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Old 26th March 2003, 05:44 PM   #1
Ford_V6 is offline Ford_V6  Romania
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Default Amp on fire

Hy

My TDA7250 based amp went on "fire" today. The problem is that i do not know what's toasted. The 7250 or the TIP142/147.
How can il tell what's fried ?

Thanks

P.S. I want to replace the 142/47 tip's with TIP 36C and 35C. Does anyone knows how they sound ? However they have maximal ratings higher than 142/147.
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Old 26th March 2003, 08:21 PM   #2
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Default Re: Amp on fire

Quote:
Originally posted by Ford_V6
Hy

My TDA7250 based amp went on "fire" today.
First thing to do is try to find out why it toasted.
Now, measuring a bad transistor is much easier than measuring a bad IC. Hope you know how to measure transistors. In case you don't know, here's a link:
http://www.eatel.net/~amptech/elecdisc/trnsistr.htm
If you feel things are really toasted, I wouldn’t hesitate and replace the 7250 as well.

Quote:

P.S. I want to replace the 142/47 tip's with TIP 36C and 35C. Does anyone knows how they sound ? However they have maximal ratings higher than 142/147.
TIP142/47 are darlingtons, TIP36/35 are normal transistors.
You can't just switch them.

/Hugo
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Old 26th March 2003, 08:27 PM   #3
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US in MJ/E is the best for TDA7250.....
personal.... i dont like the TIP's Transistors

tip142/7 125W = tip35/6 125W
tip142/7 10A -/+ tip35/6 25A
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Old 27th March 2003, 10:57 AM   #4
Ford_V6 is offline Ford_V6  Romania
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The amp was running without the speakers connected when toasted. Is this the reason ?

I have read in another thread that this amp requires a 100 nf cap. between the + an - right next to the ic.

Now i will add this capacitor too.

I still don't know why the amp is shutting down at high volume.

When the amp toasted R17 and R19 toasted too.

I have attached the link to schematic after wich the amp is built.

http://home.eunet.cz/rysanek/tda7250.gif
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Old 27th March 2003, 11:35 AM   #5
Netlist is offline Netlist  Belgium
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Quote:
Originally posted by Ford_V6
The amp was running without the speakers connected when toasted. Is this the reason ?
Probably not.
Quote:

I have read in another thread that this amp requires a 100 nf cap. between the + an - right next to the ic.
If you mean pin 4 and 14, they are required.

Quote:

I still don't know why the amp is shutting down at high volume.
Did he play? What do you mean with shutting down? There is an overload current protection build in the 7250. Could be that.
Quote:

When the amp toasted R17 and R19 toasted too.
Can't see R17/19. BTW, wich voltage do you apply on the +/- Us?
And, are your transistors broken?

/Hugo - needs a schematic with part names.
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Old 27th March 2003, 12:15 PM   #6
Ford_V6 is offline Ford_V6  Romania
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I apply +/- 38 V

When i raise the volume the amp stops playing.
When i lower the volume the amp starts playing again.

When the amp toasted it was running only with one speaker conected. The TIP's are toasted too. ( C and E pins are in short circuit )

The amp played a few days.

The 100 nf cap. is not on the schematic. it has to be installed on pin 4 and 14 ?


Thanks for helping me out here

I have atached the schematic with part numbers.
Attached Files
File Type: zip tda7250q.zip (35.5 KB, 58 views)
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Old 27th March 2003, 12:50 PM   #7
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Quote:
Originally posted by Ford_V6
I apply +/- 38 V

When i raise the volume the amp stops playing.
When i lower the volume the amp starts playing again.

When the amp toasted it was running only with one speaker conected. The TIP's are toasted too. ( C and E pins are in short circuit )

The amp played a few days.

The 100 nf cap. is not on the schematic. it has to be installed on pin 4 and 14 ?
Depends how loud you go. If you raise the volume towards the limit of the amp, it will mute. (protection) If the amp mutes at low volume, it is likely the 7250 is broken or other broken parts are causing the mute.
First replace all bad components. Remember there's a major difference in schematic, using transistors vs. darlingtons. Look at the datasheet and study it:
http://us.st.com/stonline/books/pdf/docs/1472.pdf
Forget the 100nF for the moment.

/Hugo
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Old 27th March 2003, 05:50 PM   #8
Ford_V6 is offline Ford_V6  Romania
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You are so wright.

I'll keep use the darlingtons for the moment.


Thanks for all the help
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Old 27th March 2003, 05:58 PM   #9
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You're welcome.
Enjoy your amp!

/Hugo
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Old 28th March 2003, 12:29 AM   #10
Diode is offline Diode  United States
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How do you check the chip?

Check the output pins for DC volts. If you have the rail voltage, chances are that your chip is blown. I'd replace it anyway.

That is very weird topology to me. I don't see that ever in my line of work. I only see collector resistors on a quasi complimentary amp. All others use emitter resistors.

Good luck with the amp though!

Chris
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