Bad Capcitors in Mac Classic

[cjtmacclassic]

Hi all-

I'm new to this site, however, i do know that it is an excellent resource for information. Many people have experienced this exact same problem, but i may need

assistance in this. my mac's screen has been twitching very badly these past few weeks, so i decided to open my mac. when i looked inside, i removed the motherboard. upon further inspection, i found that the capacitors near the video processor had small visible rings of liquid around them. so, i have decided to purchase a desoldering kit and use my iron to remove these caps. any idea on where i could purchase capacitors? and also, of what type? ceramic, snap caps, or use the same liquid filled type? help would be much appreciated. :simasimac:

-CT

 

[Osgeld]

The best place to get them is either a local electronics distributor (not radio shack) or online such as farnell or mouser

Theres a tiny amount of debate of which type to buy that pops up once in a while, some say the original electrolytic can types are better, to make a 1:1 replacement because of their behavior in certain situations, most around here will strongly advise the use Tantalum types.

if you use Tant's you will need more because they don't come in the same values as electrolytic can types (so you have to stack them up) and they cost more, most people say they wont ever leak, which is FALSE, but they have much much less chance of doing so, your going to have to practically blow them up first

If you use electrolytic can types (i keep calling them can types because Tantalum's are electrolytic also) they will be cheaper and easier to deal with, and probably will perform better in certain areas (like the power supply) but your going to have to replace them again in another 10-20-30 years

PS: if your new to soldering, save your mac, goto a thrift store and get some old looking VCR or something to practice on first, it does take some getting used to

 

[cjtmacclassic]

ok. well, i'm really quite good at soldering, and i suppose i could get some of these caps @ Radioshack, since it's not officially been converted to 'the shack' and really, it's not the type of Radioshack where the cashiers think you're crazy when you come in looking for a specific part. really, i think it's the only good Radioshack left!

back to the point: i will most likely go to town saturday to get the caps. i'll post pictures of my progress. comments or help are always a nice thing to see.

-

[/quote"I will write on a huge cement block 'BY ACCEPTING THIS BRICK THROUGH YOUR WINDOW, YOU ACCEPT IT AS IS AND AGREE TO MY DISCLAIMER OF ALL WARRANTIES, EXPRESS OR IMPLIED, AS WELL AS DISCLAIMERS OF ALL LIABILITY, DIRECT, INDIRECT, CONSEQUENTIAL OR INCIDENTAL, THAT MAY ARISE FROM THE INSTALLATION OF THIS BRICK INTO YOUR BUILDING.' And then hurl it through the window of a Sony office and run like hell."

 

[JRL]

Hmm... I think that the jittering issue is caused by the analog board. While you only really need to recap the analog board, you're best off recapping both.

AFAIK, it's one cap that causes the jittering; let me check.

Edit: Yup, it's here. Actually you just need to fix some cold solder joints. (quoted from tomlee59's great Compact Mac repair guide)

4.1 No display; Wobbly display; Single vertical line down the middle If the Mac seems to function well (e.g., you hear the boot bong, disk accesses occur the

way they should, etc.), but has certain display problems, this section is for you. Many dis-

play-related problems are due to the notoriously unreliable solder joints on the yoke con-

nector J1. These should always be resoldered as a matter of course because a visual

inspection does not always reveal problems such as hairline cracks. Flakiness here results

in symptoms that include an intermittent raster, wobbly/shaky/jittery raster, no raster,

uncorrectably narrow raster, or a single vertical line down the center of the CRT. Quite

commonly, slapping the side of the Mac can make these symptoms come and go if the

connector is indeed the problem. Without question, this is the most common fault with the

analog board. It’s sad that so many old Macs are tossed in the trash because of this prob-

lem, because it’s trivial to fix, most of the time.

To repair, simply freshen up the yoke’s four solder connections to the analog board, while

leaving the connector halves mated, or else the heat will melt the connector plastic and distort its shape. You’ll never be able to reconnect the two halves if you fail to fol-

low this advice.

And don’t be lazy and simply reheat the old solder that’s there -- use new solder. Use

enough heat/duration to get the solder to flow well, leaving a shiny, smooth surface upon

cooling. After it’s cooled down, disconnect the two halves and inspect the four mating

pairs of contacts for signs of oxidation or burning. Repair or replace as necessary. If you

can’t locate a replacement (or don’t want to wait for one), you can always simply hard-

wire the connections (e.g., desolder J1 from the analog board, remove its mate from the

yoke cable assembly, and just solder the four yoke wires directly to the analog board). The

drawback is that if you need to remove the analog board later for some reason, you’ll have

to undo the connections.

 

[JDW]

Tantalum's are electrolytic also

Tants are tants. They are not the canned, fluid-filled electrolytic type. This is why tants will last as long as your circuit board, since they have no fluid inside. Electrolytics in most cases will leak after 12-15 years. But electrolytics come in bigger sizes than tants, so you cannot always replace electrolytics with tants.

Perhaps you meant to say that both tant caps and electrolytic caps are "polarized." But that's not always true either.

 

[H3NRY]

Some tantalum caps have liquid electrolyte and some are solid. The liquid-filled ones may leak or dry out like aluminum Caps. The solid ones are very long lived.

 

[JDW]

Thanks for the correction, Henry.

While I have read about the old "wet slug" tants that do have fluid inside, for more than 15 years I have never (neither professionally nor in my repair hobbies) used any tantalum caps other than the "solid electrolyte" variety, in either dipped or chip form. The big benefit of the "solid" tants is their shelf-life versus fluid-filled canned electrolytic capacitors. I therefore don't see why anyone would want to use a wet tantalum as a replacement cap in a vintage computer.

 

[H3NRY]

Eggs-actly. Avoid the wet-slug style tantalums when buying replacement caps. Nearly all caps you will find today are solid, but there are some of the old wet types in surplus catalogs.

I picked up a bag of 47uF / 16V caps in a surplus store last week and when I got home, I happened to notice the date code - 1989. D'oh! Great idea, Henry! Replace a failed 20-year old cap with a "new" 20 year old cap? I think not! :I