need some help on my Mark Levinson No23

loveaudio · 19th March 2015, 11:02 AM

any one here work on one of these before ?
i just need to know the resistor next to the x2 rated cap on the front panel board , what it job in the front panel circuit ? mine is just smoked , but i need to find out what cause it to overheat .
attathed is the pictures of the board and resistor in question.
thanks
Peter

llwhtt · 19th March 2015, 08:32 PM

I have one sitting here that I just finished last week. The resistor is a 11kohm/2 Watt carbon comp that appears to just power the front panel LED. That's all I can tell by just looking behind the front panel. I am NOT going to disassemble it again, too much time involved.

Craig

JonSnell Electronic · 19th March 2015, 08:59 PM

11k? that is an odd value. Not a discoloured 12k?

llwhtt · 19th March 2015, 09:17 PM

It is definitely 11k, brown, brown, orange, gold, looks brand new, big two Watt CC.

Craig

srh · 19th March 2015, 09:42 PM

11k is a standard value in the E24 range and above.
Steve.

loveaudio · 19th March 2015, 11:09 PM

Thanks Guys.
yes the resistor is 11K as Graig have said ( brown-brown-Orange ).
this amp first fired some of the 4700pf x2 rated caps in near by area with this is resistor . i changed those and now this resistor firer , hence my reason to findout what cause and what this resistor function in this board .

also Graig. did you have to adjust the bias on this amp after you done the repair ?
Cheers
Peter

llwhtt · 11:51 PM

This amp came to me with shipping damage and that's all I repaired. Replaced all 12 of the big PCB mounted electrolytic capacitors (because several broke off), transistor insulators, and thermal compound. I did NOT adjust the idle current because I couldn't find a reliable source on how to do so. I measured THD at 20, 200, 2k, and 20kHz at 2, 20, 200 Watts all were in .00x range or so and it idles only warm so I figured I'd just leave it. Did I mention these are a PITA to work on?

Craig

loveaudio · 19th March 2015, 11:59 PM

Quote:

Originally Posted by llwhtt

This amp came to me with shipping damage and that's all I repaired. Replaced all 12 of the big PCB mounted electrolytic capacitors (because several broke off), transistor insulators, and thermal compound. I did NOT adjust the idle current because I couldn't find a reliable source on how to do so. I measured THD at 20, 200, 2k, and 20kHz at 2, 20, 200 Watts all were in .00x range or so and it idles only warm so I figured I'd just leave it. Did I mention these are a PITA to work on?

Craig

Thanks Graig.
indeed it is very time consuming to work on this amp . too many screws to take off

nice to know you replace the caps . can you kindly let me know where you souse the caps ? i might consider change them on mine too .
i ask about the bias is that I can see after i run mine for around 15 mins one side of the heatshink seem a bit warmer than the other side therefore i think one channel bias might be off a bit ? no ?
cheers
Peter

llwhtt · 20th March 2015, 12:32 AM

In order to replace those capacitors the PCB needs to removed from the heat sink. All of the TO-3 transistors are soldered to the double-sided board thru eyelets making them very hard to remove without damaging the board. So unless you have a very strong desoldering station I would leave the caps alone unless the PCB needs to be removed for other reasons.

I used the only caps I could find in the short time I had to do the job. They were Nichicons from Mouser. The 680uf and 330uf 100v caps had to be increased to 200v as that's all I could find. The original caps are long gone.

Craig

tiefbassuebertr · 31st March 2020, 09:53 PM

for additional pictures check out this thread:
Mark Levinson No23 repair help
who can upload the schematic ?

19th March 2015, 08:59 PM	#3
JonSnell Electronic diyAudio Member Join Date: Dec 2012 Location: The Jurassic Coast, England. GB	11k? that is an odd value. Not a discoloured 12k? __________________ Support for Fender, Marshall and all Valve Equipment; Audio Innovations, Audiorama FU29, Quad and Leak. www.jonsnell.co.uk

19th March 2015, 09:42 PM	#5
srh diyAudio Member Join Date: Mar 2004 Location: Whangarei. NZ	11k is a standard value in the E24 range and above. Steve. __________________ The older I get, the more simplicity appeals.

19th March 2015, 11:47 PM	#7
llwhtt diyAudio Member Join Date: Jun 2008 Location: SoCal	This amp came to me with shipping damage and that's all I repaired. Replaced all 12 of the big PCB mounted electrolytic capacitors (because several broke off), transistor insulators, and thermal compound. I did NOT adjust the idle current because I couldn't find a reliable source on how to do so. I measured THD at 20, 200, 2k, and 20kHz at 2, 20, 200 Watts all were in .00x range or so and it idles only warm so I figured I'd just leave it. Did I mention these are a PITA to work on? Craig Last edited by llwhtt; 19th March 2015 at 11:51 PM.

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19th March 2015, 08:32 PM	#2
llwhtt diyAudio Member Join Date: Jun 2008 Location: SoCal	I have one sitting here that I just finished last week. The resistor is a 11kohm/2 Watt carbon comp that appears to just power the front panel LED. That's all I can tell by just looking behind the front panel. I am NOT going to disassemble it again, too much time involved. Craig

19th March 2015, 09:17 PM	#4
llwhtt diyAudio Member Join Date: Jun 2008 Location: SoCal	It is definitely 11k, brown, brown, orange, gold, looks brand new, big two Watt CC. Craig

19th March 2015, 11:09 PM	#6
loveaudio diyAudio Member Join Date: Dec 2004 Location: victoria	Thanks Guys. yes the resistor is 11K as Graig have said ( brown-brown-Orange ). this amp first fired some of the 4700pf x2 rated caps in near by area with this is resistor . i changed those and now this resistor firer , hence my reason to findout what cause and what this resistor function in this board . also Graig. did you have to adjust the bias on this amp after you done the repair ? Cheers Peter

20th March 2015, 12:32 AM	#9
llwhtt diyAudio Member Join Date: Jun 2008 Location: SoCal	In order to replace those capacitors the PCB needs to removed from the heat sink. All of the TO-3 transistors are soldered to the double-sided board thru eyelets making them very hard to remove without damaging the board. So unless you have a very strong desoldering station I would leave the caps alone unless the PCB needs to be removed for other reasons. I used the only caps I could find in the short time I had to do the job. They were Nichicons from Mouser. The 680uf and 330uf 100v caps had to be increased to 200v as that's all I could find. The original caps are long gone. Craig

31st March 2020, 09:53 PM	#10
tiefbassuebertr diyAudio Member Join Date: Jul 2005 Location: D-55629 Schwarzerden	for additional pictures check out this thread: Mark Levinson No23 repair help who can upload the schematic ?