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Old 11th December 2013, 09:25 PM   #1
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Default TDA7396 trouble!!!!!

I am attempting to repair a radio shack PA amplifier using the tda7396 chip amp with no output. I do not have a schematic or currently a model number.
I have a good audio signal at pin 2 and a tiny signal on pin 1 (assuming neg. feedback)
I have 18v on pins 3 and 9.
I checked pins 7 and 5. they have good connections to the output transformer. I disconnected the transformer and put an 8ohm load on thinking maybe it was shorted. I did not find any shorts to ground on pins 5 and 7.
I have 9v on pin 8 (standby).
I have .9v on pin 11 (mute) I can not tell from the data sheet if that is normal or not.
I checked pin 4 voltage, it is .6v. The data sheet seems to say that if the self diagnostics pin (4) is showing a fault it will be low. Is .6v low or high? I have a good ground connection on pin 6.
My limited experiance with these is that when then fail they usually short and blow the main fuse. this is not the case.
Befor I replace the chip out of desperation, I am hoping somebody can help me decipher the data sheet and give me some ideas on other things to check. Thanks, Fred
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Old 12th December 2013, 03:39 PM   #2
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Wanted to add that I tested capacitor CM and resistor RS and thay both appear to be okay. Thanks in advance for your help, Fred
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Old 12th December 2013, 03:56 PM   #3
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Quote:
Originally Posted by jeeptechfred View Post
I am attempting to repair a radio shack PA amplifier using the tda7396 chip amp with no output. I do not have a schematic or currently a model number.
I have a good audio signal at pin 2 and a tiny signal on pin 1 (assuming neg. feedback)
I have 18v on pins 3 and 9.
I checked pins 7 and 5. they have good connections to the output transformer. I disconnected the transformer and put an 8ohm load on thinking maybe it was shorted. I did not find any shorts to ground on pins 5 and 7.
I have 9v on pin 8 (standby).
I have .9v on pin 11 (mute) I can not tell from the data sheet if that is normal or not.
I checked pin 4 voltage, it is .6v. The data sheet seems to say that if the self diagnostics pin (4) is showing a fault it will be low. Is .6v low or high? I have a good ground connection on pin 6.
My limited experiance with these is that when then fail they usually short and blow the main fuse. this is not the case.
Befor I replace the chip out of desperation, I am hoping somebody can help me decipher the data sheet and give me some ideas on other things to check. Thanks, Fred
I do not think 0.6V can be high in any case. Looks like tda7396 chip fault.
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Old 14th December 2013, 12:07 AM   #4
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Turns out on a closer look pin 4 is not used in the design of the unit. Requires v ref to get a high reading. I foun d low resistance from ground to pins 5 and 7. I pulled both pin out of board prior to measuring. I ordered a replacement chip and going see. I think it is shorted.
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Old 19th December 2013, 02:51 AM   #5
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Today I measured the new chip amp from pin 5 to the ground pin and pin 7 to the ground pin. In both situations I got a measurement of several kohms. I removed the old chip amp. I then rechecked the inputs and outputs on the board. All checked okay so I installed the chip and it worked correctly. Thanks for your help!!

Problem solved
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