Question about component on Marshall Amp circuit board

[Carlitto]

I have a small Marshall practice amp G15RCD the power turns on but no sound.  I checked the speaker and it works.  The problem seems to be one of the four black chips marked IC4, as the prongs on the bottom are not connected to the board and look broke.  There are four black chips IC1, IC2, IC3 and IC4.  Can anyone tell me what this IC4 chip does and where I can get the part.  I would rather not take it to a shop and pay more than what the amp is worth to fix.  Thank you

[PRR]

> Marshall practice amp G15RCD the power turns on but no sound

Schematic:

http://www.eserviceinfo.com/downloadsm/48727/Marshall_G15RCD.html

> tell me what this IC4 chip does

Main power amplifer.

IC2 brings weak guitar up to decent level. IC3 works with tone-control and master volume. IC1 works with a reverb unit. When everything is shaped to perfection, IC4 brings it up from moderate signal level to BIG signal to shake the speaker.

> IC4,.. the prongs on the bottom are not connected to the board and look broke.

Did that just happen? Or did it have some accident? Did it ever work for you or did it come to you in sad condition?

IC4 should be screwed to a big chunk of metal to carry-off heat. Is that there?

Can you take a good picture of this area?

The model seems to be well-regarded on amp comment sites, so it is worth fixing; it isn't a big amp so it isn't worth a lot.

> where I can get the part.

Mouser.com as part LM1875T/NOPB for about $3 plus $5-$15 shipping. However you want to see if other parts are missing or mangled so you can order them at the same time.

[Carlitto]

> IC4,.. the prongs on the bottom are not connected to the board and look broke.

Did that just happen? Or did it have some accident? Did it ever work for you or did it come to you in sad condition?

IC4 should be screwed to a big chunk of metal to carry-off heat. Is that there?

> The amp has been in fine working condition for 11 years and just this year after frequent transport to students homes have I noticed it making noise like something was moving around in the head. One day after taking it out of the car the power turned on but it would no longer produce sound.  After taking it apart and testing speakiers is when I noticed that the IC4 chip was the problem.  The IC4 chip is screwed to a big chunk of metal but I notice the prongs not connected and some busted. 

[Carlitto]

I don't have a way to post a picture of the cicuit board at the moment.  But thanks for the information PRR I will look into getting the part and see if anything else looks faulty

[mertsolak]

  There are four black chips IC1, IC2, IC3 and IC4.  Can anyone tell me what this IC4 chip does and where I can get the part. 

 Can anyone tell me what this IC4 chip does and where I can get the part?" A picture of the board would help us greatly, if you can simply upload it to any of your personal folders on the internet and share it with us, would be great. Also, since you've noticed the prongs of the IC4 chip are not connected anymore, it probably means that it's only because of wear and tear over the time and rest of the board should be working fine. Are there any markings on the IC4 which can help us identify it?