No sound from TDA7492P Amp

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OK, at least we now know that the logical inputs are as they are supposed to be.

Most of the TDA7498 inputs serve both channels such that, as one channels works, they should also allow the other channel to work.
Non-regulation of a channel normally is caused by 1) a faulty chip 2) a fault in the external components on the input pins 3) an error in the feedback signal.

For TDA7498, the cause 3) is little likely because the feedback signal is internal in the TDA7498.
Cause 1) we cannot do much about, should it be the case.
So, we have to examine cause 2). For doing that I suggest that you switch off the power to the board and measure the impedance:
from pin 22 to ground and to the power supply line (+),
from pin 23 to ground and to the power supply line (+),
from pin 32 to ground and to the power supply line (+),
from pin 33 to ground and to the power supply line (+).

The reason for these measurements is that the two channels have similar external input circuits. When you cut the power, the chip inputs normally become high impedance. Then you can see any difference in impedance as an indication that the external circuits are actually not similar though they are supposed to be. Then you will get a good hint to where to look for the fault (if there are differences).
 
It seems that the external input circuits have got no apparent flaws.
When we isolate the amplifier part (TDA7498) with correct logical input signals, one channel works but the other not. It seems more and more likely that the chip is faulty.

If you still have some energy left, there are a few test to do but mainly to indicate that the chip is actually faulty:

Connect a 47KOhm resistor between 3.3V and pin 28. 1KOhm on the faulty output. When you turn on the power, does the voltage on pin 28 go to 3.3V? (if yes, it indicates that the chip itself sees a fault)

No power on the board. Figure 19 of the datasheet in front of you. Concentrate on the chip-pins on the right side in FIG.19 (output pins). Do any of the chip-pins seem to have a rather low impedance to ground or power-supply "+" except for those pins that are supposed to be connected to ground or power-supply "+"?
 
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Sorry for having been away on travel for some days.
These measurement results unfortunately show nothing conclusive. The chip itself seems not to recognize the fault as pin 28 remains low.
The chance that the chip is defect is high. You can try to change the chip but it is a delicate job.

I am sorry that you now have two defect boards. I have bought more than 20 amplifier boards from the cheapest suppliers (in Asia) and only very recently I got one that was defect on arrival (a TDA7293 board where the low side push-pull transistor had shorted to "-").
I hope you are not too disappointed in DIY from this annoying experience.
 
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Thats alright FauxFrench, I appriciate your help.

No, i am not disapointed in DIY, i like it.
Not that i have 2 broken boards. but to make things i do like.

most disapointed is that it takes 3 weeks before a new board arrives.

Another question:
I have lying around another board, i use it and wait for the replacement board.
but every time i power up the board the volume is trown back to a lower level.
Is it possible to stay on the loudest volume on the board?
 
Hi All,

I found the same problem as the dutchronnie found on my board. Bluetooth SANWU connect to phone, but I cannot heard anything from the speakers. A months ago work correct.
First of all try the method as FauxFrench describe use the screwdriver to hear the Brum in the Speaker, and it work but the level is so quiet, after I check the Mute function and the Bluetooth module send a 3,3 V To the Mute pin, when play music. I cannot found anything not function coreect, but the module not work. I use the hotgun to resolder all the solder joints, and remove the stage with NE5532 and connect the different output of the Bluetooth module with the TDA.
After that all thinks suddenly work correct .....

Best regards
Roland
 

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Hi All,

I found the same problem as the dutchronnie found on my board. Bluetooth SANWU connect to phone, but I cannot heard anything from the speakers. A months ago work correct.
First of all try the method as FauxFrench describe use the screwdriver to hear the Brum in the Speaker, and it work but the level is so quiet, after I check the Mute function and the Bluetooth module send a 3,3 V To the Mute pin, when play music. I cannot found anything not function coreect, but the module not work. I use the hotgun to resolder all the solder joints, and remove the stage with NE5532 and connect the different output of the Bluetooth module with the TDA.
After that all thinks suddenly work correct .....

Best regards
Roland

There is an old saying: Not even the best planning or method can replace plain luck.
 
