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Krell KSA 100mkII Clone
Krell KSA 100mkII Clone
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Old 29th October 2006, 10:32 PM   #601
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Quote:
Originally posted by Mark A. Gulbrandsen

Q-5 50.4 32.1 30.9

Q-6 50.4 32.2 29.7
?
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Old 29th October 2006, 10:53 PM   #602
Mark A. Gulbrandsen is offline Mark A. Gulbrandsen
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Yep, thats what I measured on the working channel, the negative side Q-7, Q-8 measures the same. The non working channel measures about the same on those devices. There is not any real difference till I measure the collectors of Q-9 and 10... those are a volt lower than the good board.

Those readiings taken are in this order...... Drain Gate Source

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Old 29th October 2006, 11:12 PM   #603
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do you have same readings on R24,25,26 and R27 on good and bad board?
around 1V5?
also -same case with R22,23,28 and R29 ?
each predriver (mosfet) must have 1mA5 through......
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Old 29th October 2006, 11:36 PM   #604
Mark A. Gulbrandsen is offline Mark A. Gulbrandsen
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Quote:
do you have same readings on R24,25,26 and R27 on good and bad board?
Yes, both boards measure within one or two tenths of a volt of each other on the MOSFETS. I had not mreasure across the resistors though and will do that in a little while. Am re-mounting the drovers after testing and am screwing heatsink and board together to make it easier to mount the drivers. Holding the heatsink, board, and hardware at same time is a bit difficult while keeping it aligned.

I will get back in an hour or so on the reading across those resistors.

Thanks
Mark
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Old 29th October 2006, 11:41 PM   #605
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If that doesn't work, get the scope out and try tracing the signal, see how far it gets.
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Old 29th October 2006, 11:45 PM   #606
Mark A. Gulbrandsen is offline Mark A. Gulbrandsen
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Actually the board drives my YAmaha NS-10 just fine so signal is flowing as normal... I had looked with a scope and it all seems fine. The problem is with that low voltage in both Q-9 and 10. It may be related to something behind it though... The OP stage doesn't even get warm!
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Old 29th October 2006, 11:47 PM   #607
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Dodgy bias pot?
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Old 29th October 2006, 11:51 PM   #608
Mark A. Gulbrandsen is offline Mark A. Gulbrandsen
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It checks good... I measured all the resistors in the circuit... all good.
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Old 29th October 2006, 11:54 PM   #609
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Hmm. Other than a soldering error, I can't think of anything else offhand. It's past midnight here, so I'll sleep on it and see what I can think of in the morning, assuming of course you haven't got it fixed by then.
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Old 29th October 2006, 11:58 PM   #610
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Quote:
Originally posted by Mark A. Gulbrandsen
It checks good... I measured all the resistors in the circuit... all good.

replace everything (or one by one part) after mosfets,IF voltages on mentioned resistors are OK......

bad resistor ,or transistor or pot;
start with pot
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