Mastodawn

#retrocomputing #macintosh

ax man cap run

also a TOPS LocalTalk card for a PC

gonna pass that to a friend for #marchintosh shenanigans 🫡

switcher silicon sanity check: rectifier bridge not shorted, main switching transistor not shorted, no shorts on the output rails 👍

welp i'ma pull all the caps anywhere near the corrosion and check 'em, then see about cleaning up the mess

big bulk caps look clean and measure bang on spec on my cap meter

these will go back in ✅

dead center of the corrosion is little ol' C19, lets pull that out and... ewww that's crusty not even going to test it STRAIGHT IN THE BIN WITH YOU ❌😵

think we found our culprit

of course this is the one i couldn't find a good match for at ax man

today i learned it may be one of the littlest electrolytics on the board that may betray you 🗡️

hope i got something in my stash

#retrocomputing
#macintosh
#marchintosh

also in the kill zone:

C62 looks clean and meters good ✅

C63 meters good, hope this is flux on it, don't have great replacements for these so i guess i'll let it fly ❓

oh boy C67 on this sub-board is another 27uf 35v making a mess of things

TO THE BIN WITH YOU ❌

C60 is right on the edge of the corrosion zone, lets pull that and check it

that's... 5.5% low? Nichicon PL(M) is 20% precision so i guess its in spec but it seems Nichicon PL are notorious for alkali contents corroding the leads and leaking so i should very much replace all these ☠️

really wanted to take this out and hose it down with QD electronics cleaner today but the weather is not cooperating

this is turning into more of a detail job than i expected, i thought i could just replace some caps but nooo 😮‍💨

here's a trick i learned from watching clips of canon factory workers

got a pile of vintage Pentax 50mm F2.0 kit lenses collecting dust because you have way cooler lenses to use?

they make very nice hand lenses!

guess i spend some hours scraping at it with a dental tool until i get bored

lot of nasty black corrosion bubbling up under the solder mask but it hasn't penetrated and the copper is still lookin' good

painstakingly scraped all the dodgy solder mask off

a good q-tip scrub with IPA to clear the flux, a vinegar scrub and rinse to maybe neutralize whatever alkaline cap juice is left, and a water rinse to clear the vinegar

and let it dry in front of a fan all night

yup it's a good day to stay inside 🥶

#marchintosh

welp nothing to do but soak it in moar flux and solder and see if we can cut through the corrosion

the nastier bits are very stubborn and i resort to a good sharp pocket knife and a few more rounds of solder wick scrubbing to scrape the black crusties off and get a good tin on the exposed copper

a bit worse for wear but perhaps we can get another 30 years out of it 🫡

time to put caps back in it

these Nichicon LQs test good and aren't known to be problems, they go back in

the PLs all gotta go, it seems they are well known board destructors 🧨 🤬

peeping at them with the lens they do look corroded all up in there

C62 came out clean but sure looks to be the center of the other bit of corrosion

to the bin with thee! ❌

C60 is a 1200uf 10v cap that appears to be the output filter for the 5v rail

closest ax man match i could find is a 1200uf 12v cap

but its a chonker and it seems the PLs may have been chosen because they are smol beans for their capacity

fitting one in the available space seems infeasible

PL caps are "Extremely Low Impedance" but they use them everywhere, the definition of such has changed over time, and its unclear how much that actually matters

digging through my stash i have some Panasonic 2200uf 16v i could drop in and overspec it quite a bit

or play cap addition with an Illinois Capacitor 1000uf and a 220uf

resistors in parallel baby 😎

squinting at datasheets two of these should drop the ESR to the same spec as a PL

but the date codes a little scary, nichicons are from 1980? a nippon chemi-com from 1973??

may just go with 1000uf + a 470uf Panasonic that's at least younger than me 🫠

Chip Mar 16

@Seg The ones from the 70s and 80s might well be better than the ones from the 90s and later, if various YouTubers are to be believed. Depends on the particular series, I expect. Anecdotally, I swapped all the caps out of a 1084 and most of them tested fine.

@bytex64 true, in which case i wanna save them for more interesting purposes 🤔

you know they're old when you can't find a datasheet for them on the internet

just "here's what new cap series to use instead" lmao

Stewart Russell Mar 16

@Seg welp, at least you'll likely have weather radio warnings tomorrow. Canada's Weatheradio signs off tonight, forever.

slembcke Mar 16

@Seg Ah Marchintosh in Minnesota. We never know what we’ll get!

Patrick Georgi Mar 15

@Seg At which point are you better off redoing the PCB and then transplant the parts (except for the caps, which should be all new)?

Chip Mar 14

@Seg That’s been my experience, too. It’s often the little guy in the critical feedback loop, baking next to a hot component.

Chip Mar 9

@Seg Oh yeah that looks bad. Doesn’t look like cap corrosion to me, though. That’s maybe water damage? In any case, the caked fan suggests it got hot in there, so dollars to donuts you’ve got some bad solder joints and cooked caps. That where I’d start.

GEM is truly truly outrageous Mar 9

@bytex64 squinting at it some more, it is directly south of the big caps if it was sitting on its front

dunno i'm really confused about how super clean the inside of this thing is, except for the caked up cooling fan. nasty black dust. toner maybe?

Chip Mar 9

@Seg Hmm I think if it were toner you’d see it everywhere. It collects on anything even a little bit electrically charged (used to admin machines in a server room that was also a copy room - yeah, it was bad).

I’d guess maybe the rest of it got cleaned separately or the PSU was from some other machine, but I dunno.

GEM is truly truly outrageous Mar 9

@bytex64 they do use carbon dust to clean fancy optics so i suppose it may have just got a good air hosing out

i worked at an IT place that shared an open warehouse with a toner refilling operation, so i'm familiar with how that gets into everything 😷

kaaswe Mar 9

@Seg
The component side and all components looks good, caps are the once’s to worry about. They are probably all good

The bottom side of the card might not be that bad after a clean up. Use warm water/soap solution and a sponge to clean the card. Don’t use any chemicals or detergent. Clean the card dry with a cotton cloth. Let it rest for a day.

Let’s inspect the card after the cleanup, you might have to redo some joints

OutOfSpace - 不割席 Mar 9

@Seg gross