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1
Repair / Re: DIY magnetic probe to find a short?
« Last post by duak on Today at 03:56:56 PM »
hp used to make a current probe, the 428x, that used a ferrite core as a flux gate magnetometer.  Applied Physics makes a newer version.  Here's a link to one person's experience with the ilk: http://www.prc68.com/I/HP428.html  The article discusses how it works and alternate solutions.

Low voltage ceramic and tantalum caps can also short circuit.  Since this is a 5 V circuit, could there be any transorbs or ICs that have failed?

A good 4 1/2 digit DMM can easily show the mV voltage drops through typical traces with currents on the order of 100 mA.  It may take a little while to puzzle it out though and a map with the various voltage readings can make it easier.

Cheers,
2
Now I need to get the USB HID Vendor Class Device up... Do you know how to get Windows enumerate it properly? It enumerates for now, but it says "requested operation failed."

What do you mean "It enumerates for now". Do you see the HID device in the device manager?

Who says "requested operation failed"?
It says HID, but there is a yellow exclamation mark on it, and Windows is the one claiming "requested operation failed."
3
Test Equipment / Re: US$200 VNA kickstarter launched
« Last post by usagi on Today at 03:53:27 PM »
i guess the only thing now is to decide who your primary target market is.

ham market will be considerably different than typical RF builder. ham guys dont care much for two port. and no <10mhz from the beginning (no stretch) will limit ham interest. also, most hams rarely care about >500mhz.
4
Metrology / Re: Ultra Precision Reference LTZ1000
« Last post by Andreas on Today at 03:42:19 PM »
Interesting to know, for some reason Rhopoint has changed the specification for their 8G16D resistors from ±3ppm/°C to ±5ppm/°C.

-branadic-
Hello,

I have seen that on the web-page. (from one week to another).
But if you look at the data sheet the 5ppm/K were always the "standard" tempco.

If you look at a very old data sheet of 8E16 (not the 8G16) they have stated
5 ppm max for -55...125 deg C
3 ppm typ for 0..85 deg C

with best regards

Andreas
5
Beginners / Oscilloscope with UPS?
« Last post by dwonga on Today at 03:33:02 PM »
Hi!

I want to have an oscilloscope in a place where is no electricity available (for example, in a field crop), for safety reasons (no main ac) or maybe in a blackout (just imagine that). Would it work fine? Obviously, I would disconnect it and move the UPS along with oscilloscope with no ac/ground.

I've searched extensively through the forum and I have not found an answer to this question.

Warm regards,

David.
6
Repair / Re: Resetting Microcontroller
« Last post by Armadillo on Today at 03:25:13 PM »
https://www.dataman.com/media/datasheet/Holtek/HT48x30x-1.pdf

The data sheet says anywhere between 2.5v and 5.5v is ok.

No, it's with respect to the VDD voltage. The datasheet says 0.9VDD minimum at the reset pin.
7
Projects, Designs, and Technical Stuff / Re: uSupply Custom LCD
« Last post by boffin on Today at 03:23:17 PM »
Please please please make the decimal points bigger

(and at least line up the watts under the volts/amps)


More like this

8
Repair / Re: Resetting Microcontroller
« Last post by Dubbie on Today at 03:20:27 PM »
Good idea. I just hooked up 5v supply and bingo. Everything works. You guys were right. Stop chasing complicated stuff and concentrate on the most likely culprits! So this board is fine. The other high voltage one has the fault. I should be good from here. Thanks to all who gave their 5c!
9
Repair / Re: Resetting Microcontroller
« Last post by Dubbie on Today at 03:14:56 PM »
Sorry I missed your post armadillo.

I have checked the crystal frequency. It is good.
The mains sync comes in and goes through q2 and then into the processor. It looks perfect.
The gate drive going out works fine until the uC resets and it stops
10
Repair / Re: Resetting Microcontroller
« Last post by Armadillo on Today at 03:12:47 PM »
Can you hook up external 5v power supply to troubleshoot.

Edit: wire the laboratory power supply 5v directly solder to the microcontroller for troubleshooting.

Edit: for TTL circuit, the voltage cannot deep below ~ 3.5volts. So look for dried joints from wires or connectors etc... Did you board suffered any water damage lately e..g. forming conductive path now...? The voltage at the Reset pin must be SOLID ~ say 4.8V to 5.0V.
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