline Dave murrey  England
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Cant find ksa 50 mk2 but this is simular.
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File Type: jpg 20190316_133332.jpg (285.1 KB, 74 views)
File Type: jpg 20190316_133103.jpg (554.3 KB, 75 views)
File Type: jpg 20181112_133146.jpg (805.0 KB, 72 views)

Last edited by Dave murrey; 16th March 2019 at 01:38 PM.
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Old 16th March 2019, 02:19 PM   #9078
neychi is offline neychi  Croatia
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Dave, this is your schematic, trust me
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File Type: jpg 3500 Krell KSA 50Mk2 Original Schematic.jpg (32.2 KB, 60 views)
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Old 16th March 2019, 02:34 PM   #9079
Dave murrey is offline Dave murrey  England
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Originally Posted by neychi View Post
Dave, this is your schematic, trust me
Thank you does this picture help.
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File Type: jpg 20190316_143222.jpg (474.1 KB, 50 views)
File Type: jpg 20181112_133153.jpg (693.3 KB, 41 views)

Last edited by Dave murrey; 16th March 2019 at 02:40 PM.
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Old 16th March 2019, 03:57 PM   #9080
Dave murrey is offline Dave murrey  England
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It does play music
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