Replacing EMI Capacitor - Type X on HP 6291A - Need value suggestion - Page 1
Forum section: electronics / repair

author: edtyler
author_rank: Contributor
timestamp: June 15, 2022, 03:07:12 am
content: Hi,I was using a HP 6291A to charge some LiFeMnSo batteries and woke up to a smoke alarm going off. It turns out that C901, a Type X metalized paper capacitor had overheated and charred the paper media inside. Interestingly, it did not blow the line fuse, althogh it tested as a short later.The original part # is 0160-4065, but I can't find any reference to its value. This component was added to the supply by HP as part of fixing various errata as the design progressed.For now, it can just be cut out of the circuit, but I'd like to replace it with an appropriate value. This supply is a 115V 60Hz model that is fused for 6A. As a linear supply, I find it a little hard to believe that any significant EMI could make it past the massive line transformer out through the power cord, but HP must have been convinced that it was needed.Can anyone give me a suggestion as to an appropriate value? I have some X1 rated .1uF and .01uF caps that are about the right physical size, but can always order other values, if needed.Thanks!

author: coppercone2
author_rank: Super Contributor
timestamp: June 15, 2022, 03:23:04 am
content: I think its for diode noise. Just pick any capacitor that is the same value from the manual with a voltage rating for your mains.RIFA PME271-M-610

author: edtyler
author_rank: Contributor
timestamp: June 15, 2022, 04:09:21 am
content: Hi Coopercon2,Unfortunately, the Service manual for the 9261A from HP does not list the value for C901. The device itself was largely destroyed and the markings are illegible. I suspect the type X1 caps I have are overkill as far as voltage tolerance, but the capacitance is a mystery. A swag would be 0.1 uF, butCan you elbortae on 'diode noise'? There is a full wave bridge setup on the secondary side of the transformer. What would the characteristics (frequency) of the noise you wold expect to be reflected back through the transformer?Thanks

author: jonpaul
author_rank: Super Contributor
timestamp: June 15, 2022, 06:52:19 am
content: Bonjourthe X and Y line filter capacitors form a normal ( differential) and common mode filter with the filter inductors.The function is both to prevent EMI generated in the equipment from conducting to the mains, and to attenuate EMI incoming from the mains.X caps are in the 100 nF..470 nF range.They are specified to be fail safe.Y caps are limited by leakage AC current safety, usually 4.7 nF in USA.The old yellow rectangular RIFA caps from 1970s..1980s eventually fail due to crazed case plastic and humidity.Hopefully this answers your questionsJon

author: Kleinstein
author_rank: Super Contributor
timestamp: June 15, 2022, 01:50:15 pm
content: In most cases 100 nF should be OK, unless the part is especially noisy.AFAIK a capacitor before the switch, that is connceted even if the power is off should be X1 for a little extra safety (must work unattended - though systems like cargers work unattended anyway).In the US the voltage rating is a bit more relaxed as many capacitors are made for 230 V and thus have extra headroom.

author: coppercone2
author_rank: Super Contributor
timestamp: June 15, 2022, 10:05:56 pm
content: I think the rectifier makes noise, which is what I meant by diode noise

author: floobydust
author_rank: Super Contributor
timestamp: June 15, 2022, 11:52:04 pm
content: HP 0160-4065 is Rifa/Kemet PME271M610M 0.1uF +/-20% 275VAC X2 24x7.6mm, 14H. LS=20.3mm.Digikey399-PME271M610KR30-ND(I hate that 271 series of capacitors, notorious for cracking and shorting).So the lead spacing, either 15mm or 22.5mm is standard and the old part at 20mm is oddball.PHE820ED6100MR06L2close I'd bend the leads in.

author: edtyler
author_rank: Contributor
timestamp: June 16, 2022, 06:19:05 am
content: Thanks to all who answered my questions, especially floobydust. I've got plenty of space in this power supply, so I'll go for the 820 series or similar. I have some NPXF X1 caps that use metalized polypropylene.DaleIssue Resolved

author: factory
author_rank: Super Contributor
timestamp: June 16, 2022, 07:18:03 pm
content: Quote from: floobydust on June 15, 2022, 11:52:04 pmDon't know about the 6291A, but my 6237B has extra holes, to allow the choice of two different length caps to be used. Ended up replacing the RIFAmadness with something not made by RIFA or Kemet, I refuse to buy any of their X/Y caps, while they still make paper crap.David