Ask Electronics

I recently bought a thinkpad T470 for a good deal, and it turns out that it was a good deal because the BIOS is locked with an admin password so I can't install an OS, or change any BIOS settings.

I also recently came across a paper that describes a "security flaw" in most thinkpads where you can bypass, then reset the admin password by shorting the SDA and SCL pins on the BIOS chip.

Does anyone know where this chip is located on the MOBO? I would be hugely appreciative if you would be so kind as to point me in the right direction. Thanks in advance!

Hello,

No formal training, but do like to repair devices at home (and keep vintage electronics and computers going).

Yet another alkaline battery has leaked prodigiously into a device (after only a few months). A wall-mounted thermostat.

Is the sort of clip pictured, which contacts an AA battery negative terminal at one end, and seemed to just clamp onto a conductive trace at the edge of PCB at the other, an easy-to-find standard form (for replacement) or a custom piece?

It is quite corroded and even peeling, and suspect replacing the clip would be better than devising a work-around.

Visually searching through product photos on supplier websites (like Digi--- and Mous-- here in the US) has not been effective.

Thanks for any comment.

I'm currently looking into various DC DC converters and was confused that the Meanwell DDR-60 series only shows a typical rating but says nothing about the efficiency at idle. From AC/DC converters I'm used to have a curve that starts at idle and maybe 70% and goes to 100% load, having the peak at ninetee something.

(Edit: link goes directly to the PDF)

I got it with https://sabrent.com/collections/hard-drive-accessories/products/ec-ch2b. But since I bought it in EU, it has that charger. Is there no alternative other than buying a whole new charger?

i can’t find ANYWHERE this ic chip, not even in chinese online stores. code is FMM862, laptop model is a Gateway GWTN141-10. it can also be another one that works. thanks in advance.

Hi all! I recently purchased some push-lights for my kitchen from my hardware store, and I stupidly didn't read the package that said that they shut off after 30 mins. This is super inconvenient in my dark kitchen, and I can't return them. I figured I might as well tinker with them, and any help would be greatly appreciated. The first picture is the small, round push-light (it was in a 3 pack, so I've got room for error with these), and the second picture was the even bigger disappointment because it's a larger strip light.

I found them online for reference here and here. It doesn't say they shut off in the description of these, but it says it in the user manual under "product guides and documents" for the rectangle light.

TL;DR: Help me bypass the "power saving" mode that shuts these off after 30 mins please!

Hello! Someone suggested this "If the MOSFET is put into diode connection mode (connect the gate to the drain), you can force a small current (I recommend 1 uA–10 uA; 1 mA would probably be OK; 100 mA would result in significant power dissipation and could influence the results) and record Vds (which is equal to Vgs in this configuration).” There are just some questions i had in mind. *Is it possible to connect the gate and drain on a breadboard to put the MOSFET into diode connection mode? *How to force a small current in the drain. Is voltage divider will be enough? *Is it still possible to apply voltage source after putting it into a diode connection? Also, what is the expected measurement at the Vds terminal. If there will be no voltage source, will it be in the range of 0.1 to 1 V increase? *Why should the MOSFET be connected into a diode?

*Can a MOSFET handle low dosage for example, Cs-137 (666 keV)

I've got an old oscilloscope and a function generator that I'm trying to use to play around and get more familiar with this kinda stuff. I'm mostly new to electronics (especially analog ones) and I'm having a hard time getting them setup properly.

Both devices turn on and the controls seemingly work, but I never get anything more than a flat line or random noise on the scope.

Any help would be appreciated!

The scope is a Sencore PS148A and the generator is a Heathkit SG-1271.

Looking to replace the male connector in this picture. Any idea what it is called and where I can get it? I'm in Germany.

I have a acer c740 chromebook that has a cracked charging jack hoping I can find replacement part for it. Picture attached shows what's left of some number on it I think it's 150726+F4 not sure what the symbol is. The male end end is 3mm od 1.1mm Id if that helps.

