Mac Plus, safe to remove C33, C36?

[Andrew]

Hello everyone, happy new year.

I just became an owner of a working Macintosh Plus '88 from ebay. It has analog board 630-0108. Upon initial inspection, the battery had been removed, no corrosion whatsoever, and all caps seem fine except rifa C33 and C36. These two seem to have a lot of cracks. Until I order replacements, is it ok to desolder them and use the computer without them? I am worried about smoke and stuff.

Also, C37 is not a rifa. It looks like a ceramic one. I think it can stay where it is. Do you agree? I have found many posts with cap lists, however they do not mention which are necessary, which are recommended and which do not need to be replaced.

Many thanks,

Andrew

 

[JC8080]

I don't have an answer for your rifa cap question, but as far as the general capacitor replacement, I would strongly recommend watching @JDW youtube video on recapping the 128k - Plus analog board: (43) Macintosh 128K~Plus Analog Board Recapping Walkthrough - YouTube  He talks a lot about the analog board and the parts, it's more than just a "how to replace a capacitor" video.  Definitely worth a full watch.

If you click the "show more" button, there is a lot of additional info there, including a list to a spreadsheet showing a list of capacitors: https://bit.ly/3diHUUG  There are three tabs, one shows a list of all capacitors, one a list of electrolytic only, and one is a list of all the "recommended" parts to replace.  The "recommended" parts includes a couple diodes as well.

 

[desertrout]

The Rifas just look like that over time. I can't speak to the sensibility of simply removing them without replacing them... but as I understand it the machine will still function without them. But if it's just a matter of a few days while you wait for replacements, I see no need to take them out (though I say that as someone who has never experienced a Rifa explosion). As for C37, it's still a safety cap even if it's not a Rifa box, and it can stay put.

I will echo @JC8080's recommendation of @JDW's video. Lots of insight there and worth a few watch-throughs. (If I'm not mistaken, JDW actually recommends the Rifa boxes over the ceramics...)

 

[Andrew]

Hello,

thank you both for your advice. I have already watched JDW's videos. Unfortunately he deals with US boards which differ at least from my board, in respect to the quantity and type of caps used. Do you think it will be ok to use the pc for a few days with the rifa's in this condition? Could you please also take a look at the attached photos in case you spot something that I do not notice?

Thanks

 

[JC8080]

Ah sorry I didn't realize you have the international analog board.  I believe JDWs list of recommended replacements is based on Larry Pina's book Macintosh Repair & Upgrade Secrets.  I think if you look at page 126-131 you will see Larry's recommended upgrade parts, which I believe are for the US analog board.  If you look at page 335 of the book you will find a listing of all parts on the international analog board.  You could probably do a bit of cross referencing, and you might be able to find which diodes/rectifiers need to be upgraded.  On the US board, CR1, CR5, CR15, CR18, CR19, CR20, and CR21 are recommended to be replaced.  I think the general recommendation is to replace every electrolytic capacitor on these boards, so at least that will be easy!  For the electrolytic caps that are on both the US and international boards you can use JDWs excel schedule to find the current Mouser part numbers.  For the international-specific caps you should be able to find replacements pretty easily on Mouser's site, their search feature is pretty robust.

Hope that helps a bit!  If you don't have Macintosh Repair & Upgrade Secrets, you can find it with a google search.  I have seen a searchable and non-searchable version, look for the searchable version.

 

[JDW]

I've not had the time to add the International Analog board to my Google Docs Spreadsheet.  Another problem is that I do not own one so I cannot give it a physical look-over like I did with the US Analog boards.

The yellow glue/epoxy in the photo of the flyback looks to be in great condition.

The axial caps on the motherboard can be replaced with tantalum, as I demonstrate in one of my recent videos.

I can't really comment to much further on the Analog board without a high-resolution top-down photo.  But take a magnifying glass and look for any dark spots on resistors, as such is evidence of burning.  Changes are you'll need to replace that resistor and any transistors connected to it.

While removing the RIFA caps will still allow the board to work, as I mention in my videos, removal of those will eliminate some noise filtering on the AC input, which isn't a good thing.  They have a plastic outer shell that cracks after many years.  They are still probably in functional condition, but I would recommend replacing cracked parts when you have the opportunity.  For now, following the Larry Pina Int'l Analog Board capacitor list is the best thing to do, just as @JC8080 said.  Here's a copy of the Pina book that's keyword searchable.

 

[desertrout]

Do you think it will be ok to use the pc for a few days with the rifa's in this condition? Could you please also take a look at the attached photos in case you spot something that I do not notice?

I think it will be just fine. I see nothing to worry about on either of your boards. In fact, they look to be in very good condition (including the flyback, which is nice to see... I have seven of these, none with the sealant looking as good (yellow) as on yours).

Have you tried to turn it on yet? Are you experiencing any issues?

 

[Andrew]

Thank you all so much for the information and comments on the photo. @JDW great work on your videos, keep them coming!

I purchased a capacitor set from console5.com. I don't know if they are any good or if they are tantalum, I should have asked here before. Anyways.

I am happy with my purchase around 210euros + shipping from ebay. @desertrout the computer is in great shape, works perfectly, even the eject gear. I am still trying to figure out what color it is supposed to be. The serial number (C8290SNM0001AP) suggests it was built in 1988, after the platinum model came out. However, the rear label has the "1mb" suggesting it is the beige. Judging by its color, it is either a not-very-yellowed beige, or a yellowed platinum. Is there any other definite way to distinguish the two models?

By the way, I retrobrighted the mouse today (my first attempt - bath in hydrogen peroxide in the sun) and went very well. The mouse was very yellowed. It turned out how beige would be when it was not yellowed.

Have a great weekend

 

[desertrout]

The 'Macintosh Plus 1MB' nameplate is the same for either beige or platinum. The only external difference I can see between the beige and platinum cases is the color of the nameplate itself, or the color of the power switch - the beiges are darker, the platinums are nearer to white. The inside of the battery cover plate is also good guide to the original color of the case.

Congrats on the Plus - it's a charming machine.

 

[bibilit]

The Plus will work that way without issue for a short period. 

Probably also without the Rifa caps, never tested myself, but more than once had those going bad while using a Plus, only the smell is disgusting, but won’t prevent it from working. 

 

[Andrew]

@bibilit I think I will probably leave it the way it is until the new caps arrive. 

@desertrout I've read online that most (not all) of the latest platinum models do not have the 1mb nameplate. I am 99% sure that the mouse is beige, because the insides change in the platinum version. The inside of the battery holder, the bottom of the computer and the bottom of the keyboard look like the platinum color. I think that probably my set is not matched.