First attempt at a LM1875...and smoked it...literally!

rg24

Member
2008-11-01 4:00 pm
So I powered everything up and it did not go really well. Gain was all of the way down, hit the switch and it started to hum and then poreded smoke. I attached some images for you to look at. At this point I really don't know what to do, I mean how do I find out what parts I toasted and why? I wonder if the power supply could be toasted as well?

Any help would be greatly appreciated as I really don't want to shelf this project as I have a lot of time and money already invested into it.

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If you managed to cross + to - you've probably cooked the IC and all the Electrolytics.

The PSU can be tested by disconnecting it from the amplifier and measuring its output.

The amplifier resistors are probably OK, you "should" be able to see any burnt ones.

In my honest opinion, the components are so cheap in a Gain Clone that I would just re-populate the amplifier boards, test the PSU as suggested above, and try again.
 

rg24

Member
2008-11-01 4:00 pm
Andy/Done

The ship is insulated, used a 220 insulating kit from Radio Shack. I found my error, I rushed the project and had just one connection mismatched.

I did manage to cook some components, luckily when I ordered the parts the first time I ordered enough to make 2 so I will be repopulating the boards completely. As well as part of the PS because one channel is reading only .2V.

I checked the trans and it is measuring fine on both channels, though would there be any way I could have possibly shortened its lifespan or even reliability by my mishap?

Back to the drawing board...
 
High Power Transformers are pretty Bomb Proof. They usually only fail if they are operated for long periods of time over their rated output. If you turned the amp ON and saw smoke and turned it OFF fairly quickly, I would guess that the transformer is unharmed. The PSU capacitors will similarly be unharmed. It looks, if there are no PSU fuses, that one or more of the PSU diodes has failed. Again these are pretty robust, if they measure correctly they will usually be OK.