EEVblog #620 - Repair: Stanford Research SR650 Programmable Filter - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: May 25, 2014, 12:39:36 am
content: Dave scored a cheap non-working Stanford Research SR650 8 pole programmable elliptical filter on ebay. Can it be fixed?http://www.thinksrs.com/products/SR600.htmMains Filter datasheet:http://www.jameco.com/Jameco/Products/ProdDS/1174803.pdfPartial schematic:http://www.ens-lyon.fr/DSM/AGREG-Physique/oral/Notices/N041-023.pdf!Private video

author: dentaku
author_rank: Frequent Contributor
timestamp: May 25, 2014, 01:51:27 am
content: It amazing how much stuff I see here that relates to my history with synthesizers. So much of the terminology is the same.Of course a programmable filter that's not controllable in real time wouldn't be terribly useful in a musical instrument

author: EEVblog
author_rank: Unknown
timestamp: May 25, 2014, 02:09:07 am
content: Quote from: wilfred on May 25, 2014, 01:43:10 amYup.I've noticed a missing heatsink on a 7805 reg, and the 5V rail is playing up. Haven't measured anything else yet.Looks like there will be a part 2...

author: Shock
author_rank: Super Contributor
timestamp: May 25, 2014, 02:55:25 am
content: Dave your video reminded me of some parts I needed thanks!I instantly spotted the voltage selector (recently swapped a voltage over on one myself) I'm glad it didn't end up too embarrassingIf someone has one of those plastic sliding doors please see my post here.

author: EEVblog
author_rank: Unknown
timestamp: May 25, 2014, 07:27:57 am
content: For those interested, there is an SR650 in sorry state from our friends in Israel:http://www.ebay.com.au/itm/Stanford-Research-Systems-SR650-Dual-Channel-Pass-Filter-SRS-/321057054340?pt=LH_DefaultDomain_0&hash=item4ac07dde84

author: VK3DRB
author_rank: Super Contributor
timestamp: May 25, 2014, 09:01:42 am
content: Thanks Dave. A good tear down and repair. I get a great sense of satisfaction and achievement fixing something that was junked but was worth a mint. Who hoo! For sure.I would have thought most mid 90's stuff would have been SMD. But maybe with filters PTH was more appropriate.Hey, I am in Vichy in France as I write this and wore the negative feedback T shirt yesterday No English speakers around here, but I did notice one chap staring at the message. It appears the Vichy WW2 notoriety has been wiped from memory here. No mention, note even in any museum.

author: Psi
author_rank: Super Contributor
timestamp: May 25, 2014, 09:04:41 am
content: Check the supply rails with the scope.Might be a supply rail issue causing the random overload states.The PSU maybe injecting lots of noise/spikes into the analog logic due to its old filter caps.

author: IanJ
author_rank: Unknown
timestamp: May 25, 2014, 10:21:51 am
content: Quote from: EEVblog on May 25, 2014, 07:27:57 amOk, I like a wee challenge, have been looking for something to repair/refurb and this will do nicely. Quite a useful bit of kit really.Am in the middle of a PM3585 logic analyzer repair.......so heck! all this old kit is huge am gonna need a biggerboatbench.Ian.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: May 25, 2014, 10:29:45 am
content: Looks like it's been damp - could be that PCB track in the filter has corroded away.Re. the wire into that multiway plug on the secondary - those IDC connectors sometimes go dodgy so could just be it was pulled out of the cable tie to cut down & re-terminate .

author: Tek_TDS220
author_rank: Regular Contributor
timestamp: May 25, 2014, 10:52:24 am
content: Nice video - I hope that Dave goes through the schematic a bit. It's difficult to follow because of the way the manual was scanned.Have these analog devices been replaced with digital signal processors? Maybe DSP plus the ADC/DAC chain introduces too much distortion for the intended applications? There's a lot that DSP can do that is very difficult with analog (such as linear phase response).

author: BUkitoo
author_rank: Contributor
timestamp: May 25, 2014, 12:13:11 pm
content: hI!Regadring the packing, I do not know if it this is the case, but for a product we manufactured once, there were 3M "instant" packing products that were a tiny bag with two compartments filled with two chemicals inside. When you need to pack something you just break a couple of bridges between them and mixed them by hand. Than you place it into the box, your instrument inside, another on the top and the thing grows as a foam inside the bags taking the shape of the instrument.No machine needed...

