Apple II+ Astec Power Supply - no Yellow RIFA, only a Red WIMA

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Apple II+ Astec Power Supply - no Yellow RIFA, only a Red WIMA

Hello All,

I recently discovered my old Apple ||+ while cleaning out my father's workshop and I brought it home with me. Before attempting to power it up I checked online to see what I could find out about reviving this old tech, and was fortunate enough to find this community.

 

I've read several posts warning about the likely failure of the yellow RIFA capacitors in the Apple || power supplies. Before even attempting to power up the ||+, I decided to proactively replace those capacitors. I opened my power supply (had to drill out two rivets to get inside), and I was surprised to find a red WIMA capacitor instead of a yellow RIFA.

 

I haven't pulled the circuit board out of the power supply enclosure yet. My view of the capacitor is obscured with wires and components, but I can see:

WIMA

MKS4-R

0.1 (additional characters obscured, but I'm assuming that's the uF capacitance rating )

300 (additional characters obscured)

212 (additional characters obscured) A

 

The datasheet says it is a Metallized Polyester (PET) Capacitor. I found the datasheet for the WIMA MKS4 series capacitors here: WIMA MKS4 Datasheet 

 

Before I go any further and remove the circuit board, I thought I would create a post here asking for advice. Should I just assume that since it's not a RIFA, that it's probably good? Or should I proceed to remove the circuit board, and replace the capacitor anyway?

 

Thanks for the help! I'm looking forward to rolling up my sleeves and getting this II+ running again!

 

-Fritz

 

 

 

 

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No need to replace the WIMA.

No need to replace the WIMA.

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A burned capacitor is seen in

A burned capacitor is seen in the upper right corner of the picture.

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retro_devices wrote:A burned
retro_devices wrote:

A burned capacitor is seen in the upper right corner of the picture.

 

Where??

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or MOV

The burned component may actually be a MOV, the red disc shaped "VDR1".

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CVT wrote:No need to replace
CVT wrote:

No need to replace the WIMA.

 

I agree with this.  The WIMA type are not generally known to fail in the way that RIFA brand does.  I believe it is because the type of plastic they are made of is different.  The RIFA branded caps use a hard translucent plastic that deteriorates over time, turns brittle and develops micro cracking that eventually lets air in which oxidizes the material inside and causes it to short out and eventually burn up.  The red plastic seems softer and perhaps more flexible and doesn't seem to dry up and turn brittle so it seems to hold up a lot better.

 

I pre-emptively replace vintage RIFA brand with some new ones that I have made by a different brand which are also yellow but use similar opaque plastic like the red WIMA ones.  Hopefully they will hold up for another 30+ years.  They may likely outlive me.

 

 

 

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Thank you all for taking the

Thank you all for taking the time to read my post and reply.

I think I'll leave the power supply as-is right now and see how it goes after I apply power. I'm not sure what component appeared burned to retro_devices.  robespierre suggested it might be VDR1, but that looks ok to me (see photo below).

The only component I see on the board that looks like it may have been a little toasty is labeled R4, its a large green resistor. The circuit board shows some signs of heat discoloration where the leads for that resistor are connected. I don't see any leaking or bulging from the electrolytics. A few additional photos are attached below.

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The discoloration around the

The discoloration around the leads on that big green resistor is pretty normal and almost surely not really anything to worry about.  In fact it isn't nearly as bad as a lot I've seen.  Those resistors do indeed get hot but they are made out of a ceramic material that can take quite a bit of heat for long periods of time without failing.

 

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Thanks for the reassurance

Thanks for the reassurance that the discoloration isn't anything to worry about. I'll probably fire up the 'ol Apple II+ tomorrow and see what it does....

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