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2245 Audio Adjustments

Mr. Creasote

Mr. Creasote

Member
Hi Guys

I got to the audio adjustments on my 2245 and have an oddity. It may be me, but I think I have the right pin terminals. Im using a Fluke 29. Voltage adjustment, was real close and adjusting the trim, R809, dialed it right in to 35V. DC off-set, Again, Was real close and adjusting trim, R762, dialed it in to "zero". Now.. Idle-current, connected the fluke to J753 and J754 and read 38V!! on both sides. Adjusting R763 made no change. Am I measuring off the right points? I have heard there are errors in the service manual. The manual says to use a VTVM for the idle-current. Can I do this with a Fluke 29?

Thanks for any help
 
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The service manual is wrong. For the bias adjustment connect your meter to J754 and J760. Since you are measuring across both emitter resistors you will want to set R763 for 10mV instead of 5mV. Use mini or micro clips on your meter leads and turn the power off before connecting or disconnecting them.

Tom
 
Thanks Catrafter!!! I have the little mini clips, you push the plunger and a little hook grabs the pin. I know to turn it off before making connections but thanks for the reminder, all it takes is one laps of attention. I'm off to the garage.. Thanks again.
 
I made the adjustment, but I have a question about the procedure. I'm assuming this is done on a quiet input, like AUX and no speakers connected. It was at about 15mv, I adjusted it down to 10 but noticed it tends to creep up. The manual says to turn it all the way down and then up to the adjustment. I noticed once it warmed up a bit, I left it on for about 20 minutes, the creeping slowed way down. I assume again that you turn it all the way down then up to 10mV and thats it. Dont worry about the creeping?
 
The creeping is normal, as long as it finally settles. It's thermal, due to the fact that the power transistors don't get the heat to the bias circuit immediately.

If it takes too long to settle, you might notice some crossover distortion until the unit warms up.
 
Okay, It did settle down after a bit. I got everything according to the service manual and Catrafter. Thanks for the quick replies. The receivers in the rack and I been enjoying it all afternoon. Thanks again guys!!

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You have to agree-Marantz has some of the best looking recievers period. I love my Pioneer's, the black/blue dial, but marantz had a good thing going! "Looks" sell!!
 
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