author: stranger
author_rank: Newbie
timestamp: May 25, 2014, 01:28:13 pm
content: Quote from: wilfred on May 25, 2014, 01:43:10 amHi Wilfred, seems to be common, I had similar thing with a Schaffner filter input on a Solartron 7150 DVM. It took several months before the failure and even after the smoke cleared there was a big mess inside the instrument as the potting melted around the failed capacitor and leaked out. The cost of a replacement new filter was £25, the instrument cost £20 so I took a saw to the filter and cut the bad stuff out (all of the filter). Dave was very lucky with this filter. More seriously it left me wondering about the safety of some of the old equipment I use and when this is going to happen again - I do have proper current trips on the workbench.

author: ultranalog
author_rank: Contributor
timestamp: May 25, 2014, 01:53:26 pm
content: I thought I noticed a 'chirp' signal source on the HP 35660A. And you said it wouldn't do swept sine? Confused...

author: madires
author_rank: Super Contributor
timestamp: May 25, 2014, 02:35:24 pm
content: Quote from: stranger on May 25, 2014, 01:28:13 pmMost likely that is caused by a bad cap. I heard of a lot of issues with old Schaffner IEC filters with Rifa caps. If the cap fails shorted and if the circuit braker isn't triggered, you'll get smoked potting. That could also explain Dave's burnt PCB trace. A cap failed open releases just some magic smoke. Please seehttp://www.vintage-radio.net/forum/showthread.php?t=88137for more line filter issues.

author: madires
author_rank: Super Contributor
timestamp: May 25, 2014, 02:45:31 pm
content: Quote from: wilfred on May 25, 2014, 02:08:36 pmAnother one :-( It's caused by a failed Rifa cap in the Schaffner line filter. AFAIK just the age matters, not the hours of operation. If you replace the filter get a brand new one and not an official spare part covered with dust of 15 years.

author: ultranalog
author_rank: Contributor
timestamp: May 25, 2014, 03:44:49 pm
content: Quote from: mojo-chan on May 25, 2014, 03:35:24 pmPower wasn't on, power button was in the on position, closing the circuit.

author: Khashoggi
author_rank: Contributor
timestamp: May 25, 2014, 06:09:44 pm
content: Quote from: madires on May 25, 2014, 02:45:31 pm+1

author: smashIt
author_rank: Contributor
timestamp: May 25, 2014, 07:49:35 pm
content: dave, at 15:40 you get a connection to one side of the fusebut when you briefly touch the other end of the fuse your multimeter didn't beep.was there no fuse in the holder or is the holder broken?

author: corrado33
author_rank: Frequent Contributor
timestamp: May 25, 2014, 11:01:55 pm
content: Quote from: BUkitoo on May 25, 2014, 12:13:11 pmDamn, I was thinking of inventing what you just mentioned as Dave was talking about the packaging.Anyway, good repair Dave. Only you would wish for more of an "electronics" repair.Looking forward to part 2!

author: diyaudio
author_rank: Frequent Contributor
timestamp: May 25, 2014, 11:28:44 pm
content: amazingly one dsp processor can replace majority of guts.

author: Rory
author_rank: Frequent Contributor
timestamp: May 26, 2014, 12:34:18 am
content: Quote from: diyaudio on May 25, 2014, 11:28:44 pmDSP not even necessary. LT or Maxim 8th order elliptic switched capacitor filters could do the job just as well.

author: Harvs
author_rank: Super Contributor
timestamp: May 26, 2014, 12:47:57 am
content: So can these bits of kit do anything you couldn't do with a high end sound card and some filtering software?