Hi, I'm new here (never used this entire platform before, but as the askElectronics reddit is down I thought i'd follow the trail to lemmy and see what's what). Hopefully this works!

Ok so I have the following -

A variable boost converter This - set to 12v output.

Two sets of 2x 18650 batteries

A 12v LED strip.

The two circuits I'm sanity checking -

1. Two 18650s in series, outputting about 8v, going to the boost (which ups it to 12v) and lighting up the 12v LEDS.

2. Two 18650s in parallel, outputting about 4v, going to the same boost (which still ups it to 12v, so that's working fine and seems to be within its working range), lighting up the 12v LEDs.

Question I wanted to check - Far as I am aware, both of these circuits should be fine and do the job. And I'm aware of how series vs parallel usually works (eg. double the voltage, vs double the capacity). However I've never used them with a voltage booster that sets things to a fixed output voltage.

I am assuming that the way the voltage booster works, means it will 'drain' the parallel circuit twice as fast as the series circuit. And so both will end up running the LEDs for the same amount of time. This sounds right in my head but wanted to confirm before I soldered all my connections.

Also wondered if, in this scenario, the general recommendation is to go with the parallel or the series circuit. I wonder if the series might have less losses through the boost circuit through heating etc, but I was just guessing.

Thanks! Long first lemmy post haha. > Unfortunately after posting this I discovered the TP4056 board won’t charge 18650s in series, only in parallel!

Edit: While it seems that running the cells in series would be more efficient, I have the issue that I recharge them using a TP4056 board, and they are only compatible with charging cells in parallel and not in series!

Hi, I've been unable to ID the pictured capacitor to track down a spec sheet or source. Do any of you folks recognize it? Pictured are two different capacitors that look to be identical except for slightly different markings.

Right to the point: On a BPI-R3, should connecting the UART debug pins directly to the appropriate pins on a DB9 USB serial adapter (rx->tx, tx->rx, gnd->gnd) work? Because I’m just getting a garbled mess in my serial console. I’ve tried all different baud rates. I’m using a high quality serial adapter (Keyspan Tripp Lite). I’ve tried on Linux and Windows. I assume I’m missing something stupid.

To make matters more annoying, I have a $5 almost certainly counterfeit USB serial adapter with USB on one end and DuPont connectors on the other end and it works fine, so at this point my problem is mostly academic. I would like to know what I’m doing wrong, though.

The recent post on using a lamp in series to limit potential fault currents has had me thinking about using them as above. Has anyone done this? I can see advantages, cost for one - wirewound resistors can be expensive. Visual indication of a varying load. Make it "short-circuit proof"..

I'm taking apart a broken tape recorder produced in the 70s (a Tesla B57, made in Czechoslovakia), to harvest some parts (inductors, switches, ...) and maybe reuse the case for some project.

Which made me wonder: are there any dangers to protect myself against? I know about lead, so I'll take precautions when desoldering things. Is there anything else to be aware of? Some fumes, other toxic materials, ...?

I'm not planning to connect the device to power in any way, so from an electrical perspective there should be nothing to worry about (except for caps maybe). Am I wrong?

Hello, I recently bought a USB A to C cable and it is pretty weird. It is a USB A to USB C cable, seemingly USB 2.0 but the A connector has 5 pins, the 4 pins of USB 2 and what looks like pin 7 of USB 3.0 so in the middle of the back row, the other pins of USB 3.0 are not there and the plasting moulding only allows for that one pin (moreover the USB type C end looks like it only has the few middle pins so it's probably 2.0). The weirdness continues because when connected to a USB power supply the led on the USB C connector lights up but it can only charge simple devices like flashlights or things that generally just accept 5V, anything with fast charging capabilities gets no output. I am probably going to test it with breakout boards and eventually even disassembly it and maybe replace the connectors but in the meantime does anyone have any explanation?

