r/AskElectronics • • 2h ago

Why do some computers have bipolar junction transistors on the outside of their case?

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5 Upvotes

I’m not to good with how computers work so I took a computer/networking class and they let me take some stuff from broken computers (speakers, power supplies, batteries, that kinda stuff) and something that caught my eye is a lot of them had a BJT attached to the outside of the front of the grounded case and whenever I looked up why it was there all I got is what a transistor is.the transistor is a 2n3904, my theory is it’s like temperature regulation or some other version of using a component to do something it wasn’t made for.


r/AskElectronics • • 6h ago

What are the potential difficulties in creating a generic TV mainboard?

8 Upvotes

Given the recent revelations about smart TVs spying on owners, how feasible would it be to design a generic mainboard with off the shelf parts? A Raspberry Pi for example.

As I understand, there is usually a power supply board, and a board that actually talks to the panel, presumably they could stay?

HDMI ports wouldn't line up with the casing, I suppose, but that's not an insurmountable problem.


r/AskElectronics • • 21h ago

I damaged a flex while repairing a camera, how hard is flex repair without a micro soldering station ?

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70 Upvotes

I have access to a Fablab's electronic repair equipment but they don't have a micro soldering station, just a regular soldering iron . I'm not sure how fine are the available soldering tips ! is it feasible with a regular iron or do I really need a micro soldering station?


r/AskElectronics • • 17m ago

How do i connect mic wires (red and golden) to this mother board

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• Upvotes

Please help, I'm working on a project for 12 hours, its the last thing i cant solve, where do i put the mic wires?


r/AskElectronics • • 4h ago

How do I know which capacitor I'm dealing with in this obscure flash drive?

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2 Upvotes

This is an extremely obscure flash drive my librarian mom got at work, it has no indications whatsoever. The c8 cap is busted, reads 0,3 ohms, shows continuity to C6 from the top and C4 from the right but doesn't look shorted. How do I know what type of capacitor I should buy? As you can see there are no markings on any of the caps, my multimeter can't read Farrads, but if it helps, I can borrow one. I heard there are 3 types: 100 nF, 470 nF, and 1 uF but I have zero clue which caps are used in this particular flash drive. On the other side (on the memory card) two pins at the bottom are soldered into one slot (it's been manufactured like this), however to the left of those two I've accidentally shorted two pins (I'll fix it as soon as I replace the USB connector which is also busted). Could it be that the short I made is now shorting the cap on the other side? Seems hella unlikely but I'm not that good at repairing electronics. I'm fixing this one for fun. I guess the cap is simply busted and I need to replace it, so I need to know which cap I should buy. Thanks in advance!

EDIT: Since I have no idea what flash drive/manufacturer it is, I cannot find any schematics for it, which makes it impossible to even see which component should be connected to which underneath the first layer.


r/AskElectronics • • 52m ago

Utility of pull-down resistor in a reverse polarity protection ?

• Upvotes

I'm looking to implement a reverse polarity protection for a 9V DC powered circuit.

I'm seeing a lot of schematic using pmos with pull-down resistor and even some with schottky diode.

I'm wondering when is all of that usefull ? Couldn't i just connect the gate to ground and call it a day ?

I simulated it in spice and does seem to confirm that it doesn't change the circuit but i may be missing something.

Also any specific value should i look for when choosing my transistor ? (except Vgs)

Thanks


r/AskElectronics • • 1h ago

Safely Switch Voltages Between USB 5V and 18650 Battery

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• Upvotes

I am working on a light driver circuit which is powered from 2x18650 batteries.

I would like a circuit to safely switch to the usb-C circuit 5V when there is enough current advertised (Have this through an IC which checks the USB CC1 and CC2 lines).

I initially was planning on doing this via 2 Schottkey Diodes, but the reverse current was still getting through. I am after advice on switching this safely by a mosfet circuit arrangement or similar.

The bottom highlighted net is the voltage I need, the 18650s are connected via the right Schottkey, and the left Schottkey is currently the USB 5V.

I am seeking any advice :-)


r/AskElectronics • • 3h ago

Low side inductive switch not working on PCB

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1 Upvotes

Hello,

The BRAKE Signal is 3.3V from an ESP32-C5-WROOM-1(U)(GPIO5). The brakes are disengaged when active. The issue repeated itself on multiple boards and on different chips which make me think that there is something wrong with the board. The brake draws 24V 0.2A to disengage.

