TNP #44 - AT&T 938A LED Optical Loss Set Repair, Teardown & Experiments

In this episode Shahriar takes a look an AT&T optical loss set which is equipped LED sources 875nm & 1300nm. The unit has been storage for over a decade with heavily leaked batteries.
After the cleanup, the unit powers on and is able to measure optical power as well as generate light from the LED source. The accuracy of the photodetector is verified against a calibrated optical meter. The wavelength of the 875nm LED source is also measured using a spectrometer.
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[@poormanselectronicsbench2021]

Wow, I worked for Illinois Bell / Ameritech/SBC/AT&T, used many a Optical loss meter, since the late 1980's, never saw one branded by AT&T, we had Noyes, EXFO and AFL, were brands they would provide for techs, and we didn't even see handheld units until the mid 90's, they were small units in housing with wall wart power packs, and Biconic connectors were the standard , then ST connectors before SC/LC's became the current single fiber standards.

[@campbellmorrison8540]

Wow what a neat dumpster find

[@johncundiss9098]

No matter how vigilant I try to be, I always find something I let batteries sit in too long. Good video.

[@NiHaoMike64]

Is there a reason why there's both 850nm and 875nm options? They're clearly too close together to multiplex with. I would have expected 950nm as an option, a common IR LED wavelength.

[@blahfasel2000]

Some (non-standard) single strand bidirectional protocols use 850nm and 900nm, so maybe they used 875nm because it's right in the middle. But even 850nm and 875nm would easily be far enough apart for multiplexing. CWDM has a channel spacing of 20nm, and modern DWDM can go down to only 25GHz/0.2nm channel spacing.

[@catsmr]

Neat!

[@thomasleerriem6872]

Duracells leaking... what a surprise. If a device I buy comes with Duraleak batteries, then I dispose of them immediately. Regardless the expiry date.

[@Dennis-uc2gm]

This thing had my favorite leaking batteries. I know cheaper ones will leak too but that particular brand has got me almost every time I left them beyond their practical stay and I think they used to be better than that 20 + years ago. I bet that cost $$$ for that company when the requisitioned them. I remember the TDR meters the guy's used in the early days of DSL when I did my stint with them and they weren't cheap.

[@joopterwijn]

Although it looks like a simple meter, it would probably have cost a arm and a leg in his days. Can’t imagine it would have been a large production run, so limited series with development must have been lots of $$$$

[@scottpelletier1370]

Cool stuff! what makes InGaAs so good for photodiodes?

[@lmamakos]

"Do not look into laser with remaining eye." but doesn't apply here..

[@Worsdier]

Duracell batteries suck, they tend to leak more than other quality brands. I've learned the hard way to remove them from meters I don't use often.

[@borisj4054]

I do not list Duracell as quality batteries. The company was bought out by a Chinese concern and the quality dropped and leakage rose to unacceptable levels. They are utter rubbish and a liability to equipment these days. You see them being flogged in discount $2 stores in Australia. They must account for a lot of lost items that use them.

[@Worsdier]

@@borisj4054 yes, Duracell is not a quality brand. I meant to say that they leak more than the quality brands.

[@R2AUK]

👍 😺

[@borisj4054]

The number of instruments that have been destroyed by those inferior Chinese Duracell batteries!

[@SidneyCritic]

Glued pots - lol -. In the old days aftermarket EFI had pots, and if you hit a pothole your car would go out of tune - lol -.

[@TKomoski]

I don't see you looking in dumpsters

[@Thesignalpath]

Dumpster diving is an old and proud tradition. :)

[@TKomoski]

@@Thesignalpath True that how I found lots of used equipment

[@WisdomVendor1]

You could at least throw some used coffee grounds on it to make it look like it's been near a dumpster sometime in its life.

[@sjfriedl]

Dave is going to be pissed that you dove into his dumpster!

[@trevorvanbremen4718]

@@Thesignalpath It appears that YOU have access to some rather 'upmarket' dumpsters. Based upon the typical content I've seen on your channel, that doesn't surprise me one bit!

[@pfifo_fast]

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