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Old 6th February 2011, 12:21 AM   #11
jazz is offline jazz  Netherlands
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Hi,

So I changed the led and it seems to work again. Thanks guys! I changed the led first and after that the resistor, next i soldered the resistor to ground. It seems to be stable now but i'm gonna do some more tests before I change the other channel as well.

What bugs me still, is the question what actually happened. I mean i don't know this failure mode and assume that if a led emits light, it works. I would like to know if this is a known failure behaviour for a led? Now that i calculated the differences for connection to ground versus plus rail, i got a hint. But why doesn't the resistor fail and/or shows signs of distress at twice it's rated dissipation before the led dying?

I mean like I suspected the fet's and transistors first, and changed them straight away. First the output fets and source resistors. check and close up. next output fets, source resistors, the bias pot and reflow/solder all components. check and close up, next output fets, source resistors, bias pot, transistors and fet in the vbe/bias (how should it be named). check and close up. Stop and ask for help.
Channel to channel measurement, bias and voltage readings done during the checks but started measuring longer and longer and play with temperature. so I learned to look for the moment of run away and be ready to pull the plug.

Is this what you would have done when fault finding?

Thanks for the help and thinking with me. I think i can finish it up now, but I'm still bugged about not finding the obvious problem earlier.

Regards,
Joris
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Old 6th February 2011, 08:40 AM   #12
nar is offline nar
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Quote:
Originally Posted by jazz View Post
Hi,

So I changed the led and it seems to work again. Thanks guys! I changed the led first and after that the resistor, next i soldered the resistor to ground. It seems to be stable now but i'm gonna do some more tests before I change the other channel as well.

What bugs me still, is the question what actually happened. I mean i don't know this failure mode and assume that if a led emits light, it works. I would like to know if this is a known failure behaviour for a led? Now that i calculated the differences for connection to ground versus plus rail, i got a hint. But why doesn't the resistor fail and/or shows signs of distress at twice it's rated dissipation before the led dying?
It's likely that the resistor hasn't reach yet the rated dissipation factor, that's all

Led is semicon as the transistors are, in a way. I think it could be damaged whilst you saw it having 10V or more across the pins before "pulling ou the plug".

Quote:
Originally Posted by jazz View Post
I mean like I suspected the fet's and transistors first, and changed them straight away. First the output fets and source resistors. check and close up. next output fets, source resistors, the bias pot and reflow/solder all components. check and close up, next output fets, source resistors, bias pot, transistors and fet in the vbe/bias (how should it be named). check and close up. Stop and ask for help.
Channel to channel measurement, bias and voltage readings done during the checks but started measuring longer and longer and play with temperature. so I learned to look for the moment of run away and be ready to pull the plug.

Is this what you would have done when fault finding?
I todl you, lol, change all the fets and led lol

Quote:
Originally Posted by jazz View Post
Thanks for the help and thinking with me. I think i can finish it up now, but I'm still bugged about not finding the obvious problem earlier.

Regards,
Joris
The best thing to do is : th next time you set up a board, don't reverse polarities ... or be ready to bug check and find the culprit(s)

Best,

nAr
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Old 18th September 2012, 07:11 AM   #13
kamis is offline kamis  Serbia
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I kindly ask X-Ono designer to explain the way of R-5 connection in the real, manufactured Pass-Xono.
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Old 18th September 2012, 08:16 AM   #14
Zen Mod is offline Zen Mod  Serbia
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irrelevant

just calculate it's value to feed LED with 3-5mA
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Old 18th September 2012, 09:01 AM   #15
kamis is offline kamis  Serbia
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irrelevant

just calculate it's value to feed LED with 3-5mA
LED voltage is important for CCS , not current. I know how to solve problem, but I just wish to know how Mr. Colburn connected R5 resistor in the original circuit.
BTW, how about DC servo for X-Ono second stage ?
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Old 18th September 2012, 09:06 AM   #16
Zen Mod is offline Zen Mod  Serbia
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whatever you say......

put BF245A CCS instead resistor

LED voltage will not change wherever you put (appropriately sized) resistor - gnd , +Ub , +3MV

regarding servo ..... you said you're capable of solving problems

edit:

btw , in original XONO that resistor is connected to GND

for putting it to 3MV , you'll need resistor string of ~ 600 MOhm , 30KW

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Last edited by Zen Mod; 18th September 2012 at 09:19 AM.
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Old 24th October 2014, 07:07 PM   #17
kamis is offline kamis  Serbia
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whatever you say......

put BF245A CCS instead resistor
Do you suggest using CCS as an improvement ? Better power supply rejection for LED?
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Old 24th October 2014, 07:54 PM   #18
Zen Mod is offline Zen Mod  Serbia
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well , yes

will you hear difference , in this case , is dubious
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