HP8656B Sig Gen. Can you smell smoke? - Page 1
Forum section: electronics / repair

author: SNGLinks
author_rank: Regular Contributor
timestamp: November 08, 2014, 09:23:08 pm
content: I was watching TV when someone on TV said 'Can you smell smoke?' Sure enough I could!I traced the smell to my HP8656B which I was using about an hour ago and had put it into standby.I found that the input filter was badly burnt. The fuse in the unit was still ok as it's after the filter. Only the 5A fuse in the IEC lead had gone.The filter is part of the IEC input connector, fuse and mains voltage select unit. I don't think I'll be able to get a replacement so I'm thinkingof just fitting a new IEC connector with fuse and filter, then hard wiring the voltage selection wires. (if I can work out the connections)The nearest I could find for a circuit of the mains input is attached but it's not quite the same as my unit as it shows the fuse before thefilter and the voltage section is by card whereas in mine it's a roller.

author: c4757p
author_rank: Super Contributor
timestamp: November 08, 2014, 09:33:44 pm
content: What a surprise, it's a Schaffner.

author: Andy Watson
author_rank: Super Contributor
timestamp: November 08, 2014, 09:35:27 pm
content: Ah! The infamous Schaffner filter smoke generator. I believe they are still available. Last one I purchased was from RS. You might not like the price thoughEdit: If any of the internal goo (resin) has contaminated other components or surfaces, IPA will remove it.

author: TheBay
author_rank: Unknown
timestamp: November 08, 2014, 09:57:13 pm
content: OMG the amount of times I've seen these fail! If something has one and pops fuses 99% of the time it's that stupid device!May be wrong of me, but I just bin it and don't bother with one lol, though on test equipment that might not be a good idea....

author: SNGLinks
author_rank: Regular Contributor
timestamp: November 08, 2014, 10:27:54 pm
content: Does the RS item include the voltage selector?

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: November 08, 2014, 11:27:21 pm
content: I have used the FN372-2-21 variant for my Solartrons. They have the voltage selector and 2 fuses. Yours looks like it only has one. The last digit indicates the fuse length USA or EU. 1=EUR 2=USAThe newer voltage selector wheels have 230 printed on them instead of 220. You can swap out the new for the old to match the original.I cannot see your sticker but I am guessing it is FN370-2-21

author: Andy Watson
author_rank: Super Contributor
timestamp: November 09, 2014, 01:24:42 am
content: Quote from: SNGLinks on November 08, 2014, 10:27:54 pmAs Manatee suggests, go by the Schaffner part number. The FN 370 is the basic form of the unit, the suffixes indicate the current rating and voltage rating. Doing a search by "Schaffner FN 370" returns hits for both Digikey and Mouser, and some others.Edit: Yes - the FN nnn part number specifies an IEC socket and voltage selector and fuse and whatever else is in the whole plastic snap-in unit. Just had a quick squint at the RS site and it looks like they do everything but the 370 model.

author: amyk
author_rank: Super Contributor
timestamp: November 09, 2014, 02:06:25 am
content: It might not be wise to replace it with another Schaffner assomeone in this thread hadtwoof them (the original one, and a new one he bought) release the magic smoke.Apparently only the Switzerland-made ones are problematic but you never know where the one you're buying is from.

author: Andy Watson
author_rank: Super Contributor
timestamp: November 09, 2014, 02:35:25 am
content: I've experienced this problem on two Solartron DVMs. This was a few years ago and the wisdom at the time was that the problem was due to a bad batch of capacitors (RIFA brand I believe). Both DVMs were of the same vintage but one had been used and the other was as new, less than one hours running time. It appears to be a problem that is related to the age of the capacitors, not the running time. In the thread that you linked the unit that failed after 35 mins has a BS613 mark and possibly a date stamp indicating 1991 - i.e. it was NOS.I replaced the capacitors in one unit and purchased a replacement Schaffner for the other DVM. Neither unit has failed (yet).

author: SNGLinks
author_rank: Regular Contributor
timestamp: November 09, 2014, 07:15:05 pm
content: I was at an amateur radio rally today and I spotted a transformer with the same mains unit that blew up on me.It was only £10 so I bought it.When I took it apart (see second pic) I saw that it was Swiss made.Is it worth risking it in my sig gen?

author: SeanB
author_rank: Super Contributor
timestamp: November 09, 2014, 08:29:39 pm
content: Plug it in and leave on for a day and see if there is heating or smoke. Do so on a fireproof surface just in case.

author: free_electron
author_rank: Super Contributor
timestamp: November 09, 2014, 09:54:33 pm
content: they should change their name to Paffner ..

author: SNGLinks
author_rank: Regular Contributor
timestamp: November 09, 2014, 10:49:37 pm
content: This is what I bought for £10:http://www.qmstore.com/9100-4865-Talema-Toroidial-Transformer-110-220-input-16VAC-40-VAC-output/p823271.html

author: Makila
author_rank: Newbie
timestamp: February 27, 2016, 02:45:28 pm
content: I was in the workshop, yesterday, with the 8656B in standby when I heard a fizzle and crackle, sure enough, it was the 8656B sig gen making a cloud of smoke with the associated bad smell. What happens if you are not nearby, does the house burn down? I thought the power supply board had a blown cap but it was the Schaffner connector. I never realized these connectors were prone to failing so spectacularily, and was surprised to read this thread. However I am glad it was not the board as half of the power supplies are running through it on standby. So will replace the connector and pull the plug to isolate the damn thing when not in use. My room still stinks... Happy days.We should have a contest on whose Schaffner blows up the best.Steve

author: VK5RC
author_rank: Unknown
timestamp: February 27, 2016, 08:34:44 pm
content: Some time ago when repairing my 3458A, I prophylactically replaced the EMI filter, an older Schaffner, there are some discussions about this elsewhere. It seems to be mainly a paper capacitor made by Rifa, paper type that age not use seems to be the culprit.http://www.vintage-radio.net/forum/showthread.php?t=88137In looking for a replacement, Schaffner seems to be one of the major manufacturers of these devices and as some people leave a lot of their Units powered to the IEC socket, a moderate number of Schaffner failures would be expected. mains filter caps blowing is not an uncommon failure.http://www.kb6nu.com/2215-problem-found/For my electronics area, I have two types of mains, one I leave powered on all the time, for clocks etc, the other (the majority) links to one switch and plug which gets switched off and pulled out if lightning around / when I leave the area. I have quite a bit of older gear and have had a few smoke-releasing incidents e.g. a transformer selling out etc.