author: nitro2k01
author_rank: Frequent Contributor
timestamp: May 26, 2014, 03:06:19 am
content: Quote from: mojo-chan on May 25, 2014, 03:35:24 pmEach side of the transformer is an inductor, so they will pass DC current. He first probed the line and enutral terminals of the IEC socket. Since everything in that whole circuit (fuse, input filter, wires and transformer primary) will happily pass DC if functional, the expected result is some relatively low resistance. The result he got was of course an open circuit, at which he probed the individual parts of the circuit to find where the break was.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: May 26, 2014, 03:14:01 am
content: Quote from: Harvs on May 26, 2014, 12:47:57 amThis unit will pass the DC component of the circuit (if in DC coupled mode) which sound cards typically don't do, by design. It also has zero latency, down to the phase shift of the filter, which may or may not be relevant to your application.

author: jancumps
author_rank: Unknown
timestamp: May 26, 2014, 05:51:34 am
content: Quote from: nitro2k01 on May 26, 2014, 03:14:01 amand it goes to 100 kHz.

author: Stonent
author_rank: Super Contributor
timestamp: May 26, 2014, 06:20:21 am
content: I was hoping for more of a inspection of the guts "tear-down" style, maybe a follow-up with some more details on the theory of operation?

author: Taucher
author_rank: Frequent Contributor
timestamp: May 26, 2014, 08:17:11 am
content: I really like that you did put the good old Rigol scope back to work -but still wondering why not even a peek with the Flir thermal camera.I know you already know that such issues are getting instantly visible with that equipment - even heated traces etc. - so why not use it as USB connected capture device and get perfect 9fps videoEven bad ESR caps could start heating up etc ... and for anybody without a thermal cam it's still a valueable (visualized) lesson what can heat up etc.Suggestion: Fundamentals friday on LM78xx junction temperature calculation?

author: nitro2k01
author_rank: Frequent Contributor
timestamp: May 26, 2014, 08:29:44 am
content: Part 2 of the repair is up!I think the fact that you removed the lid may have also contributed to the heat problems. Maybe time to bring out the VFC500 and systematically measure the temperature with and without the lid, and at 230V and 240V set voltage. Though the voltage selection switch board clearly says 240 V, so you would think they would have designed for that.And I'm curious how exactly the heatsink went missing. My theory would be that first the input filter broke. Especially if it looked like that from the factory, with electrical tape etc. (That part is suspicious as well.) And then someone nicked the heatsink from the "broken" unit to use it with something else.Quote from: Taucher on May 26, 2014, 08:17:11 amSeen this old episode? It may not have been uploaded on a Friday and it may not be about LM78xx specifically, but it may cover enough of what you're asking for.

author: moemoe
author_rank: Regular Contributor
timestamp: May 26, 2014, 08:45:02 am
content: Quote from: BUkitoo on May 25, 2014, 12:13:11 pmThey are available in multiple variants, the one you mentioned with the two components, a machine filling and sealing the bags for you, but still outside of the packaging, or the version Dave mentioned:http://www.sealedairprotects.com/ap/en/products/foam_packaging/instapak.aspx

author: Taucher
author_rank: Frequent Contributor
timestamp: May 26, 2014, 08:53:33 am
content: Quote from: nitro2k01 on May 26, 2014, 08:29:44 amSurely - seen it a long time ago

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: May 26, 2014, 01:13:44 pm
content: With apologies for the lighting, perhaps this picture of my unit will help?As you can see, you are missing a large aluminium heat sink. Look closely, and it also explains why the nuts appear to missing from the mains transformer.My unit also has larger heat sinks on the analogue supply regulators. I haven't measured the temperature of these when running, but am happy to do so if you like.Hope this helps,Mark

author: EEVblog
author_rank: Unknown
timestamp: May 26, 2014, 01:42:37 pm
content: Quote from: Mark Hennessy on May 26, 2014, 01:13:44 pmOh wow, thanks, that explains everything!

