EEVblog #922 - Mailbag

More Mysterious Mailbag

SPOILERS:
Tektronix / Promax RFM90 SignalMini Receive Signal Level Meter teardown
A mysterious FM receiver that transmits!
IntegriFuse USB Protection
Digilent Analog Part Kit
Digilent PmodIA Impedance converter
Raspberry Pi Proto Boards:
DC-AC mechanical vibrator inverter
RED Digital camera battery charger teardown

Datasheets:

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[afitzy]

Sorry about the foam in the case holding the RF Signal Strength Meter falling apart. It was not like that when I sent it to you. Thanks for a great tear down.

[knivd]

Hi Dave, thanks for including RoutaBoard in your Mailbag review. Those were the earliest generation samples which I sent you right from the first prototype batch (best suited for the museum now). 
The recent model is improved with a better layout on the two sides, two more global buses, solder paste pre-applied over the contacts, so they can be bridged together by simply touching them with the iron. Still black soldermask, though. But point taken, I might try out a few different colours in the future, and see which one will work best.
Don't rush yet having a test go with the old ones. :-)
KnivD

[tengelgeer]

14:39 I don't think that's a transformer tap but a glued on temp sensor ;)

[PlasmaHH]

A while ago I was reading a story from the ministry that is responsible for tracking down radio frequency disturbances, and they found a similar radio with a similar error (though the story reads in the 180MHz range, might have been the harmonics though). All the story said was that some "components responsible for coupling the LO into the receiver failed, diverting the signal" so my guess here is that some rf related cap failed short.

[mikeselectricstuff]

As it's for a pro camera, chances are there is gas-gauging in the pack to tell the operator how much time is left, and do stuff like lifetime management. A bad battery on a film set could be very expensive.

[williefleete]

IF for FM is usually 10.7 Mhz 455 Khz is for AM

[urdnal]

"Dry as a dead dingo's donger." Looks like I've got a new favorite Aussism

[Teukka]

I don't know about failure modes, but in my wild and careless youth, I had this habit of turning old superhet FM receivers into FM transmitters.
Long story short, even if you have proper variable caps for the tuning, you very often have varicaps for AFC. So, find the afc control voltage net, add a chain of components consisting of an RF choke, DC block cap and pre-emphasis network and apply appropriate voltage level signal and you have a low-power transmitter...
So if you go ghost-hunting on the clock radio, my chief suspect would be some component failure or crud in the LO signal net.

[ourplesoop]

I'd love to see the waveform from that mechanical inverter. Should try running something off it too.

[jabelsjabels]

Ok I've watched your videos for going on four years now, and that dog device is by far the weirdest thing I have ever seen in a mailbag, well done lol

[FortyTwoAnswerToEverything]

For another video, I'd love to see what kind of output that vibrating inverter puts out, and maybe compare with a modern inverter (modified or pure sine)

[sadface]

I'd love to see Dave make something on the RoutaBoard

[bradscott]

THANK YOU! And this is why I have, since I was a teen, been completely ANNOYED by Gilligan's Island! There is no way a know-it-all "Professor" who could make batteries from coconuts and seawater would NOT KNOW you can make essentially ANY receiver into a transmitter simply by pumping more current through the local oscillator!

You have a radio that works!
You are supposed to know everything!
HOW DO YOU NOT KNOW TO SHORT THE EMITTER OF THE LO AND TRANSMIT CW ON AM BROADCAST?

Shortest TV series ever.

[armpitdew]

RE: transmitting radio, I had a LM318 blow in a way that turned it into a microphone when it was being used as a speaker amp.

[justsean]

Did you say, "Dryer than a dead dingo's donga?" You're killing me! Keep up the good work. Thanks for everything!

[TheEPROM]

I liked the fact there was less commercial stuff in this one. A suggestion I have would be to minamise the commercial stuff which is probably impossible, however you could put it all at the end so it can be skipped if desired. Not sure if other agree, lets hear what everyone has to say on this =-)

[Hopesedge]

What's the most well designed circuit board you've had the pleasure of inspecting?

[burkezillar]

"It's a mechanical vibrator..."

That isn't the vibrator that I thought it was.

[oambrosia]

Dave, Lancaster CA is about 65 Klicks north of Los Angeles. It is a true desert climate. It is not a place people typically aspire to live :)

[scotshabalam]

I think that Tektronix SignalMini was(and probably still is in some places) used by cable companies to determine if there is strong clean signal flowing through the cable line. I remember seeing my cable guy use something like that back in the day.