Did this kill my chips?

ormo · 22nd July 2009, 08:21 PM

I have a stereo amp with one LM3886TF on each channel. Thanks to a c*ck up in the markings on the supply rails they were connected wrong: one chip got the ground and both positive supply rails, one chip got the ground and both negative rails.

Is this likely to have fried my chips beyond use? Both speaker coils were cooked.

pacificblue · 22nd July 2009, 09:32 PM

Yes, it is likely. Strange as it may seem however, they could have survived. When you have them connected right with no speaker at the output, check the output pin. If the voltage there is at rail level, the ICs are fried. If the voltage is next to zero within 100 mV, they will probably still be working.

Next time use a light bulb tester and measure the output before connecting anything to the amplifier.

Minion · 22nd July 2009, 10:44 PM

These chips are surpriseingly durrable so it could have survived ... I recently screwed up and connected the -35v rail to the speaker out as well as a speaker connected to the board ..... I got a super loud hum , then figured out my mistake and fixed it and they worked fine ...

I would also be worried about the local filter caps cuz if you connected it backwords the caps would be reverced biased and could be damaged , make sure they aren"t bulging or leaking ....

Cheers

ormo · 22nd July 2009, 11:30 PM

Thanks pacificblue, very peculiar findings when I tried what you suggested:

One of the chips gives about -10v between Pin 3 (output) and ground, so I presume that one is busted.

The other chip gives a reading of 0v between Pin 3 and ground, which suggests it may have survived. I tried connecting it to a (cheaper) speaker, but it gives absolutely no output when I give it an input. I confirmed this with a voltmeter - still a reading of 0v on the output pin when I give it an input.

Any advice - do I need two new chips or may there be a way to resurrect the later one?

Thanks

Redshift187 · 23rd July 2009, 01:34 AM

0V may be busted too. It shouldn't be exactly 0, but a few millivolts above or below that.

star882 · 23rd July 2009, 02:01 AM

There's your excuse to upgrade to a hybrid digital. Most hybrids are single rail BTL, which reduces the chance of wiring it wrong.

pacificblue · 23rd July 2009, 06:41 AM

ormo · 23rd July 2009, 10:07 AM

Tested the 0v one again with a more accurate voltmeter... I get about -9.7mV on the output pin with no load. Still no actual output if I give it an input.

I've already got 2 new chips on order now anyway

22nd July 2009, 08:21 PM	#1
ormo diyAudio Member Join Date: Jan 2009	Did this kill my chips? I have a stereo amp with one LM3886TF on each channel. Thanks to a c*ck up in the markings on the supply rails they were connected wrong: one chip got the ground and both positive supply rails, one chip got the ground and both negative rails. Is this likely to have fried my chips beyond use? Both speaker coils were cooked.

22nd July 2009, 09:32 PM	#2
pacificblue diyAudio Member Join Date: May 2008	Yes, it is likely. Strange as it may seem however, they could have survived. When you have them connected right with no speaker at the output, check the output pin. If the voltage there is at rail level, the ICs are fried. If the voltage is next to zero within 100 mV, they will probably still be working. Next time use a light bulb tester and measure the output before connecting anything to the amplifier. __________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

23rd July 2009, 02:01 AM	#6
star882 diyAudio Member Join Date: Mar 2007	There's your excuse to upgrade to a hybrid digital. Most hybrids are single rail BTL, which reduces the chance of wiring it wrong. __________________ "Fully on MOSFET = closed switch, Fully off MOSFET = open switch, Half on MOSFET = poor imitation of Tiffany Yep." - also applies to IGBTs!

23rd July 2009, 06:41 AM	#7
pacificblue diyAudio Member Join Date: May 2008	__________________ If you've always done it like that, then it's probably wrong. (Henry Ford)

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22nd July 2009, 10:44 PM	#3
Minion diyAudio Member Join Date: May 2006	These chips are surpriseingly durrable so it could have survived ... I recently screwed up and connected the -35v rail to the speaker out as well as a speaker connected to the board ..... I got a super loud hum , then figured out my mistake and fixed it and they worked fine ... I would also be worried about the local filter caps cuz if you connected it backwords the caps would be reverced biased and could be damaged , make sure they aren"t bulging or leaking .... Cheers

22nd July 2009, 11:30 PM	#4
ormo diyAudio Member Join Date: Jan 2009	Thanks pacificblue, very peculiar findings when I tried what you suggested: One of the chips gives about -10v between Pin 3 (output) and ground, so I presume that one is busted. The other chip gives a reading of 0v between Pin 3 and ground, which suggests it may have survived. I tried connecting it to a (cheaper) speaker, but it gives absolutely no output when I give it an input. I confirmed this with a voltmeter - still a reading of 0v on the output pin when I give it an input. Any advice - do I need two new chips or may there be a way to resurrect the later one? Thanks

23rd July 2009, 01:34 AM	#5
Redshift187 diyAudio Member Join Date: Aug 2008	0V may be busted too. It shouldn't be exactly 0, but a few millivolts above or below that.

23rd July 2009, 10:07 AM	#8
ormo diyAudio Member Join Date: Jan 2009	Tested the 0v one again with a more accurate voltmeter... I get about -9.7mV on the output pin with no load. Still no actual output if I give it an input. I've already got 2 new chips on order now anyway

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