you fed 70Vac to the transformer.
What is the transformer output?
What is the transformer connected to?
etc??????
What is the transformer output?
What is the transformer connected to?
etc??????
Figured that was self explaned....
70Vac in to a 110 to 24-0-24 transformer
transformer secondary to bridge rectifier, to get the +\- DC supply, filtered by 2 4700uf/50V caps to the amps power rails...
does that supply ~+-25Vdc to the amplifier?
What currents are flowing to the amplifier?
What is the output offset when the amp input is shorted?
What is the output offset into 1k0?
into 100r?
What currents are flowing to the amplifier?
What is the output offset when the amp input is shorted?
What is the output offset into 1k0?
into 100r?
Just for future reference, when solving problems like this, other forum members need to know all the information you have got and all the information they need to help solve a problem. Putting comments like that and being reluctant to take on suggestions is unlikely to get the problem solved quicker and is more likely to drive other members away from answering your question.
I have sufficient patience to take most willing Members through whatever.
There are some who refuse to share the workload or have an attitude.
I'll pull out when I can no longer stand the stress.
There are some who refuse to share the workload or have an attitude.
I'll pull out when I can no longer stand the stress.
If you suspect a short, the easiest way is to switch the amp off and measure resistance from pin to pin or from solder point to solder point.
Are you measuring with the speaker connected ?? If not then that could be the problem , 35v into your speaker should quickly cause your speaker to start smoking .....
I once made the mistake of measuring the DC offset of a LM3886 amp without the speaker connected and got the same results that you are experiencing .....
I once made the mistake of measuring the DC offset of a LM3886 amp without the speaker connected and got the same results that you are experiencing .....
I did have that with and without the speaker on. I changed the chip since I ruled everything else out. Also I found a few other bugs on my board that shoukd have been as they were. Also I misunderstood the operation on the standby and mute functions but all seems to be working now except I think I'm getting an open loop gain.
You do know that there is a PCB design in the TDA7293 datasheet that works for the TDA7294 ?? that is if you can do a home PCB etch job ....
I have used the PCB before and it works pretty good .....
I have used the PCB before and it works pretty good .....
Its pretty boring if things work first go.
When things go wrong thats when you start to learn.
Start with basics like is everything getting the right volts?
Have yo uwried everything up correctly ?
If the amplifier is built AC-coupled as per datasheet, the output offset is below 10 mV with or without speakers connected. There must be a wrong connection (short or open circuit) or a wrong component (wrong value, wrong polarity, defective, etc.)
Perhaps its the Bootstrap cap. I have a similar (the same) problem, and will try to remedy tonight with a new 22uF cap. Holding Thumbs. And I will be double checking all solder joints and tracks. -Removed this chip twice already, all other 6 tda7294's are working beautifully.
see: http://www.diyaudio.com/forums/chip-amps/100721-tda7294-bootstrap-svr-pins.html
see: http://www.diyaudio.com/forums/chip-amps/100721-tda7294-bootstrap-svr-pins.html
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Still no luck, replaced both 22uF caps, bootstrap and the other one on the input side, still a silly -30V on output.
I removed the bootstrap on another working channel, and it has not broken or cause a -30V on the output.
Anyone know what specifically causes this -30V output? I've replaced the chip twice and still no luck, I think it may be the veins in my wrists requiring replacing next.
I removed the bootstrap on another working channel, and it has not broken or cause a -30V on the output.
Anyone know what specifically causes this -30V output? I've replaced the chip twice and still no luck, I think it may be the veins in my wrists requiring replacing next.
SCKentrol do you have a working same type amplifier that you can take notes from to aid repair... or build afresh unit and put your faulty one to the side for now.. as all of us at some point have been in the same place as yourself, even track lay out's can drive us nut's. well you have some voltage readings to use so there's a start.....As Andrew T said he has the patience to walk members with what ever... help is on hand and we will try our best to help out..
Problem with Bridged TDA7294
I have a bridged TDA7294 amp. I'm using it with +\- 35 V supply,
And Schema is according to ST Datasheet,
It was working well, But Now It is giving 78V DC out on RL Out😕
What could be the problem.
I have a bridged TDA7294 amp. I'm using it with +\- 35 V supply,
And Schema is according to ST Datasheet,
It was working well, But Now It is giving 78V DC out on RL Out😕
What could be the problem.
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