P.S. I will make a follow up post (or an update here) when I open it up, with photos of course.

I'm planning to add a momentary switch to a single loop DC circuit. Will this cause any amount of resistance in the circuit? I'm a complete noobie when it comes to electronics, any resource links or clarification is appreciated. I know the type of material/width of wire and a pot will cause resistance but will any component put in line with the circuit cause resistance, and if so how do I go about measuring the resistance for each component within the circuit?

Salutations to Davide A. for this creation as an alternate.

Hello, we are making a thesis where we use MOSFETs as an alternative radiation detector. So to explain it, it works when the mosfet is irradiated with an external radiation source; its voltage threshold increases, which will be used to determine the radiation dose. I'm currently asking for help on how we measure the voltage threshold. BTW, we are using an n-channel MOSFET (model: IRFP250NPbF). Also in the datasheet provided by the manufacturer, it says here VGS(th)/Gate Threshold Voltage Min: 2.0 ––– Max: 4.0 V. There is a condition here with VDS = VGS, ID = 250 A. Does this mean that to measure the VGS, we need to first satisfy the conditions? To measure the voltage threshold, what node will we use to measure the VGS (th)? Is it at the drain to the source terminal or still at the gate to the source terminal? Feel free to share your thoughts, if you have any. I would also like to add that we have already tried to supply a voltage at the gate with respect to the source terminal. We use a 4 V supply voltage, and when we tried to measure the VDS (drain to source voltage), there was a voltage drop, so we've got a 3.5 V. Also, we are using an Arduino to measure its voltage and a multimeter for checking.

Hello. I'm a hobbist on electronics repairs, and I did some repairs on stuff powered from the wall socket before, using a serial bulb to protect the circuit in case there's a short. Now I want to troubleshoot a board that works at 3V and very low current (like no more than 100mA). So, how can I properly size the bulb I need for this circuit before powering it? Or is there a better way to protect the circuit than a serial bulb? Thanks in advance.

Solution

Using an open drain buffer like the 74LVC1G07 did the trick. Note that this part only works for inputs with a pull-up resistor. There are other parts from the same lineup that can work with any input.

Problem

I have an ebike computer that has two inputs that accept square wave signals. The range is 0-5V. One of the inputs has no pull-up/down resistors on it. When I hook up a device producing signal, the signal is detected correctly. Both highs and lows are detected correctly. The other input has a built-in pull-up resistor. When I hook the same signal to it, only the high side is detected. Measuring the voltage of the low side, it's a bit higher than when hooked to the other input and I'm guessing it isn't crossing the low threshold the computer expects in order to register the low.

Am I right in thinking that the pull-up resistor is increasing the lows?

Is it possible to counteract the internal pull-up resistor by hooking a pull-down resistor to the input?

I'm a software guy with decent soldering skills and minimal knowledge in electronics so please answer like I'm not the brightest electronic bulb on the tree.

Thank you in advance!

Cross-posting my question from StackExchange.

I have a few old posts on the subreddit and i need to view one of them as i am reviving an old project. there is a comment on one of them that has the info i need. I never screenshotted that info.

this is the link: https://old.reddit.com/r/AskElectronics/comments/73f8d2/microwave_control_panel_keypad_stops_working_when/

i'd use google's cache page but it doesn't have this cached.

I'm working on adding extra access control to elevator calling buttons and i would like to identify the connector type of the wires connecting elevator buttons to the elevator panel

I have tried Micro JST 1.25MM 3-Pin Male & Female Connector Plug, it has the same Pitch Mating size of 1.25mm but unfortunately the connector itself is smaller than the original one.

I've been watching a couple of YouTube videos doing component-level repair. I've noticed some of them have super fine multimeter probes, often with insulation covering most of the length of the probe. I haven't found ones like this on my usual sites, but I'm not sure if I'm just missing something. Can anyone suggest some meter probes like this?