Sound Board Question

I'm wondering if an electrolytic capacitor has gone bad and started leaking - looking at the top of the board (the side with the components mounted on it), are any of the caps swollen, or leaking anything?

They all have that from what I have seen.  Probably a residue from the cleaning after the board was made.

Your sound issue can be from a speaker going bad, the volume pot dirty (cycle it several times), reseating the chips of this RS 2.5 board.  G

One other common sound board issue is oxidation of the contacts on the two PLCC chips.  I have fixed a number of these by simply reseating the chips.  Note that you MUST have a PLCC extraction tool to do that task, trying to pry them out with a screwdriver or other such tool will most likely break the socket.

If GGG's suggestions don't do the trick, reseating those chips is the next step.

It looks like thermal grease.  This is used to improve the transfer of heat from the heat producing components to the heat sinks.  It appears that the white substance is confined to the end of the board where the heat sink is mounted. 

Thermal grease is most often seen with complex integrated circuits like CPUs and DSP (digital signal processors, i.e., sound chips) and voltage regulators. 

I expect that a person handled the board got excess grease from the components on their fingers. 

Jan

The white residue is likely from the water soluble flux reacting with humidity.

You can clean it with isopropyl alcohol, but usually this is not the root cause of what is going on here.

I actually recommended reseating the chip.  G

You're right, skipped it in after the volume pot.

Everything on the board on both sides looks okay to my untrained eye. I cycled the volume pot several times.  I can try the speaker on another engine to at least test it.  Correct?

I did what you suggested in another thread, Gunrunner, and went to Radio Shack for a plastic leaded chip carrier extractor.  They no longer carry them according to the store associate, so I will order one.  Is there a particular size I need or are they pretty much one size fits all?  When I get one, I will have to ask which components to "extract."  What are the two PLCC chips and is there anything else to be reseated?  Thanks.

One size fits all.  The two PLCC chips are the problem ones.  The other stuff is soldered on the board, no reseating there.  I'd use some alcohol and clean the white residue off the board, though as previously stated, that's very unlikely to be significant.

Here's a PLCC Extractor for $5.99 with free shipping.

When you extract the chip, you make sure the hooks are all the way to the bottom of the socket on both sides.  Start squeezing and make sure a hook doesn't slip off as the chip start moving.

All you really have to do is pull it up, remove the tool, and immediately press it back into place with your thumb.  The object of the exercise is to just move the contacts and remove any corrosion that may be causing the problem.

I agree that is looks very much like thermal grease.

check out the video linked https://www.youtube.com/watch?v=VG5N95xsvrM

Gunrunner, I ordered the extractor from your lead at Amazon yesterday and it just came. Now just to be sure I pull on the correct things, I assume one chip is the rectangular one on the underside on the left in the photo and the square one opposite it on the top.

Correct, the square chips in the sockets.  Make sure the fingers get a good grip on the bottom of the chip and slowly squeeze the tool.  It's only necessary to move them up and down a bit in the socket to reseat them, you don't have to physically totally remove them.

Fixed!  Thank you for the help!

It did lead me to another question just for education.  In my all thumbs manner I pulled both wires loose at the Control switch that lead to the LCRU in this unit.  While soldering them back I noticed the slide switch is wired so when the switch is in what the manual calls the "ON" position the blue and white wires are connected through the switch. In the "Program/Lock" position the switch is simply disconnecting those two leads. So, in general, for programming, is any control switch really just disconnecting the "Run" or "On" circuit, or is it a lot more complicated than that?

It depends.  On the original LCRU, the switch was open to program and I suspect the LCRX as well.  On the later stuff, I believe it's universally closed for programming and open for running.