LCIII ADB port not working :(

[timetorelax]

Hi All,

During the end of each year I normally take out all my old gear (gaming consoles, amiga's, macs etc) and power them and give them a bit of a clean. 

When I connected my LCIII (with matching screen) and powered it on, it all appearing to be working perfectly (ie: booted into OS 7.6.1) but then I noticed the mouse and keyboard would not respond.

Thinking faulty ADB cable or keyboard/mouse I quicky tested them with my Powerbook 1400 and proved they worked fine. Next, I checked for 5V from the ADB port and that tested fine.

Next step, I opened the case and finally decided to re cap as there were some suspect caps.

Once re capped, everything boots except (you guessed it) no keyboard/mouse.

Getting desperate, I also replaced the crystal near the IC behind the ADB port but still no go

Any thoughts?

Would love to keep this old Mac going.

Cheers

Ed

 

[AlpineRaven]

Did you replace some caps or all of them?
Cheers

AP

 

[BadGoldEagle]

Bad Tokin filter?

 

[timetorelax]

Bad Tokin filter?

Oh that’s interesting. Is there a way to test these? Can they be easily bought?

 

[timetorelax]

Did you replace some caps or all of them?
Cheers

AP

Yes I did but a cap near the expansion port was in bad shape and I think may have caused too much damage to the board. 

 

[sutekh]

Did you ever get this resolved? My LCIII started having the same problem intermittently, and it's now escalated to a permanent condition!

 

[MrFahrenheit]

Did you ever get this resolved? My LCIII started having the same problem intermittently, and it's now escalated to a permanent condition!

This could well be a condition of capacitor residue remaining around (not being cleaned off properly when recapped) and continuing to corrode traces/ICs.  Have you tried reflowing the solder for the cap near the ADB port ?

 

[sutekh]

Yes, tried re-flowing that and the ADB port itself it on your suggestion to no avail. Board was recently re-capped and thoroughly cleaned at the time, but the caps had leaked fairly badly. I guess it's possible some electrolyte remains under an IC or in a via doing further damage.  I'll check for 5v on pin 3 and start crawling through the schematic I suppose...

 

[sutekh]

Mystery solved! With apologies for continuing the thread hijack, I'm posting the resolution here for posterity. Pin 3 of my ADB port was NOT reading 5V, nor was ZL1, or F(use)1. The via that feeds 5V to F1 from an inner layer was rotten, no doubt with electrolyte leaked from C8 prior to when I recapped the board. I ran a wire-gauge bit through the via and augured out a bunch of filth. then pinned it with a length of transformer winding wire. I also cleaned up his neighbors while I was at it.