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Beat up Marantz 2226b bias help

Richs_Trains

Richs_Trains

Well-Known Member
Thanks for all your help on the Marantz 140, Marantz 170dc, and the Marantz 1180dc all seemed to turn out well. I had a choice of a 2226b or a 1152dc next. The 1152dc was at the bottom of a stack and the 2226b was much more accessible, so the 2226b is it. I bought this several years ago and it is pretty beat up, faceplate heavily scratched and very dirty. When I first hooked it up it had a suspect right channel and it won't tune any FM stations. I am going to try to fix it with your help, it will never be pretty but maybe it will work. After cleaning all the controls it has a clear left channel and a right channel that flutters and has trouble with bass notes. The only thing I can spot on the power amp board is a discolored resistor R756. It looks as if it got a little warm at one time. There are some burn spots on the inside of the top cover, but I can't find any matching damage on the boards. Trying freeze spray on the transistors had no effect on the right channel. R756 seems to be in line with 1/2 of one channel, is it possible that this might be my problem? I have to admit this "b" unit is not easy to get the major boards in. It looks to be quite an ordeal to pull the power amp board and the power supply is being obstructed by the filter caps mounted horizontally underneath. I know this is not a common model, but any help or insight would be much appreciated. Thanks, Rich
 
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So, I checked R756 and it is 120 ohm as spec'd, but while in that area I noticed a transistor split completely in half Q728, a 2SA777p. What is the proper modern replacement for a 2SA777p and should I change any others if I replace this one to maintain balance? Thanks, Rich
 
Richs_Trains said:
So, I checked R756 and it is 120 ohm as spec'd, but while in that area I noticed a transistor split completely in half Q728, a 2SA777p. What is the proper modern replacement for a 2SA777p and should I change any others if I replace this one to maintain balance? Thanks, Rich
Click to expand...

I would probably try KSA1013 for that one, similar package, higher voltage ratings and appears to have marginally better power handing.
 
2226b_2.jpg

2226b_3.jpg

2226b_1.jpg

In the last picture, you can see the 2SA777p that has split in half. What would cause this, I don't want to replace it and have the replacement split in half also (it is just below the mini-grabber in the photo).
 
If it were I, I would test the output transistors before I replaced that transistor and it's complement Q726.
It is a PITA to get to that board.

Tom
 
catrafter said:
It is a PITA to get to that board.
Click to expand...
Thanks, Tom, if you think so, I have no hope! The channel connected to this transistor plays, but it is fluttery and does not handle bass notes very well. I tried to set the bias on each channel and the left set up just fine, the right would not adjust at all and stayed at 10.7 mv. Does it look like you can loosen the whole module by removing the heat sink screws? Thanks, Rich
 
Richs_Trains said:
Thanks, Tom, if you think so, I have no hope! The channel connected to this transistor plays, but it is fluttery and does not handle bass notes very well. I tried to set the bias on each channel and the left set up just fine, the right would not adjust at all and stayed at 10.7 mv. Does it look like you can loosen the whole module by removing the heat sink screws? Thanks, Rich
Click to expand...

I see at least one resistor that is likely either dead or about dead in line with that transistor. I would test them all around that area, I have had small resistors go OC with absolutely no signs of it.

As for taking it apart, not certain, I usually avoid silver dial B models for that very reason
 
If you remove the screws back at the speaker switches, you can get those long extensions out of the way.
You can loosen the filter cap clamps and let them hang free, ditto for the rectifier, just undo the heat sink and let it hang free.
If you carefully remove the screws holding the board and big heat sink, you can manage to get the assembly out where you can work on it. Be careful to not short anything out if to try to test under power.
The 2226B,2238B and 2252B are quite similar, including being a PITA to work on.

Tom
2238B filters.JPG 2238B PA.JPG
 
catrafter said:
Be careful to not short anything out if to try to test under power.
Click to expand...
Thanks, Tom, I'm going to wait until the new transistors come in and try to get it working before I try to refresh anything inside. The pictures don't really show it, but this unit looks pretty sad. I bought it cheap hoping it was something simple and it wasn't so it's been sitting in the closet for a couple of years now. Thanks for all your help! Rich
 
Well, the replacement transistors arrived Saturday, and being somewhat hesitant, I waited till today to change out Q728. I found some A777 transistors online and ordered 4 just in case. I removed the one that was literally split in half and put in the new A777. Changed the DBT to a 40watt bulb just in case and turned it on. Dim bulb! Pushed the "a" speaker button slowly and I have clear sound on both channels! Will attempt to set the bias and then I guess I'm going to have to clean the face and find out what's up with the AM/FM. Onward. Thanks, Rich
 
So, I tried to set the bias on the left channel and I cannot get it down. It starts about 30mv and slowly climbs and I shut it down at about 55mv. If I power the unit on without the speakers engaged and then add the speakers, I get a clear sound. If I power it up with the speakers engaged I get a pop in the left channel and a momentary flash of the DBT after the initial power-on flash. Where should I look? I tested all the resistors around the A777 and they were all good. I also tested a diode in that area and it was also good. I did not change the complementary transistor. Thanks, Rich
 
Get rid of the green/black diodes if you haven't already. I've seen those cause all sorts of issues, probably not this one but still.
 
Did you replace the diff pair - Q702, Q704? It might be worth a try. Looks like KSA992FBU works as a sub for 2SA750. Matched gain, of course.
 
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