On 27/07/12 03:17, Tom Miller wrote: > I agree with Ron. Clean the board up real good then do an inspection. > With a microscope if you can get your hands on one. Look for cracked > SMT parts. The high heat from the oven could very well stress the > parts causing a failure. Flux the board up and hit all the connections > with a small iron. When you melt the solder on each end of a part, if > one is broken, it will then show up. Thanks for the tips. On further reflection I think that the foam probably has disintegrated over time (mostly). The pattern of what is melted/stuck to components is wrong for an exogenous heat source. I might have to play around with solvents as IPA didn't have much effect on the really stuck down stuff. I agree it's likely to be a dry joint or cracked SM part so the plan of a thorough clean and visual inspection is a good one - I don't have access to a microscope but do have a couple of decent hand lenses. I suspect careful use of the heat gun and freezer spray will help as well. I'm going to be away for a week so will pick this up again when I get back. I'll update the list with any progress.

Ron Ward sayeth: > Hi: > I have been looking at the poor quality solder joints on the oscillator. > If you have a steady hand and a small tipped soldering with silver > baring (about 2% silver) solder, I would re-solder the connections. Many > of them do not look properly "wetted" and cold. Some of the heat from > removing the top may have re-soldered a problem connection. > I wondered whether that was possible but I don't think the inside got anywhere near reflow temperatures - the only heat damage was that bit of SRBP like stuff and the foam behind that looked much the same as everywhere else. It probably did get above 100deg C for a while. I'll give it a thorough clean and have a close look at all the joints and SMT components when I have chance.

Silver solder has a higher melting temperature so make sure you adjust your soldering iron to the right temperature otherwise you will just make another cold joint. Also wick all the old solder before making a new joint with different solder. Didier KO4BB Ron Ward <n6idlron@comcast.net> wrote: >Hi: >I have been looking at the poor quality solder joints on the >oscillator. >If you have a steady hand and a small tipped soldering with silver >baring (about 2% silver) solder, I would re-solder the connections. >Many >of them do not look properly "wetted" and cold. Some of the heat from >removing the top may have re-soldered a problem connection. >Ron > >-----Original Message----- >From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On >Behalf Of Paul Flinders >Sent: Thursday, July 26, 2012 2:59 PM >To: Discussion of precise time and frequency measurement >Subject: Re: [time-nuts] 5MHz ocxo- Opening Solder sealed cans > >On 26/07/12 20:49, Tom Miller wrote: >> Pick up a few sticks of ChipQuik and mix it in with a good iron. >Then, > >> you may do just what you say. It should melt below about 95°C. >> A good hot air heat gun would most likely do the trick. Maybe use >some > >> solder wick first to lower the amount of tin/lead solder. Then add >the > >> chipquik. >> >> You might also just solder a tab on the bottom then you could clamp >> the top in a leather jawed vise. Hit it with a hot air gun while >> pulling on the base tab. >> > >Well, a few exploratory attempts confirmed my initial suspicion that I >don't have a soldering iron big enough for the job - the largest I have > >is 60W or so, and the hot air gun didn't touch it even set to 480deg C > >So, I reached for the next larger source of heat which is a small >blowtorch I have, set a small flame and ran it round the whole seam >then > >pulled the top off with a gloved hand. Things did get a bit warm but >only for a short while. > >The first thing I encountered was some insulating foam - this was >rather > >sticky. Not sure whether it had gone like that over time or due to my >heating the whole thing a bit too much. On three sides the foam was >separated from the case by what looks like some thin SRBP. This had >blistered a bit so obviously things were a bit hot just there but the >foam was much the same whether "protected" by the SRBP so I'm wondering > >whether this has just disintegrated over time. > >Pulling/washing the foam off reveals three PCBs and a further enclosed >metal case with the crystal. A TIP21 bolted to this acts as the heating > >element. Originally there had been some cable ties anchoring the >crystal > >enclosure but these were brittle - presumably from the heat of the >oven. > >Hooking the unit up to 12V and an oscilloscope shows that it has >survived the encounter with the blow torch and produces a nice 5MHz >sine > >wave at 2.5V p-p (into 10Meg ohm). Irritatingly it doesn't really want >to misbehave - presumably because whatever didn't like the heat is now >cooler with the insulating foam removed. The inner metal case gets too >hot to touch but the thermostat seems to be working because the current > >drawn drops from about 380mA to 240 or so. It should probably be lower >but, again, without the usual amount of insulation it's likely to draw >more keeping the oven up to temperature. > >So, as it doesn't want to misbehave, I'm not totally clear which way to > >go. The output does drop to about 1.8V p-p when the oven is fully warm >which might be related to the original fault. I suppose the fact that >the fault has "gone away" eliminates the oven assembly or crystal >itself > >as the source of the problem. > >Photos for comments or curiosity. The black stuff all over the PCBs is >the remains of the foam. > >http://www.wild-pc.co.uk/images/P1020364.jpg >http://www.wild-pc.co.uk/images/P1020367.jpg >http://www.wild-pc.co.uk/images/P1020368.jpg >http://www.wild-pc.co.uk/images/P1020369.jpg >http://www.wild-pc.co.uk/images/P1020370.jpg > >_______________________________________________ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. > > > >_______________________________________________ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. -- Sent from my Motorola Droid Razr phone with K-9 Mail. Please excuse my brevity.

