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Old 31st July 2005, 03:05 AM   #1
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Default emergency chip help!

ok heres the deal. I won grand champion with my amplifier at hendricks county 4-H, and was selected to go to state. The electronics judge told me to redo the circuit board befroe state fair because the ancient soldering iron I was useing was cruddy and didnt allow me to do a good job at all. Well, I redid the board today but when I went to plug it in and play it nothing happens. You can only get sound out of it when you do this: one of the channels on your output source to BOTH inputs on the amp- no ground, only one channel + and ground into + and + in on the amp. Both channels play fine that way, but its not the way its supposed to be. You hook up your ground and the sound cuts off immediatly. If you unconnect it and touch either of the inputs on the amp you will get the normal buzz sound out of the speakers, but grab the ground and it theres a pop and the speakers jump and theres no sound at all. Do you think my chips are fried? ( I tryed two chips I had- one was the one that did work in the amp before I redid it and another was one I had used in a circuit and desoldered again- I dont know if it worked to begin with. I did try it on the circuit board and got the same problem, and I even hooked it up on my solderless breadboard to try and diagnose it, SAME PROBLEM! forgot to mention my chip, its the TDA7264 chip. Also one more problem, if you hook it up like normal ( left/right/ground) obviously no sound, but if you turn my cd player up to full and turn the bass up all the way theres an intermittent ( horribly distorted ) sound every time you get bass in the music, but it wont have any high end at all. Only chopped off distorted bass... almost sounds like repeted farting only short and stiff.. haha. Anyways, I have to have this fixed before tuesday august 3rd, 3 days away. Anyone know anything that might be wrong? If its my chip, does anyone know anything about ST's samples program? would they do free next day air?

thanks for any help

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Old 31st July 2005, 09:08 AM   #2
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Schematic?

Pics?
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Old 31st July 2005, 10:22 AM   #3
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yes, probable that the internal partsof the tda7264 was fried by the soldering iron....as far as i have known from this chip amps and because of my experience building chip amps...i do encountered the same problems...if i was not that amused by the looks of my pototype...i sometimes desolder all parts on my board then re attached all of them to a new etched PCB...and the outcome was busted chip amps...a waste of money....so whenever i build something i see to it that i have a good etched pcb...and no more detaching its parts to avoid it...i've learned my lesson after that....so my suggestion is to buy new chip and re attached it to your new PCB....and take care not to over heat the chip again...for its their vulnerability.....
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Old 31st July 2005, 04:42 PM   #4
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http://www.st.com/stonline/books/pdf/docs/1477.pdf

schematic. I modifyed it a little, removing the capacitor to ground on pin 5 and running it directly to ground and adding a ripple rejection cap ( 100 uf) to ground from pin 7. I also added the usual output decoupling capacitors ( 4700 uf). These modifications were to convert it to single supply operation. Theres no fault in my work ( that I know of) because I've had the amp working for over 2 months just fine. No problems, wonderful sound, snr is incredibly high. must be around 115 -120 db. Anyways, I talked to an electricion and he said that the chip cant be fried from soldering because you would have to cook it for 10 mins at least at high temp to do it any damage. Also please note that these chips have tons of protection , so short circuit on the output or input or reverse polarity etc wont hurt it. The chip is working, just absolutly not the way its supposed to. Can they do that and still be fried?
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Old 31st July 2005, 06:41 PM   #5
inguz is offline inguz  United States
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Default What's on pin 7?

You just have pin 7 to a the +v of a 100uf electrolytic, with its -v to your ground? (Is that cap OK, too? If it shorted you might get something like what you describe)

For single-ended I would have thought you'd want to get pin 7 steady at half the supply voltage, e.g:

(+v) -------------
|
R (47k?)
|
|----- to pin 7
|
R (47k?)
|
(0v) -------------
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Old 31st July 2005, 07:39 PM   #6
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no no, this is not split supply this is single supply. Here, I have a better schem I redid. Yes the capacitor is ok, because I tryed like 4 other caps and it did the same thing. Remember, all these parts were in working order before I redid the circuit board. I have no idea what you mean by single ended....I meant single supply ( + and ground, not +/- and ground)

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Old 31st July 2005, 08:53 PM   #7
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I recently worked on a TDA2030 that was put together by somebody else that was exibiting similar behaviour.

It was popping, spluttering and going mad. I tracked it down to the terrible soldering that was done and a whole lot of dry solder joints

Make sure you got no dry solder joints. Pull and push all components while looking at the relavent solder joint to see if there is any movement.
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Old 31st July 2005, 09:07 PM   #8
inguz is offline inguz  United States
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Default Yes, I mean single supply too

The cap from pin 7 is fine (but I suspect it's maybe shorted or busted - check polarity too, should be +ve to pin). But also try putting two equal resistors from pin 7, one to negative(zero) supply, one to positive(+32) supply... anything from ~2k to ~100k should do fine as long as they're the same value... it's just to force pin 7 to be +16 volts.
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Old 1st August 2005, 11:35 PM   #9
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does it have to be 16 volts ( or half the supply voltage)? and why? Its not cold solder joints,btw ,I put it together on a solderless breadboard and got the same problem.
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Old 1st August 2005, 11:50 PM   #10
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btw, that didnt fix the problem. I think I might have somehow shorted the outputs?
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