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Macintosh 128k~Plus Analog Board, Safety Capacitors C33, C37, C38


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I tend to swap out the electrolytics in a recap and leave the film or metalized paper caps alone if they are good.  Some among us have experienced blown filter caps near the power input on the original Macintosh analog boards, specifically these Rifa caps:

 

C33: 4700pf 250VAC Minibox (sometimes found to be 2200pf?)

C37: 4700pf 250VAC Minibox (sometimes found to be 2200pf?)

C38: 0.1uF 250V Minibox

 

The stock Rifa caps all appear to be metalized paper capacitors. A directed replacement for C33 and C37 would be the KEMET PME271YA4470MR30, also metalized paper.  But would a Polypropylene version safety capacitor like the WIMA MKY22W14703F00KSSD be a better choice?  There is also the KEMET F462AG472J1L2A polypropylene cap, but it is not classified as safety and therefore I do not know if it's failure mode would be open circuit when it blows.  Similar thinking should apply to replacements for C38

 

Please let me know your thoughts.  

Thank you.

 

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  • 2 weeks later...
8 hours ago, JDW said:

Since everyone appears afraid to reply, let it be known I am open to "speculation" too.  

@Bolle?

No idea. If I was to replace them I would go for what was in there originally.

I yet have filter caps to get blown on any of my machines. I'd probably try and see what happens when I just leave them out.

Edited by Bolle
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I have had a lot of RIFA caps failures, most of them in the Apple II series PSUs, but also in the Macintosh 128/52 and Plus units.

 

When they failed, it's a real mess, so i replaced all of them as a matter of fact.

 

Indeed, i have replaced more RIFA filters than electrolytics in the Macintosh Analog Boards.

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2 hours ago, beachycove said:

Thanks for this!

 

Too bad they don't sell a ready-made set for analogue board/ps repair in an SE/30 too.

Probably because they haven't looked at one and made a list yet.  If you take your phone and take really close up photos of every capacitor with its board assignment number  such as C1, C2 etc and then one photo of the top and bottom of the entire board and send it to them, they will make a kit.  That is how I got them to make one for the plus, 128 and 512.

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8 hours ago, bibilit said:

I have had a lot of RIFA caps failures, most of them in the Apple II series PSUs, but also in the Macintosh 128/512 and Plus units.

When they failed, it's a real mess, so i replaced all of them as a matter of fact.

Indeed, i have replaced more RIFA filters than electrolytics in the Macintosh Analog Boards.

I had a RIFA cap explode in the PS in my Profile HD.

Also had one go in a 512K also.

Yep, replace them while you're in there.

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16 hours ago, marcelv said:

C33 and C37 replace with 4n7 300Vac

481044_1.jpg.88d2d677028ae7456468c1efb2bf000b.jpg

 

Polypropylene (PP)?  Can you please post a link to that exact part on Mouser?  If not, what is the exact part number?  I want to see the datasheet for it.  Thanks.

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