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Old 17th October 2008, 12:21 AM   #1
zeppo4 is offline zeppo4  United States
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Default Kenwood KAC848 amp

I have a Kenwood KAC848 amp with the rail voltage fluctuating from about 28v to 33v. The 494 chip has many pins also going up and down. I will list the pins below. Please let me know where to start with this.
thanks Jeff

494 pins
1. 2.5 - 2.7v
2. .8 - 2.5v
3. 4.8 - 1.8v
4. .63
5. 1.69
6. 3.7
7. 0
8. 14
9. 0 - 4v
10. 0 - 3.7v
11. 14
12. 14
13. 5
14. 5
15. 5
16 0
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Old 17th October 2008, 06:12 AM   #2
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Is there any DC voltage on the speaker terminals?

Is the amp drawing excessive current (more than 2 amps)?
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Old 18th October 2008, 02:54 AM   #3
zeppo4 is offline zeppo4  United States
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Hi Perry

Yes, I am getting 1.8vdc to 1.89vdc on the outputs

the amp only draws at most 1 amp

This is with no signal running through it.

Thanks Jeff
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Old 18th October 2008, 07:28 AM   #4
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Have you checked the output transistors to determine if any were shorted?

For the following, the meter will be set to DC volts and the black meter probe will be on one of the non-bridging speaker terminals.

Do you have positive voltage on the center leg of D11 and negative voltage on the center leg of D12?

Do you have either positive or negative rail voltage on the center leg of each of the output transistors?

Do you have both positive AND negative voltage on the power supply pins of each of the op-amps?
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Old 19th October 2008, 01:26 AM   #5
zeppo4 is offline zeppo4  United States
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The outputs don't seem to be shorted. D11 has positive voltage going from 22v to 33v and D12 has negative voltage going from -22v to -33v.
The 2SA1908's have negative rail going from -22 to -33v and the 2sc5100's have positive rail going from +22v to +33v.

I connected a signal and the amp will turn on and work good for about five minutes. then turn off for about ten minutes. the readings are from when it turns off. when the amp is on the rail voltage becomes steady.
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Old 19th October 2008, 09:55 AM   #6
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When the amp is working normally, if you push on the board at various points with a non-conductive probe, can you make it shut off?
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Old 23rd October 2008, 04:27 AM   #7
zeppo4 is offline zeppo4  United States
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Perry, thank you so much. I checked the board for a broken solder joint and found the transister between two of the outputs. I resolder it and other's that looked bad and now the amp is working great. Thank your help. Jeff
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