author: lewis
author_rank: Frequent Contributor
timestamp: May 26, 2014, 01:52:43 pm
content: Dave, I found myself screaming at my monitor THERMAL IMAGING CAMERA! THERMAL IMAGING CAMERA! THERMAL IMAGING CAMERA!Poke it in there, you'll see all sorts. It's the first thing we do when we're troubleshootinganything

author: Dave Turner
author_rank: Frequent Contributor
timestamp: May 26, 2014, 01:54:51 pm
content: Man - if that's the EEVblog curse - can I have it too?To score a non-working unit for $100 and get it working that simply

author: max_torque
author_rank: Super Contributor
timestamp: May 26, 2014, 02:04:32 pm
content: Are you being a bit harsh on the designers of that PSU Dave? I mean, it's like over 20 years old, and still working, even after being run with the large heatsink missing! So, yes, those VRs are getting to 70degC, but so what. I'd say it would be a lot more annoying to have an instrument that drops out when the mains voltage dips a tad etc!Also, for instruments like this, you often can't control the environment they are run in. Yes, it's nice to think they might all be running in 25degC ambient air conditioned labs, but i bet a load of them end up in equipment racks, getting baked by large power hogs next to them etc. And for that, you just can't beat having a proper fan to boost cooling way beyond that provided by natural convection etc!

author: EEVblog
author_rank: Unknown
timestamp: May 26, 2014, 02:05:10 pm
content: Quote from: lewis on May 26, 2014, 01:52:43 pmIt was at home. I was too lazy to drive back to get it.

author: EEVblog
author_rank: Unknown
timestamp: May 26, 2014, 02:08:04 pm
content: Quote from: Dave Turner on May 26, 2014, 01:54:51 pmYeah, in that respect I'm not complaining. I could flip this thing for 10 times what I paid for it. But because I'd never get another one (or any programmable filter) at this price again, it's a keeper.

author: Taucher
author_rank: Frequent Contributor
timestamp: May 26, 2014, 02:09:10 pm
content: Quote from: EEVblog on May 26, 2014, 02:05:10 pmFAIL... get them to supply you with a secondary one - maybe the new one for smartphones

author: jancumps
author_rank: Unknown
timestamp: May 26, 2014, 02:19:41 pm
content: Quote from: Taucher on May 26, 2014, 02:09:10 pmOr get one of them Mµs !

author: miguelvp
author_rank: Super Contributor
timestamp: May 26, 2014, 04:42:49 pm
content: Quote from: jancumps on May 26, 2014, 02:19:41 pm

author: corrado33
author_rank: Frequent Contributor
timestamp: May 26, 2014, 04:45:50 pm
content: Quote from: Mark Hennessy on May 26, 2014, 01:13:44 pmHow about a video of dave manufacturing a heatsink to match the one in the picture above? Bending sheet metal is pretty simple, even without a dedicated metal bender.A large heatsink that spanned both of the packages back there was my first guess since only the regulator had the electrically insulating pad on it.

author: edpalmer42
author_rank: Super Contributor
timestamp: May 26, 2014, 05:49:24 pm
content: Quote from: corrado33 on May 26, 2014, 04:45:50 pmI noticed that, but the mounting tab on a regulator is grounded so electrical insulation isn't required. But if you look at Mark Hennessy's picture you'll notice that both devices use Sil Pads and insulating washers. The transistor typically needs it for electrical isolation. The regulator might need it for thermal performance.Ed

author: pickle9000
author_rank: Super Contributor
timestamp: May 26, 2014, 07:55:44 pm
content: One thing you can say about Dave's unit is that it was scavenged. Probably by the seller to get a couple other units up and running.- missing heat sinks- missing screwsLuckily it was not worse. To be honest I'd probably do the same.

author: corrado33
author_rank: Frequent Contributor
timestamp: May 26, 2014, 08:22:12 pm
content: Quote from: edpalmer42 on May 26, 2014, 05:49:24 pmI said it was my first thought, not necessarily the correct oneAlthough in this case, the thought was correct, but with incorrect reasoning, so therefore I was still wrong.Also, when I've seen similar packages lined up in a row close together like that, I think shared heatsink. Otherwise it would have been designed to accommodate a larger heatsink for the regulator. If it was my repair, I probably would have ended up throwing sil pads on both of them and put a large heatsink there anyway. I mean, is there a downside to doing that?Either way, interesting to watch dave with the repair.We recently cleaned out one of our labs that had a lot of old stanford research stuff in it. Maybe I'll see if I can snag one and send it off to Dave. I really have no use for them (neither does our lab). I think they're... lock-in amplifiers and boxcar averagers.