The issue is that they don't either disengage at all or don't disengage completely. VDS varies between 2V to 6V when INPUT = 3.3V. I am missing Rsupply and a decoupling capacitor at the input but i'm assuming that shouldn't cause this specific problem.

I'm left with guessing ESD damage but the chip should have sufficient protection. I'm posting this here incase anyone has any ideas or feedback. Supply pins are ~5V and input ~3.3V

Thanks


r/AskElectronics • • 20h ago

Are there situations where you would use LDO instead of buck converter even if LDO wastes more power?

19 Upvotes

For example on a board with CAN and I2C lines going out of it to communicate with other boards. If the board can take the excess heat is it worth it to use ldo to not deal with the EMI?

If people could give other examples where you may still use ldo instead of buck converter that would be helpful!

Thanks


r/AskElectronics • • 12h ago

PCB connector identification and how to buy more?

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3 Upvotes

Hi guys, I'm totally new to this. I want to find another 2 pin connector that is identical to the picture here so I can easily switch them out.

How do I tell what it is and where to buy one?

Thanks!


r/AskElectronics • • 1d ago

Would you consider this 2 chips burned up?

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21 Upvotes

There are some shorted caps around the second photo IC which is a SN74AHCT367 and everything seems fixable but I still have some thoughts on this supicious burn mark on the Atmel.


r/AskElectronics • • 17h ago

What’s the best way to connect to UART pads in the middle of a board?

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4 Upvotes

This is a BW4 battery/solar WiFi camera I’m planning to do some firmware modding to. I need access to the serial console to do so, but the UART pads are in the center of the board. (GND, RX, TX, BOOT) The chip on the board is an Ingenic T23N.

Is soldering the best option here? I am very green when it comes to soldering, so was hoping there was an easier way. I saw [Mini Grabber Test Clips](https://digilent.com/shop/mini-grabber-test-clips-with-leads/) suggested, but those look like they connect to standoffs (?) on the actual chip.

Also, there’s a GND, RX, TX pads on the other side right next to the WiFi chip. That’s most likely for that respective chip, and not the main chip, right?

Thanks!


r/AskElectronics • • 14h ago

Can someone help me find this LED COB?

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3 Upvotes

I have 2 fixtures with 4 each of these LED COBs. After a recent electrical storm they became discolored. I looked on Mouser and Digikey, but can’t seem to find the match. Any help would be appreciated.


r/AskElectronics • • 15h ago

Replacement option for sheared 1st Gen Kohler 1481020 Connector

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2 Upvotes

House I moved into had a Kohler Verdera medicine cabinet mirror with embedded lights (similar to https://www.kohler.ca/en/products/mirrors-and-medicine-cabinets/shop-mirrors-and-medicine-cabinets/verdera-lighted-medicine-cabinet-24-x-30-99007-tlc?skuId=99007-TLC-NA ). Unfortunately the connector wire going from power to the lights in the mirror was designed poorly with a straight female adapter. Over time the opening/closing of the cabinet led to stress on the female adapter and eventually the wires sheared (pic 1). We ordered a replacement from Kohler for the part (1481020), but it turns out they made a 2nd Gen that had come out 2 months after my model, and when they fixed the defect by making the connector a right angle, they also changed the size of the connector. The replacement (pic 3) doesn't fit.

Kohler's solution was to give me 20% off an entire new mirror, but I'm not paying $2K+ and replacing a mirror because of a broken wire.

Has anyone ever dealt with something like this? It doesn't seem like the 4-pin adapter they used is common. I was thinking of opening the existing connector and trying to solder the wires, but there was a possibility it would break while opening. Any other suggestions?

Edit: Forgot dimensions!

  • Outside thread diameter: 18.7mm
  • Inner thread diameter: 15mm
  • Connector diameter: 9.5mm
  • Distance between from center of one input to another: 5mm (best guess with the caliper I have)

r/AskElectronics • • 1d ago

What kind of capacitor is this? Never seen this type before.

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7 Upvotes

Saw one of these in an old scanner I have, never have seen a capacitor like this before, no luck on google either.

Scanner is a realistic patrolman PRO-10, manufactured around 1977-1980’s according to the chip markings.

