BrianGT's 3886 kit, a little help required..

MrSensitive · 16th August 2005, 12:33 PM

Hi all,
I just finished 6 3886 PCB's from chipamp.com.

a few days ago I started connecting things up. when 3 PCB's where mounted and connected i decided to test these.
connected mains and nothing happened (this is good i thought)
when measuring the DC on output I have 7 mV on one channel, but 24 Volts (!) on the other two plus really hot chips (they started smelling, no smoke)

I disconnected everithing, checked the connections and resistor values, everithing seems to be OK.

could these be faulty chips? is there any way to find out what could be wrong?

I also checked the power supply's but this is all fine..
I did a search and found a few threads describing this, but could not find much help in there..

many thanks for your help..

Russ White · 16th August 2005, 01:01 PM

I would suspect a couple of things right off the bat:

1) Are the chips isolated from gnd either by using the TF package LM3886 or by using an isolator on the T package?

2) Look for a solder bridge/short on your PCB.

I hope you find you trouble. I would suspect the hot melted chip is dead... But you may have gotten lucky.

MrSensitive · 16th August 2005, 01:08 PM

chips are isolated,

there were no shorts on the PCB
i will start with the remainig PCB's .

is there any way to see is a chip is dead?

thanks for your tips..

16th August 2005, 12:33 PM	#1
MrSensitive diyAudio Member Join Date: Jun 2004 Location: Ghent	BrianGT's 3886 kit, a little help required.. Hi all, I just finished 6 3886 PCB's from chipamp.com. a few days ago I started connecting things up. when 3 PCB's where mounted and connected i decided to test these. connected mains and nothing happened (this is good i thought) when measuring the DC on output I have 7 mV on one channel, but 24 Volts (!) on the other two plus really hot chips (they started smelling, no smoke) I disconnected everithing, checked the connections and resistor values, everithing seems to be OK. could these be faulty chips? is there any way to find out what could be wrong? I also checked the power supply's but this is all fine.. I did a search and found a few threads describing this, but could not find much help in there.. many thanks for your help..

16th August 2005, 01:01 PM	#2
Russ White diyAudio Member Join Date: Jan 2005 Location: Nashville, TN, USA	Re: BrianGT's 3886 kit, a little help required.. I would suspect a couple of things right off the bat: 1) Are the chips isolated from gnd either by using the TF package LM3886 or by using an isolator on the T package? 2) Look for a solder bridge/short on your PCB. I hope you find you trouble. I would suspect the hot melted chip is dead... But you may have gotten lucky. __________________ Less pulp more juice Twisted Pear Audio.

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16th August 2005, 01:08 PM	#3
MrSensitive diyAudio Member Join Date: Jun 2004 Location: Ghent	chips are isolated, there were no shorts on the PCB i will start with the remainig PCB's . is there any way to see is a chip is dead? thanks for your tips..

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