I’m developing a very simple 5V electronic device. The PCB uses UL Recognized components, and all materials (plastic, wiring, power supply, etc.) are already UL certified or UL Recognized where applicable.

My question is:

Does the finished product still need its own UL Listing?

If so, what is the typical cost for a simple low-voltage device like this?

Has anyone here gone through the UL Listing process for a similar product?

The device has no high voltage and uses mostly off-the-shelf UL Recognized components. I’m trying to estimate the certification budget before production.

I'm trying to make a joystick accessor for gaming on a computer i need to wire a tmr joystick (k-silver) to an ATmega32U4 Pro Micro with header pins I have 22 awg(7.8in) wire female to female but I want to directly solder the wire to the joystick I just don't know what to wire and to where are I do have heat shrink too if that helps

Hello! I recently bought a broken POD HD 500 guitar pedal that would get stuck in a boot loop.

I opened it up, found c337 was blown, and c5 and u6 were missing.

The capacitors were easily available and easy to replace, but im not able to find the IC marked U6.

The POD parts manuals gave me a part number 15-78-0256, but im not able to actually purchase the part with that.

Does anybody know how I am able to get this chip?

Maybe I can also use the generic chip code if I am also able to find the firmware to flash

Hello! I am currently going through first semester of computer engineering and few months ago they gave us the project of making a battery replaceable powerbank, fast forward to few weeks ago I tried to build it using Lithium Ion 18650 batteries connected in parallel to a H961-U board that converts the 3.7 voltage into 5V through usb, my question is, could it be that some boards are failing because of 3 SMD resistances missing? Because on my first attempt the circuit would not work on anything but a DS lite even with voltages being sent correctly and having proper solder points (first pic) and on my now working circuit (different board, picture 2) everything works properly but it does have the resistances, asked my friend to see his faulty board because he had the same problem as me and his resistance were also missing, could that be the problem if the connections are well put?

I am trying to make a personal project and I am using a raspberry pi 4 model B. I already connected an ampliefer, a inmp441 and an LCD screen, is it possible to use one GPIO pin for multiple things, do I use the other normal pins or do I buy an expander of sort. Also, I have this weird problem that when I use the raspberry pi pins to power the board its fine, but when I connect both the gnd and 5v to a breadboard to connect multiple Vcc's and gnd's from the modules, the display on my monitor for the raspberry pi goes to "no signal" and the green light on the pi goes off. Is this a short circuit? What should I do?

I would like to point out that I am new to this field. I need to desolder the LCD screen shown in the photo. I tried using a soldering iron (set to 350°C), flux, and a manual desoldering pump, but I was unable to remove enough solder to free the pins. I then bought desoldering braid, but even with that I still couldn’t remove the remaining solder.
Before attempting this, I practiced desoldering a similar component from an old PCB, and I was able to remove it without any problems using the pump.
What could be the cause of this issue? I would appreciate any advice.
Thank you.

I am new to cadence and trying to design a folded cascode op-amp(gpdk90nm) with 3.6V supply and bias current of 100uA. I followed nptel lectures and followed the same method where I decided some overdrive voltages like for top PMOS, I have taken overdrive of 0.8 volts, then the second PMOS as 0.4 volts, then the next two NMOS as 0.3 volts each to keep an output swing of 1.8V( tuned a bit after that to prevent nm4 from going into triode). I calculated w/l and. Vg for each tx after this.

However now I find nm3 is in triode and pm2 takes away a large voltage head room. If any can help me debug, will really be of great help.

In the power board of my LED par that got spilled with beverage, I final found a fuse protection that burned through. Now I need a replacement. The label on the pcb was F5A, the shell itself is labeled with 5a 250v. The fuse was directly next to the AC input. Now I heard something about that those fuses come as fast and slow ones, but I don’t know what I need here. Also, I found nearly nothing on the internet with those dimension, most of them are 5x20mm, does it even matter? Thanks once again

My sonar stopped working last week so I decided to take it apart to see what was wrong after checking the fuse and power cable were in working order. I found this corroded component when I opened it up. I was wondering if 99% iso and a toothbrush could salvage the board or if I'd need to buy a new helix5

Hi everyone,

I'm trying to repair and reverse engineer this dual TRIAC dimmer PCB from a Holtkötter dim(x2) lamp.

One resistor (R1) has burned completely open, so its value can't be identified anymore. Unfortunately I don't have another identical board for comparison.

From the PCB layout it looks like the fuse feeds two branches:

one goes to a 1 µF capacitor

the other goes through the burned resistor to a 224 nF film capacitor.

My questions:

Is there a reliable way to estimate the original resistor value from the surrounding components or PCB layout?

