Mains input filter on an HP 1652B  - Page 1
Forum section: electronics / repair

author: Minifig666
author_rank: Contributor
timestamp: October 26, 2014, 10:25:00 am
content: Hi All,I recently got myself a good deal on a HP 1652B 80ch logic analyser and 2 channel 100MHz scope all in one. Unfortunatley last night, it decided to release the magic smoke from its mains input filter.Course, the instrument still powers up just fine, but I don't really want to sit waiting for the thing to burst into flames!It's fitted with a Schaffner FN 393-2,5-05-12, which by the looks of things I could replace at £30. I don't really want to spend 20% of the cost of the instrument on a new filter though.If I simply replaced the filter with a normal IEC inlet, would I impact the performance of the instrument in any way? Course it might put some nasty stuff back on the mains, but eveything else is supposed to be noise immune!Thanks for the help,Mini

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2014, 05:12:19 pm
content: You can buy them new, and it is common enough that there are threads here about them. Just using an IEC inlet will work, but will compromise the RF rejection of the unit. You can just buy any filtered IEC socket that fits and use it, but avoid the old ones as they will smoke again. IIRC the non Swiss made Schaeffner ones are fine.

author: tautech
author_rank: Super Contributor
timestamp: October 26, 2014, 07:06:16 pm
content: Quote from: SeanB on October 26, 2014, 05:12:19 pm+1Seems not a month goes by without another old Schaeffner unit letting out the magic smoke.Shame, but often no other harm done.FollowSeanB's advice.

author: Minifig666
author_rank: Contributor
timestamp: October 26, 2014, 07:38:10 pm
content: Replace it with a new one? That was the plan, but as I say, they seem to be ~£30 on RS, which is a little more than want to pay to be honest. Though looking at things, a normal switched & fused inlet is going to set me back £10 anyway!Are these parts really this expensive, or am I just looking in the wrong places? (Perhaps I should have a look round the cupboars at work!)Thanks for the help,Mini

author: krivx
author_rank: Frequent Contributor
timestamp: October 26, 2014, 07:55:03 pm
content: Quote from: Minifig666 on October 26, 2014, 07:38:10 pmThere are cheaper filtered inputs, I don't know if anyone has tried swapping in a cheapie to see if it makes any difference

author: tautech
author_rank: Super Contributor
timestamp: October 26, 2014, 08:01:10 pm
content: Mini, if you put your country flag in your profile maybe you will get a local source recommendation.

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2014, 08:14:53 pm
content: Used will do, just connect them to mains ( with the exposed terminals covered well) in a flame proof box overnight to see if they are going to cook as well. If they are Schaeffner and are Swiss made then do not bother, they are all time bombs if they have not been powered continuously from new, and even then they are likely to pop if turned off for a day. they were very good devices for the first 10 years of life, but fail as they age. Later production used a different construction internally and do not have as high a failure rate.

author: Minifig666
author_rank: Contributor
timestamp: October 26, 2014, 08:44:56 pm
content: Fair point, UK flag set.It's just occured to me that I don'treallyneed a fused switched inlet, as the plug is fused, and sockets are switched! It seems the inlet only versions are much cheaper. I'll try the cheapie and let you know how it works.Thanks again,Mini

author: macboy
author_rank: Super Contributor
timestamp: October 27, 2014, 01:52:57 pm
content: Quote from: Minifig666 on October 26, 2014, 08:44:56 pmAdd a chassis mount inline fuse. Operating without any fuse (other than that in the cord) is probably against some fire code, and is marginally safe. It's safe as long as you use a fused cord, but not all cords are fused. There is no such thing in North America for example, and I am sure this isn't the only place. So what happens when someone plugs in an unfused (or high-amp fused) IEC cord? Drill a hole and add the chassis mount fuse.

author: cowana
author_rank: Frequent Contributor
timestamp: October 27, 2014, 02:24:59 pm
content: Could something likehttp://uk.farnell.com/schurter/da22-4121-11/inlet-filter-iec-screw-2pole-4a/dp/2253569work as a replacement? It might be annoying to fit, but it's fused and filtered...Andy

author: Minifig666
author_rank: Contributor
timestamp: October 27, 2014, 11:40:41 pm
content: Yeah, I think I might go for something along those lines. Perhaps I can convince someone to 3D print me a bracket to hold a smaller socket and a fuse holder!Not sure what the regs are in the UK regarding devices with removable flexes and fusing and whatnot. I guess it's something of a safety concern that elsewhere in the world stuff can go totally unfused. Worst case here is an IEC lead fitted with a 13A fuse, as plugs are always fused.Anyway, thanks very much for the help. I'll make a trip to RS and see how the repair goes.Cheers,Mini