iMac ethernet connection quit - help?

Tapley, Mark mtapley at swri.edu
Sun Oct 1 16:10:22 CDT 2017


On Jul 20, 2017, at 1:11 PM, Noel Chiappa via cctalk <cctalk at classiccmp.org> wrote:

>> Next stop, I'll pull the cover off the machine and see whether I can
>> spot any spilled battery electrolyte from the old battery or anything
>> else suspicious looking on the logic board in that area
> 
> It probably wouldn't hurt to clean that area with a Q-tip dipped in distilled
> water. (If you get noticeable grup on the Q-tip, repeat with a new Q-tip,
> otherwise you'll just be spreading the ook around.)

	...re-animating a thread I let get dormant for around 2 months - sorry for the delay and thanks for the help so far! 

	The machine in question is an iMac G3, Summer ’01. The presenting symptom was odd ethernet behavior and never any packets transmitted over ethernet, starting while the PRAM battery was bad (went bad with the machine running) and not corrected by replacement of PRAM battery. I had tried multiple good suggestions to diagnose and command ethernet status via software, but to no effect.

	I did pull the cover and cleaned the area around the battery holder (and I/O board including ethernet port) with Q-tip, though humidity was ~100% so I elected to use 91% isopropanol rather than water. No obvious contamination near the battery or on the interface board; I also cleaned the ethernet connector on the outside of the IO board.  I have not re-tested, though - see below.

	However, while in the process of doing that, I noticed 3 big electrolytic caps on the power board which look failed to me. All 3 are 3300 microFarad, all 3 have bulging upper ends (the ends with the strain-reliefs, away from the circuit board), and one has a brown contamination stain on it. One more has a single spot right at the convergence of the strain-relief grooves, so it might also be leaking.  I grabbed a few bad photos with my phone, which are available on request. I note that the brown stain on the one is on the lower end of the cap as installed in the computer when the computer is right-side-up, so if that component is leaking electrolyte, it makes sense that it would have accumulated and evaporated there leaving some residue.

	My inclination is not to re-start the machine until those capacitors have been replaced; I have no good idea whether they could affect the ethernet, but whatever they are supposed to be doing, I’m pretty sure they are not doing it properly by this point and I think that’s the next thing to pursue. I do have an ESR meter but I’ll have to pull the main and power boards out in order to get to the terminals, and I shied away from that the other night. I don’t have a working O-scope to test noise on the power lines, although that would be relatively easy since the power connector has easily accessible wires with the cover off.

	Questions for the list:

1) the capacitors are hot-melt glued to a central capacitor and to the circuit board. Do I need to replace that hot-melt glue when I replace the caps?

2) What is a good source/brand for replacement capacitors (in the USA, San Antonio TX if that makes a difference)?
My priorities for replacing are: same specs, same diameter, better reliability. The labels say:

	Su’scon
	3300 (mu) F
	10 V

and on the other side:

	SEK105°C
	07/01
	A3

(or) 

	SD105°C
	0124(V)

	As always, many thanks for any help you can offer; I can’t make any more progress this week (work :-P) but hope to get back on this next weekend.

													- Mark



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