The scanner is having problems with clarity, speaker sounds shot and I’m assuming some capacitors could be the issue.


r/AskElectronics • • 13h ago

Necesito ayuda para retirar estaño de los pads

0 Upvotes

Que tal gente, espero tengan un excelente dia.
Estoy trabajando con una Rog Strix G18, en especifico un componente llamado TAS2781 el cual se averio, lo retire sin problemas con mi estacion de aire caliente, el problema vino al querer limpiar el estaño viejo con malla de cobre y cautin, no logro extraer ese estaño y se me esta haciendo un cochinero, algun consejo?


r/AskElectronics • • 13h ago

Battery charger rectifier shorting

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0 Upvotes

My Energizer model CHFCV2E AA, AAA, 9V NiMH battery charger started crackling, randomly. took the bottom off and found this, 'round the full wave bridge rectifier. Do you think that glue strip became conductive? Maybe for a moment... Will clean it up & put under test again.


r/AskElectronics • • 14h ago

Shorted charging module. See text below.

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1 Upvotes

I’m (almost) completely new to all this but ‘long story short’: I bought a replacement charging module for a 9000mah 3.7v lithium battery and once it was soldered on it worked great. I picked it up while my phone was plugged in and charging from the battery and heard a faint pop followed by the smell of burning. Dead board 🙄

I assume I caused a short circuit but I have a couple of noob questions for curiosity’s sake:

  1. Neither of the terminals touched any part of the board (I was careful about that) but as I was holding both the board and battery with one hand is it likely or possible my hand/fingers caused the short? Is this something basic that happens enough that you know not to do it?

  2. Do you have any YouTube video recommendations for diagnosing exactly what popped? I assume one of those tiny capacitors but I know nothing. This is just for educational purposes and I’ll probably just buy another board from AliExpress as it was ridiculously cheap. I don’t see any obvious black marks from the pop and the battery is perfectly fine- I just tested it. I’d like to know what happened, that’s all.

Many thanks for any and all answers.


r/AskElectronics • • 18h ago

No question in title I need advice for an electronics-related gift (tools)

2 Upvotes

Hello tech nerds!

My (35) bf is very interested in doing himself the electronics in the house. He built our PCs and now wants to move on to repairing old phones, opening circuits and stuff (I don't know I'm a literary nerd, pls don't hate me).

As he's only starting, he doesn't have the adequate tools yet. So for Christmas I was thinking about giving him a repairing kit with all the basic tools required for this kind of stuff. But I know literally nothing about it.

Can you recommend brands and/or specific sets that would be nice?

Keep in mind that:

-he is a software engineer and is very curious and crafty, he knows already the basics of electronics (especially PCs and phones)

-i don't want necessarily all the tools needed in each specific situation, all basic tools would be nice as a start

-my budget is about 250 USD or 230 EURO max

I hope my post is OK, thank you in advance! 🙌🏻


r/AskElectronics • • 15h ago

Flashlight Replacement Button Compatibility

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1 Upvotes

Hey geeks, I have an ArmyTek Wizard C2 Pro warm whose on-off / mode selection button has been mangled. I think I have found a button that is a direct replacement due to dimension, construction, and connection styles being from what I can tell identical.

If this replacement button checks out I am going to order it and allow a electronics repair store to replace the button since I don't have the tooling required for this job.

Also do any of you have a resource for ~11.5mm tophat style button caps, I've lost the original to this flashlight.

Here's the replacement button make and model.

C&K PTS815 Sjk 250 Smtr Lfs (https://www.digikey.com/en/products/detail/c-k/PTS815SJK250SMTRLFS/9947849)


r/AskElectronics • • 15h ago

Request - Designing a Function-Key keyboard and pc not picking up inputs

1 Upvotes

So I had a custom board manufactured thats a split F-key keyboard. F1 through F6 on one half and F7 through F12 on the other. Both boards are identical except for the firmware which designates which key presses which. I'll attach a screenshot of the schematics for the board below:

https://imgur.com/a/aIbLTeN

So my issue, I soldered keys to the boards (the keys were the only things in the manufacturing process that weren't available to be soldered on by them), uploaded firmware, then the devices weren't recognized by Windows (Unknown USB Device (Device Descriptor Request Failed)). So I took one of the spares, changed the firmware and uploaded it. So that is recognized as a keyboard but is not recognizing key-presses. I try to upload edited firmware to the board I already flashed, and it can't find the board to do it.