author: Tothwolf
author_rank: Regular Contributor
timestamp: May 26, 2014, 08:30:17 pm
content: Darn, Mark beat me to it.I wonder if Stanford Research could supply a replacement heatsink or at least a drawing for the original part? With a drawing, a good sheetmetal shop could fabricate one easily, but you'd still have to source the threaded inserts (4-40 for the two TO-220 devices and 8-32(?) for the transformer and fan screws). Don't forget the plastic insulating/shoulder washers for the two TO-220 devices thoughIt looks the thermistor for the fan speed control is right in front of the bottom edge of the fan. Maybe the fan will slow and quiet down once the cover is on and there is better airflow?

author: tsmith35
author_rank: Frequent Contributor
timestamp: May 27, 2014, 02:47:11 am
content: Grab a new Corcom 6J4-2 filtered input module while you're fixing things.Now owned by TE Connectivity...

author: daveshah
author_rank: Unknown
timestamp: May 27, 2014, 07:58:24 am
content: Quote from: pickle9000 on May 26, 2014, 07:55:44 pmMore likely, in my opinion, they removed the heatsink in an attempt to troubleshoot why it wasn't turning on, and forgot to put it back on.

author: RupertGo
author_rank: Regular Contributor
timestamp: May 27, 2014, 02:42:09 pm
content: But what was the function of the banana at 20:03 in the first video?

author: Bored@Work
author_rank: Super Contributor
timestamp: May 27, 2014, 04:57:06 pm
content: Quote from: Tothwolf on May 26, 2014, 08:30:17 pmI think a DIY heatsink wouldn't mind if you just use washers and nuts.

author: retrolefty
author_rank: Super Contributor
timestamp: May 27, 2014, 05:11:42 pm
content: Quote from: daveshah on May 27, 2014, 07:58:24 amI agree, heatsinks rarely go bad and need to be savaged from a bone-yard unit.

author: rsjsouza
author_rank: Super Contributor
timestamp: May 27, 2014, 05:39:53 pm
content: Good videos.Dave, I feel your annoyance with the botches caused by previous fiddling with the equipment. I recently got a working TRS80 model 100 and had to power it up upon arrival just to be sure the item was as described. After all seemed ok, I opened it up to mainly replace caps and the NiCD battery and found out four loose screws inside!These were deliberately let loose as the others were tightly in place (fortunately none shorted anything).Anyhow, I am glad it was a simple fix. In my case I am still chasing an irritating intermittent power up issue (perhaps broken PCB tracks, bad solder joints, etc.)

author: Tothwolf
author_rank: Regular Contributor
timestamp: May 27, 2014, 06:25:43 pm
content: Quote from: Bored@Work on May 27, 2014, 04:57:06 pmPossibly...but not using threaded inserts would make it much more difficult to install (and remove) the heatsink. Unlike individual washers and nuts, threaded inserts are also far less likely to work their way loose and rattle around on top of your pc boards. This is especially true for applications such as this where you have a long screw going though the flanges on a fan made of glass filled nylon, since that plastic can over time (vibration) flex and deform just enough to allow the screw to work loose. A small amount of low or medium strength loctite on the threads before installing a lockwasher and nut would help, but then you'd have to either clean the fasteners or replace them any time you removed the heatsink so you could then apply fresh loctite.These sort of threaded inserts aren't difficult to obtain, and the cost of a Keps nut (or even just a plain nut and external star lockwasher) will cost as much or more than a press-fit insert. Threaded inserts may or may not even be required for the two TO-220 devices, depending on the particular gauge and alloy of the aluminum.As for installation, I use a PanaPress to install these type of inserts for repairs and small volume stuff but they can also be installed with a hammer and drift, or sometimes even just a washer and screw to pull the insert into place (along with a small amount of oil on the threads to prevent galling), depending on the insert and material.

author: Bored@Work
author_rank: Super Contributor
timestamp: May 27, 2014, 07:04:40 pm
content: You did notice that the other edges of the fan and transformer are just hold in place with nuts? So really, the world will not come to an end if you use a few more nuts.

