LCii sounds cause screen to jiggle

[NickNick]

Hey there. So I decided to take out my Mac LC's and play with them...Its been a while since and I found out that they do not like to sit for periods of time with no use. Two of the Macs had stuck HDD's, but a quick flick of the wrist with the HDD in hand fixed those issues. One LCii developed a bad PSU, replaced it with a working one from a soundless LC and it solved that issue. However the one that has me baffled is another LCii. Whenever any sound is played through the speaker; it causes the screen to jiggle. Not to the point where I can not use it but its just rather annoying. Playing games on there like alone in the dark or robotron sux as the screen jiggles with any noise.

It is however still useable. It has been recapped and I even lifted the speaker off the case and played some sound through the speaker and still the same results so its not vibrations from the speaker causing that. I really have no idea what this could be. Anyone have any thoughts perhaps??

Thanx a bunch!

 

[Elfen]

Switch the PSU on that LCII with the jittery screen. It could be the PSU is at the edge of failing.

Or has it been recapped? Looks like a possible rotted trace or two to a regulator on the board at the sound or video circuits.

 

[NickNick]

Thank you for your reply. I will swap out PSU's and see if there is any change. I actually thought the same thing but didn't think that could cause that but its worth a shot. And the computers have all been recapped but the PUS's have not been. I have only had to recap one PSU thus far. I have the replacement caps to change out if need be.

 

[uniserver]

Any Psu that says tdk on it needs a re cap I'm sure others would vouch for that.

 

[Elfen]

Any Psu that says tdk on it needs a re cap I'm sure others would vouch for that.

I can vouch for that!

I had a LC TDK-PSU die on me last summer. Recapping it fixed it.

But also, look at the PSU Connector. Any pins that look dark are corroding as can make it look like the PSU is dying. If you put a jeweler's screwdriver to them, they will break apart and crumble on you. I replaced the Pins on 2 LC PSUs that has "died" and now they work great! Just for the hell of it, I recapped them for more insurance.

If you order the clips from DigiKey, they might send something else if they do not have it, which will fit the LC plastic connector but it is a howling rabid female dog to get it in there! See the second post on this thread:

https://68kmla.org/forums/index.php?/topic/23956-another-lc-tdk-psu-repair-no-recap/

 

[NickNick]

Ok so I swapped out PSU's and the LCii did not start up. So I put the other PSU back in and it still did not start up. Fan spun, HDD spun up but that's it. So I unplugged the HDD and then the machine bonged and screen came on. Turned it off and plugged in the HDD and started it up. It started up this time fine. However I did not notice the screen moving when noise. I don't know if its because I had it hooked up to a CRT monitor this time and last time it was an LCD monitor where I saw the movement with sound.

I will put it back on the LCD screen later and see the results but I do feel you are right Elfen as I feel its the PSU that is defective. Do the LC and LCii use more power than the LCiii and LC 475's by chance? The borrowed PSU was from an LCiii even though they looked exactly alike.

 

[NickNick]

So I hooked it back to the LCD monitor and the sound issue has seemed to  fix itself. Maybe it was because it has been sitting for a few months with no use or what. But the sound issue is no longer a problem. However after that machine is turned on for the first time of a day it starts perfectly with any LC PSU installed. Turn it off, and then turn it back on in like a min or so and the computer wont start back up. I get a grey screen, no mouse pointer, no start up chime, no booting.

I can hear the fan and HDD spin but nothing else. If I turn off the computer for like five mins, then back on, it will fire up again with no issues. It will run for hours fine with no issues but when i turn it off and go to turn it back on I get the grey screen issue every time. The LCii works perfectly otherwise and it has a 500 mb. HDD installed in it. Any ideas what would cause this issue?