Removing the Ms. Pacman sound amp heatsink

elekTRONarcade

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Is there an easy way to remove the heatsink on the Ms. Pacman sound amp? Seems like its cold soldered on there pretty good, and I've tried with a 15, 30 and a 50w iron, and both a sharp tip and a chisel tip. I can't even get the solder to reflow to either use a solder sucker or wick on it.
 
They are huge... and the problem is... it's doing its job - sinking heat away from the component, or in this case the soldering iron.

When I desolder them (which is RARE to do since they don't fail very often) I use both the soldering iron and the desoldering iron at the same time to get enough heat into the joints to desolder them.
 
I actually use two soldering irons at the same time to get enough heat to get the solder off. Works pretty good. Space Invaders (Midway) uses the same type, and I've had to change some out to fix sound issues...
 
Thanks for the input guys. Channel, since you seem to have a pretty good grasp on Ms. Pacman's sound issues, what would be my likeliest candidates for no sound on a working board? I've pulled and cleaned the 1M and 3M and replaced the 330uf cap, yet I still get the variable pot hum and nothing else, hence why I suspect its the lm377. I get no static when I touch the pins, yet I do get weird sounds when I touch the 3M pins, or the hum cuts out completely when touching them. Is there anything else I can do to check the sound?

I will also mention that I seem to have the humbar issue with my monitor, not sure if that would have any role in it, though the distortion is very faint and more like a slightly darker band moving left to right.
 
look at pinout of audio amp and then use a set of amplified pc speakers, and connect the input to the pc speakers to the input of the audio amp on the pc, what do you get?

dont forget to ground the input of the speakers as well.
 
I'm guessing you don't have a logic probe with audio capabilities or access to an oscilloscope.

That would tell you in quick order where the issue is. Without those you are stuck with swapping parts.

You could try feeding in an audio signal into the board where the pot is to see if you get amplified sound out.
 
Thats an affirmative on no oscilloscope or LP. I'll try the speaker idea tonight when I get home. I may just sell this board and replace it with a known good board and save myself the hassle of repairing it though.
 
I use a soldering gun (yes one of those big honkin' soldering guns) - turn the board upside down and grab the heatsink with a pair of needlenose pliers. Apply heat for awhile and the heatsink comes right out. Then remove the solder using your favorite technique. To get the excess solder off the heatsink, CAREFULLY heat the metal tabs then bang the pliers on the bench - the momentum will throw off the excess solder.

A quick audio check is to grab the volume control's flat sides between your thumb and forefinger - you'll usually pick up a radio station and hear it through the speaker.

Bill
 
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