Sony CR-45 4.7uF cap replacement for real?

[DevyDevly]

Hi All,

I really don't trust the physical size difference between these old orange caps and the new, hopefully, replacement caps (sitting on top).
Is this physical size difference ok - it seems huge?
Old 4.7uF 250V ChemiCon KX Series (40mm tall) vs new 5.6uF 400V ChemiCon KXE Series (17mm tall)
(I know the new cap is 5.6uF and 4.7uF but I got better specs on the 5.6uF cap (250 mA @ 100 kHz ripple) and figured the small difference wouldn't matter here (20%).)

I'm recapping my Macintosh II PSU Sony CR-45. These orange caps sit inbetween the 780uF 400V big mother caps AC side of the PSU.
All the new replacement caps are the same size or 10% smaller or so, but not this huge difference. I do have a 4.7uF 400V cap replacement if needed but it's even smaller (phsically) and has worse ripple specs.

Hopefully there's wise capacitor nerds out there who can help me please.

 

[GerrySch]

The change in size is simply materials improvements in the foil and electrolytic fluid. What I'm concerned about is the QUALITY of the capacitor. If it has worse ripple specs then it doesn't work as well at its rated value as your original cap. Remember, your replacement caps should be the same or a higher voltage value rating and you can go no farther that +/-20% above/below the original's Farad rated value. Voltage puts a physical stress on the plates (foil) of a capacitor and Farads is a measure of how much charge it can hold in a circuit.

When I recapped my SE/30, I used Tantalum caps as they are not prone to leaking like electrolytics but that might not always be possible. For power rail filtering (+5v, +12v, -5v and -12v), use electrolytics and use the Tants in signal processing circuits.

Good Luck,
Gerry

 

[DevyDevly]

Thanks Gerry.
I’ve purchased the best specced caps I can find (12000 Hrs @ 105°C; 100 mA @ 120 Hz; 250 mA @ 100 kHz).
I can’t find the ripple specs for the original but can’t imagine they would be better than the best available today - unless there was a different subclass of cap that use to exist and doesn’t today?

I’ll let you know if there’s success and the house doesn’t detonate… otherwise…

 

[DevyDevly]

Sitrep: PSU and House intact.
It sure looks weird but everything fired up ok and I let it run for 5 mins or so.
Got to fix brokern traces on the Mac II motherboard now...

Thanks @JDW for your SE/30 Sony PSU recap where you drill holes in the board for the big caps - it gave me the confidence to give it a go.

 

[JDW]

I really don't trust the physical size difference between these old orange caps and the new, hopefully, replacement caps (sitting on top).
Is this physical size difference ok - it seems huge?

You are right to not be trusting. I dislike the modern tiny caps that replace the old huge one's because the ESR is often lower on the old caps. But the biggest issue is cooling, for boards that get hot. The bigger the cap, the more surface area, and the easier it is to keep them cool.

So why I try to do is go up in voltage when selecting replacements so as to get a physically larger capacitor. And that often helps solve the Lead Spacing issue too, but not always. As you pointed out in your last post, there are reasons why you may need to do a little drilling to make a replacement fit.

When choosing replacements keep your on on ESR when you review those hi-temp and hi-Hour caps because what I often discover is those caps have a bit higher ESR than the ones with lower 85°C ratings and lower hours. So its a balance between the Temp/Hour/ESR ratings.

 

[DevyDevly]

Thanks JDW - it’s good to get confirmation that it’s a tricky task to get an optimal fit and that I wasn’t missing something major (I’m relatively new to electronics and retro repair).
I went for the best ripple specced caps (EKXE401ELL5R6MJ16S) I could find and went up to 5.6uF from 4.7uF (plus 250V to 400V) - I’m figuring the increase in capacity in this case is ok given that they’ll be some sort of smoothing vs timing. Also figuring is that the ESR/ripple specs from 1989 won’t be as good as these new caps.
For cooling I’m hoping that all the lovely space around the caps now will be enough to keep them coolish for the few hours per year I’ll use the Mac II (if I can ever finish repairing it (chime, no video)).
So, like you mentioned, hopefully I have the right Temp/Hour/ESR balance.
It would be great to measure with an IR camera but that’s a lottery win away
Love your YouTube posts!

 

[JDW]

Thank you for your kind words and for the added info.

Normally, it's best to retain the stock capacitance value when possible, unless you have a schematic and know the operation of the circuit in question. But capacitors normally have a 20% tolerance, so if your replacement measures right at 5.6uF or below, your replacement is still within the tolerance spec of the original 4.7uF capacitor. It may not matter much at all because it very well could be that they chose 4.7uF back then only because a 5.6 or higher capacitance cap wouldn't have physically fit in the space available. Very possible.

The UTi260B thermal camera I have is very nice, but it takes a while to get used to it. There's a setting in the menus which tells the camera how far it is from the device being measured. When I first got my camera, I didn't pay strict attention to that, and I think that contributed to my getting some questionable results. I've refined my usage of it over time, and the measurements are better and more repeatable.

Thermal cameras are like good desoldering guns (e.g., FR-301 from Hakko), they are very nice to have, but they set you back a lot of money. I'm a real penny pincher, and it took me YEARS to get the FR-301, but it really changed my desoldering work for the better. Fantastic tool. I get less use from my 260B thermal camera, but when I need to measure heat from multiple components at once, it's the right tool for the job. And then of course when you want to measure the output of power supplies before and after a recap, having a good oscilloscope like a Rigol DHO804 is invaluable.

All of this is why the hobby can get rather expensive. It's not worth getting all those fancy tools for only one or two vintage Macs in one's collection, but when you have multiple Macs, you tend to do a lot of work on them, and then the tools start to make more sense.

 

[DevyDevly]

You latest YouTube post using the IR camera was very timely. I can’t believe those temps - especially those when powered off!