The short circuit may have destroyed the TDA7492 chip. Perhaps not the current itself (there is probably an over current protection) but voltage spikes generated by the filter coils.

First the 10 Ohm test: No power supply or input signal. With an Ohm-meter in the 20K range. Looking at the two power terminals ("+" and "-") and the four speaker output terminals. If you measure between any (two) of these six terminals, do you get an Ohm-meter reading of less than 10 Ohm?

IF you have a combination with less than 10 Ohm, the chip is very likely defect, if not, it may still be defect.

If both channels are dead, it is not likely to be any other component than the TDA7492 because any other component would affect only one of the two stereo channels.


I connected mine to 4ohm speakers, no sound Then I connected it to 5.5ohm speakers, no sound
I ran those tests and got infinite resistance all around which is a lot more than 10ohms Should this play with speakers less than 8ohms?
 
I connected mine to 4ohm speakers, no sound Then I connected it to 5.5ohm speakers, no sound
I ran those tests and got infinite resistance all around which is a lot more than 10ohms Should this play with speakers less than 8ohms?

I use the 10 Ohm test whenever I have a doubt and until now, if the amplifier passed this test, the problem was not the chip. Evidently, this is no guarantee but a good indication.

It is not that you use a 4 Ohm or 5.5 Ohm speaker that you get no sound. It may be that the amplifier simply doesn't start up and could be muted or disabled at control pins.
Try to put the 4 Ohm or 5.5 Ohm speakers on the outputs of the amplifier, let it start up and measure the voltage between supply "-" and each of the two outputs lines for each channel. When you start up a class D amplifier with BTL configuration, the voltages on each output line slowly increase toward half the "+" supply voltage before turning the sound on. This is in order to avoid the start-up "blob". If the voltages on each output line does not increase, it is because the chip gets an internal "instruction" not to start. That can be due to detection of a failure.
 
I'm using a univeral laptop charger It's lowest voltage setting is 15V so that's what I'm using I think with 15V power it's not going to power up it's amplifier in order to protect it's own circuitry

The smallest laptop chargers I know can do about 65W. It is not a matter of if the amplifier can play at its maximum. It is a matter of if the amplifier can start up and that should be possible with 15V/65W. Please check that your speaker cable does not have a short-circuit.
If it is your power supply that will not start, you do not have the 15V on the supply terminals with power on the charger.
 
I use the 10 Ohm test whenever I have a doubt and until now, if the amplifier passed this test, the problem was not the chip. Evidently, this is no guarantee but a good indication.

It is not that you use a 4 Ohm or 5.5 Ohm speaker that you get no sound. It may be that the amplifier simply doesn't start up and could be muted or disabled at control pins.
Try to put the 4 Ohm or 5.5 Ohm speakers on the outputs of the amplifier, let it start up and measure the voltage between supply "-" and each of the two outputs lines for each channel. When you start up a class D amplifier with BTL configuration, the voltages on each output line slowly increase toward half the "+" supply voltage before turning the sound on. This is in order to avoid the start-up "blob". If the voltages on each output line does not increase, it is because the chip gets an internal "instruction" not to start. That can be due to detection of a failure.


Any of the four corners of the power connector would be the negative?
 
Hi

Any of the four corners of the power connector would be the negative?
NO !

please be careful with the name of the parts!!!
the power connectors are for power up the amp board - 2 connectors + and GND (ground). this amp needs a single voltage supply e.g. 24V - 0 -2 cables

the speaker connectors are "floating" and are for the R/L speakers marked as +/-. do not connect here a power supply!

please make a pic and send us a nice foto of your board. outside there are many version of amp boards - then we can help better

chris
 
It seems if it's 50W per channel then I would need 24V 5A power supply?


Hi


if you want to calculate the power into an 8ohm speakers impedance you have to calculate:
for class D its 2x24V is the max peak to peak - Vpp- swing of the theoretical of the output of the amp. under load you will loose lets say 2V = 2x22V.
for the calculation of the power (rms) you need the rms voltage into 8R.

22V*0,707 = 15,55 Vrms---> P=U^2/R = (15,55^2)/8R = 30Watt rms per channel

chris


V peak to peak to Vrms conversion calculator
 
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