melted lm3886tf in my Event ASP8 monitors PLEASE HELP!!! - Page 2 - diyAudio
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Chip Amps Amplifiers based on integrated circuits

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Old 22nd November 2012, 06:00 PM   #11
Mooly is offline Mooly  United Kingdom
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Bulb in series with the mains (the live) to limit current. It works well in place of a "fuse" and limits the current that the whole circuit can draw.
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Old 22nd November 2012, 06:06 PM   #12
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Powering Up Your Radio Safely With a Dim-bulb Tester
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Old 22nd November 2012, 06:18 PM   #13
CJ900RR is offline CJ900RR  Sweden
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Ok good.

First, I have cracked some LM3886 in the past due to oscillation.When they oscillated and got broken they where cracked and burnt on the legs, so my guess is that it has oscillated somehow.

Oscillation can happen due to a different number of reasons. One thing I noticed in the schematic is R18, a trim-pot connected to the inverted input of the LM3886. It look's like it's there to adjust the DC-offset of the LM3886.

I would suggest that you replace the broken LM3886, connect a bulb-tester as suggested, but before starting it up, disconnect the speaker connected to U1. Add power, use a volt-meter and measure (DC) on the output of the LM3886, it should not be greater than 100mV, preferably under 50mV. You should be able to reduce the DC-offset by turning R18. Try to get as close to 0 as possible.
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Old 23rd November 2012, 12:49 AM   #14
johnr66 is offline johnr66  United States
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Even with thermal protection, the ICs can fail if the operated at high temps for a long time due to insufficient thermal path or insufficient heat sinking. Heat is the enemy of electronics. Would be helpful if you could post pics of the circuit and heat sinking.
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Old 23rd November 2012, 04:37 PM   #15
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Originally Posted by bobodioulasso View Post
This test circuit looks good and handy. I have a PYE radio that stood unused for 30 years and the moment I got it I needed a tuning cap for a antenna tuner. I then just for old time sake powered the chassis up AND IT PLAYED no problem! Is this just a fluke or were those caps used on transistor sets of inferior quality as those old sets? Mine was made in September 1950 that's right 62 years ago and she sounds better than new sets of today? Just one question I found those old Mullard PYE and Philips sets WITH ONE LOUDSPEAKER MOUNTED DIRECT ON A PLANK SEALING IT OFF!!:
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Old 15th December 2012, 11:13 AM   #16
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Hi, I have Event TR8 speakers which are pretty similar to the ASP8.

The same thing happened to me, chip amp blew.

Luckily the drivers were ok.

I eventually went for Tripath amps mounted externally along with a digital active XO, and they are up and running again, and they sound smoother now also which is nice.

If you do replace your amp chip, consider upgrading the heatsink as Event seem to be cutting corners here.
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