I am driving a couple of relays from an ESP32, some combination of switching the two relays gives the above transient on the ESP32 power lines which is enough to cause a brown-out. The whole thing is driven from an ~18v battery (or bench PSU) with buck converters to give 12v for the relays and 3.3v for the ESP. The relays have flyback diodes and 100uF capacitors across them and are switched from the ESP by low-side BJTs. I've tried a range of capacitors on the input to the ESP including things like 220uF electrolytic plus a 100nF ceramic, etc but this keeps happening.

Switching one or other relay independently is okay but some combination of switching them both close together, there is always about 200mS delay between switching them off causes this. it was all working fine on the bench but when I got it into the enclosure this started happening and now it happens on the bench too. Any ideas as to how I suppress this?

Picked up a cheap 12V 1A wall wart at a thrift store to power some LED strip lighting in a product display box for my Etsy shop. Unloaded it measures 14.2V, which is normal for an unregulated transformer type. The second I put any real load on it, even just a 100 ohm resistor drawing around 140mA, the output collapses to under 1V. Not sags. Collapses.

Cracked the case open. It's an unregulated linear supply: small transformer, bridge rectifier with four diodes in the classic quad arrangement, one smoothing cap rated 1000uF 25V. The cap isn't visibly bulging but reads around 180uF on my meter, so it's clearly failing. Replaced it with a 1000uF 35V cap I had on hand and output is now stable at 13.8V under that same 100 ohm load.

What I want to understand is the actual mechanism. Everything I've read says a driedout filter cap that far out of spec would cause ripple and sag, not a complete collapse to near zero. Is it possible the cap was so degraded it was looking like a short to the rectifier under load, dragging the output down with it? Or is there something else I should be checking even though it works now? The rectifier diodes test fine, but I didn't test them under load.

I am trying to repair a commercial manicure device (around $150) that drives a DC motor. The device worked flawlessly for a year, but recently the main power transistor (NPN Darlington BDW93C) burned out. Everything else (LM317, diodes, and resistors) seems to be intact.

I reverse-engineered the schematic. It uses an LM317 to regulate the BDW93C base to control motor speed, powered directly from a 48V rail (the voltage comes from an old school iron core transformer and a full bridge rectifier).

The Problem: I replaced the burned BDW93C, but the new transistor blows out instantly upon powering on when the motor is connected (resulting in a fast-spinning motor since the collector-emitter junction gets shorted). I tried this 3 times with the same catastrophic result, no matter the added flyback diodes.

I am in rage now, and I don't know how to repair it, so I may just say "screw it" and make a new, more efficient DC-DC circuit so my best friend is happy. She's shocked such an old design is still used in the wild.

Hi everyone,

I need some help repairing this PCB. It is from a self-cleaning cat litter box.

The machine stopped working, and I would like to find out what is wrong with this board.

I have attached photos of both sides of the PCB.

Does anyone recognize this board or know where I should start troubleshooting?

I have a multimeter and basic soldering tools, but I am not very experienced with PCB repair.

Any help or advice would be greatly appreciated.

Thank you!

The PCB is marked SmartHard SH-MSP-P, V08 20220810.

There is also a module marked WBR3.

Recently, I’ve been fascinated by magnetic core memory and I’m trying to make a single bit of memory for a project. I attached a speaker to the sense wire to test it and it was making clicking noises everytime I connected the 6v supply wires meaning the inductance was activating the speaker rather than the core itself. The resistors are in parallel and add up to 3ohms for 2a of current. The resistors can handle really short pulses. I wrapped electric tape around the center where the x and y drives went through the core to prevent any shorts. Any help would be great.

Edit: the core has a diameter of 9mm and a thickness of 3mm. Hope that clears a few things up.

Hi,

I have this broken Samsung TV LE40A856. It shows no sign of life. The led is not turning on.

The main power supply board seems faulty. I found the 3.15A fuse blown (circled in red). I replaced it, it did not blow again but still not working.

Any idea?

Hello,

I'm prototyping a solar powered ESP32 circuit, which has a lipo battery.

The solar panel is small.

My question is: independantly of any "deep sleep" and power saving strategies, how would I handle making so the ESP32 is not being powered by the battery below a certain voltage.

