• Updated 2023-07-12: Hello, Guest! Welcome back, and be sure to check out this follow-up post about our outage a week or so ago.

LC II no sound after recap

I ran into the same issue after recapping my LC II.
However it was just a bad trace between one side of the 50v cap.
Ran a trace wire & it was fixed.
View attachment 36573

Just to be clear @zezba9000 and @mitchkramez : you found that restoring that connection restored your sound? I have damage in that area and hard-to-diagnose sound problems that aren't directly affected by the presence or absence of that capacitor (I had sound with the capacitor completely missing at one point, restored the capacitor and got distorted sound, then removed it again and got no sound). I am wondering if my problem is actually related to trace damage in the area that is incidentally affected by the recapping, and if you would share some information about your traces.

Can you (or anyone) tell me if UB10 pin 12 (immediately to the left of the green circle in the picture above) is connected to ground or some power rail? The BOMARC schematic only shows it connected to C22, but there is obviously also connected to a via with no obvious connection on the other side of the board. My via is damaged, so I cannot check.
 

mitchkramez

Member
Just to be clear @zezba9000 and @mitchkramez : you found that restoring that connection restored your sound? I have damage in that area and hard-to-diagnose sound problems that aren't directly affected by the presence or absence of that capacitor (I had sound with the capacitor completely missing at one point, restored the capacitor and got distorted sound, then removed it again and got no sound). I am wondering if my problem is actually related to trace damage in the area that is incidentally affected by the recapping, and if you would share some information about your traces.

Can you (or anyone) tell me if UB10 pin 12 (immediately to the left of the green circle in the picture above) is connected to ground or some power rail? The BOMARC schematic only shows it connected to C22, but there is obviously also connected to a via with no obvious connection on the other side of the board. My via is damaged, so I cannot check.
yep, reconnected and sound was restored. i'm not sure on your other question unfortunately.
 

zezba9000

Well-known member
Just to be clear @zezba9000 and @mitchkramez : you found that restoring that connection restored your sound? I have damage in that area and hard-to-diagnose sound problems that aren't directly affected by the presence or absence of that capacitor (I had sound with the capacitor completely missing at one point, restored the capacitor and got distorted sound, then removed it again and got no sound). I am wondering if my problem is actually related to trace damage in the area that is incidentally affected by the recapping, and if you would share some information about your traces.

Can you (or anyone) tell me if UB10 pin 12 (immediately to the left of the green circle in the picture above) is connected to ground or some power rail? The BOMARC schematic only shows it connected to C22, but there is obviously also connected to a via with no obvious connection on the other side of the board. My via is damaged, so I cannot check.
About C22 I'll have to find mine after moving. Do you have a picture of exactly what you're trying to test for?

But as mitchkramez stated & in my older image that trace around the 50v cap being re-connected fixed completely dead sound.
 

GutBomb

Member
I just had a pretty similar experience with my LC II. When I got the machine the power supply worked, but the logic board was not booting, it was causing the power supply to constantly click. After recapping the logic board everything worked fine including the sound. After about 20 minutes the entire machine started glitching out like crazy (weird display and the sound cut out) and wouldn't come back on. The power supply just gave up. I ordered some caps for it and while I waited for the caps I just used my bench power supply to power it with only 5v. I don't use an internal hard drive, I use an externally powered RaSCSI, so I didn't need 12v, and I was not planning on using localtalk, so I didn't worry about the -5v either. Everything worked fine EXCEPT the sound was extremely quiet. Like I'd have to hold my ear right up to the speaker to hear anything. Once the caps for the power supply arrived I recapped that and the sound returned to normal and everything has been working great since. It's interesting to me that the sound didn't work when I didn't have 12v or -5v present, as I thought the 12v was ONLY used for the fan and powering a hard drive, and that -5v was only for localtalk, but apparently one of those was necessary for making the sound work. Check your voltages on the PSU connector to see if you've got good voltages on each rail if you're still having sound trouble.
 
Top