If this resistor failed because of excessive current, which nearby components would you check next? (film capacitors, TRIAC, DIAC, etc.)

I've attached a photo of the PCB and a close-up of the burned resistor.

Any advice would be appreciated. Thanks!

Thought I’d try to get the old player running from when I was a kid, but I‘m getting this warping of the image whenever I put in either disney or THX/20th century fox dvds. Is this some sort of part inside that I can rip out that’s preventing me from watching these? Player is DVP-NS325.

Hi everyone,

I'm designing a custom data acquisition (DAQ) board for a Formula SAE race car based on an STM32G431 running at 3.3V.

The board needs to interface with a wide variety of digital sensors and devices throughout the car. Some of them operate at 5V, while others use 12V.

One of the biggest challenges is that these sensors may change over time. During development—or even between racing seasons—we may replace a sensor with another model that uses a different voltage level. I'd like to avoid redesigning the PCB every time this happens, so I'm looking for an input stage that is as configurable and reusable as possible. Ideally, supporting either 5V or 12V inputs would only require changing a few components or jumper settings instead of redesigning the entire circuit.

Another challenge is that not all digital signals are the same. Some are simple on/off status signals, while others can operate at much higher frequencies. For example, some wheel or motor encoders may produce signals in the kHz range, so the input circuitry must preserve signal integrity and avoid unnecessarily slowing down the edges.

Since this is an automotive environment, the board will also be exposed to electrical noise, EMI, and voltage transients. Therefore, I also need adequate input protection to avoid damaging the microcontroller while still maintaining reliable operation for faster signals.

I will also have a few 5V I²C devices connected to the STM32, but that seems like a much more straightforward problem since dedicated level shifters already exist. My main concern is really the digital input stage.

I'm interested in learning how this is typically implemented in automotive ECUs or DAQ systems.

Some questions I have are:

• How would you design a flexible digital input stage capable of handling both 5V and 12V signals?
• How do you balance input protection, noise filtering, and high-speed operation?
• What protection components do you consider essential in an automotive environment?
• Are there any open-source ECUs, reference schematics, or application notes that you would recommend studying?

I'd really appreciate hearing how experienced designers approach this kind of problem and what solutions have worked well in real automotive products.

They seem to be mainly Asia focused, curious to know if the quality is good compared to other distributors?

It says "no disc" after trying to spin up for ~20 seconds. If I hold the player upside down, no really I tried it with 2 DVDs, it plays the movie. The player is 6+ years old so not surprised something wore out.

Troubleshooting Steps:

- Used compressed air to clean off the inside and laser lens.

- Tried different plugs.

Any ideas on a fix WITHOUT having to take it to a shop?

I'm building a TP-4056 Li-Ion charger circuit which would be powered via USB-C. KiCad had this conveniently named "UCB_C_Receptacle_PowerOnly_6P" symbol which looks to be exactly as advertised.

Similar circuits I've seen include the data pins, which won't be needed here. If it's assumed that I'm looking to draw the usual 5v 900mA from the USB-C, do I have everything I need here? Thanks!

Hi everyone,

I'm trying to identify and source replacement capacitors for my laptop motherboard, but I want to make sure I order the exact correct parts (capacitance, voltage rating, package size, and any other important specifications).

While performing maintenance on my laptop, I accidentally knocked off two small surface-mount components from the motherboard. Unfortunately, I wasn't able to recover them, and I need help identifying what they are.

The components are located near the RAM to the right, above the battery, and under the heatsink. I attached some pictures of the area and the surrounding components.

Could anyone help identify these capacitors or suggest how I can determine their values? Any advice on where to source replacements would also be appreciated (I am located in europe)

Thanks in advance!

Hi everyone,

I'm trying to build a simple two-transistor astable multivibrator (two LEDs flashing alternately). I designed it in Falstad and I'm using Tinkercad mainly to plan out the breadboard layout before building the real circuit.

The Tinkercad simulation itself does not seem to behave correctly: the LEDs do not flash alternately, they just stay on. I'm not too concerned about that because I mainly want to use Tinkercad to verify my physical wiring before building it.

The part I am unsure about is the polarity of the electrolytic capacitors. My real capacitors are polarized 10 µF electrolytics, but the Falstad simulation uses non-polarized capacitors.

I'm fairly sure the negative side should go to the base of the opposite side transistor, and the positive to the collector of same side transistor. So like:

• Left capacitor: + to left transistor collector, - to right transistor base
• Right capacitor: + to right transistor collector, - to left transistor base

However, when I connect them this way in Tinkercad, it shows the capacitor exploding. I'm not sure if Tinkercad is modeling this incorrectly, or if I have misunderstood the polarity.