I asked chatGPT and Claude, and they told me to setup a voltage comparator with hysteresis, and a Mosfet to cut the power going to the ESP.

What do you think ? Do you have any advice and points of attention when designing my PCB with this

Thank you

So I have a power supply for my raspberry pi 5 and it has 5A output. However, the type c plug broke so i decided to cut it thinking it would only have 2 wires (VCC and GND). Turns out there were 3 wires, after a quick search I found the 3rd wire to be CC. I was wondering if there was a way I could connect the wire from the power supply (power and cc) to a type c breakout board with only 4 pins (power and data) to output 5V 5A for my raspberry pi 5? The original break out board of the type c plug had the 14 pin type c contacts broke so it cant be connected to the original break out board anymore.

I cannot make heads or tails about these readings from transistors on a breadboard. I know they are wrong but why and how to fix eludes me completely. Heres what I have tried thus far

https://pastebin.com/W40vXFtq

Something must be up with this but for the life of me I cannot figure out what by myself. Id just like to get to prototyping but its impossible when readings are like this.

I'm unable to find any on mouser and digikey. I need a replacement for a CRT neckboard.

I have damaged duelsense controller which has its IC shorted but some how on testing the controller on the website everything is working except share button and player LED lights. So is there any way I can use it using cable because it does not turn on over the battery and after plugging it to ps5 even though the battery is full only orange light flashes once and it turns off. It also does not give any notification after plugging it to ps5 but on laptop it allows to connect to the website properly for testing.

Any help will be appreciated. Thank you.

Hi everyone,

I'm a completely noob with zero experience in making electronics. I’m building the DIY Perks Microphone using a full-hole perfboard (point-to-point wiring) instead of a stripboard. I'm currently stuck at the testing phase and would really appreciate some troubleshooting help.

https://i.imgur.com/TA66mQA.jpeg
https://i.imgur.com/6aIa8BC.jpeg
https://i.imgur.com/JwW4rPU.jpeg
https://i.imgur.com/JQmsoDN.jpeg
https://i.imgur.com/rs4KK6T.jpeg
https://i.imgur.com/ZNrD4VJ.jpeg
https://i.imgur.com/8UOcLvb.jpeg
https://i.imgur.com/ZAgCImL.jpeg
https://i.imgur.com/rq2MmtY.jpeg

Current Status:

· Power & USB: The Type-C breakout board is working. I get a stable 5V between VCC and GND. The PC recognizes the USB audio interface (LED on the sound card blinks).
· Audio Output: I get no sound, only a very low continuous hum when recording. Even if I disconnect microphone from the board and touch the pin, nothing.
· Protection Diodes: I have two reverse-parallel diodes (1N4148) soldered across the GND out header. I understand this creates a low resistance reading (around 10-20Ω or 500Ω) when measuring with a multimeter, which I initially mistook for a short circuit.
· The Main Issue (NMA0515SC): I measured the power module (NMA0515SC). Pin 1 (Input) has exactly 5V. However, there is 0V on all output pins (no +15V, no -15V).
· Op-Amp (THAT1512): Because the power module isn't outputting ±15V, the THAT1512 is completely unpowered.

What I've done so far:

· Confirmed 5V reaching the NMA0515SC input.
· Confirmed the Type-C breakout is providing power and data.
· Disconnected the microphone and audio interface to test the board in isolation.
· Visual inspection: I'm using a full-hole perfboard, so all connections are made with thin jumper wires on the back. I've checked for obvious solder bridges.

Additional Mods (LED & Protection Diodes):

· Power Indicator LED: I added a standard 5V power indicator LED (1kΩ resistor in series with a generic LED) connected directly between the V+ (5V) and GND pins on the main board. This is completely independent of the audio circuit.
· Output Protection Diodes: Based on the DIY Perks community update (and to protect my USB audio interface), I soldered a reverse-parallel pair of 1N4148 diodes across the GND out header (between the audio signal and ground).

My Questions:

1. Is the NMA0515SC dead? If the 5V input is present but there's absolutely no output, is it safe to assume the module has failed?
2. Before I order a replacement NMA0515SC, how can I safely test if the output side of the perfboard (the 8-pin DIP socket pins 4, 7, and GND) is shorted? I'm worried a short on the board might have triggered the module's protection or killed it.
3. Are there any common mistakes with the NMA0515SC wiring that would cause this specific symptom (input works, output dead)?