author: corrado33
author_rank: Frequent Contributor
timestamp: May 27, 2014, 07:11:38 pm
content: Quote from: Bored@Work on May 27, 2014, 07:04:40 pmI think he's trying to make the point that if you were using a nut and bolt to mount the packages to the heatsink, and the heatsink looked like the original, there'd be no EASY way to hold the nuts in place on the other side of the heatsink as you tighten the bolts. (It's enclosed.0 Unless you removed the mains filter of course. All in all, it'd be a bit of a pain.

author: Tothwolf
author_rank: Regular Contributor
timestamp: May 27, 2014, 08:02:30 pm
content: Quote from: Bored@Work on May 27, 2014, 07:04:40 pmHow do you propose to get access to the nut at the bottom of the transformer and heatsink behind the large filter capacitor? The bottom nut on the other side where the fan and heatsink meet is also extremely close to a small signal diode and bypass cap. It would be very easy to break those components if you were using a regular nut and washer. (A tip for those having to service this sort of thing, a set of "ignition wrenches" makes things much easier.)You did notice that the other nuts on the transformer and fan are keps nuts? Even though this is a low-volume production item, they still used keps nuts instead of individual nuts and washers.Something else to consider are potential metal shards from a lockwasher digging into the aluminum plate. This isn't going to be an issue with the fan's glass filled nylon plastic housing or the transformer's steel laminations.My point is the designers used threaded inserts for a whole host of reasons. Unless you are doing a failure analysis and re-engineering something due to a faulty mechanical design, it is generally best to stick with what the original designers used since they will have already worked out all the assembly issues and there may have been non-obvious reasons they did something the way they did.Dave, are U8, Q3 and Q102 part of a PWM circuit for the fan?

author: Tothwolf
author_rank: Regular Contributor
timestamp: May 27, 2014, 08:17:44 pm
content: Quote from: corrado33 on May 27, 2014, 07:11:38 pmThat too, but they could have also tapped holes in the aluminum plate for the TO-220 devices. Maybe Mark can let us know how his is made?I did find it interesting how the insulating shoulder washer for the 7805 in Mark's photo is discoloring (from heat) compared to the transistor beside it. I guess it just tends to run hot. It is also interesting to see how they reduced the size of the four heatsinks for the LM317 and LM337 regulators in Dave's filter compared to what they used a few years earlier in Mark's.

author: Tothwolf
author_rank: Regular Contributor
timestamp: May 27, 2014, 09:08:26 pm
content: Dave, I think this is the correct input filter (Corcom 6J4), but you might want to double check the voltage selections against the datasheet to make sure.ENG_CS_1654001_CORCOM_PRODUCT_GUIDE_J_SERIES_0611.pdfENG_CS_1654001_CORCOM_PRODUCT_GUIDE_0611.pdfFarnellDigikeyMouser

author: lewis
author_rank: Frequent Contributor
timestamp: May 27, 2014, 11:39:22 pm
content: Quote from: Tothwolf on May 27, 2014, 08:17:44 pmThey'd use self-clinching nuts.

author: tsmith35
author_rank: Frequent Contributor
timestamp: May 28, 2014, 02:08:11 am
content: Quote from: Tothwolf on May 27, 2014, 09:08:26 pmI believe the model # is on the filter, but the schematic of the 6J4 and 6J4-2 is attached.Note 1 says, "Jumper required if only SPST power switch is used"Note 3 says, "Use only 120V and 240V positions for 2 volt selection units"

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: May 28, 2014, 11:34:28 am
content: Quote from: Tothwolf on May 27, 2014, 08:17:44 pmI imagine that the TO-220 devices are secured using the same type of inserts that were used elsewhere - it makes sense, as to tap the holes would involve another manufacturing process. Also, the aluminium is perhaps a little bit on the thin side for tapping...As soon as I get the chance, I'll have a look. I'll also try running it for a while to see how hot things get. And I'll look determinedly for date codes, as there is quite a range in there. Might take a day or two, as I have a more pressing job on the bench at the moment.All the best,Mark

author: tsmith35
author_rank: Frequent Contributor
timestamp: May 28, 2014, 06:33:18 pm
content: If you want a thread insert in sheet metal, but don't have the means to install it, you can mount a thicker backer plate to the sheet metal using conventional fasteners. Once installed, you can drill & tap the sheet metal and backer. No worries about fasteners pulling out of the sheet metal, since the fasteners are retained by the backer.Brazing a nut in place is also doable, but you must use care to prevent warping the sheet metal. For something like a TO heatsink, you can probably get by fine by just soldering a nut in place.

