Re: Setting bias current and DC offset on marantz 2235b

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Technical and speculative discussion of amps, cables and other topics.

In Reply to: Re: Setting bias current and DC offset on marantz 2235b posted by Tweekeng on November 15, 2005 at 09:52:36:

I have a 2235b that has been humming so I have opened it today with the idea of replacing the power caps (and maybe the bridge rectumfrier). I happened to run across this page. Here are some things I have learned about Marantz amps over the 20+ years I have worked on them. First, replace all the caps in the amplifier stage. Make a list of each value and type (ie mylar, silver mica, electrolytic, etc.) and buy them online at Mouser (cheap!) or your favorite parts house if you have one locally (I don't). If you are getting DC on the speaker outputs that can't be adjusted out, you likely have a shorted power transistor. Did you put them back in the correct places when you removed them? You can remove them and check for a short between the case (Collector) and either of the 2 pins (base and emitter) by using a volt meter set on Ohms scale (be sure to test them out of circuit!). There should be no shorts between any of the combinations. That rumbling you hear is a bad component, likely a bad cap. Freeze spray might find it, but you should really replace all the caps considering the age. Electrolytics especially.
The transistors can be obtained through Phillips ECG replacements. do a search on it or Mouser will likely have them. My amp has C897 and A757 power xistors which cross to ECG280 (npn) and ECG88 (pnp) respectively. If you replace the xistors, be sure to get 2 matched complimentary pairs. I am going to be setting the bias and dc offset on this amp for the next few days as the parts arrive and I would be happy to answer questions... rbowdish@pacbell.net

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Follow Ups Full Thread

Topic - Setting bias current and DC offset on marantz 2235b - eighty6accord@yahoo.com 01:51:36 11/14/05 (6)

Re: Setting bias current and DC offset on marantz 2235b - AudiophileINRecovery 15:43:32 12/07/05 (0)

Re: Setting bias current and DC offset on marantz 2235b - Tweekeng 09:52:36 11/15/05 (4)

Re: Setting bias current and DC offset on marantz 2235b - rbowdish@pacbell.net 13:59:23 11/18/05 (0)

Re: Setting bias current and DC offset on marantz 2235b - eighty6accord@yahoo.com 11:48:28 11/15/05 (2)

Re: Setting bias current and DC offset on marantz 2235b - Tweekeng 14:28:27 11/16/05 (1)

Replacing the caps is a cheap fix...don't worry - seadzz 04:40:34 11/27/05 (0)

Follow Ups

Re: Setting bias current and DC offset on marantz 2235b - rbowdish@pacbell.net 13:59:23 11/18/05 (0)

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