Recent Posts

1

Test Equipment / Siglent SSA 3021X... Ooops

« Last post by Joel_l on Today at 12:03:54 am »

Hi,

I think I accidentally overloaded the input to my SA one too many times. My input impedance is no longer 50 Ohms. It still functions sortof.

I took the input board out and started looking around. I saw a 49R9 resistor which I assume is the termination resistor, it actually measures fine. I it looks like there are some clamping diodes on the input pat and they seem fine. the input cap measures at 1uF, seems OK. Nothing looks like it got toasty.

The first IC in the input path is U1 a 956p, the 49R9 resistor is after that component in the path. Makes me wonder if that is the part I damaged.

I can't find any info on what that part is, anyone here know? Has anyone found schematics for this SA?

Thanks
Joel

2

Beginners / Re: Convert US standard 115V to International 230V

« Last post by soldar on Yesterday at 11:59:21 pm »

I understand what you are saying, but surely the design would have to be very marginal before this had an impact on the following section of the power supply?

My point, as I said, is that You have to be very careful when making such very general statements. That is all. In most cases you can get away with it but you have to be aware of these issues because they can bite you.

Electrolytics degrade over time. Sometimes not much, sometimes a lot. About 45 years ago the company I worked for imported two machines from America. I went there to do the training etc and the machines were shipped here and installed in customers premises. Almost immediately one started giving problems and it turned out to be a faulty capacitor which was marginal in the USA but insufficient here. I replaced it not only with a good one of the same value but with a higher value. It was a linear PSU and headroom was tight. With 60 Hz it still worked, with 50 Hz it was starting to fail, with 400 Hz it could have gone on for years.

With tolerances, failures, etc. the question is whether you would say absolutely and with no qualifications to a medical life support machine manufacturer or to a Boeing assembly plant "yeah, sure, plug it in as it is, no problem".

Those machines needed some weird adaptations. Instead of changing the electric motors (120 v 60 Hz) we installed a transformer to lower the voltage from 220 V 50 Hz to 100 V 50 Hz because at 120 V they would overheat. And they turned slower so we had to change the pulley diameter and make it bigger. The entire adaptation was quite complex and a bit on the Mickey Mouse side of things. The minicomputer read the program from a paper tape which took forever. Good times.

The loss of headroom with diminishing frequency is something which most of times will not cause problems but the engineer must be aware if life or limb of Boeing shares are on the line.

In summary, you should be very careful when making general absolute statements. And doubly so with electrolytics.

3

Beginners / Re: Convert US standard 115V to International 230V

« Last post by IanB on Yesterday at 11:57:06 pm »

Capacitor ESR decreases as frequency decrease and ESR increases as frequency increases. So whether it 50 to 60Hz or 100 to 120Hz it won't make any difference worth worrying about to output voltage ripple. This can be easily tested with any LCR meter with variable frequency. If your getting a huge change in value between 50Hz and 60Hz then the capacitor is nearing end of life anyway and needs to be changed.

Neither ESR, nor change in capacitance with frequency, has been mentioned as of any significance to the discussion at hand. So it remains puzzling why you keep introducing them?

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Beginners / Re: RS232 intermitted issue

« Last post by tzc24 on Yesterday at 11:52:04 pm »

You can try a different terminal emulation software, such as PuTTY or HyperTerminal, to see if the issue persists.

I have tried different terminal and unfortunately all come out with the same output.

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Beginners / Re: RS232 intermitted issue

« Last post by tzc24 on Yesterday at 11:49:48 pm »

I had checked all the tx voltage there are no abnormality found.

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Projects, Designs, and Technical Stuff / Re: Vacuum Fluorescent Display Driver

« Last post by bostonman on Yesterday at 11:49:09 pm »

I assume you mean the wires behind the glass?

Nothing seems to glow even faintly. Tomorrow I’ll reflow the pins, but I tend to go heavy with the solder regardless. A quick look earlier didn’t reveal any indication of bad solder or lack of, however, anything is possible.

Odd it was working and nothing more than a power recycle resulted in the display not lighting.

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Projects, Designs, and Technical Stuff / SX1280: anyone?

« Last post by SiliconWizard on Yesterday at 11:48:44 pm »

Just wondering if anyone here has used the SX1280 in a project, any feedback would be welcome.

https://www.semtech.com/products/wireless-rf/lora-connect/sx1280

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Test Equipment / Re: Heads up on MicSig Probe

« Last post by J-R on Yesterday at 11:46:52 pm »

Looks like it is actually a "SainSmart Official" store-wide sale.  So be sure to check out their other items if you have money burning a hole in your pocket...

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Projects, Designs, and Technical Stuff / Re: 3D printing company similar to PCBWAY for circuit board

« Last post by ataradov on Yesterday at 11:40:10 pm »

Where can you get machined metal for the same price as 3D printed ones? I just tried with a basic half box and 3D printed one was $1.55 at 50 pcs. Machined aluminum one was $17.

You can probably get it cheaper with extruded stuff, but that limits your options quite a bit.

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Projects, Designs, and Technical Stuff / Re: PC74hct4046ap Replacement

« Last post by PCB.Wiz on Yesterday at 11:38:08 pm »

I keep wondering what that 1N4148 is even doing there? It's the oddest circuit I've seen.

It looks like a deliberate decision was made to run the PC2 output at not-quite-zero phase.
To balance the 4M7 drain resistor, PC2 will need a steady small pulse offset.

The circuit shows a CLK coming from elsewhere, so that likely dominates here, the PLL may be just for sampling purposes.