EEVblog #735 - Mailbag

Another movie length Mailbag.
What have people sent in this week?

SPOILERS:
Why are cheap Ebay LED light bulbs so bad? Dave investigates why some of them are doomed to fail. DaveCAD and thermal camera time.

CPM700 Countersurveillance unit from Research Electronics Inc for cold war spy bug sweeping.

Cheap Ebay voltage sources for multimeter calibration

Raspberry Pi I/O Hat Kickstarter, the Hatilogico:

Industrial RS232 modem teardown

Bricked Assus TF300 Transformer Tablet

Annoy-a-tron

Belkin router teardown

Cypress Parachute Automatic Activation Device.

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[FranLab]

@51:45- HEY - NOVUS!  My first calculator!  Part of my The First Light Emitting Diodes Vlog!  I still use it too....

[mpy]

Thanks Dave, don't know why but this mail bag felt like one of the best I've seen from you. Must have something right! Enjoy the view looking forward to that bug sweeper teardown.

[Antiath]

Man, I really miss fundamental fridays and similar technical videos.

[GadgetAddict]

A man with a watch knows what time it is. A man with two watches is never sure.

[CPZeroDue]

About the LED stuff.
Poor thermal design makes temperature increase too much. This leads in VF of leds dropping, maybe by 3-4% for those LEDs at 70°C. Rectification diodes also drop VF. That leads to an increase of current since resistors are fixed. Another point is: you supply 12V from a bench PS, maybe the PS used to turn on those LEDs has higher voltage even staying in the declared tolerance. Looking at the datasheet I also see the VF of those LEDs can change by 0.7 volt between opposite bins but I hope at least they selected the right LEDs for that design.

[davidriley]

I can see a static decimal point calculator being useful in some situations. I'd want a '00' key though

[CommanderZx]

That counter surveillance piece of tech looks very interesting.

[proyectosledar]

excellent video Dave.  I agree with you, those leds (5050 or 5060) are 60mA.

[dumeinar]

Best mailbag in a long time. Swedish stuff, spy gear, weird parachuting electronics. Only thing missing was one or two more quick teardowns.

[CarstenBauer]

Maylands Western Australia by the way :D
Glad you enjoyed my mailbag :)

[AndreasKoepkeAU]

The iiNet modem brings back memories. I was one of the initial beta testers of that device, I had one of the non-wifi models. All of the beta units had a USB port which didn't actually do anything and couldn't be firmware upgraded due to some changes in the new firmware.

When the beta period ended we had to ring them up and they sent us out the production units free of charge. Still have that modem kicking around as a spare.

[garyhunkin]

I love that.. who is CSR, only Cambridge Silicon Radio. The largest Bluetooth RF designer in the world.

[williamhayden]

Big thumbs up for the mini-troubleshooting segment in this mailbag!

[Tangobaldy]

Modem noise eeeek! I had forgotten about that. I used to put tape over the speaker or stab it with a screwdriver.

[ScottHenion]

Those LED boards usually don't consider use in automotive applications. At 13.8 or 14.4V they will definitely cook ;)

[Mostlyharmless]

Ultrathin and tablet type PCs aren't terribly easy to disassemble if you are uninitiated. Check iFixit and see if someone ventured before you to get a tear down. Sometimes the service manuals are leaked online that shows the breakdown procedure, and SOMETIMES the company doesn't have their head up their asses, and give access to to the end user for how to break down their product line.

Barring that they are almost always press fitted and you need to use a silicon spudge tool to separate the piece far enough to wedge a guitar pick in, and then you can roll the guitar pick around to complete the separation. It's super important to check for any screws that are holding the screen in place first.

[kruppin]

The burnt up leds are probably more because the original driver in the light fitting was made for halogen lamp at much higher watt, so the voltage is probably more like 16v when using it with leds. You almost always need to change the driver as well when changing to simple resistor dropper leds like these.

[fuzzydk]

CSR "Cambridge Silicon Radio" is one of the really big players in Bluetooth

[BenjaminEsposti]

40:39 .... You should have smelled the inside of an electronic florescent ballast I tore down after it failed. It had significant arcing damage on the output (lamp) side. Smelled so horrible! Also, almost all the components were covered in a layer of soot. I've torn down similar models as well, and they all have the same failure ... I think it initiates from bad solder joints, as there are cracked solder joints all over the place! At least the ballast has a metal case ... not flammable plastic.

[wesofx]

I worked for an estate sale company just last year. I never want to see another casset tape/casset player, vhs tape/vhs player, crt television, or land-line phone for the rest of my life.
You can't give the crap away.