Favourite DIY test gear

[dmeek]

Here is a link for a lo-ohms tester. I've ordered the IC but haven't built it yet. No. 236 on my list...

Improved short-circuit detector | Boards content from Electronic Design

You have to click a link to see the schematic.

Doug

Anyone build a short tester? The type that uses a tone to locate tiny resistance changes between points on a PCB. Looks like a nice thing to have to find a shorted parallel component in say a PSU where you may have several caps either side of a regulator and one shorted out.

It looks like many of them use a (relatively) high-current source and low voltage across the probes, and use an op-amp to give a proportional DC output which drives a simple VCO.

[Mick Bailey]

I like the look of that. I located the original version, but the dual 12v supply was a bit of a limitation in a handheld unit. That looks much more interesting and now on my to-do list.

[Tom Phillips]

...I located the original version...

Mick,
Would you post the link to the old article? I searched but didn't find it. Apparently, the older article has more background and info. (The newer article seems very lean)
Thanks,
Tom

[Mick Bailey]

Here's the circuit and description;

SHORT-CIRCUIT BEEPER - Circuit Diagram - TradeOfic.com

I may just breadboard this to see how well it works.

Here's another interesting circuit. The video shows how sensitive these can be;

https://hackaday.io/project/3635-sho...circuit-finder

[diydidi]

Here are some test gear I built.
There is an LED tester to check led's at different currents.
There is a Ring tester, an ESR meter, and a Transistor tester/ matching jig for Mosfets and BJT's.
I use them almost everyday. Love Diy

[nosaj]

Here are some test gear I built.
There is an LED tester to check led's at different currents.
There is a Ring tester, an ESR meter, and a Transistor tester/ matching jig for Mosfets and BJT's.
I use them almost everyday. Love Diy

Can you give any details on the LED tester and Transistor tester/ matching jig ? Schematics that kind of stuff

Thanks,
nosaj

[diydidi]

Send me your email.

[nosaj]

Send me your email.

Hey there I did Pm my email to you.

Thanks,
Jason

[nosaj]

I did the upgrade for my oscope mentioned in http://music-electronics-forum.com/t44678/#post459788
Used Ch1 out with a BNC T one side going to a Frequency counter and the other side going to a BNC cable with a DC blocking cap installed on a instrument cable with a 1/4jack. For the amp sectin I used a Teisco checkmate 10 little SS plastic guitar amp.

I am really happy with turning my scope into an Visual Audio sniffer. really cool.

I also saw something where a guy took his scope probe and clipped the ground lead to the tip to catch RF signals any chance this might work like Toms hum sniffer?
RoGeorge Attacks a Pulse Meter | Hackaday
nosaj

[Enzo]

You got a scope probe with a clip? Try it and see.

[Tom Phillips]

As Enzo says you can always try it. Even if you don't have success, it is a learning experience you will remember.

However...here is why I say that it won't work as a hum probe.
The probe with the ground clip connected to the tip will look like a short to low frequencies that we hear as hum. I.e. 60 Hz, 120 Hz and related low order harmonics. To really high (Radio Band) frequencies, or the leading/falling edge of a pulse, the loop acts as a loop antenna. That antenna is allowing the author of the hacking article to see the pulses on the scope. The radio frequency world is a strange place for audio people. It gets even stranger when you get into microwave circuits where the parts start to look more like plumbing and small values of parasitic capacitance or the inductance of a short jumper wire become important considerations. We hear about 75 Ohm or 300 Ohm antennas such as used for an FM receiver and those numbers are marked on the receiver's antenna terminals. However, if you measure the DC resistance of some types of antennas intended to be connected to the radio receiver the may measure as a near short.

[nosaj]

You got a scope probe with a clip? Try it and see.

I will but that brings up another question. I've pretty much always used my scope without the ground clip attached. Is this wrong ? Are there situations that this is ok ? As stated before I'm always learning. I do know that sometimes I need to turn off the florescent shop light to get a clear signal but not always.

Do you think I can make this work as a hum probe?
There are three terminals on it though. I get grab bags of stuff from a guy who is going through an old radio shop. So the best I know is that it's a coil

nosaj

nosaj

[Enzo]

It is a coil with a tap, pick two terminals and try it. Again, just trying it is faster than wondering about it.

And if any of these do work, remember coils and loops are directional.

Tom analyzed the freq thing, in fact when I posted I thought about adding you might have better results if you clipped in a longer piece of wire wound into a coil of several turns, another simple and quick experiment.

But I think you may be a bit off on chasing hum. That probe trick would pick up radiated hum, like from a transformer field or heater wires, but would not pick up hum from power supply ripple, heater to cathode leakage, ground loops, etc.


Using the probe clip bears discussion. For most large signals or voltages, I don't use it. Like B+ ripple or even 15v ripple, or signal through a tube amp. This assumes the UUT is grounded by its power cord, as is my scope. Most scopes have a ground post on the panel. I have a long test lead plugged into that with a clip on the end, so I can clip that to a chassis as my ground reference when it makes some difference or the power line ground is absent. Any slight hum introduced disappears in the face of the much larger signals.

But for low level signals, like most noise, or tiny signals in high gain circuits, this lack of immediate probe ground can add noise, so in those cases the short probe ground clip keeps the ground path short, and is recommended. Try it, probe around some low signal level circuits relying only on the power cord grounds of the scope and the unit under test to connect grounds together. Then add the probe clip to the mix. See what difference if any you detect.

One way or another you must provide a ground connection between the scope and the unit.

[nosaj]

Can you give any details on the LED tester and Transistor tester/ matching jig ? Schematics that kind of stuff

Thanks,
nosaj

Transistor checker jig
Matching Power and Driver Transistors

[nosaj]

I will but that brings up another question. I've pretty much always used my scope without the ground clip attached. Is this wrong ? Are there situations that this is ok ? As stated before I'm always learning. I do know that sometimes I need to turn off the florescent shop light to get a clear signal but not always.

Do you think I can make this work as a hum probe?
There are three terminals on it though. I get grab bags of stuff from a guy who is going through an old radio shop. So the best I know is that it's a coil

nosaj
[ATTACH=CONFIG]44185[/ATTACH]
nosaj

Ok I hooked it up to the scope. I have 2 fans in the shed. one is a box fan and i can vary the sine wave it produces by how close I put it to the fan or rotate it. The other fan is connected to my B&K power supply which has a solder iron temperature control the voltage is control by a pot which alows me to vary the fan speed to pull smoke. It produces what looks like a ringing pattern that repeats which I take to be short bursts of electricity. I know on the inside it is just a pot and a transistor(scr or a triac I'm not sure). But it is definitely interesting to play with.

Thanks,
nosaj