Krell KSA 100mkII Clone - Page 61

jacco vermeulen · 29th October 2006, 10:32 PM

Quote:

Originally posted by Mark A. Gulbrandsen

Q-5 50.4 32.1 30.9

Q-6 50.4 32.2 29.7

?

Mark A. Gulbrandsen · 29th October 2006, 10:53 PM

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

Mark

Zen Mod · 29th October 2006, 11:12 PM

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......

Mark A. Gulbrandsen · 29th October 2006, 11:36 PM

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

pinkmouse · 29th October 2006, 11:41 PM

If that doesn't work, get the scope out and try tracing the signal, see how far it gets.

Mark A. Gulbrandsen · 29th October 2006, 11:45 PM

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!

pinkmouse · 29th October 2006, 11:47 PM

Dodgy bias pot?

Mark A. Gulbrandsen · 29th October 2006, 11:51 PM

It checks good... I measured all the resistors in the circuit... all good.

pinkmouse · 29th October 2006, 11:54 PM

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.

Zen Mod · 29th October 2006, 11:58 PM

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

29th October 2006, 11:12 PM	#603
Zen Mod Official Court Jester diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	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...... __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; BAF Forum & Gallery

29th October 2006, 11:41 PM	#605
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	If that doesn't work, get the scope out and try tracing the signal, see how far it gets. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

29th October 2006, 11:47 PM	#607
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Dodgy bias pot? __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

29th October 2006, 11:54 PM	#609
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	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. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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29th October 2006, 10:53 PM	#602
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	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 Mark

29th October 2006, 11:45 PM	#606
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	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!

29th October 2006, 11:51 PM	#608
Mark A. Gulbrandsen diyAudio Member Join Date: Sep 2001 Location: Salt Lake City	It checks good... I measured all the resistors in the circuit... all good.

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