7294 chip went bang??? - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th March 2014, 05:13 PM   #1
diyAudio Member
 
radiosmuck's Avatar
 
Join Date: Jul 2012
Location: Montreal
Default 7294 chip went bang???

Hi,
I have just purchased a stereo 7294 board that required me to add a heatsink, which I did!
The amp was working well for quite a while until I touched the heatsink to check the temperature. There was a flash, bang and a plume of smoke.
On checking the blown chip I noticed that I had not installed the mica insulator quite parallel the the chip body.
Winters are very dry here and static shocks are regular when touching a water tap or radiator. Is it possible that when I touched the heatsink a spark jumped the gap between it and the chip where there was no insulation?
Thanks.
  Reply With Quote
Old 12th March 2014, 05:42 PM   #2
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Quote:
Originally Posted by radiosmuck View Post
....Is it possible that when I touched the heatsink a spark jumped the gap between it and the chip where there was no insulation?.....
I doubt it. However it might have caused a spike on the ground line killing the chip. This chip IS sensitive to anything beyond what they strictly specify. So maybe lifting the ground momentarily caused something to blow on the chip.
Remember that the spark is between the hand and the heatsink. However it could cause a momentary disastrous voltage spike on the ground line !
__________________
AM

Last edited by ashok; 12th March 2014 at 05:45 PM.
  Reply With Quote
Old 13th March 2014, 02:24 AM   #3
jayadev is offline jayadev  India
diyAudio Member
 
jayadev's Avatar
 
Join Date: May 2006
Location: Kerala
Could this be a case of fake TDA7294?

Mine was purchased Locally in December, Used for 4ohm 12" Subwoofer with 2sc5200/1943 boosters.

It sounded pretty powerful and satisfactory with 36-0-36 volts dc input and a generous heatsink.A day of operation would make it warm(I can keep my hands on Heatsink without any casuality. viz50-60 degree celcius)


Approximately after 5 weeks there was only a loud buzz in woofer .I desoldered the chip and found output pin 13 and pin 15 has shorted. Output transistors are still intact.
__________________
"One good thing about music, when it hits you, you feel no pain." - Bob Marley
  Reply With Quote
Old 13th March 2014, 02:38 AM   #4
diyAudio Member
 
Join Date: Jun 2002
Location: non
It depends on where you purchased it, if you bought it from TayDay in china, or some place like that then all bets are off. Even local suppliers can bulk purchase these from places like this for peanuts, and you get fakes. Ideally you want a reputable supplier.

But the TDA7294 in itself is an overly sensitive component. I have seen many amplifiers and subwoofers built around that IC, even Bose, failed with no rhyme or reason as to why. One minute they work, and the next minute they spontaneously combust and I have seen something as simple as a power-on transition explode these ICs. I stayed away from this IC and avoided it like the plague. That goes with most of STs products.

Last edited by mbates14; 13th March 2014 at 02:42 AM.
  Reply With Quote
Old 13th March 2014, 03:11 AM   #5
jayadev is offline jayadev  India
diyAudio Member
 
jayadev's Avatar
 
Join Date: May 2006
Location: Kerala
Quote:
Originally Posted by mbates14 View Post
It depends on where you purchased it, if you bought it from TayDay in china, or some place like that then all bets are off. Even local suppliers can bulk purchase these from places like this for peanuts, and you get fakes. Ideally you want a reputable supplier.

But the TDA7294 in itself is an overly sensitive component. I have seen many amplifiers and subwoofers built around that IC, even Bose, failed with no rhyme or reason as to why. One minute they work, and the next minute they spontaneously combust and I have seen something as simple as a power-on transition explode these ICs. I stayed away from this IC and avoided it like the plague. That goes with most of STs products.
Thanks for quick response.

I have used a power on transistor at mute pin for soft start and quick turn off.

Is there a way to identify fake TDA7294 from the batch code ,I have tested pin 11 and 12 method.?
Attached Images
File Type: jpg tda.jpg (57.9 KB, 295 views)
__________________
"One good thing about music, when it hits you, you feel no pain." - Bob Marley

Last edited by jayadev; 13th March 2014 at 03:36 AM.
  Reply With Quote
Old 13th March 2014, 03:41 AM   #6
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Where do you take your drive for the power transistors ? A single resistor from the 7294 output or two resistors one on each the supply rail ?
If it's the latter , you are in a position that any glitch on the output 'could' cause failure.
__________________
AM

Last edited by ashok; 13th March 2014 at 03:44 AM.
  Reply With Quote
Old 13th March 2014, 03:55 AM   #7
jayadev is offline jayadev  India
diyAudio Member
 
jayadev's Avatar
 
Join Date: May 2006
Location: Kerala
Quote:
Originally Posted by ashok View Post
Where do you take your drive for the power transistors ? A single resistor from the 7294 output or two resistors one on each the supply rail ?
If it's the latter , you are in a position that any glitch on the output 'could' cause failure.
This is how power transistors are configured.
It worked 5 weeks perfectly,went off while turning on next day( so no thermal runaway or short circuits.)
Attached Images
File Type: jpg tdatrans.jpg (271.7 KB, 287 views)
__________________
"One good thing about music, when it hits you, you feel no pain." - Bob Marley
  Reply With Quote
Old 13th March 2014, 04:34 AM   #8
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
It is easier to identify a real TDA7293 because all 15 pins work in the real thing.

Problematically, the datasheet schema for TDA7293/4/5/6 tends to make them under-perform and eventually quit.

Suggestion: Treat the fake TDA7294 as if TDA7296--much lower power voltage.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 13th March 2014 at 04:37 AM.
  Reply With Quote
Old 13th March 2014, 07:12 AM   #9
diyAudio Member
 
Join Date: Feb 2013
Location: The Lowlands
Could most of these failures be caused by bad insulation between chip and heatsink? Negative rail and ground are only separated by a thin insulator. The current would only be limited by the PSU.
__________________
Regards Mark.
  Reply With Quote
Old 13th March 2014, 07:53 AM   #10
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Quote:
Originally Posted by jayadev View Post
......went off while turning on next day.........
Your output stage is OK and the rails of your input and output must be connected directly. So one possibility is that your supply rails didn't come up together ( or go down together when last switched off ....maybe like power off when music is playing loud !). I think the chip is sensitive to this.
Wish Ilimzn is reading this. You could search for him and send him a message. He understands this chip well.
__________________
AM
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
PCB TDA 7294 CristianValentin Chip Amps 5 24th July 2014 04:34 AM
Question about this 7294 amp Elkaid Solid State 22 3rd February 2010 03:03 PM
Amp on TDA 7294 maris24 Chip Amps 4 17th November 2006 10:11 AM
TDA 7294 Subwoofer abid_rehan Chip Amps 6 18th December 2003 03:36 PM


New To Site? Need Help?

All times are GMT. The time now is 06:51 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2