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New Project Marantz 2250b
New Project Marantz 2250b
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Old 3rd February 2018, 04:36 PM   #21
pjf610 is offline pjf610
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Thanks Mooly, Do i need a dummy load to check the channels on this unit with an Oscope??
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Old 3rd February 2018, 05:09 PM   #22
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No load needed, and in fact its best not to have one connected until you are sure its all good and with no DC offset present.
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Old 3rd February 2018, 06:26 PM   #23
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Great Thanks
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Old 8th February 2018, 06:56 PM   #24
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Well I received my parts yesterday, I replaced the R731 which was burnt out and located another burnt resistor R736 and replaced that while i was in there, i changed out capacitors while i was in there, I did fine one not up to spec. I checked the transistors the H702-H703-H710- and H711 checked out fine I did replace the H714 and H715. Put it all back together ran it through my DBT and the relay clicked on, One thing i noticed the light went dim and then came up a little not bright but a little more than dim, do not know if that means anything, so i preceded to check the P800 power supply board and could not get the voltage up to 35v, could that be because i was still on the DBT?? I have not checked the DC offsets yet wanted to take care of the power supply board first. Any feed back would be greatly appreciated
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Old 8th February 2018, 07:04 PM   #25
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The bulb may be glowing because the bias current is to high. Ideally you need to check the current and see what it is, and if altering preset R719 reduces the current.

Also remember the current drawn by the other channel could be adding to problem.

If the bias seems to adjust OK on test you can then turn it back down until we are sure its all fixed.

Also check the DC offset and make sure it is low. It may be a little way off zero because of the low supply.
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Old 8th February 2018, 07:09 PM   #26
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Thanks Mooly, will give that a go and get back at you tomorrow
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Old 8th February 2018, 07:11 PM   #27
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OK
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Old 8th February 2018, 09:49 PM   #28
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OK here are the readings I got;
Main Amp DC Offset LC= 0v RC=1.87 v
Idle Adjustment;
LC=90.5mv RC=3.1mv
Voltage adjustment at between pin 804/805 =29.9v
I checked the voltage at pin810 to chassis and 809 chassis and got
809=0.3v 810 1.819v
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Old 8th February 2018, 10:11 PM   #29
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One other thing i noticed i plugged in my headphones just to see what comes out of the unit and to my surprise no sound from the left channel
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Old 9th February 2018, 08:59 AM   #30
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Left channel.

Does the 90mv alter as you turn the bias preset ?

Is the 90mv present across ALL four of the 0.22 ohm emitter resistors or are there massive differences in the voltage between them.

(90mv would equate to a current of 4 amps flowing which can't happen with a bulb tester and so something is amiss somewhere)
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