indibil
Well-known member
I'm at work and I can't take a photo right now, but can a photo from the Internet be useful to identify critical areas?
LC III - No video, no sound, and weird schematic
- Thread starter EffingController
- Start date
indibil
Well-known member
Tomorrow I try to check the egret, today it's late here.
Attached photos. C18 is temporary and the legs don't are in short, because since I heated the area to change the RAM chips and I want to put the original ones back, I put that temporary capacitor, so as not to damage the new one.
You will see that C13 has a "repaired" pad, connected to another point, I will also put a capacitor just like the original repairing the track, it is only there to validate.
It takes a couple of days for the sound chip to run cold, very strange, but the most worrying thing is the chime of death. I can't think of what could cause it.
Thanks everyone for your help!
Attachments
jajan547
Well-known member
Hey there @indibil I have had a chance to look over your photos and I see a few things I'd like to offer as suggestions. First being add a VRAM simm to this Lciii, you'll want one. Secondly I see you went with through hole capacitors which is okay but when it comes to stuff like this its ideal to use SMD electrolytic capacitors or tantalums (I personally go with tantalums but that's up to your personal preference). The capacitors you have here will work fine its just not ideal is what I'm saying. I would definitely cut the legs on these and make them shorter and closer to where they belong. Also I see by C13 you have a missing pad to fix this simply scratch into the trace and run a bodge to the negative side. Also clean up the legs on that EGRET chip with alcohol and carefully reflow them with new clean solder and flux. I see you have a few capacitors that are original to the board, you'll definitely want to replace these as I am sure they are no doubt leaking and are starting to fail if they haven't already. Last but not least the death chimes indicate bad RAM so I'd try a new RAM simm and if that doesn't make a change definitely look at those on board RAM chips, clean, and reflow them with new solder and flux. Ive added your original photos below with some comments/pointers let me know if they help and we'll hope to see your LC iii back up and running.
EDIT: You can get a full board recap kit HERE at Console5 and its pretty reasonable.
EDIT: You can get a full board recap kit HERE at Console5 and its pretty reasonable.
Attachments
indibil
Well-known member
Thank you very much, I will try everything you suggest. Just to indicate that I have changed ALL the capacitors already, I am waiting to receive the SMDs to replace the ones in legs, which are temporarily. The 4 SMDs near the audio zone are new. The very long legs capacitor was only there while I changed the RAM chips, I have an SMD saved to put it in, but I don't want to damage it with the air soldering iron.
I tried to add a VRAM SIMM but the error remained, if I get it to work I'll add it, at the moment I don't invest money (I removed it from the LC475 temporarily).
Regarding the RAM, in the photo there is a SIMM but I do the tests without it. I have replaced the soldered RAM chips on the board with other compatible ones and it still fails the same, I will put the original ones back.
Phipli
Well-known member
Chimes mean the self test failed, which is most likely RAM, but can be other things.
indibil
Well-known member
Hello again. I have removed the egret chip, cleaned and re-soldered, but the problem persists. C13 is soldered so that the negative leg contacts where the missing pad hits. It is temporary, until you receive the correct caps.
I think you're absolutely right. I will tell you about the test that I have carried out.
I have removed all the RAM chips from the motherboard. When turning on the chime is heard and the chime of death does not occur. Means something? Without RAM it does not even perform the diagnosis?
Then, before placing the original RAM chips, I added a working RAM SIM, taken from the LC475, and as soon as I turned on I had the chime, followed by the chime of death.
Could the fault be in the chip that controls the RAM? what chip is this?
Could it be a failure of the onboard VRAM? if i remove these chips and add a VRAM SIM would it boot?
Phipli
Well-known member
I'd expect it to death chime in this configuration, but I could be wrong.
I'd take the SIMM out and spray contact cleaner in the socket. Then before latching the ram down, I'd mostly insert it and wiggle it about a bit to make sure it gets good contact.
Ram not reading right is really common. It's more common to need to take the ram in and out a few times when you disturb it on an old machine than it works first time.
