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Old 16th June 2019, 02:26 AM   #1
Bills amps is offline Bills amps  United States
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Had a very badly arched amp come in for repair. One whole side of the amp section was burnt. Pulled all the output fets and audio driver card. This amp has a drive circuit for the gate driver. All the BTJs were shorted. Replaced them. Replaced the ir21844 on the one side that was blown(driver card only has two shown in picture below). Replaced a small resistor on the card as well. Also replaced all the 1 ohm resistors in the gate drive circuit. Problem is i still have no low or high side drive wave with fets reinstalled.(only 1 per bank). Also had to replace all the gate resistors. Can anyone identify U6, U4, U3 on the card? The amp died a bad death.
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Old 16th June 2019, 02:34 AM   #2
Bills amps is offline Bills amps  United States
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I found part of my answer. Now just trying to figure out why I dont have drive wave on low and high side.
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Old 16th June 2019, 02:59 AM   #3
Perry Babin is offline Perry Babin  United States
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You stated that you had no drive with one FET installed. Did you have drive with no FETs installed?
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Old 16th June 2019, 12:23 PM   #4
miniman82 is offline miniman82  United States
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If the totem pole transistors blew it might have taken out the next chip back as well? Perhaps there’s a PWM controller driving them that let go as well, are you able to find data on any of the chips on that card to tell what they are?
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Old 16th June 2019, 05:27 PM   #5
Bills amps is offline Bills amps  United States
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Quote:
Originally Posted by Perry Babin View Post
You stated that you had no drive with one FET installed. Did you have drive with no FETs installed?
Yes i did test with no fets. and also applied a signal to see if that might bee the case. I know some amps wont have drive without a small signal.
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Old 16th June 2019, 05:40 PM   #6
Perry Babin is offline Perry Babin  United States
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There's no reason for the drive to stop with the FETs in the circuit.

Did you trace the input from the input of the driver board, to the op-amp, to the LM211, to the driver ICs?

What is the DC voltage on pin 2 of the 21844 driver ICs?
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Old 16th June 2019, 10:59 PM   #7
Bills amps is offline Bills amps  United States
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i have not traced the input through the amp. just done the simple checks.
The DC voltage on pin 2 of the 21844 is 152.5 and 154.0. That was measured using the the speaker ground int on the board.
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Old 16th June 2019, 11:14 PM   #8
Perry Babin is offline Perry Babin  United States
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All 21844 voltages except for the 3 high-side terminals will be measured with the black probe on the negative rail terminal. The low-side shunts are an easy location to place the black meter.

Do NOT ground your scope to those shunts unless it's a battery operated scope with no connection to the mains.
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Last edited by Perry Babin; 16th June 2019 at 11:20 PM.
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Old 19th June 2019, 10:58 PM   #9
Bills amps is offline Bills amps  United States
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Then the corrected voltage for pin 2 is 0.0v
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Old 19th June 2019, 11:03 PM   #10
Perry Babin is offline Perry Babin  United States
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With that pin at 0v, the IC will not produce output. Is it being driven to ground or is the IC defective (or possibly a solder bridge)?
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