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Macintosh Plus Extended Keyboard CAPACITORS

JDW

Well-known member
Do any of you own a Mac Plus extended keyboard with numeric keypad? Could you please confirm the capacitance & voltage ratings of axial capacitors C1 & C3 shown in the photo below?  I think there are only those 2 electrolytic capacitors, but if there are more, please ket me know that too.  Also, if you have calipers, could you measure the distance between the PCB and the bottom of the metal frame so I know the maximum diameter of replacement axial capacitors?

Thank you!

NqhTrG0Jl8fGoiXlZ3LCzqX88Aj6OSEhC3GsJaIHleQ.jpg

 
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JDW

Well-known member
Another photo I found below indicates there are two different versions of the Mac Plus extended keyboard.  I see 2 Radial caps in that photo below, whereas there are 2 Axial caps in the photo in my opening post.

2011-04-02 20.11.56.jpg

 

JDW

Well-known member
@desertrout Thank you for the link. It is interesting as the SMK version photo doesn't show any capacitors at all, indicating they are probably hidden under the metal frame.

The Mitsumi Japan edition seems to have only 2 radial electrolytic capacitors, both of which I confirmed are 1uF 50V and can be replaced with this Nichion type.  The problem is, I also want to know the values of the Axial capacitor types too.

All said, if anyone owns one or all of the 3 non-Mitsumi edition extended keyboards, I would like to hear from you regarding the capacitance, voltage and size data on the electrolytic capacitors. Please mention if the type is Radial or Axial too.

 

JDW

Well-known member
First, there is no fluid-filled electrolytic capacitor on earth that has eternal life.  Next, I have experienced bad caps on my IIgs ADB keyboard attached to my SE/30.  My SE/30 would hang suddenly for no apparent reason, and then I traced the problem to the electrolytic cap.  After changing the cap, I never had that problem again.  So yes, they do go bad, just like any other cap of that sort.  Replace with tantalum and then you never need to worry about it again.

The reason I am asking is because I've just finished a new video (not yet public) about the recapping of the 128K-512K motherboard and keyboard.  The procedure is similar for the Mac Plus, so I want to add those caps too, in the text description below my video on YouTube.  I know the motherboard caps, and I know the Japanese variant of the extended keyboard's caps.  I just don't know about the axial caps on the other extended keyboard variants.

So any kind help you can offer in that regard would be appreciated.  Specifically...

1. Capacitance Spec (printed on capacitor)

2. Voltage Spec (printed on capacitor)

3. Type: Axial or Radial

4. Quantity (please check under the black metal frame so you don't miss any electrolytic caps)

5. How much clearance, or how fat (diameter) can the replacement cap be, to fit into the stock location?  This is important because it seems some axial fit underneath that metal frame, so I want to know the maximum diameter it can be to fit there.

THANK YOU!

 

Mighty Jabba

Well-known member
I'm not very knowledgeable about capacitors, but here are some photos of my boards if it will be helpful (I also have one more that I can't find at the moment). One of mine is a Japanese board and one is American. I don't see anything else that looks like a capacitor to me.

plus_keyboards4.jpg

plus_keyboards1.jpg

plus_keyboards2.jpg

plus_keyboards3.jpg

 

JDW

Well-known member
Thank you for the clear photos!  I now have 2 questions:

Q1: Does the right side (not shown in your photo) of capacitor C1 say "50v 1µF"?

Q2: Do you have calipers or another means of measuring the distance between the top of that circuit board (onto which the capacitors are soldered), and the bottom of the black metal frame?  (The reason I ask is so I can know the maximum diameter of the replacement Axial lead capacitors.)

 

Mighty Jabba

Well-known member
Thank you for the clear photos!  I now have 2 questions:

Q1: Does the right side (not shown in your photo) of capacitor C1 say "50v 1µF"?


Yes.

