LCII Squealing noise from speaker

[reallyrandy]

I pulled out a spare LCII board I had to see if it worked and it chimes and boots fine but it squeals from the speaker. When I push and pull on the speaker connector the pitch goes up and down. Attached is a video. Any ideas?

 

[Arbee]

Has that board been recapped? If not, I'd strongly suspect goo from leaky capacitors.

 

[reallyrandy]

That's what I suspected but figured I'd ask around first.

 

[ymk]

Right, a recap should come first.

On the LCIII, the noise can persist after a recap. Changing one of the cap values breaks the oscillation. This may also apply to the LCII, though likely with a different designator:

My LC III wants to be a DJ.

When powered on, my LC III intermittently emits whining noises in varying tones through its speaker. I've swapped the speaker to no avail. The kicker is that if I touch miscellaneous chips on the motherboard with varying degrees of pressure, I can alter the pitch and repetition rate of the...

68kmla.org

 

[mikes-macs]

My Performa 400 did this too. After recap the screeching sound stopped.

 

[reallyrandy]

I'll have to recap it first I guess. I hesitated because I just recapped my other one and it still gets no chime and a black screen. LCs are a pain to recap, lot's of caps and some are in really tight spots, like C10.

 

[mitchW]

I can also confirm that I repaired multiple LCIIs that all did this. Every time the problem were capacitors. They are just bad.
And the first one that I came across with this problem was back in 2011, so at that time the machine was "merely" 19 years old, this is the same age now a G5 iMac or a late Pentium 4 machine is.

Also they need PSU recapped, especially if they are TDK brand.

 

[reallyrandy]

After recap all is well.