Polk MOMO 400.4 crackles

[LITEZONER]

Hello all, I have a polk audio MOMO 400.4 Amplifier that I am attempting to repair, I have so far replaced some old cheap caps and a couple of suspiciously low reading transistors, I have found that when I hook this up I get a static noise through one channel on the front and one side on the rear, It goes away when I apply pressure or (FLEX) The board which leads me to believe I have a loose solder joint somewhere in that area. I have never done any reworking, My idea was as dumb as it sounds is to stick the thing in the oven for a while??????? Or can I hit it with a heat gun??? Not sure what exactly what to do? Any suggestions are welcomed. Thank you very much appreciated.

[midibob]

Re: Polk MOMO 400.4 crackles

Hi,

I wouldn't stick it in the oven as you're more likely to damage other components long before you fix the suspected bad joint. Same goes with a heat gun if you're not careful.
I would look around any high current areas for microscopic rings around solder joints and reflow them with an iron. (if you find any) Difficult to be more specific without seeing the board. Can't see anything on the Web either.

Good luck
Midibob

[LITEZONER]

Re: Polk MOMO 400.4 crackles

Hey Thank you for that, Probably saved my amp, I think I have found the suspected joints, it seems the SMD caps in a couple of spots have come loose, I can push down on them a bit and the audio comes back clear. Not sure weather to remove them completely,? or to just try and resolder around the pads? what do you think? If I use my heat gun to remove the cap will it damage it?
Thanks again

[midibob]

Re: Polk MOMO 400.4 crackles

Assuming you have a proper SMD heat gun and not just a 'paint stripper' type then using the regulated temperature for no longer than the SMD component profile states, it shouldn't do any damage. You can remove and rework, although most manufactures would not recommend re-using components.
If what I'm saying doesn't make any sense then I would suggest you carefully use the iron and attempt a resolder.

Good luck
Midibob

[LITEZONER]

Re: Polk MOMO 400.4 crackles

ever replaced an SMD aluminum cap with a radial electrolyte? Can this be done? There is tons of room in this particular application for the caps, any advantages to using the surface mount other than the size? Thanks again,

[lti]

Re: Polk MOMO 400.4 crackles

Yes, you can do that. People do it all the time. Bend the leads and solder them onto the pads. Make sure you leave the leads long enough to get the soldering iron under the cap.

You could probably put a little flux on the solder pads and remelt the solder with a soldering iron to stick the original caps back down without removing or replacing them.

[LITEZONER]

Re: Polk MOMO 400.4 crackles

Now That's freaking awesome, THANK YOU!!!

[smason]

Re: Polk MOMO 400.4 crackles

+1 for flux. Flux is your friend with surface mount.