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

rg24 · 5th September 2010, 11:37 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.

Bill_P · 5th September 2010, 11:52 PM

Suggested transformer for stereo kit: Avel Lindberg 2x18vac transformer

That's a quote from the chipamp.com site. I don't see a transformer in your amplifier - is it in a separate box or did you really plug the amp right into the AC line?

rg24 · 5th September 2010, 11:55 PM

No I have a separate ps in a separate case, I just found out what I did-some wire got reversed and + went to -. Now I think I have a channel out on the PS as well.

Bone · 6th September 2010, 08:41 AM

Are you sure the LM1875 is isolated from the heatsink? Did you check with a meter?

Andy5112405 · 6th September 2010, 08:57 AM

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.

AndrewT · 6th September 2010, 10:06 AM

build and use a mains bulb tester for every new project!

rg24 · 6th September 2010, 01:32 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...

Andy5112405 · 6th September 2010, 02:28 PM

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.

Andy5112405 · 6th September 2010, 02:33 PM

Depending on the quality of the PSU, also check all and any PCB tracks, or even cables, as they may have "Fused".

rg24 · 6th September 2010, 03:34 PM

Thanks Andy, thats what I thought about the trans.

I will be pulling everything and making sure to check all component before I reinstall.

5th September 2010, 11:37 PM	#1
rg24 diyAudio Member Join Date: Nov 2008	First attempt at a LM1875...and smoked it...literally! 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.

6th September 2010, 10:06 AM	#6
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	build and use a mains bulb tester for every new project! __________________ regards Andrew T.

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5th September 2010, 11:52 PM	#2
Bill_P diyAudio Member Join Date: Sep 2009 Location: New York, the vampire state	Suggested transformer for stereo kit: Avel Lindberg 2x18vac transformer That's a quote from the chipamp.com site. I don't see a transformer in your amplifier - is it in a separate box or did you really plug the amp right into the AC line?

5th September 2010, 11:55 PM	#3
rg24 diyAudio Member Join Date: Nov 2008	No I have a separate ps in a separate case, I just found out what I did-some wire got reversed and + went to -. Now I think I have a channel out on the PS as well.

6th September 2010, 08:41 AM	#4
Bone diyAudio Member Join Date: Jun 2004 Location: Dorset, UK	Are you sure the LM1875 is isolated from the heatsink? Did you check with a meter?

6th September 2010, 08:57 AM	#5
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	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.

6th September 2010, 01:32 PM	#7
rg24 diyAudio Member Join Date: Nov 2008	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...

6th September 2010, 02:28 PM	#8
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	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.

6th September 2010, 02:33 PM	#9
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	Depending on the quality of the PSU, also check all and any PCB tracks, or even cables, as they may have "Fused".

6th September 2010, 03:34 PM	#10
rg24 diyAudio Member Join Date: Nov 2008	Thanks Andy, thats what I thought about the trans. I will be pulling everything and making sure to check all component before I reinstall.

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