Missing cap on my Macintosh LC motherboard

[MrGasS27]

Hi everybody!

Today I received a beautiful Macintosh LC with stuck HDD head and obviously I have to recap it completely, from the speaker comes a lot of weird sounds like a cap that is charging and discharging (a stupid example: *I power on the Mac* *boot sound* uuuuiiIIIIIIIIIIIIII IIIIiiiiiiiiiiiuuuuuuuu), however, it booted up 7.1.2 an 7.5.3 from my SCSI2SD on the external SCSI port and I played Shufflepuck for 5 minutes, it “works” good.

I’ll recap it soon together with my IIsi, but I can't explain a little thing on the LC's motherboard:  why on C105 there’s no cap? I think that a 10uF 16v cap goes here,  I have to put it while recapping it?

It came with a PDS ethernet card with a wire soldered on it, and I can’t explain myself why, I see no interrupted traces on the ethernet card, can someone explain me why there's this soldered cable?

Can someone help me about these two things? Thank you all.

 

[MrGasS27]

Quantum 40MB HDD repaired, it works perfectly also with the internal HDD with 7.1

 

[Bolle]

One can clearly see that there was a cap installed. Its legs are still there but it must have fallen off the board (or got knocked off when inserting the ethernet card)

You want to put one in again when you do the recap. Also be sure to wash the board really well... lots of residue between those IC legs.

Jumper wires are common on old hardware. The one on your ethernet card looks factory installed. I would leave it there.

 

[MrGasS27]

Okay, I'll put a cap also on C105, 5 minutes ago I saw again my LC motherboard and I noticed too the cutted leg of the cap, I also saw a lot of photos on Internet and I noticed the cap on C105 in every motherboard.

I provided also to search informations on Google about the annoying noise from speaker on Google, obviously the problem are caps, looks like a common problem on LCs.

I have the same problem of this video:

 

[MrGasS27]

However, in my life I saw wire traces only on Amigas (mostly 1200)

 

[MrGasS27]

UPDATE - 20/03/2018

I just finished recapping my LC motherboard and I added the missing cap, now works perfectly and it doesn't do weird sounds from internal speaker anymore.