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Test Equipment Anonymous (TEA) group therapy thread

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25 CPS:

--- Quote from: TERRA Operative on June 26, 2022, 01:27:34 pm ---
--- Quote from: Vince on June 26, 2022, 01:20:51 pm ---
- An 84LS chip. Yes 84 not 74. Sure knew about the 54 military prefix, but 84 no, never heard of that one. Some more Googling required again...


--- End quote ---

Interesting. I know of the 64xx series that were a Texas Instruments Industrial Grade (−40 °C to +85 °C) that sat in between the standard 74xx and the milspec 54xx. It was only around for a short while.

Sometimes you'll find earlier versions of TTL logic that would have different numbers depending on the manufacturer before it was all standardised to 74 and 54 prefixes.


[EDIT] It seems that 84xx was also used for Industrial Grade parts in Europe. (−25 °C to +85 °C)

--- End quote ---

Yes.  Back in 2019, I did a bit of reverse engineering a card that came out of a Siemens-Du Wag LRV and it was all SN84##N series TTL chips on there but they were all TI chips except for a couple, very small number, of Siemens-Halske which looked like they may have been replacements installed during previous repairs.  My recommendation was to go with standard 74-type replacements unless the card cage was known to get REALLY hot, in which case 54-type military would probably be a better replacement since 84-series stuff looked hard to get at the time.

factory:

--- Quote from: bd139 on June 26, 2022, 03:14:23 pm ---Ok Newbury megapost. It has been 3 years since the last one. Bloody COVID.

So what did I bag?


Next we have the HP 3311A function generator. Again it works absolutely fine. Paid £20 for it too. One of the feet fell to bits in the car but this is sort of expected.



Very nice



Will work out a new foot solution to this...




--- End quote ---

Didn't you 3DP one of those feet sometime ago?
Don't know why, but that rear foot always seems to crumble, on that type of case, the front one for the tilting bail, must be made from a different plastic.

David

Robert763:

--- Quote from: tggzzz on June 26, 2022, 07:01:28 pm ---OK, so my haul was

* a Fluke 515a portable calibrator for £20. Quick check shows Vdc excellent, µVdc cockeyed, resistors good, Vac not bad, missing the unique front panel switch
* three Muirhead decade resistors for £5. Looks good.
* Cropico 4 decade resistor box. A few resistors o/c, but can be replaced
* and the thing below, which is probably as near as I will get to having a slice of the one lying around in my first job


--- End quote ---

Ooh submarine telephone cable?

mnementh:

--- Quote from: mnementh on June 26, 2022, 03:54:50 am ---
--- Quote from: Cubdriver on May 28, 2022, 07:46:52 pm ---
--- Quote from: mnementh on May 28, 2022, 07:01:12 pm ---
   damn you. damn you to... New Jersey.  >:D

mnem

--- End quote ---

You’re welcome.   ;D ;D ;D   -Pat
--- End quote ---

On the Bench Tonight: INFINITY RS-3000 Driver Refurb
...Next up will be the relatively boring part of doing cabinet rehab. I'm knackered, so we'll visit that tomorrow after all the cement has time to cure overnight.   :=\

mnem

--- End quote ---
On the Bench Tonight: INFINITY RS-3000 Cabinet Rehabilitation And Assembly



One of these speakers had drop damage on the corner; it broke this corner of the grill frame and made a ding in the top edge of the speaker with a noticeable separation right at the seam.

I almost passed on these speakers as it had been a long time since I did such repairs; but then the fixer in me took over, saying "You know how to fix this; just do it ya fukkin' baby!" After a little goading from Pat, here they are on my bench.




Here I am doing rehab on the speaker grilles. This is the broken corner; as there is little contact area at the diagonal crack, I printed up a little corner bracket to make a lap joint with the epoxy. Note the little holes to give the epoxy something to sink into. This took about 5 minutes in fusion360, then 15 minutes to print at 0.28mm DRAFT Layer height. :-+

The broken support peg will just be epoxied in place; there's a lot of contact area there. To give the epoxy something to bond to, I've made a lot of crosshatch scoremarks with a sharp paring knife on the mating surfaces. Note the scrap of cardboard between the grillcloth and the frame as a drip barrier. Epoxy soaking through the grillcloth is very noticeable.  :P




The finished repair. I tacked down the edges of the grill cloth that had come loose by touching the edges with a soldering iron; I used the hot-knife blade and temp at 250°C. This is essentially how they make the grills at the factory.




The correct way to "renew" this speaker would be to replace the grillcloth; however I'm already into these for $40, and there isn't budget for that in either money or assache. I'll clean things up as best I can and see how good I can make it look.

Cleaning is done first with a towel soaked in Windex. I support the back of the grillcloth with my hand and arm and scrub gently against them; moving from area to area until the entire surface of the grill has been scrubbed. Any spots that don't come clean with Windex (like tracks on the back from marshmallowy speaker roll foam) will get followup with a towel soaked in IPA. In both cases stop and re-wet the towel frequently. If grillcloth rips or stays stretched when you try this, it was already past time to replace it. ;)




Next problem to address is slubs in the fabric from where it got snagged on stuff over its life. I used to do this with a Bic lighter, but I found that it is too easy to burn a hole in the cloth if you're just a moment too slow pulling it away.