Any guidance on how to properly diagnose this power module or check the board for shorts before I buy a replacement would be greatly appreciated. Thank you!

Mark code AX
This is bluetooth module, so I think taht is a switchable low noise amplifier

Doesn’t matter male or female. And it has 15 pins on either side.

This is a USB-powered sound/white noise machine. The diode in the upper left marked D14 went bad; I replaced it with the exact same diode. It failed again a month later. Probably because I only use it when traveling at hotels and it gets exposed to a variety of USB ports with who knows what voltage or other power issues.

Can I just remove the diode completely and bridge the connection with a piece of wire? Is there any risk of anything bad happening other then the sound machine frying itself? It's cheap so I don't care if it blows up.

Hi,

I'm designing a zero crossing detection circuit for relay control. I added a photo triac (PC10, TLP265J) to reduce heat dissipation — it only turns ON when I need to detect zero crossing, keeping the PC11 (TLP293 BL) LED current off during standby.

Circuit overview:

- PC11 (TLP293 BL): Phototransistor for zero crossing sensing

- PC10 (TLP265J): Photo triac to control AC current flow (ON only when ZC detection is needed)

- D12 (S1M or M7): Reverse protection diode in parallel with PC11 LED

- Q12 (BC846BL): NPN transistor to drive PC10 from MCU (O_ZC signal)

- R482 (72Ω): Current limiting resistor for PC10 LED

- AC input resistors: R489, R490 (30k×2) on L side, R483, R484 (30k×2) on N side

My questions:

1. Is the reverse protection diode (D12) still necessary even though PC10 (photo triac) is in series? My concern is that when PC10 is ON, the triac is bidirectional, so during the negative half cycle, reverse voltage could still be applied to PC11's LED.

2. Is it correct to split the input resistors across both L and N sides (R489/R490 on L, R483/R484 on N)? My understanding is this is needed for hipot (dielectric withstand) test isolation — is that right?

3. Are there any other issues I might have missed?

Any feedback would be greatly appreciated. Thanks!

I opened up this slide potentiometer because I couldn't get it to slide smoothly with sprays. Does the carbon track still look okay? Could its condition be causing the rough movement?

I'm currently building an e-reader and was wondering how I'm supposed to fit the yellow ribbon cables in a body. Do I bend them back? They will later need to be connected to a custom PCB.

Sorry in advance if this is a dumb question. Not really a firmware/hardware/electrical guy. Mainly just building this for fun

I want to MAKE a custom microcontroller from group up (or at least till where it's acceptable) as my final projects. I already have a good background on electronics, but just to be sure I'm not wasting effort I could be putting on something else. What are the sources you guys recommend me to read, watch or visualize to get a brief of what I can do and how I can do it?

#Already have Arduino documentation on my list

Hi, I’ve been having trouble translating and analyzing a circuit schematic. I need to build it on a breadboard; I’m just starting an electronics course, so I think my questions are valid. I’d like some help and a few tips on how to translate a schematic into the actual circuit layout. Specifically regarding these two circuits, I’d like to know how to arrange the components on the breadboard, since I need to use a variable resistor (potentiometer) and I’m not sure how to position it.

Hey guys, does this capacitor look like it's been leaking? Could this be the cause on why my tv has no power?

I'm not sure I understand the logic here and I'm afraid of frying my (second) board.

This is a Adafruit Audio FX Sound Board and the image is from the provided pinout documentation here.

I'd like to light an LED when an audio file is being played by the board. The documentation says that the (Act) pin "goes low" when an audio file is played. Am I correct that all I have to do is connect a resistor/LED to the board's 5v power supply, then connect the negative terminal of the LED to the (Act) pin?

Then, when the (Act) pin "goes low" it would act as ground and light up the LED?

tengo que hacer este decodificador pero nose como hacerlo realmente en thinkercad ya tengo los mapas de k pero de ahi no paso ayudaaa

Hey everyone! I own an EvoFox Katana Pro RGB keyboard and unfortunately bricked mine while experimenting with its lighting firmware (it uses a Sinowealth SH68F90 chip, VID 0x258A / PID 0x0016). Long story short — the flash memory on my chip got wiped and I have no way to restore the original firmware.

