Jump to content
DistantStar001

Attempting to recap my LC III and may have run into a problem

Recommended Posts

So I'm trying to recap my LCIII motherboard.  I managed to remove all of the old capacitors, clean all the pads (all of which survived) but I just noticed that the resisters at R1 and R2 are missing, and one of the pads at R1 seems to have fallen off.  The pads on R2 are still there and I cleaned them as well as the remaining pad at R1.  The board did work before all of this but would take forever to boot.  
 
I don't know how long R1 and R2 have been missing, but I can't imagine that it's a good thing that they are.  The old capacitors clearly leaked but thankfully didn't corrode any of the legs on the ICs.  So do I have a problem?  Can R1 and R2 be repaired?  Do I even need to?
Below are pictures of the board and a closeup of R1 and R2

Screen_Shot_2020-05-06_at_4_08.28_PM.png

Screen_Shot_2020-05-06_at_4_08.39_PM.png

 

Edit: I was just looking at the closeup and now realize there appears to be some corrosion that I didn't see before.  Guess I'm going to have to go over this thing with a magnifying glass.

Edited by DistantStar001
Additional Information

Share this post


Link to post
Share on other sites

The first Mac I recapped was an LC III :-) 

 

Not sure if you could do without R1 and R2 but here’s a pic of mine showing their markings:

4C990324-2246-4FD3-B2F7-5D489726F4A2.thumb.jpeg.40673d8db0d75c85d4737c89f80f0e84.jpeg

 

I’m a bit embarrassed how crooked those caps are, but hey it worked!

Edited by Fizzbinn

Share this post


Link to post
Share on other sites
2 hours ago, Fizzbinn said:

Not sure if you could do without R1 and R2 but here’s a pic of mine showing their markings:

Thanks for this.  I've been Googling images and every picture I've found shows those resisters populated, but I was never able to clearly see their markings.  Now at least I know what to get.  My guess is that they are necessary and may have fallen off from corrosion, or they weren't as secure as they should have been and I inadvertently knocked them off removing the capacitor.  In either case, it seems that there is a trace in between connecting them.  If you have a multimeter, could you possibly confirm this?

 

1 hour ago, Fizzbinn said:

I’m a bit embarrassed how crooked those caps are

Don't be.  If it works, that's all that matters.  You're already way ahead of me! :-)

Share this post


Link to post
Share on other sites
11 hours ago, DistantStar001 said:

In either case, it seems that there is a trace in between connecting them.  If you have a multimeter, could you possibly confirm this?

Yes, there is a trace connecting them, confirmed with multimeter continuity check.

 

Share this post


Link to post
Share on other sites

That incredible amount of crud around the legs of U1 should also be dealt with to make sure it isn't causing any issues.

Share this post


Link to post
Share on other sites
On 5/7/2020 at 8:20 AM, Fizzbinn said:

Yes, there is a trace connecting them, confirmed with multimeter continuity check.

 

Thanks.  I think I can bridge that between the resisters.  If I had to lose a pad, at least it was that one.

On 5/7/2020 at 8:39 AM, LaPorta said:

That incredible amount of crud around the legs of U1 should also be dealt with to make sure it isn't causing any issues.

Yeah, I noticed that too.  I've been scrubbing this thing under a magnifying glass with alcohol and q-tips for a while now.  It looks a lot better, but it's clear that the caps leaked more than I had originally thought.  The damage isn't too bad, but R1 appears to be a casualty (not sure how though).  

Edited by DistantStar001
spelling

Share this post


Link to post
Share on other sites

One way to get in there if you can't desolder the chip is to use interdental brushes. Those things get in between almost anything, are available in different sizes in the drug store, and don't cost too much. Use with alcohol.

Share this post


Link to post
Share on other sites

So sorry for the lack of update, but I've been looking for the replacement resisters for a while now with no luck.  Does anyone know where I can find 582 and 204 surface mount resisters?  The former seems to be the hardest to locate.  My local electronics store has the 204s, but I'd prefer to get both at the same time if I can.

Share this post


Link to post
Share on other sites
13 hours ago, DistantStar001 said:

Thanks for pointing them out.  I actually hadn't before, but from what I could see, they, unfortunately, don't have them.

And you’ve tried Digikey as well?  
 

Your last resort if you can’t find them may be to track down a donor parts board that also has them. Might be easier. Won’t be new but unlikely to matter. 

Share this post


Link to post
Share on other sites

I have checked them out, but I've had some trouble identifying the product I need.  I think the markings on the 582 indicate a value of 5.8 kΩ, however, the images on their site are unmarked.  Also, they didn't seem to have any stock from the results that came up.  I also checked out Mouser with no luck.

 

As for seeking a donor board, I'm not sure what other boards might have the necessary.

Share this post


Link to post
Share on other sites
On 7/3/2020 at 6:59 AM, elemenoh said:

Thank you!  I wasn't sure because of the font, but after comparing it to the pictures of my board, I think you're right.

 

I think I'm going to check with my local electronics store first, but thank you for the link.  Now, one way or the other I'm getting my LC back!  :-) 

Edited by DistantStar001
Additional information

Share this post


Link to post
Share on other sites

Update:

 

First, Elemenoh, You were absolutely right!!!  I managed to get some 682 and 204 resisters, soldered them in (lost one since I suck at micro soldering) recapped the board, and plugged it in.  It powered on and booted, but no sound.  So I checked continuity and found a broken trace between R2 and Q1.  No problem.  I bodged it, plugged it in, and BONG!!!   I was very happy!! Then I rebooted and again no sound???  So I powered down and turned it off and back on again (I T Crowd stile) and still no sound.  I'm ashamed to say that it took me several hours to notice that there was a lot of white crud built up around the ram on the other side of the board.  I sprayed it with IPA and scrubbed it with a q-tip (did the same around the sound chip just to be safe).  Now it's back to its full functionality!!

 

Thanks to everyone who helped me.  I'll try to post a picture of it set up and running when I get a chance. :-) 

 

Oh, one more question:  How do I enter a 2020 date in System 7.5?  I keep trying, but it always reverts to 1920?  I don't seem to have this problem in 7.1 or 6.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×