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Old 11th June 2008, 02:17 PM   #1
reiver is offline reiver  United States
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Default Replacing Hafler 9130 transistors- 2 techie question

I was soldering in new caps on my Hafler 9130, and damaged the rt channel. When I started playing music I heard a pop and lost the music. I now have .400 DC offset on that channel but the bias is fine. I figure I overheated a transistor at the input because that was where I was soldering. There is no DC offset trimpot so I suspect Hafler matched the transistors at the factory, so....


- If I replace Q1 with a new 2N5550 I plan on also replacing Q2 to keep the parts "matched". Should I also replace Q3/4 to keep everything "matched"?

- To keep characterics/imaging the same between the channels, should I also change the same transistors in the other channel, even if they are ok?

After 20 years of modding this will be my first time replacing a transistor....thanks for any input. See the attached image.

-Bryan
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Old 11th June 2008, 02:25 PM   #2
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Are you sure that you haven't left any solder bridge at your intervention area ?

Haven't you put the capacitors backwards?
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Old 11th June 2008, 02:56 PM   #3
reiver is offline reiver  United States
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The only caps I changed were small value film caps (220pf, etc). Could be I have a short, I'll double check tonight for solder bridges...I was getting pretty tired and didn't want to mess it up more.

The "pop" and suddenly no music made me think of a transistor going though....
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Old 11th June 2008, 03:04 PM   #4
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Quote:
Originally posted by reiver

The "pop" and suddenly no music made me think of a transistor going though....

Or a solder bridge "making connection" with the vibration or warm up dilatation of the PCB...

Inspect the new capacitor for internal short, also...
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Old 12th June 2008, 02:45 AM   #5
reiver is offline reiver  United States
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Default The cause...

Well, I took my meter and checked Q1 and it didn't seem shorted.

I, ummm, then noticed, ummm, that one of the fuses on the board had blown. I replaced it and the problem mysteriously vanished(!) DC offset is fine and it sounds excellent now.

Thanks for the tips on looking for shorts....as it slowed me down from ordering transistors I didn't need.

Cheers, Bryan
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Old 12th June 2008, 01:15 PM   #6
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Default Re: The cause...

Quote:
Originally posted by reiver
Well, I took my meter and checked Q1 and it didn't seem shorted.

I, ummm, then noticed, ummm, that one of the fuses on the board had blown. I replaced it and the problem mysteriously vanished(!) DC offset is fine and it sounds excellent now.

Thanks for the tips on looking for shorts....as it slowed me down from ordering transistors I didn't need.

Cheers, Bryan
Sometimes is good to take some time ...

Cheers
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