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For a test set that was protected against overvoltage and reverse voltage input, open circuit and short circuit output, the technician universally known as "Bigfoot" managed to set the PCB on fire.

It was correctly detecting a marginal fault in the unit-under-test (a solenoid switch), but our hero didn't think to believe that.

He had heard that many marginal problems were caused by excessive power supply ripple. He had also heard that ripple was reduced by large capacitors, so he connected an effing big capacitor across the UUT and test box output.

You can make things foolproof, but you can't make them damnfoolproof because damn fools are so ingenious.
There is something very interesting in the instance right before something breaks.

Avalanche mode in transistors come to mind. (or jim williams app notes).

Sometimes very interesting things can be seen with non standard operation.
It sends you here:

And I didn't find another place that as the code.
Have you tried to find a tech manual on that server?  If you're lucky, it might have a wiring diagram with the info you need.  Figuring out an unknown power supply can be time-consuming.  You could try the following:

1.  Figure out which pins are ground.  They might be tied to the case or the mains ground wire.

2.  Plug in the power supply

3.  Check the small pins for one that's at 5V.

4.  Make sure it's not a power pin by grounding it through a 10K resistor.  If the voltage doesn't drop at all, it could be a power pin.  Try 1K.  If the voltage still doesn't drop, assume it's a power pin and move on.

5.  During the above test, monitor one of the output voltages to see if the unit turns on.  If the power supply has a built-in fan, you don't have to do this.  The fan will start up when you turn the unit on.  If it doesn't have a fan, you'll have to provide an external one!

6.  If you find one or more pins that isn't a power pin but sits at 5V when unloaded, and the supply still hasn't turned on, cross your fingers and try grounding the pin through a 100 ohm resistor.

7.  If none of the leads have 5V (or 12V) and you're sure you've got your ground connection right, you might have a dead power supply.  That's a whole different problem!

The idea of the above tests is to hope that this power supply uses the same type of startup circuit as a standard power supply.  That might not be true.  Other than this, you'll have to trace everything out.

I don't think this test will damage anything, but no guarantees!  You could end up with a big paperweight.

It is not missing. You have just soldered 10 x too high value resistors to highest range ;)

A mistake that anyone could make, real problem is only the silkscreen.  :P
Test Equipment / Re: Need SysComp Mac software - download links broken.
« Last post by JFJ on Today at 03:10:16 AM »
You can download the software from a cached copy of the SysComp web site on the Internet Archive:
About CMRR.. is it reasonable to assume that any of the cheap diff probes (sub 300$) will not be able do 60dB up to something like 100kHz? I'm thinkin of getting one to measure gate drive signals, but without good CMRR I would waste my money on a cheap probe and then would need to get a better one after that.

The spec sheet for the probe states a CMRR of >60DB at 100khz but I would be good idea to wait until someone can do a test to confirm the real world figures.

I have purchased a set of 2 in the Batterfly deal because they seemed such good value. My only comments so far is that I would have preferred if the probes had been  X10 and X100, also the output seems a bit noisy buy I don't think that is uncommon for a differential probe.

What I would really interested to see done is a detailed comparison between the performance of Dave's HVP70 probe and one of these Micsig probes.
Beginners / Re: Where to get valves tested in Essex, UK
« Last post by MosherIV on Today at 03:06:49 AM »
You could come along to

On a Sat and ask one of the volunteers if they can get your valves tested.
Guy who wired a mains plug to a microphone lead and used that to connect power.  Worse, the cable had been damaged and he'd joined it with tape.  Boss threw him out of the shop and told him never to return. When he started to protest, the biggest guy in the place was called on to perform the summary ejection. 

Oh, and the guy who linked out a blown fuse on a piece of audio gear, then when that burned out the mains transformer, he linked the primary to the secondary. Result was a big hole in the PCB, and the amplifier it was connected to had its inputs blown.

It's always a worry with this kind of nonsense going on, that there might be a fire or electrocution,and that if so the guy who last signed-off the item most likely takes the rap. Even if it was safe at that time. Thus I tend not to get involved. As an employee in the past I've had some altercations with employers over my stance on this, but hey, I'd rather have lost my job than ended up in court.
Projects, Designs, and Technical Stuff / Re: Resistor decade and Murphy
« Last post by NANDBlog on Today at 03:05:56 AM »
Well, it is kinda on the silk-screen.
I started the assembly of the first one from the 10M side. An then i switched to the right side. At the 1k-10k range, I was reaching for the last 10 resistor. Wait a minute... there is no space for this...
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