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2252B Concerning Readings During Adjustments

AlexHempel

AlexHempel

AK Subscriber
Subscriber
Greetings AKers,

Hoping a Marantz whiz can help me out with this one. I'm currently checking a 2252B that I restored for my grandparents a year or two ago when I was just getting into working on hardware. The unit has already been given new caps and a new speaker protection relay (which was the cause of the original issue). I'm listening to music with it as I write this and it sounds perfectly fine; the OPT heatsink doesn't even get warm.

However, the readings it's giving me are a bit concerning. First, I checked J726 to J723 as instructed in the manual. This is supposed to be 8mv (it doesn't give an acceptable variance) but it slowly drifts -- I'm getting anywhere from 3mv to 15mv depending on when I check it. Same situation for the other channel, and neither really responds to the pot. And then I checked J723 to J709 (ground), which is supposed to be 0mv. However, I'm getting a whopping 9v DC and 20V AC on both channels. Honestly, I'm amazed it's even working. Is there a possibility these results are some sort of DMM artifacts? It does say to check all the voltages with a VTVM, but I don't have one of those.
 
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You have to be measuring something very wrong. 20V AC on the outputs is like full rated power. I've done the exact same service on a 2252 and a 2238B using a DMM with no issues. Errors in the Marantz service manuals aren't uncommon. Try measuring across the emitter resistors for your 8mV. The bias should be steady after it's idled for an hour. It'll wander all over if the thing is cold. I like to measure the offset at the posts.
 
Be sure and take measurements in Aux mode with volume at zero. If nothing changes when adjusting trimmer, it usually means incorrect test points or wrong trimmer. I would check Offset at speaker terminals, as mentioned above.
 
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@ReactiveLoad Yeah, I had the same suspicion -- 9v is a nonsense reading. I was thinking about it today and realized I might have been using the wrong manual. Sure enough, the one I downloaded was for the 2252, not the 2252B, and the procedures are different. Grabbed the correct one off hifiengine and ran through the checks again; power supply and left channel were bang on, right channel was quite over-biased but the pot fixed it. Cheers and thanks for the help!
 
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