I am just looking for help figuring out what I'm doing wrong. These are CH552 boards, here is the output from Arduino IDE when I uploaded the working firmware the first time here is what it outputted:

usbRertySeconds 2

target: CH552

config bytes: 3

Load file as hex

Loaded 5463 bytes between: 0000 to 15A2

ch375Version 35

CH375GetUsbID 0

DeviceVersion of CH55x: 2.50

MCU ID: 52 11

Found Device CH552

Bootloader: 2.5.0

ID: 13 45 62 BF

XOR Mask: 79 79 79 79 79 79 79 CB

Write 5539 bytes from bin file.

....

Upload complete

When I tired to re-upload firmware here's what I got:


usbRertySeconds 2

target: CH552

config bytes: 3

Load file as hex

Loaded 5463 bytes between: 0000 to 15A2

ch375Version 35

CH375GetUsbID 0

No CH55x USB Found, retry...

No CH55x USB Found, retry...

No CH55x USB Found, retry...

No CH55x USB Found, retry...

No CH55x USB Found, retry...

No CH55x USB Found, retry...

No CH55x USB Found, retry...

No CH55x USB Found, retry...

No CH55x USB Found, retry...

No CH55x USB Found, retry...

.......

No CH55x USB Found, retry...

Found no CH55x USB

Time limit reached, exit process

Failed uploading: uploading error: exit status 1

I've tried taking my multimeter in continuity mode and bridging multiple spots during the upload which is difficult with only 2 hands mind you and same error. If anyone can help me with this I would appreciate it. I want to get this fixed before I finish printing my enclosure to this becuase I'll have to solder around the case so that it'll look clean on top.

Here is my firmware for the first board (F1-6). The firmware for the second board is identical but for the other F keys. I used Board: CH552 Board, Port: COM3, Bootloader Pin: P3.6 (D+) Pull-Up, Clock Source: 16 MHz (internal), Upload Method: USB, USB Settings: USER CODE w/ 148B USB RAM:

* Pin map (confirmed from the uploaded Split_Keyboard.kicad_pcb netlist,
 * CH55xduino numbering = PortNumber*10 + PinNumber):
 *   Row 0      -> P3.2 -> pin 32
 *   Column 0 (SW1) -> P1.1 -> pin 11
 *   Column 1 (SW2) -> P1.6 -> pin 16
 *   Column 2 (SW3) -> P1.7 -> pin 17
 *   Column 3 (SW4) -> P3.1 -> pin 31
 *   Column 4 (SW5) -> P3.0 -> pin 30
 *   Column 5 (SW6) -> P3.4 -> pin 34


#include "src/userUsbHidKeyboard/USBHIDKeyboard.h"

#ifndef USER_USB_RAM
#error "This sketch needs USB RAM. Set Tools > USB Settings to USER CODE w/ 148B USB RAM."
#endif

const uint8_t ROW0_PIN = 32;
const uint8_t COL_PINS[6] = { 11, 16, 17, 31, 30, 34 };

// Column 0..5 -> SW1..SW6 -> this board's keycodes (left half: F1-F6)
const uint8_t KEYCODES[6] = { KEY_F1, KEY_F2, KEY_F3, KEY_F4, KEY_F5, KEY_F6 };

bool keyState[6] = { false, false, false, false, false, false };
bool keyStatePrev[6] = { false, false, false, false, false, false };
uint32_t lastChangeMs[6] = { 0, 0, 0, 0, 0, 0 };
const uint16_t DEBOUNCE_MS = 12;

bool readMatrixPin(uint8_t colPin) {
  pinMode(ROW0_PIN, OUTPUT);
  digitalWrite(ROW0_PIN, LOW);
  delayMicroseconds(3);
  pinMode(ROW0_PIN, INPUT);

  digitalWrite(colPin, HIGH);
  delayMicroseconds(8);
  bool pressed = (digitalRead(ROW0_PIN) == HIGH);
  digitalWrite(colPin, LOW);

  return pressed;
}

void setup() {
  USBInit();

  pinMode(ROW0_PIN, OUTPUT);
  digitalWrite(ROW0_PIN, LOW);

