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Old 10th November 2006, 03:54 PM   #1
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Default directed 1500d

im working on this amp and the inputs do not work and only 1 rca output works just wondering what i might check or could it be the preamp drivers
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Old 10th November 2006, 04:43 PM   #2
sdoom is offline sdoom  Germany
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Hi

sometimes the RCA jack itself is not ok, best thing is to check the power supply voltages across the op-amps (usually +15 and -15V). Usually pre-amp section faults are easy to find if you feed a small sine signal to the RCA inputs and trace the signal with a scope.
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Old 10th November 2006, 05:17 PM   #3
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just wondering if anyone knows if the i think lm361n ic chip controls the outputs theres another ic chip right next to it but cant tell the numbers because someone sratched them off dont know if the factory does that so u gotta send it back for repair
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Old 10th November 2006, 08:42 PM   #4
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I can't believe they didn't deface that IC.

That IC accepts the triangle and audio waveforms and generates the PWM output. If you have audio (it could be shifted or straight DC if the feedback circuit is working properly) on one input and the triangle waveform on the other input and DC offset on the output, it's likely that the IC is defective. Generally, when they fail, both outputs of the IC swing the same direction (both go high or both go low). That's not possible if the IC is in proper working order.

If it's like some of the other amps that use that IC, there are unused pins. The unused pins have solder pads that lift easily when heated. To prevent damage to the board/pads, use chip-quik solder (desoldering system). It's relatively expensive but you don't need much. chip-quik will send you a sample for free. Digi-key sells it when the sample runs out.

http://www.chipquik.com/
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Old 10th November 2006, 09:47 PM   #5
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thanks perry i will check that ic out the lm361n do you know if thats the only chip that controls the outputs or does that other ic control them also if so do u know the number of that chip because the defaced it so i have no clue what part number it is
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Old 11th November 2006, 12:38 AM   #6
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For amps that use those ICs, the IC next to the blue crystal generates the carrier wave (square wave ~80kHz).

There is an op-amp that takes the square wave and converts it to a triangle wave (op-amp used as an integrator).

There is another op-amp that compares the output to the preamp signal and corrrects for errors (simple servo/feedback circuit).

These op-amps may be on the same IC or on different ICs. It varies by amp.

The triangle waveform and the audio drive waveform (out of the op-amp being used for error correction/feedback) are driven into the lm361 (could also be an NE529). The 361 drives the outputs through a driver stage.

If you post the voltages on all of the pins of the lm361, it will help in troubleshooting.
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Old 11th November 2006, 01:11 AM   #7
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well kinda hard now to i was testing the voltage on the pins of the lm361 and i touched one of the pins with my meter probe and well the power supply decided to take a crap on me it poped a trace from the remote wire to the diode took out the diode and i fixed the trace and the diode but now the amp is in protection
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Old 11th November 2006, 02:02 AM   #8
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How did you blow a diode in the remote turn-on circuit (this may help in troubleshooting)? That's nowhere near the 361 in most amps. Were you probing the 361 when it the damage occured?

Whenever testing an amp, you should always use an inline current limiter (resistor or headlamp if your supply doesn't have current limiting) or a fuse rated no higher than 10 amps. These won't always provide complete protection but they will save many components from damage when something goes wrong.

Since I don't have any notes on a 1500, you may need to post some photos (better than those on ampguts).

justonemoreamp may have a schematic to help you troubleshoot the protection circuit if it was damaged.
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Old 11th November 2006, 01:32 PM   #9
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just wondering how i might get the amp back out of protection mode??
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Old 11th November 2006, 06:40 PM   #10
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I asked questions that may have helped diagnose the problem. They were not there because I like to type.
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