Hey guys,
After some diagnostics with my friend, he concluded that one of regulators that is providing Vcc +/- 18v on board is dead, (-18v works fine, positive is broken) and he told me to wire two bridge TDA7294 chips to "manually" activate them. He drew me a little schematic, but im not sure if its right, maybe i miss draw something.
If you could guys check it out and provide some feedback, that would be awesome, and i can start with soldering
P.S. shematic is super bad, i dont have any drawing software, used photoshop
Imgur: The most awesome images on the Internet
After some diagnostics with my friend, he concluded that one of regulators that is providing Vcc +/- 18v on board is dead, (-18v works fine, positive is broken) and he told me to wire two bridge TDA7294 chips to "manually" activate them. He drew me a little schematic, but im not sure if its right, maybe i miss draw something.
If you could guys check it out and provide some feedback, that would be awesome, and i can start with soldering
P.S. shematic is super bad, i dont have any drawing software, used photoshop
Imgur: The most awesome images on the Internet
An externally hosted image should be here but it was not working when we last tested it.
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So, those two resistors shouldn't be connected at all ? If you could please elaborate on my schematic ? I fairly new to this and its bit hard to follow what goes where
Yes, i looked at data sheet, but to be honest, it is only confusing me more.
Your schematic is incomplete. For the chip to operate both pins need to be taken to the positive supply voltage via the resistors shown. A 10k for pin 10 and a 20k for pin 9. So the junction of the two resistors in your diagram should go to the positive rail. That turns both mute and standby functions on and off together (not ideal).
The best solution is in the data sheet as shown here. This gives much better sequencing of the two signals during power on and off.
The best solution is in the data sheet as shown here. This gives much better sequencing of the two signals during power on and off.
Attachments
I got caught out with standby and mute circuit on a hybrid design.
I had the valve heaters running off B- via resistors. This meant on power down negative rail died first causing TDA to give loud pop through speaker.
I had to change circuit so heater was running off B+ and so standby/mute went low before negative rail died.
You should be ok if you have a balanced supply system.
I had the valve heaters running off B- via resistors. This meant on power down negative rail died first causing TDA to give loud pop through speaker.
I had to change circuit so heater was running off B+ and so standby/mute went low before negative rail died.
You should be ok if you have a balanced supply system.
Pin 15 is the negative supply (or ground in a single rail application). That's no good.
It needs to go to pins 7 and/or 13 which are the positive supply pins but remember this is not ideal and not the recommended way to do it. For the sake of one extra resistor and one extra diode you should do as the manufacturer recommends.
It needs to go to pins 7 and/or 13 which are the positive supply pins but remember this is not ideal and not the recommended way to do it. For the sake of one extra resistor and one extra diode you should do as the manufacturer recommends.
Great, thanks for help, much appreciate. I will get parts tomorrow and hopefully make this dam thing work again
Well, with a de-solder pump (mechanical) or -wire it's not very hard. But if you are going to replace them, there's a very easy practical tip: Snip the legs and de-solder the remaining wires separate.
Do You have the control pod too or only the sub ? There is a thread here regarding powering those speakers without the pod. Bear in mind that although the rail voltages could be powering the chip, You need a control voltage on the standby or mute pin in order to hear something... and I own one and I am very satisfied with the speakers.
Yes, that works very well. I prefer to cut quite low though because the IC might not be faulty (or only partly probably) and that way you could still test and recycle it in another project. Despite being very cheap it doen't have to be wasted.
Anyway, it's been already said, if the IC didn't blow up by periphereal circumstances (power supply, lack of cooling etc.), it might be a good idea to replace it with the TDA7293 since it's a bit more sturdy and you can often even get it cheaper than the 7294, depending on where you can buy it. They are pin-compatible and exchangeable in most cases.
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