RIFA safety cap PME277 - x or y?

[mpwdhc]

Hi guys, new member here, trying to fix an 80s B&O TV which suffered a failure of the 0.1uf safety cap up by the power switch/fuse. This is clearly marked as x2. The replacements are half the size, but have the same rating.

Having read about RIFA failure, I also ordered replacements for the other two caps. Now that they've arrived, I'm not sure they are correct. The originals are rated 4700pf, and are marked as follows

40/085/21 GPF
PME277 MB447
CT5
250V ~ MP
LD2
VDE reg nr 5201.212222

Is this an X or Y cap? I have ordered X2, but can't remember how I decided on them over Y, and can't help but think I really needs to order Ys.

Thanks in advance

[mpwdhc]

Re: RIFA safety cap PME277 - x or y?

I'll try and attach a few pics

[Th3_uN1Qu3]

Re: RIFA safety cap PME277 - x or y?

X cap definitely just by the physical dimensions. X class caps are generally wide with short straight legs. Y caps are generally round with long, sometimes bent, legs.

[mpwdhc]

Re: RIFA safety cap PME277 - x or y?

X cap definitely just by the physical dimensions. X class caps are generally wide with short straight legs. Y caps are generally round with long, sometimes bent, legs.

Thank you but is that really so? It seems at the time the RIFA caps looked similar whether X or Y?

[redwire]

Re: RIFA safety cap PME277 - x or y?

Just look at where the old caps are in the TV - across the line, on/off switch, to chassis etc. to know if X or Y is required. Lower value 4,700pF are usually Y-caps and go from mains to the set's chassis.

The old Evox/Rifa caps are from an era before X and Y class and mains overvoltage Cat. II or III etc. were well established.
So the transient voltage rating and test was not as good as today, and the part's size is not really a figure of merit because of the paper dielectric. I would use a modern film cap instead, something polypropylene.

PME271 is rated X2, 275VAC w/paper dielectric and only 2,150VDC one-time factory screening test.
PME277 no data anywhere they must have burned down a few houses.

[mpwdhc]

Re: RIFA safety cap PME277 - x or y?

Just look at where the old caps are in the TV - across the line, on/off switch, to chassis etc. to know if X or Y is required. Lower value 4,700pF are usually Y-caps and go from mains to the set's chassis.

The old Evox/Rifa caps are from an era before X and Y class and mains overvoltage Cat. II or III etc. were well established.
So the transient voltage rating and test was not as good as today, and the part's size is not really a figure of merit because of the paper dielectric. I would use a modern film cap instead, something polypropylene.

PME271 is rated X2, 275VAC w/paper dielectric and only 2,150VDC one-time factory screening test.
PME277 no data anywhere they must have burned down a few houses.

[mpwdhc]

Hi,

Apologies, I wrote a reply and then it disappeared.

The RIFAs in question are C15 and C4 in the middle of the pic, they seem to go down to the flyback ground.

Since they go to both sides (live and neutral), could they be filter caps rather than X or Y rated safety caps?

Re: RIFA safety cap PME277 - x or y?

Just look at where the old caps are in the TV - across the line, on/off switch, to chassis etc. to know if X or Y is required. Lower value 4,700pF are usually Y-caps and go from mains to the set's chassis.

The old Evox/Rifa caps are from an era before X and Y class and mains overvoltage Cat. II or III etc. were well established.
So the transient voltage rating and test was not as good as today, and the part's size is not really a figure of merit because of the paper dielectric. I would use a modern film cap instead, something polypropylene.

PME271 is rated X2, 275VAC w/paper dielectric and only 2,150VDC one-time factory screening test.
PME277 no data anywhere they must have burned down a few houses.

[redwire]

No, they are Y-caps. C4+C6 in series, as well as C15+C16 4.7nF, for extra safety, connecting to the set's chassis I think.
The Rifa paper-dielectric are not reliable, I would not use them yet Kemet still make them.

For alternates, use modern 4.7nF ceramic safety Y-caps rated for 300VAC mains or better. Whatever fits decent for lead spacings. Sometimes I'll use a 440VAC-rated Y-cap because the lead spacing is wide.

Also ensure C2 is not a Rifa, as an X-cap. It would not catch fire with fuse F1 there but it is nonetheless an old part and stressed by mains transients.

[mpwdhc]

Thank you, hopefully the local supplier (Jaycar) has something, rather than having to put together a larger order from Mouser/Digikey.

C2 was the reason I delved into it, following a rather dramatic emission

Thanks again for your help