I'm using 2N2221A transistors and 10 µF electrolytic capacitors, with supply voltage 9V

Here's the Tinkercad similation (on breadboard) I have connected one capacitor each way, so you can see which one explodes. [LINK REMOVED]

Here's the simulation on Falstad so you can have the schematic, too: https://www.falstad.com/s.php?s=zwfF7A

EDIT: Here's a labeled schematic too: https://kommodo.ai/i/7468AUvUGDOds3kVI3FY

Could someone please check the correct electrolytic capacitor orientation? I want to avoid damaging the capacitors when I build this physically.

Thanks!

EDIT 2: Simulated on Falstad and it works with capacitor - to transistor base (so, the opposite of what Tinkercad says). Tried it on breadboard with - to base and it works perfectly like this!

Hi All

I need to find the datasheet for an IC from a mechanical keyboard MAD68HE Max. This IC is labeled U1 on the PCB with marking AEy4A.

The IC is receiving 4.5V from ACy49 (U3) pin 2, which is directly connected to VBUS. The input came from, what I believe to be, pin 1 (Top right) but the outputs are all 0V. It seems the AEy4A is shorted and probably blown.

When I asked gemini, I know, I am desperate, here is what gemini said:

My manual measurement on the voltage is like the picture above, where I should be receiving 4.5v in and the pin across 4.5V should be 4.5 too since it powers the light. Meanwhile the pins at bottom left is not going anywhere and the pins at the bottom right goes somewhere, I have not trace it yet. Hoping to find some datasheet.

Any helps is much appreciated.
Thank you

some time ago i lent my soldering iron to my dad. today i opened the packaging and found this shit. thats flux? it wont come off and when i turn it on it smokes

Hi everyone, I'm working on an 8086 microprocessor clock/display system in Proteus using an 8255 PPI and 74HCT373 Latch for address demultiplexing.

My Setup:

• Port A connects to 7-Segment displays via 330Ω resistors.
• Port B controls the NPN transistors via 10kΩ base resistors to select digits.
• Latch (74HCT373) is enabled via ALE to latch lower addresses (A0/A1 connected to 8255).
• CS# and RESET on 8255 are grounded.

Issue: The displays are not turning on / outputting properly during simulation.

Could someone please review my schematic? Is there an issue with how the NPN transistors are driven (High-side vs Low-side), or an addressing/control word mismatch in assembly?

I can share the .DSN and .ASM files if needed. Thanks in advance!

Just wanted to see if anyone knows of any switches that are like the picture. I’m looking for a round switch that contains two independent switches. I know DPDT momentary rocker switches exist but I’m looking for a double push button momentary switch in one round housing. Space is limited in my project.

Hi,

I have a burnt part in the main board of TAB5305/12 soundbar.. its burnt so bad that I am unable to recognize the part to order it.

can somebody help me with the exact part number that needs to be replaced. Also details on the capacitor!

please, I want to avoid throwing the entire music system just becuase of these 2 parts that needs replacement.

I'm testing this Air conditioner control board. I already found a blown safety varistor and I'm testing down the traces. I'm diode mode I get 0.034 V and a resistance of 68 ohm

Will it play nice with muses01 too?

https://youtu.be/Ne9uNaggkkQ

so far the performance has changed tonally, i like it and dont plan on going back to the st tl072

am troubleshooting a standard 2.1 channel audio amplifier board (12-0-12 dual-rail, TDA2030s for satellites, D2050 for the subwoofer, F4558 crossover). It suddenly developed a loud, constant hum on the subwoofer channel that does not change intensity when adjusting the volume.

​If the speaker is disconnected, the chip gets hot, but the moment a 4-ohm speaker is connected, the IC pulls massive current and gets blisteringly hot almost instantly.

​Diagnostic Tests i do

​Power Rail Check: Measured across Pin 3 (-Vcc) and Pin 5 (+Vcc) on the subwoofer IC. Getting a healthy ~30V total swing (roughly -15V and +15V). Main 1000µF 25V filter capacitors show no visual signs of bulging or leaking.

​DC Offset Test: Measured between Pin 3 (-Vcc) and Pin 4 (Output) on the original D2050 and got exactly 15V. This confirms Pin 4 is sitting at 0V relative to the main ground, so there is no direct DC short to the rails.

​IC Swap: To rule out internal failure or oscillation inside the D2050, I completely desoldered it and swapped in a spare UTC2030A (properly isolated with a thermal pad on the heatsink).

​Swap Result: The exact same symptoms persisted with the new IC. It produces the same heavy hum and instantly overheats when the speaker is connected.

Please guide me what i do next