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NAD 214 Protection Circuit
NAD 214 Protection Circuit
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Old 25th September 2019, 06:02 PM   #1
jaycrimson is offline jaycrimson  United States
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Join Date: Dec 2006
Default NAD 214 Protection Circuit

Hey guys,

I've got a NAD 214 that's making me nuts. The amplifier powers on, but stays in protect mode with the red light illuminated. I inspected the relay and the coil was a bit out of spec, so i replaced it with an Omron G2R 48vdc. Still showing the same problem. My voltages seem correct across the board, my idle currents are right where they should be. I replaced the electrolytic caps in the protect circuit, thinking one of them may have dried out, but still no difference. With the relay manually engaged i'm getting 348mvdc on the outputs. Nothing out of the ordinary. What am i missing in the protect circuit?
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Old 25th September 2019, 07:28 PM   #2
Ylli is offline Ylli  United States
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That unit uses a DC servo to center the output, 348 mV offset is probably excessive. Do you see this on both channels?

Take a look at the supply voltages for the servo amp IC201. Pin8 should be +15 volts, and pin 4 should be -15 volts.
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Old 25th September 2019, 07:50 PM   #3
jaycrimson is offline jaycrimson  United States
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I'm getting +14.72 at pin 8, and -14.72 at pin 4.

My voltages at TA7317 are
P1: -0.8v
P2: -194
P3: -197
P4: 0
P5: -0.77
P6: 49 (should be zero to engage relay)
P8: -349mvdc
P9: 0.5
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Old 25th September 2019, 09:53 PM   #4
Ylli is offline Ylli  United States
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Pin 8 and pin 9 are suspicious. What are you seeing on Pin 7?

Check R230 and R234. Really need to have 2.5 - 3 volts on pin 9.
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Old 25th September 2019, 11:03 PM   #5
jaycrimson is offline jaycrimson  United States
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Thanks for the replies

I'm seeing -41mV on pin 7

I checked R234 and it measured in spec. R230 however was reading 10M, instead of 18k. I replaced it and she fired right up.

THANK YOU!
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Old 26th September 2019, 06:55 AM   #6
Ylli is offline Ylli  United States
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