Recent Posts

1

Computers / Very frustrating RAM problem

« Last post by hap2001 on Today at 01:57:06 pm »

Hi friends, I'm having a RAM related problem that I cannot diagnose by myself.

So I have 2 laptops (A,B) of same model, and 2 sets of RAMs (X,Y) of different model. (Yes 2 sets and 4 sticks total, but to keep the problem not too messy, I always test them within the same set.)

Originally it's A+X and B+Y. Both exhibit random unstable behaviors (A+X more severe), such as crash and lock up, which I later guessed it's RAM related.

I use Memtest86+ to check: A+X errors a lot, B+Y I forgot...
I exchanged them: both A+Y and B+X have no errors.
I exchanged them back: A+X errors less than first time, B+Y no error.

I cleaned both DIMM and socket with ethanol, not fixed.

Since the randomness, I suspect heat related, but I tested A+Y with vent blocked, so it's hotter than first test, still no error.

One strange thing is, the errors are all across the address range (unlikely to be real bad cells), but stay constant at the same bit within same test, and shift a little across different test/reboot.

I'm really lost here, can anyone help me?

2

RF, Microwave, Ham Radio / Re: EPIG finish on 50GHz PCB

« Last post by rfengg on Today at 01:57:02 pm »

Thanks for your reply @uer166.
The only reason we did not choose ImAg is that the surface tarnishes over time and I am not sure how detrimental this could be to loss after it tarnishes.

3

RF, Microwave, Ham Radio / Re: Calculating correction data for an unknown VNA calibration kit

« Last post by joeqsmith on Today at 01:54:37 pm »

Using something closer to 50 ohms with a bit of noise and it attempts to fit the data. 

4

Test Equipment / Re: Strong internal pulses showing up at the Keithley digital voltmeter input

« Last post by bb1 on Today at 01:53:48 pm »

Screenshots

5

Test Equipment / Strong internal pulses showing up at the Keithley digital voltmeter input

« Last post by bb1 on Today at 01:52:52 pm »

Unlike analog voltmeters (multimeters), digital ones have internal pulses.
It is natural to expect that to some degree these pulses will leak to the input of a digital voltmeter.

I connected input of Keithley 199 multimeter/scanner by 50 ohm terminated BNC cable to
the Channel 2 input of a Keysight scope. The Keysight channel 1 input was connected to the Keithley "Meter complete" output.
The Keithley was set to measure DC volts at the 30 volt range.
I set the Keithley measurement interval to 115 mS to avoid confusion of seeing dummy Keithley integration signals.
Otherwise the Keithley had all the default settings. The Keithley LEDs showed 00.0000 volts.

Attached Keysight screenshot KeithleyInput_50ohm_135mV.png demonstrates that the
"Meter complete" signal indeed had period of about 115 mS.
The screenshot shows four regions of pulses, each region of 16.67 mS duration.
Obviously, these regions are related to the Keithley four integrations, each of 60 Hz period duration.
According to the Keithley manual, they are "SIG ZERO", "CAL ZERO", "CAL" and "SIG" integrations.

What is remarkable here is the amplitude of the signals. It is 135 mVpp on 50 ohm load.
So the signals are not exactly feeble "ghost" ones.

As is shown on the KeithleyInput_50ohm_20.8uS.png the pulses during the integration regions mostly come with period of 20.8 uS (48 kHz).
During each 20.8 uS time the integrator output goes up and then down.
The pulses appear at the moments of change from up to down and from down to up.
The period is determined by the U17A and U18A on the Analog board, which divide
3.84 MHz crystal Clock signal by 80.
The 20 mVpp background seen on the screenshot is this 3.84 MHz signal,
which is gated on the Analog board, and then counted on the Digital board.

It is not clear how much these short duration pulses of noticeable amplitude leaking from the Analog Board to the Keithley input change the measurement results.
They may affect the circuits inside the multimeter.
They also may affect devices being tested.

6

General Technical Chat / Re: Possible to trigger at battery explosions in pagers ?

« Last post by madires on Today at 01:52:48 pm »

I do wonder if "manufacturing" was simply reselling - think about the resources needed to make a product like that - my guess is they were simply buying from the Taiwanese manufacturer, reshipping to "normal" clients and modifying the "specials".

BAC Consulting seems to be a small vendor, just reselling stuff. And they told that they cooperate with Gold Apollo. A Hungarian government spokesperson confirmed that BAC Consulting is just a reseller.

Source: https://www.nbcnews.com/news/world/taiwan-firm-denies-making-pagers-used-lebanon-explosions-rcna171594

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General Technical Chat / Re: Possible to trigger at battery explosions in pagers ?

« Last post by MT on Today at 01:51:21 pm »

NYT: BAC Consulting, which manufactured the pagers was an Israeli shell company, citing three US intelligence officers who further said that an additional" two shell companies"
were created. So now all sorts of electronic devices will explode around the world depending if you define israel as an zionist apartheid terrorist state or not. Camera battery,
phone battery, toy battery etc?! I like to know the names of these other two IDF/Aman/Unit8200 front companies are.

8

Projects, Designs, and Technical Stuff / Re: CC/CV Benchtop Power Supply Topology Question

« Last post by nike9307 on Today at 01:49:32 pm »

Separate power transistors the CC and CV part is an odd solution, likely based on 2 LM317 regulators in series. There is no real benefit to this, bit some issues.

I see, so its a waist of time to go down that road. Good to know.

Having a scope to test the desin is a good idea. For the developement a good tool is a simulation package like LTspice.

I tend to be kind of a noob in analog design, so i always simulate heavily.

No fan and the small case kind of requires a SMPS preregulation, which adds a little extra level of complexity. To a large part one could start with the CV/CC regulator part and add the preregulator later in the developement.

That was my plan, as the linear CC/CV is more difficult for me. I've designed a lot of SMPS, so i'll leave that for when i'm happy with the performance of the linear one.

No overshoot for the current is a difficult part, as any capacitance at the output does allow for overshoot in the current. One can mainly keep the overshoot small / limit the capacitance at the output. Most regulators need the capacitance for stablity of the control loop.

You are correct. I'm aiming for minimal capacitance on the output. Less than 100uF if possible. If i use an N channel MOSFET, i should be able to stabilize the loop with less capacitance.
I'm also going to try to design an active circuit that draws current from the output cap, so it doesn't go to the output. This is however entirely an optional fun challenges and I'll be happy with the performance of 100uF on the output.

9

General Technical Chat / Re: Submersible missing while visiting Titanic wreck

« Last post by tom66 on Today at 01:46:08 pm »

I am aghast that they were using carbon fibre from a roll that looked like that... but somehow, it doesn't actually surprise me.

10

RF, Microwave, Ham Radio / Re: Calculating correction data for an unknown VNA calibration kit

« Last post by joeqsmith on Today at 01:41:53 pm »

I synthesized a 40ish ohm load for a standard.   METAS determines it is a load but when fitting, it appears to pass the data through.   

Does the software not account for any errors in the load?