  for (uint8_t i = 0; i < 6; i++) {
    pinMode(COL_PINS[i], OUTPUT);
    digitalWrite(COL_PINS[i], LOW);
  }
}

void loop() {
  uint32_t now = millis();

  for (uint8_t i = 0; i < 6; i++) {
    bool raw = readMatrixPin(COL_PINS[i]);

    if (raw != keyStatePrev[i]) {
      lastChangeMs[i] = now;
      keyStatePrev[i] = raw;
    }

    if ((now - lastChangeMs[i]) >= DEBOUNCE_MS && keyState[i] != keyStatePrev[i]) {
      keyState[i] = keyStatePrev[i];
      if (keyState[i]) {
        Keyboard_press(KEYCODES[i]);
      } else {
        Keyboard_release(KEYCODES[i]);
      }
    }
  }

  delay(20);
}

r/AskElectronics • • 23h ago

I need to find a adapter for this bios chip

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4 Upvotes

Hello All,

Ok here's the scenario, I have a micro that is not posting. Powers on and after awhile get the 2, 1 code which is for the cpu. I do all the typical checks, reseat things, power drain, measure my resistances first then my voltages there. Everything is present. Before I go injecting though, I want to take the type and do my first flash. Even though everything is archaic, I wanted to try it out before telling my boss it's time to upgrade the programmer. But from the pictures you see, the IC chip I took from the micro doesn't fit the programmer (both of them) and none of the adapters. I was hoping someone can point me to the right adapter I would need to mount it to the programmer AND if possible I would need the 8 pin adapter as well, for the smaller, more typical bios chip.

Going to eventually get the T48, but for now I have to try to give this old guy a shot before upgrading. I still will need the adapters though. Anyone know what the adapters are called the 8 pin and 16 pin adapters, I would be most appreciative. TY!!!!


r/AskElectronics • • 1d ago

What types of resistors are these? One has little holes, both are strange colors

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27 Upvotes

Asking about the types, not the values (I know that much)

They look like half watt resistors based on size alone. I’m including one pic of them next to a typical half watt carbon comp for size and color reference.

I’m thinking the gray one is probably just a different colored carbon comp, it looks like one in every other way.

The darker colored one has four little holes on one end, that end is also slightly wider than the other. It feels like it is made of a harder material.

I’m mostly curious if these would work in a high heat environment (low-medium wattage tube amp)

These were among a bunch of resistors that I am told were from some kind of computer building or servicing shop.


r/AskElectronics • • 22h ago

Looking for original PROEL WAVE12A amplifier PCB photos (33000054 VER)

2 Upvotes

Hi everyone!

I'm looking for clear photos or the original schematic of the amplifier board used in the PROEL WAVE12A active speaker, specifically PCB 33000054 WAVE AMP VER.

I'm repairing one and need to verify which components were originally installed, particularly around R12, D5 and R31.

Does anyone own this exact speaker or have access to the same PCB revision?

Even a few close-up photos of the original board would be extremely helpful!

Thanks in advance!


r/AskElectronics • • 1d ago

[Request] [Help] ASUS ROG Zephyrus G14 (GA401QM rev 1.6) — TPS65994 / CAT24C512 EEPROM dump needed

3 Upvotes

​Hello everyone,

​I am currently working on repairing an ASUS ROG Zephyrus G14 (GA401QM rev 1.6) motherboard that suffered power-related damage.

​After restoring the main power rails, I am facing an issue with the USB-C Power Delivery subsystem. The TI TPS65994 PD controller and its companion CAT24C512 EEPROM seem to have corrupted configuration/firmware data (Type-C ports are not negotiating power or working in alt-mode).

​Does anyone happen to have a known-good working binary dump (.bin) for the CAT24C512 attached to the TPS65994 on this specific board revision?

​Hardware details:

​Laptop: ASUS ROG Zephyrus G14

​Model: GA401QM

​Board Rev: 1.6

​Target IC: CAT24C512 (SPI/I2C EEPROM for Type-C controller)

Number U4603 on board view ​Programmer available: CH341A / NeoProgrammer

​Any help, a raw dump from a donor board, or advice on configuring the TPS65994 via TI Application Customizer for this specific laptop model would be greatly appreciated!

​Thank you in advance.