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Old 4th August 2009, 03:20 PM   #1
diyAudio Member
Join Date: Aug 2009
Default pioneer amp repair

Have a few questions about this amp I'm trying to repair:

In the pic provided below:

1. are reticifers
2. What are these: numbers are B1566 and D2395. What is their function?
3. Are these bias related? D1684
4. Are these drivers? c3421 and a1358
5. I think these are the power supply, FKV550n. To test mosfets using diode check on DMM, do they have to out of the board or can I test them in the circuit (no power applied)?

c4388 and a1673 are BJTs? When I test them I don't get 0.6v or close. They run B-C 0.445v and B-E .460v. Is considered defective? What does it mean when I test other lead combos, I get a voltage that quickly runs up and then meters show 0L. Often it starts at .900v then over a few seconds run up and goes to 0L. Is this defective as well?

Thanks for any help!
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Old 4th August 2009, 04:42 PM   #2
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
Read through the basic amp repair page (link below). It shows a similar pioneer amp.
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Old 5th August 2009, 03:22 PM   #3
diyAudio Member
Join Date: Aug 2009
Thanks Perry. I have read your site a few times, but reading it again, I was able to answer my own question and stop second guessing.

I still have a question: I removed the power and output transistors from the board and tested them. What looked like defected in circuit, now tests fine. However, for the BJTs I get low voltage, 0.42-0.47v. I was reading somewhere else that acceptable voltage is 0.45-0.9v. How much is "close enough" per your site/experience to the 0.6v? I don't really want to just replace "for good measure" these transistors are like 8$ a piece, almost making the repair not worth it.

What is an esay way of telling if transistors are in parallel? Do I trace the printed circuit? Of what legs? Use the DMM?
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Old 5th August 2009, 05:11 PM   #4
diyAudio Member
Join Date: Nov 2003
Location: Louisiana
0.42 would probably be OK as long as you read an open circuit when you reversed the meter probes on those same legs.

I think those numbers (0.45-0.9) were for the FETs. Are you getting the FETs and BJTs confused? The large transistors are the outputs and are BJTs. The transistors in the red rectangle are the power supply FETs. The following shows a simplified way to check the FETs.

For the output transistors, there appear to be two groups of two parallel transistors per channel. You can use a multimeter to find low resistance connections between them. If there are 2 or more low resistance connections between them, they are in parallel. You can also follow the traces.

The power supply FETs are in two parallel groups of 3. If any power supply FET is defective, you must replace all 6.
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