LC Boot Issues

[warmech]

I'm trying to get an LC to boot, but have run into some weirdness. It will not recognize the HD, even though it spins up and I can hear it clicking away, and the floppy will only read a 7.1 install disk. Any other boot or install disk is ejected - 6.0.8, 7.0.1, the Network Access Disk, etc. There's no chime on boot, but it does at least boot to the |?| screen.

I know it needs to be recapped, and it doesn't look like there's any damage, but I'm scratching my head at this point... Any thoughts? I would have assumed it would at least read OTHER floppies at a minimum if it can read one, lol.

 

[blusnowkitty]

More than likely, the board caps are the culprit here. Bad caps on the logic board make the system behave weirdly like what you're seeing. As far as the no sound issue, check the blue wire on the power supply - the LC needs -5v to generate sound and I'd be willing to bet that your power supply isn't outputting enough or flat-out isn't putting out any voltage on that rail. You'll either have to recap the power supply, or you could always buy one of my ATX conversion boards and not worry about it again

 

[warmech]

More than likely, the board caps are the culprit here. Bad caps on the logic board make the system behave weirdly like what you're seeing. As far as the no sound issue, check the blue wire on the power supply - the LC needs -5v to generate sound and I'd be willing to bet that your power supply isn't outputting enough or flat-out isn't putting out any voltage on that rail. You'll either have to recap the power supply, or you could always buy one of my ATX conversion boards and not worry about it again

Well, small update: all my 7.0.1 disks were acting screwy, so I imaged a new floppy of the first install disk and it booted to the installer. It kept complaining about not being able to install to itself (understandably) but I didn't notice that now I had the option to switch disks. I hit the button and, voila, it read the HD. Wouldn;t let me install, on account of there already being an OS (7.1) on the HD, but a reboot brought me back into 7.1 on the HD. Am I stupid, or was the startup disk selection borked in in the 7.1 instance?

As for the sound - I'm going to go ahead and say you're spot on. The -5v rail is bouncing around -3.5 to -4.3v, so it needs to be recapped at the very least. I've got an order on with Mouser for tantalum caps, so I might as well add PSU caps as well. How much do your ATX converters run (and is there a site up with a picture of one - I've never heard of this before and I'd love to see how it fits in)?

 

[blusnowkitty]

As for the sound - I'm going to go ahead and say you're spot on. The -5v rail is bouncing around -3.5 to -4.3v, so it needs to be recapped at the very least. I've got an order on with Mouser for tantalum caps, so I might as well add PSU caps as well. How much do your ATX converters run (and is there a site up with a picture of one - I've never heard of this before and I'd love to see how it fits in)?

Pictures are over here: 





The last batch I did with a $10 flat shipping charge, $30 for a DIY kit or $40 fully assembled. Bring your own picoPSU.

 

[Daniël]

More than likely, the board caps are the culprit here. Bad caps on the logic board make the system behave weirdly like what you're seeing. As far as the no sound issue, check the blue wire on the power supply - the LC needs -5v to generate sound and I'd be willing to bet that your power supply isn't outputting enough or flat-out isn't putting out any voltage on that rail. You'll either have to recap the power supply, or you could always buy one of my ATX conversion boards and not worry about it again

That, or the Digital Filter Audio Chip is bust. I have a recapped LC that still isn't outputting sound, and the PSU attached causes no sound problems with a different LC board I have. It's not super common, but I know some peeps that have had this issue, me now very likely included. Still need to find the DFAC I took off a bombed Classic II board, and swap that in.

 

[warmech]

That, or the Digital Filter Audio Chip is bust. I have a recapped LC that still isn't outputting sound, and the PSU attached causes no sound problems with a different LC board I have. It's not super common, but I know some peeps that have had this issue, me now very likely included. Still need to find the DFAC I took off a bombed Classic II board, and swap that in.

After a recap, looks like my DFAC is dead as well; no audio through the speaker nor the headphone jack. PSU is outputting the correct voltages and works fine with another LC as well.

Additionally, the hard disk I was using was just a dying hunk of junk. It's totally dead now, so it must have just been on its way out the door when I was trying all of this originally.

 

[cheesestraws]

After a recap, looks like my DFAC is dead as well; no audio through the speaker nor the headphone jack. PSU is outputting the correct voltages and works fine with another LC as well.

At least on the LC II, there's a 78L08 8v voltage regulator right beside the DFAC that the DFAC relies on (I know this because mine fell off and sound stopped working, which led to a certain amount of perusing of schematics).  Looks like it's there on the LC as well.

I've had a couple of logic boards now where it has looked fine but the legs have actually been quite eaten away by capgoo.

 

[warmech]

At least on the LC II, there's a 78L08 8v voltage regulator right beside the DFAC that the DFAC relies on (I know this because mine fell off and sound stopped working, which led to a certain amount of perusing of schematics).  Looks like it's there on the LC as well.

I've had a couple of logic boards now where it has looked fine but the legs have actually been quite eaten away by capgoo.

Huh - so 8v is the expected output from the 78L08 for the DFAC? I may go test this in a minute...

 

[cheesestraws]

Huh - so 8v is the expected output from the 78L08 for the DFAC? I may go test this in a minute...

Yup, the number after the L in that series seems to be the voltage.  According to the Bomarc schematics for the LC II, it produces an 8v supply:



which as far as I can see is consumed only by the DFAC:



So it might be worth checking whether you're getting getting a stable 8v on pins 3 and 4 of the DFAC.

(Disclaimer: I don't really know what I'm doing here, but the 78L08 fell off one of my LC II boards when I was washing it/recapping it this afternoon, so I had an "oh dear, I wonder what that did" moment.)

 

[warmech]

Yup, the number after the L in that series seems to be the voltage.  According to the Bomarc schematics for the LC II, it produces an 8v supply:

which as far as I can see is consumed only by the DFAC:

So it might be worth checking whether you're getting getting a stable 8v on pins 3 and 4 of the DFAC.

(Disclaimer: I don't really know what I'm doing here, but the 78L08 fell off one of my LC II boards when I was washing it/recapping it this afternoon, so I had an "oh dear, I wonder what that did" moment.)

Welp, it's the DFAC. It was getting a fairly close 8.11v (I would assume is within the DFAC's tolerance range), so I pulled both it and the 78L08, cleaned the area, added some fresh solder and reinstalled. Bupkis.

I'm on the hunt for another LC/LCII board, so this will wind up being a moot point; regardless, this was a nice chance to practice my hot air skills, so I'll take what I can get!

Also, thanks for the advice, cheesestraws - it was tremendously appreciated!

 

[cheesestraws]

Ah well.  What a shame!

 

[warmech]

Got the DFAC replaced with one from a very much dead Classic II (RIP, old friend) and audio is back! The LC lives again.