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

[MrSensitive]

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]

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]

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..