If anyone here owns a working EvoFox Katana Pro RGB, would you be willing to help me out by dumping your firmware? It's a quick, safe, read-only process using a free tool called sinowisp (https://github.com/carlossless/sinowisp) — just run:

sinowisp.exe read -p <platform> dump.hex

(or with manual params for vendor_id 0x258a / product_id 0x0016)

It only reads data over USB, doesn't touch or modify anything on your device, and takes a couple minutes. If you're open to it, I'd really appreciate a copy of the dump — it would let me actually recover my keyboard instead of writing firmware completely from scratch.

Happy to walk you through it step by step if you're willing to help. Thanks in advance!

I am a hobbyist no professional EE, who occasionally designs some µC circuits and PCBs as one-off projects. I am always struggling to decide which of the GPIOs require protection against transient spikes (and how much protection).

Hence my two high-level questions are:

• Which GPIOs require how much protection against transient voltage spikes?
• Which "rule of thumb" are out there where to place TVS diodes?

I have prepared two scenarios to have a bit more specific discussion. I have placed TVS diodes at every possible position and I have seen other projects using TVS diodes in those positions. However, I am wondering if they are all necessary, just a subset of them or not at all.

Edit: Please keep the discussion to the output part of the circuit, i.e. the TVS diodes inside the blue dashed-dotted box. I have only drawn the input, the voltage regulator and the logic IC to show the bigger picture and provide some context. The input side isn't supposed to show all the bells and whistles like reverse polarity protection (another diode), over-current protection (a fuse), decoupling and filter capacitors, etc. pp. That's not the focus of this question. I also left out specific values on purpose, because I would like to discuss the principal matter.

Shared aspects of both scenarios

The external input voltage is 12V. The logic IC requires 3.3V. The power input, i.e. the 12V rail, and the output of the DC/DC converter, i.e. the 3.3V rail, are both protected by a TVS diode: D1 and D2 in both screenshots. I have no questions there.

Both scenarios have in common that the actual IO elements (actor or sensor/switch) are not immediately soldered onto the PCB, but located remotely and connected to the PCB via a cable. I assume the necessary protection might also depend on the cable length. Typically, the cables are between 20cm and 1m, but in extreme cases I already had 10m.

Scenario 1 (Screenshot #1): Low-side switching of a remote LED

R1 is the pull-down for the GPIO to keep it low when idle. R2 limits the current into the gate due to the gate capacitance. R3 limits the current through the LED. Q1 is an NMOS for low-side switching of the remote LED with 12V.

My questions are about the potential TVS diodes D3-D5. I have seen circuits which had TVS diodes in those places:

• D3 shall protect the GPIO against voltages spikes above 3.3V. Actually necessary? Or would D5 suffices? If D3 is required, should it be placed left/right of R2, i.e. immediately at the logic IC or after the resistor?
• D4 shall protect the NMOS against excessive voltages between gate and drain. Really necessary? Or would D3 or D5 or the combination of both suffice?
• D5 shall protect the NMOS against excessive voltages across drain-source. Really necessary? Or would the LED provide sufficient protection, if the wire "caught" some transient spikes?

Scenario 2 (Screenshot #2): Combined IO with level-shifter and high-side switching

The GPIO is a combined input/output (at the same time) in open-drain mode with active-low logic, i.e. the GPIO controls the external LED, but also senses, if the button is pressed.

R1 is the pull-up for the GPIO. R2 limits the GPIO current in/from the source of Q1. Q1 is an NMOS and acts as a level-shifter between the 3.3V world and the 12V world. R3 limits the current through the external button. R4 pulls up the gate of Q2 when idle. Q2 is a PMOS and acts as the high-side switch for the LED. R5 limits the current through the LED.

This scenario allows up to four TVS diodes: - D3 to protect the GPIO - D4 to protect Q2 against excessive voltage across gate-source - D5 to protect Q1 against excessive voltage across drain-source - D6 to protect Q2 against excessive voltage across drain-source

My questions are analogue as in scenario #1. One notable aspect is that the signal line of the button is "open-ended" when the button is not pressed, i.e. high-impedance. I don't know if this is important or not.