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Old 09-14-2021, 10:16 AM   #1
jason123
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Default Pioneer VSX-523-K Amplifier - Identify resistors

Hi folks,
New audio equipment repair and I could use some help.
Picked up VSX-523-K Surround sound amplifer.

Upon power up for the first time (been sitting for a while) loud popping noise and smoke..

Disconnected, opened up and found many popped caps on the amplifier board.
Replaced all, replaced A992 BJT, and pre-amp transistor and power transistor. I found 0.47 Ohm resistors that are blown or have gone High impedance and I'd like to replace.

On the service manual, it shows these as 0R47(2) (assuming this is a 0.47 Ohm, 2W?)

Question is .. what type of resistors are these? Flame proof, coated, .. ?? I see the leads have insulation of some kind. Just making sure I replace with appropriate resistors.

Thank you
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Old 09-14-2021, 03:59 PM   #2
tibimakai
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Default Re: Pioneer VSX-523-K Amplifier - Identify resistors

If the 0.47ohms are blown, then the final transistors are as well.
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Old 09-14-2021, 04:03 PM   #3
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Default Re: Pioneer VSX-523-K Amplifier - Identify resistors

q6c and q7c will likely be toast .. i guess the resistors will likely be wirewound non inductive .
also other components could be blown .
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Old 09-19-2021, 12:31 PM   #4
jason123
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Default Re: Pioneer VSX-523-K Amplifier - Identify resistors

So, Channel C seems to have the issuse (Had the blown transistors and output caps)

In addition to all the Electrolytic caps being replaced, I replaced all the components in Red circuit.

Then I found the items in Blue circles blown and these are on order.

After replacing the components in Red, I'm getting "OVERHEATING" and OL 19 errors.
Does ZD2C being shorted explain this? or could there be more components that are / could be bad? I tested as many components as I can on this channel

Thank you
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Old 09-19-2021, 01:14 PM   #5
petehall347
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Default Re: Pioneer VSX-523-K Amplifier - Identify resistors

maybe best to renew all diodes in that string .
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Old 09-19-2021, 01:17 PM   #6
petehall347
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Default Re: Pioneer VSX-523-K Amplifier - Identify resistors

those ksa992 that make up the diff amp need to be closely matched for vbe and hfe .
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Old 09-19-2021, 02:05 PM   #7
jason123
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Default Re: Pioneer VSX-523-K Amplifier - Identify resistors

Quote:
Originally Posted by petehall347 View Post
maybe best to renew all diodes in that string .
Planning on it. Can't find the original zener part (zj4.3b), replacing with NZX4V3B.. hope that would do it
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Old 09-19-2021, 02:07 PM   #8
jason123
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Default Re: Pioneer VSX-523-K Amplifier - Identify resistors

Quote:
Originally Posted by petehall347 View Post
those ksa992 that make up the diff amp need to be closely matched for vbe and hfe .
I tried, bought the a992, 10 taped and i used 2 of them. Hfe is within range of original, though not exact. That wouldn't cause the overheat issue, would it?

Last edited by jason123; 09-19-2021 at 02:16 PM..
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Old 09-19-2021, 03:29 PM   #9
petehall347
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Default Re: Pioneer VSX-523-K Amplifier - Identify resistors

no it would alter dc offset .
shorted diode and bias transistor would .

Last edited by petehall347; 09-19-2021 at 03:31 PM..
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