On 27/07/12 03:17, Tom Miller wrote: > I agree with Ron. Clean the board up real good then do an inspection. Talking of which does anyone have any suggestions as to with what? I've tried IPA, ethanol, acetone and even some of the tiny amount of 1,1,1 trichloroethane I have left (yes, I know it's banned). Nothing so far has had much impact on the remains of the foam or the remains of the sticky tape (the yellow residue on some of the components in the photos). I'm running out of ideas as to what might clean it off without damaging the board.

Paul Flinders wrote: > On 27/07/12 03:17, Tom Miller wrote: >> I agree with Ron. Clean the board up real good then do an inspection. > > Talking of which does anyone have any suggestions as to with what? > I've tried IPA, ethanol, acetone and even some of the tiny amount of > 1,1,1 trichloroethane I have left (yes, I know it's banned). Nothing > so far has had much impact on the remains of the foam or the remains of > the > sticky tape (the yellow residue on some of the components in the > photos). > I'm running out of ideas as to what might clean it off without > damaging the board. I can't guarantee anything, but I'd be surprised if Fluxclene didn't do the trick: http://www.electrolube.com/docs/cleaningmain.asp?id=13 Mike

On 28/07/12 21:13, Mike Millen wrote: > Paul Flinders wrote: >> On 27/07/12 03:17, Tom Miller wrote: >>> I agree with Ron. Clean the board up real good then do an inspection. >> >> Talking of which does anyone have any suggestions as to with what? >> I've tried IPA, ethanol, acetone and even some of the tiny amount of >> 1,1,1 trichloroethane I have left (yes, I know it's banned). Nothing >> so far has had much impact on the remains of the foam or the remains >> of the >> sticky tape (the yellow residue on some of the components in the >> photos). >> I'm running out of ideas as to what might clean it off without >> damaging the board. > > > I can't guarantee anything, but I'd be surprised if Fluxclene didn't > do the trick: > > http://www.electrolube.com/docs/cleaningmain.asp?id=13 > Thanks I'll give it a try.

> > I can't guarantee anything, but I'd be surprised if Fluxclene didn't > > do the trick: > > > > http://www.electrolube.com/docs/cleaningmain.asp?id=13 > > > Thanks I'll give it a try. Also try some naptha (sold as lighter fluid, or as a product called "Goof-Off.") -- john, KE5FX Miles Design LLC

On 28/07/2012 22:38, John Miles wrote: >>> I can't guarantee anything, but I'd be surprised if Fluxclene didn't >>> do the trick: >>> >>> http://www.electrolube.com/docs/cleaningmain.asp?id=13 >>> >> Thanks I'll give it a try. > Also try some naptha (sold as lighter fluid, or as a product called > "Goof-Off.") > goof-off doesn't seem to be available easily in the UK - naptha might be worth a go. That said I did try a "label removal" solvent which I've found useful on other general gunk (the pro-power one) and that didn't touch it.

Paul Flinders wrote: > On 28/07/2012 22:38, John Miles wrote: >>>> I can't guarantee anything, but I'd be surprised if Fluxclene >>>> didn't do the trick: >>>> >>>> http://www.electrolube.com/docs/cleaningmain.asp?id=13 >>>> >>> Thanks I'll give it a try. >> Also try some naptha (sold as lighter fluid, or as a product called >> "Goof-Off.") >> > goof-off doesn't seem to be available easily in the UK - naptha might > be worth a go. That said I did try a "label removal" solvent which > I've > found useful on other general gunk (the pro-power one) and that didn't > touch it. Fluxclene is also excellent for removing glue residue left by labels, etc. Mike

On 29/07/12 07:21, Mike Millen wrote: > > Fluxclene is also excellent for removing glue residue left by labels, > etc. > Yes, I saw your previous message and certainly plan to try it (might try some lighter fluid first). In fact was going to order it from link you posted until I hit the £12 postage fee - Farnell stock it at only fractionally above the Electrolube site - £16.80 vs £16.51 for the 1L size and also sell the smaller sizes in one off quantities. Postage is then free as long as I spend the £20 minimum order value - so once I've accumulated a few more bits to buy from them I'll get some.