author: Tothwolf
author_rank: Regular Contributor
timestamp: May 28, 2014, 08:18:29 pm
content: Quote from: tsmith35 on May 28, 2014, 06:33:18 pm18ga aluminum generally accepts a 4-40 thread without issue but you can start to run into trouble when you get down to 20ga and thinner (6-32 on the other hand, would be iffy even in 18ga aluminum). Mild steel tends to accept a 4-40 thread down to around 22-24ga, but it will pull out if you over torque the fastener.A forming tap also works well on thinner metals. I've even used them to repair threads where someone has cross threaded a fastener in thin sheet metal.Another option is a thread extrusion (which you'll commonly see in manufactured items) where a punch and die are used to form a protrusion on the back side of the metal that can be tapped (with a tap or thread-forming screw). A drift/punch and a scrap of steel with the correct size hole drilled in it can suffice when you need to form a one-off thread extrusion in something.

author: Rory
author_rank: Frequent Contributor
timestamp: May 28, 2014, 09:46:04 pm
content: Probably easier to just use a 4-40 x 1/2" screw fed from the rear of the panel and insulator/washer/locknut on the package tab.

author: Taucher
author_rank: Frequent Contributor
timestamp: May 29, 2014, 02:18:07 am
content: Quote from: lewis on May 26, 2014, 01:52:43 pmThx Dave

author: max_torque
author_rank: Super Contributor
timestamp: May 29, 2014, 01:22:47 pm
content: For "one offs" that aren't too critical, i find a nice big blob of a suitable epoxy glue on the back of the thin sheet gives enough thickness to get a decent thread into

author: SeanB
author_rank: Super Contributor
timestamp: May 29, 2014, 01:44:12 pm
content: I do that too, but just lightly grease a screw and use the epoxy to hold a cleaned nut in place as well. When cured you just unscrew.

author: IanJ
author_rank: Unknown
timestamp: June 05, 2014, 05:58:24 pm
content: Hi all,So here's the faulty unit I bought off Ebay.Ebay pic:-She's in a bit of a state externally......but thankfully internally she's not bad! I see a bent display header which will be the reason behind the dodgy photo on the Ebay ad.......other than that hopefully just a full blown cleanup required if I'm lucky.With a bit of luck I'll start the video blog repair this weekend.Ian.

author: IanJ
author_rank: Unknown
timestamp: June 09, 2014, 05:34:33 pm
content: Hi all,What a difference a couple days in the workshop makes...........all fixed up.Ian.

author: robrenz
author_rank: Super Contributor
timestamp: June 09, 2014, 05:46:58 pm
content: Awesome job there IanJ! Nice sheet metal skills in straightening out that coverIf those bnc's were polished up a bit it would be hard to tell from new.

author: IanJ
author_rank: Unknown
timestamp: June 10, 2014, 06:11:07 am
content: Quote from: robrenz on June 09, 2014, 05:46:58 pmWhoa!....not so easy I hear myself saying. I have a fault on Ch.1 whereby enabling the filter causes an offset in the final output......almost as if it's jumping to AC coupled mode. Excellent!.......I didn't want it too easy!Ian.

author: M0BSW
author_rank: Frequent Contributor
timestamp: June 16, 2014, 03:24:55 pm
content: I watched your video Ian and looking forward to part 2, hope it's on soon.

author: Zucca
author_rank: Unknown
timestamp: June 16, 2014, 03:56:47 pm
content: +1IanJ,Very cool, I can´t wait to watch part 2 of your video.Any yes, the more complicated the repair is, the more fun we can get out of it.