Q2: Do you have calipers or another means of measuring the distance between the top of that circuit board (onto which the capacitors are soldered), and the bottom of the black metal frame?  (The reason I ask is so I can know the maximum diameter of the replacement Axial lead capacitors.)
It looks to be slightly over 7mm (the curve of the metal frame makes it difficult to be exact).

 

Crutch

Well-known member
Always happy to see you researching capacitor replacement for non-motherboard/analog board applications @JDW.

I expect this work will become more important with time.  Cap failure rate is, it seems, highly correlated with temperature (this is interesting http://jianghai-europe.com/wp-content/uploads/JIANGHAI_Elcap_Lifetime_-_Estimation_AAL.pdf).  So, all else equal in terms of cap quality etc. (which we know is NOT the case, but anyway), we should generally expect see analog board and motherboard capacitors to fail first, then as time goes by, we will likely be talking more about floppy drives that need recapping, and eventually more keyboards and mice which normally don’t warm up beyond room temperature.

I had a situation a few years ago where one particular mouse always restarted one particular Macintosh Plus whenever I pulled it in while the Plus was running (the mouse worked fine as long as it was already plugged in when the Plus was started up, which of course would be the normal procedure...).  I assumed something in the mouse was shorting out something in the Plus, so it was my first and only mouse recapping job to date.  Didn’t help though. :(   Still a mystery ...

 

JDW

Well-known member
@Crutch Mac Plus mice have electrolytic caps inside?  My Mac512 mouse doesn't, so I'd love to see a photo of yours!

@Mighty Jabba Bless you for more excellent photos!  The height and diameter of those radial 1uF 50V caps seems to be right at the limit of what can be installed, which means any replacements need to be considered with care.  Am I correct in assuming a replacement cap could be up to 8mm in height and 6.5mm in diameter and still fit?

 

sfiera

Well-known member
They appear to be 47µF 6.3V capacitors:

c1.jpgc2.jpg

c2-big.jpg

I don’t have a good tool for measuring size, but from the profile, the height appears to be slightly more than the switch box and slightly less than the switch button. I think the case leaves them some good clearance too.

profile.jpg

 

JDW

Well-known member
@sfiera A thousand thanks for the detailed photos of your mouse!  Did that come with a Macintosh Plus?  Also, can you measure the DIAMETER of those caps?  (D=6.3mm & L=11mm?)  The one nearest the connector in your photo seems the most critical in that any replacement cap with a bigger diameter would not fit there.

Honestly, I never though that model mouse had caps inside because my Mac128/512 edition does not, as you can see here...

Macintosh512_Mouse_NoCaps.jpg

My mouse works perfectly well, which raises the question as to why other mice (Mac Plus editions?) have the caps at all.

 
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sfiera

Well-known member
It has a M812M0100… (1988) serial number, so it was probably a Plus mouse, but I don’t know if I can say that with confidence. Your mouse matches a G447M0100… that I have. I saw another, seemingly older mouse (no chip) on the forums as well.

By the way, here’s the underside. There are a lot more components, not just on the top:

m1000-88-bottom.jpg

 

Mighty Jabba

Well-known member
@Mighty Jabba Bless you for more excellent photos!  The height and diameter of those radial 1uF 50V caps seems to be right at the limit of what can be installed, which means any replacements need to be considered with care.  Am I correct in assuming a replacement cap could be up to 8mm in height and 6.5mm in diameter and still fit?
Just guessing but I would imagine so.

 

JDW

Well-known member
@sfiera

Can you please measure the DIAMETER & LENGTH of your 47uF 63V caps?  (D=6.3mm & L=11mm?)  The one nearest the connector in your photo seems the most critical in that any replacement cap with a bigger diameter would not fit there.

True, there are components on the bottom of that PCB, but there is no space to fit a fluid filled electrolytic capacitor there, which is all we are concerned about.  Again, I am quite curious why they added those caps in later editions of the original design mouse seeing older models work fine.  Hmmm....

 

sfiera

Well-known member
Oh, the chip’s different:

chip.jpg

Yours has a 74LS14N inverter. The µPC339C appears to be a comparator.

 
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