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2270 Amp Board Transistors

Whaleman

Whaleman

Hi-Fi Rescue Mission
Been having that static storm on warm up on my 2270 left channel. Eventually the protection kicks in as it get worse with heat.

Here is a complete list of replacement transistors for my 2270 amplifier board including the outputs, the original numbers in parenthesis, please reply with proven replacement and I will update this list.

1. H751 = Zetex ZTX795A (2SA640) input pair, shrink wrapped with the one below
2. H752 = Zetex ZTX795A (2SA640) input pair, shrik wrapped with the one above

3. H753 = (2SC945)

4. H754 = (2SC735)
5. H766 = (2SA562) not in the board diagram below, but in schematic

6. H755 = (2SC735)
7. H767 = (2SA562) not in the board diagram below, but in schematic

8. H756 = 2N5415 (2SA484) with the daisy flower heat sinks - TO-39 case
9. H757 = 2N3440 (2SC484)

10. H758 = (2SC680) These are the two bigger transistors
11. H759 = (2SA566)

12. H760 = (2SC984) this one is on the backside of the board

MAIN OUTPUTS

13. H003 = MJ21193G (Motorola, Fairchild, Toshiba, etc.) PNP - Bottom position
14. H004 = MJ21194G NPN - Top position


Also, others recommended for outputs: MJ15024 and MJ15023
 

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Describe the noise...

Replacing all of them is likely unecessary. Commonly, the input pairs (751,752) need replacing.
 
After 10 minutes or so of playing, a dramatic loud static storm (like an AM broadcast in an electical storm) starts and escalates to the point of the protection kicking in. Let it cool and process repeats.

H751 and H752 seem to be both the same 2SA640? Not a PNP/NPN pair?
 
They are called a differential pair, and perform an important function. For some reason, a lot of Marantz receivers have issues with these transistors and they need to be replaced. The new ones need to be matched in pairs for replacement. I use Zetex ZTX795A's. If you went this way, the Zetex ZTX795A's are CBE layout instead of the 2SA640's BCE layout, and you won't be able to heatshrink them together like the originals are (which means offset might drift during warmup a little more than the stock transistors, but is not really a big deal).
 
Thanks Echo, will get them tonight, I was hoping you'd say ZTX694B, I have a bunch of those laying around.

Cheers and I hope this helps other 2270 owners.
 
EchoWars is correct about the differential amplifier devices.

I have, however, run into two 2270's where the output transistors were so incredibly leaky that that generated a time-and-temperature related static.

MJ15024 and MJ15023 took care of that problem.

Fred Longworth
 
I tried different ouputs on this one with th same result. But I think the 9090DB I have is doing exactly what you mention, though the static comes with a vengence and blows the speaker fuse. Say, seems like the 9090DB and the 2270 can use the same outputs.

One thing I like about the 2270 amp board is that recapping it means replacing 2 identical capacitors.
 
It is a real pain to work on the left side of this unit!

I got all the transistors listed at the beginning of the list in blue in along with the new input pair. The only one I left alone is H760 since 2sc984 is very hard to find!

Guess what, I think that is the faulty one! I was not able to get the bias down to 5 mV, the lowest I could get was 45mV with the pot fully counterclockwise and the heat sink was really warm. I was able to dial in the offset to near 0 without a problem. At least it is not shutting down anymore.

The other side was OK.

Do you all think I am looking at a bad 2sc984? I hope you all think so because I have one laying around that I think is still good. I suspect this in the transistor that controls bias with a diode in tandem.

Thanks for the advise, it will the 3rd or 4th time this amp board is out.

This thread continues here: 2270 Bias will not adjust below 45 mV
 
Some don't like them, but an NTE123AP should work in place of the 2sc984 and should not be too hard find.
Cheap enough to try any way. You could always replace it later with another.

Rob
 
Service bulletin M-2270-1 states that H760 (2SC984B) be replaced with a 2SC496-O.
Other recommended replacements are 2SC495 and 2SD669. You will have to extend the leads with short wires and you may have to add a mica insulator to keep the transistor's collector isolated from the heat sink.

Did you read this thread?

Tom

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Thanks .
there is R794 & R795 that look like a variable resistor . Do you know how to adjust them ?
 
R794 and R795 are for the ASO adjustment. This limits the drive to the amplifier under certain conditions to prevent destruction of the output devices. See Section 15 Step 6 in the service manual. Note that the manual procedure was written for the early model 2270s so you will have to sus out what the measurement points are for your later model. You will need a good quality 6uF film or PIO capacitor, an audio signal generator and two dual channel oscilloscopes capable of x/y operation. A lot of patience might come in handy, too.

Tom
 
I don't have a oscilloscopes , i hope it will be ok
what do you think if i turn the volume up and ajust it to be witn no distortion , just by hearing ?
 
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You would be better off just leaving them alone. The ASO circuit is not normally active except at certain frequencies where the speaker becomes a reactive load.

Tom
 
Whaleman said:
Been having that static storm on warm up on my 2270 left channel. Eventually the protection kicks in as it get worse with heat.

Here is a complete list of replacement transistors for my 2270 amplifier board including the outputs, the original numbers in parenthesis, please reply with proven replacement and I will update this list.

1. H751 = Zetex ZTX795A (2SA640) input pair, shrink wrapped with the one below
2. H752 = Zetex ZTX795A (2SA640) input pair, shrik wrapped with the one above

3. H753 = (2SC945)

4. H754 = (2SC735)
5. H766 = (2SA562) not in the board diagram below, but in schematic

6. H755 = (2SC735)
7. H767 = (2SA562) not in the board diagram below, but in schematic

8. H756 = 2N5415 (2SA484) with the daisy flower heat sinks - TO-39 case
9. H757 = 2N3440 (2SC484)

10. H758 = (2SC680) These are the two bigger transistors
11. H759 = (2SA566)

12. H760 = (2SC984) this one is on the backside of the board

MAIN OUTPUTS

13. H003 = MJ21193G (Motorola, Fairchild, Toshiba, etc.) PNP - Bottom position
14. H004 = MJ21194G NPN - Top position


Also, others recommended for outputs: MJ15024 and MJ15023
Click to expand...

sorry for the second bump , i have marantz 2270 s\n 57466 is this subs will be ok ? thanks udi.
 
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