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: June 16, 2014, 07:22:53 pm
content: +1 for me, too. Great video, great job...Funnily enough, I've noticed the "leakage", and considered putting black heatshrink around the LEDs to stop it. I've done the same in the past with DIY projects - heatshrink being less fiddly than black tape. You only need to do every other one, of course...All the best,Mark

author: Zucca
author_rank: Unknown
timestamp: June 18, 2014, 02:29:08 pm
content: I just got another old not working gear from ebay. Those GPIB nuts are always corroded (like in this case), what is the best way to clean them up/stop the corrosion?

author: IanJ
author_rank: Unknown
timestamp: June 18, 2014, 03:48:30 pm
content: Quote from: zucca on June 18, 2014, 02:29:08 pmI took them off and buffed them up on the grinder brush. A quick coat of paint and they'll do for me.Ian.

author: Tothwolf
author_rank: Regular Contributor
timestamp: June 18, 2014, 03:56:26 pm
content: Quote from: zucca on June 18, 2014, 02:29:08 pmI've seen this lots of times too. I guess they either made the jackscrews out of unplated steel or just did a black oxide treatment.Assuming you can find them, the easiest fix would be to replace those jackscrews outright with some that have some sort of plating (zinc, zinc with yellow chromate, nickle, etc). If you have to clean them, electrolysis cleaning is going to be your best bet. Because the parts are so small, it would be extremely easy to clean them electrolytically in a small container.As for preventing rust, you could either electroplate them (zinc, copper, nickle, etc), powder coat, or just paint them. Since most people aren't set up to electroplate or powder coat, I'd suggest spraying them with clear lacquer (not acrylic enamel). A clear lacquer will hold up much better than an acrylic enamel paint. A black lacquer paint would work too, but I've found clear to be more resistant to chipping in these applications.

author: Tothwolf
author_rank: Regular Contributor
timestamp: June 18, 2014, 04:04:42 pm
content: Mark, Ian,Any chance either of you could verify which thread and length of screws are used for the power transformer/fan/heatsink/regulator and top cover? If I knew exactly what they used, I could see if I have some I can send Dave from my stash of fasteners.

author: IanJ
author_rank: Unknown
timestamp: June 18, 2014, 08:23:54 pm
content: Quote from: Tothwolf on June 18, 2014, 04:04:42 pmThere's a parts list which includes the hardware at the back of this manual.http://www.thinksrs.com/downloads/PDFs/Manuals/SR640m.pdfIan.

author: Tothwolf
author_rank: Regular Contributor
timestamp: June 19, 2014, 12:31:03 am
content: Quote from: IanJ on June 18, 2014, 08:23:54 pmOdd, it doesn't look like it is complete. The longest screw I see listed is a 6-32 x 1-3/8" and that doesn't look like it is long enough to fit through the power transformer or fan and into the heatsink. From Dave's video, it looked like they used 8-32 screws there, too. There isn't a breakdown diagram with designations in the manual either, so I have no idea which length 4-40 they used for the two TO-220 devices or how long the original chassis cover screws are. I'm also still not sure if they used threaded inserts for the two TO-220 devices. I don't know what all I'll have in my hardware stash that will work, but I'm overdue to reorder other fasteners, so whatever I don't have already on hand I can tack onto my next hardware order.

author: IanJ
author_rank: Unknown
timestamp: June 20, 2014, 12:10:01 pm
content: Quote from: Tothwolf on June 19, 2014, 12:31:03 amI'm metric and not hot on US sizes etc. But hope these pics help.Ian.

author: Tothwolf
author_rank: Regular Contributor
timestamp: June 23, 2014, 04:18:54 pm
content: Quote from: IanJ on June 20, 2014, 12:10:01 pmThe photos help some but I still can't tell for sure what they used. I'll have to try measuring them in a photo editor using the rule in the photo as a reference. I'm still not sure if they are using 8-32 or 6-32 screws for the transformer/fan/heatsink though. The transformer/fan/heatsink screws do look to be about 35mm long, or ~1-3/8in, which means those very well may be 6-32 x 1-3/8" instead of 8-32.Are the kepnuts on the 4 small standalone heatsinks smaller than the nuts used for the fan and transformer or are they the same size? Those 4 heatsink screws can't be larger than 6-32 due to the size of the hole in the TO-220 device's tab when used without an insulating shoulder washer (when using an insulating washer, the largest screw you can use is a 4-40).Metric fasteners tend to give me more trouble than english sizes. There are more combinations of sizes and thread pitches with metric fasteners compared to the common sizes of english fasteners.