A small hot air gun like this one for heat-shrink tubing works a treat; it makes the polyester threads shrink away and much less obvious. Start about a foot away and bring the nozzle in while watching the slub(s) you're working on; the instant you see them start to shrivel up tilt the nozzle away. Repeat until you stop "seeing just one more really ugly poker"... :o




Part of the damage was a split seam right along this edge with ~2mm gap; my repair was to mask right up to the edge of the seam, then poke epoxy into the gap with a paring knife. (Sorry; no before pic  :-[) Then wipe off excess with a IPA-soaked towel, clamp the seam as  seen here and wipe off the sqweezage with the IPA-soaked towel. Set it aside and wait til the next day. I SAID WAIT TIL NEXT THE DAY, DAMMIT!!! >:D




Next morning I undo the clamp and I'm greeted with this beautiful sight. I can see there is a tiny little bit of epoxy extruded right on the edge, and of course the first instinct is to pick at it and try to make it perfectly flush. *smacks own fingers* No. You know this only results in pain and misery, like picking at sunburn scabs...




Resisting the urge, I do as I know from painful experience is the right way to finish this repair: Peel off the masking tape, then wipe it all down with a IPA-soaked towel.  :phew: Not perfect, but close enough that I know only I will notice.  8)




If there's one thing that pisses me off with a used speaker, it's to find the bottom all tore up from monkey-butts who drag a bare speaker across the floor.






It takes pretty much nothing to just pop a few of these on the bottom, which will prevent easily 90% of such mishaps from scarring your speakers, and it helps decouple them from the floor so the bass doesn't make the house rattle.

Just do it, FFS.


   

Last step before reassembly is to do a quick checkup of the XOs; these are a nice compact design well-supported by the spring-connector bung and lots of hot-snot. No loose inductors, no leaking or bloaty caps and no cracked solder joints. Caps/resistors measure well within reasonable "sanity values" indicating no opens or shorts, so no motivation to dismantle for further testing.

Not sure what this particular variant of the ubiquitous 2nd order L-R filter is called; but I'm sure there are plenty in here who can bust my chops aboot it. :-DD




Any time I open up a speaker, I re-tension the connectors before reassembling. It takes just the gentlest squeeze with the pliers; I usually prefer something with smooth jaws, like my Xuron 3mm flat-bill pliers here.




And here's the fixer's moment of joy: finally time to reinstall the drivers. I do this by hand with a bit-type driver; the magnetized end holds the screw so you can balance the speaker while getting it started, and by choosing a new bit I can make sure I minimize slippage which leaves ugly scars on the screw heads. Plus it's just too damned easy with the drill/driver to slip and poke a hole in your just refurbished driver. Much  :'( follows.

As with anything assembled using machine screws, by hand you can turn the screw backwards and feel the bump at the edge of the old "thread"; looking for this with self-tapping screws in wood and plastic helps you make sure not to strip out the hole and makes reinstalling the screw much easier.

This tactic also helps you make sure easily-deformed sheetmetal like the speaker basket doesn't get bunged up, making the speaker not seal properly. This can cause buzzing or whistling as moving air passes through that gap.


   

And here are the money shots: Both speakers finished and ready to go into service.   

Guess I need to get this     up on the bench next...

mnem
 :-/O

Robert763:

--- Quote from: 25 CPS on June 26, 2022, 07:06:56 pm ---
--- Quote from: TERRA Operative on June 26, 2022, 01:27:34 pm ---
--- Quote from: Vince on June 26, 2022, 01:20:51 pm ---
- An 84LS chip. Yes 84 not 74. Sure knew about the 54 military prefix, but 84 no, never heard of that one. Some more Googling required again...


--- End quote ---

Interesting. I know of the 64xx series that were a Texas Instruments Industrial Grade (−40 °C to +85 °C) that sat in between the standard 74xx and the milspec 54xx. It was only around for a short while.

Sometimes you'll find earlier versions of TTL logic that would have different numbers depending on the manufacturer before it was all standardised to 74 and 54 prefixes.


[EDIT] It seems that 84xx was also used for Industrial Grade parts in Europe. (−25 °C to +85 °C)

--- End quote ---

Yes.  Back in 2019, I did a bit of reverse engineering a card that came out of a Siemens-Du Wag LRV and it was all SN84##N series TTL chips on there but they were all TI chips except for a couple, very small number, of Siemens-Halske which looked like they may have been replacements installed during previous repairs.  My recommendation was to go with standard 74-type replacements unless the card cage was known to get REALLY hot, in which case 54-type military would probably be a better replacement since 84-series stuff looked hard to get at the time.

--- End quote ---

Bear in mind that GENERALLY the silicon die in a automotive, industrial or military/aerospace temp range IC is the same as a consumer one. The difference is limited to packaging, testing and sometimes reduced eectrical specifications. That said even if a "plastic" packaged industrial chip looks identical to a consumer it might have different moulding material, leadframe and or bondwire.
That said I've seen plenty of aerospace kit that was qualified for -25 to +55 but used standard commercial plastic ICs. THe equipment maker has decided it is OK and carries the risk. This might be basted on their own testing.

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