Replacement for the Siemens Bakelite caps in an early 1980s SMPS

[rewease]

Hi everyone,

There actually was a time when early SMPS and late bakelite housed electrolytic caps coexisted in high end industrial gear. A friend of mine just got himself a CNC milling machine form that time with its first set of now 41 year old caps still installed in the PSU... and it's malfunctioning.

Two of the caps have already leaked slightly onto the board. I have not desoldered or measured any so far but they should qualify for replacement.

Now I'm wondering what to put in there as a replacement. First idea was state of the art low-ESR Nippon KY, LXZ or Panasonic FR. After all it's an SMPS.
But then again it's an ancient SMPS and some folks say that super low ESR is not always the best choice for ancient gear as it may be designed expecting a certain resistance in the caps to limit current spikes. The original Siemens EK caps are probably the same as Roederstein EK but I have no idea what their properties may have been when new.

So another idea would be using something more general purpose like Panasonic EB.

What caps would you use in such a PSU?

[stj]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

i would use what i would call entry-level low esr caps.
something like rubycon YXF

and dont think that just because siemens and some audiophile company use the same series code that they are related - they probably arent.

what the are height, diameter and pin-spacing?

[Olkus]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

and dont think that just because siemens and some audiophile company use the same series code that they are related - they probably arent.

Roederstein is a part of Vishay. This caps are not audiophile, I think the replacement of the EK is Roederstein EKE or EKC.

[stj]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

i was reading on an audio forum preople checking esr on these caps - they are VERY low!

maybe as low as panasonic FM/FR series!

[rewease]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

and dont think that just because siemens and some audiophile company use the same series code that they are related - they probably arent.

what the are height, diameter and pin-spacing?

I suspect they may be some sort of OEM production for Siemens by Roederstein. The rather unique casing, marking, etc all look like they came from the same production line with just the logo stencil swapped. But I can't know for sure.

Pin spacing is 5mm. Dimensions I have to guess right now. Something like 16x35mm.

Roederstein is a part of Vishay. This caps are not audiophile, I think the replacement of the EK is Roederstein EKE or EKC.

Thanks. EKCs specs look similar to other current day low ESR caps.

i was reading on an audio forum preople checking esr on these caps - they are VERY low!

maybe as low as panasonic FM/FR series!

That's good news so I don't have to worry about going too low ESR.
I can get Panasonic FR or Nippon KY delivered by wednesday so they are on top of the list.

...

I just looked around some forums and found an old datasheet for Roederstein EK series

[stj]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

i saw that, but people esr testing the siemens caps found them reading much lower - i mean seriously better spec!

[rewease]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

Maybe they are not the same after all. Also Z in the datasheet is measured at just 10 kHz.

[rewease]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

Just replaced the caps with Nippon KY and tested the old ones with my chinese component tester.

They all measure around 500 to 600 uF and 150 to 200 mOhms ESR. Didn't solve the issue but had to start somewhere.

[PeteS in CA]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

Maybe they are not the same after all. Also Z in the datasheet is measured at just 10 kHz.

Trying to make out date codes on several ICs, it looks like that board dates to early or mid 1982. Back then it was still common to spec ESR instead of impedance, and at 10KHz or 20KHz instead of 100KHz.

[rewease]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

Yes the machine was made in 1982. I'm impressed with those Siemens caps. Other caps with Bakelite housing (Roedersteins) were also fine and went back in for lack of replacements. Found a Frako NO 10µ/63V that aged way worse measuring 140 Ohms ESR.

[Olkus]

Re: Replacement for the Siemens Bakelite caps in an early 1980s SMPS

Frako's are usually bad, they can make problems.