David Cook
Well-known member
I have found two additional causes of no video or no sound, besides the causes I described in my earlier posting on this thread.
1. If you have an LC III with no speaker sound, but sound does come through the headphones, then check continuity from pin 8 of U6 to the speaker pins. If neither speaker pin connects to pin 8, then a corroded via between C13 and the crystal could be the cause.
Drilling a hole through the via and connecting it on both sides with tinned wire should fix it.
2. If your LC has no video and no sound, then check for 5V at pin 4 on U22 while power is turned on. That chip provides the clock signal that goes to the CPU (among other things). Obviously, if this chip does not have power, you'll get no CPU clock, and thus no video or sound.
The cause is likely a leak from capacitor C18 (replaced by a ceramic capacitor in the image below) that damaged the nearby via. This via connects this +12V trace to the input of VR1. VR1 provides the power to the clock chip.
I drilled out the via using a #80 (0.0135 inch) drill bit using just my fingers. Use a carbon steel or high speed steel bit (https://amzn.to/3J6CXR5), because carbide CNC PCB drill bits are brittle and may break in the hole. Guess how I determined that!
In the picture below, note the crumbly gray chips beside the fresh shiny stringy chips. The gray material is corroded, followed by uncorroded metal.
You also need to scrape off some solder mask to expose a clean connection to the trace. Then you can solder a bare tinned wire through the hole to reconnect the top and bottom of the board.
Earlier I said you needed to test 5V on pin 4 with power turned on. That's because the clock chip is sourced from it's own voltage regulator, not the main +5V from the power supply. This is likely to keep the clock steady even as the standard +5V power supply sags and spikes due to computer and accessory usage. Therefore, do NOT test for continuity between pin 4 and standard +5V, and do NOT wire a bodge wire to standard +5V, because that is not the correct circuit.
Hope this helps,
David
1. If you have an LC III with no speaker sound, but sound does come through the headphones, then check continuity from pin 8 of U6 to the speaker pins. If neither speaker pin connects to pin 8, then a corroded via between C13 and the crystal could be the cause.
Drilling a hole through the via and connecting it on both sides with tinned wire should fix it.
2. If your LC has no video and no sound, then check for 5V at pin 4 on U22 while power is turned on. That chip provides the clock signal that goes to the CPU (among other things). Obviously, if this chip does not have power, you'll get no CPU clock, and thus no video or sound.
The cause is likely a leak from capacitor C18 (replaced by a ceramic capacitor in the image below) that damaged the nearby via. This via connects this +12V trace to the input of VR1. VR1 provides the power to the clock chip.
I drilled out the via using a #80 (0.0135 inch) drill bit using just my fingers. Use a carbon steel or high speed steel bit (https://amzn.to/3J6CXR5), because carbide CNC PCB drill bits are brittle and may break in the hole. Guess how I determined that!
In the picture below, note the crumbly gray chips beside the fresh shiny stringy chips. The gray material is corroded, followed by uncorroded metal.
You also need to scrape off some solder mask to expose a clean connection to the trace. Then you can solder a bare tinned wire through the hole to reconnect the top and bottom of the board.
Earlier I said you needed to test 5V on pin 4 with power turned on. That's because the clock chip is sourced from it's own voltage regulator, not the main +5V from the power supply. This is likely to keep the clock steady even as the standard +5V power supply sags and spikes due to computer and accessory usage. Therefore, do NOT test for continuity between pin 4 and standard +5V, and do NOT wire a bodge wire to standard +5V, because that is not the correct circuit.
Hope this helps,
David
imactheknife
Well-known member
resurrecting an old thread. I have no sound from speaker on lc3 but headphone works great. I removed and cleaned sound chip and pads. Still the same. Went over David Cooks steps and found no continuity between sp1 and the speaker pins. All other steps were fine. How to find broken trace / via. Thanks for the great info David, and other members. So great to have these forums.
imactheknife
Well-known member
Shows the possible problem area
Similar threads
