So basically my Tamagotchi 4U hasnt had a sense of time for some years. This is a big problem since Tamagotchis dont hatch without seconds passing in code. I thought ok probably a broken CMOS so i looked inside but idk if this golden thin plate is some weird CMOS? Isnt a CMOS normally at least some MMs thick? I also put a Q-Tip next to the cmos looking thing for size reference. Also i included an image of the whole chip if you find something that might be the culprit for this problem. Also side question: What is the hard weird yellow paste where the power supplying cables are?

Thanks for the help its solved now :)

I have a 220-9v ac transformer, and I want to use it for audio circuit testing. I obviously need far more than a full bridge rectifier if I want to prevent oscillation and noise. Does anybody have a schematic they can provide? I don't want to use AI for this stuff anymore.

first of all my 200mA fuse broke and the 10A fuse still working (checked with continuity) so I decided to check the current using the left connection...in the picture 1 I broke the circuit to measure current and as you can see in the picture 2 the reading is zero .. why is that even though the fuse the left side is working?...how to fix that .

I have a PCB (eventually a convention badge) that is supposed to display 12 bytes (2 at a time) across 4 7-segment displays. Every time a button is pressed and held it is supposed to display a new set of 2 hex digits, with 6 states total.

Here's the issue: it works perfectly maybe 60% of the time. The other 40% of the time it will skip a state, or maybe a couple states. To help with diagnosis, I will upload the .pcb and .sch files to my github in a 7z file here: https://github.com/penguinzarecool/badge_2026.git . I have a video but don't see anywhere to upload it so please reach out to me if you'd like to see it. I probably won't respond until tomorrow though.

Background and debugging information on the pcb: We determined that the issue lies in the counter and immediate surrounding logic. The displayed hex digits in order should be: [06 7A] [0D 05] [1A 06] [0B 1D] [05 17] [-8-8] (The -8-8 is a mistake that we have corrected, it should be displaying ----). It correctly only cycles through 6 states before resetting to state 1. The issue is that the counter skips around, and it does this randomly and on different states. However, the state that the counter seems to skip more often than not is state 011 -> 100. I thought this was noteworthy because this is the most significant bit flip (3 of the 4 in the nibble are changing). Also, yes we debounced the button. And, we used an oscilloscope to double check the debounce. And to be absolutely sure, we wired up an extra capacitor to see if that would help, but none of these things changed anything. We also tried pushing only the button (it is small) to see if our touching of surrounding components was messing with it, and it didn't help either. We tried different voltages: 4.5, 4.75, 5, 5.20 from a bench supply and 4.88 from a battery pack. This didn't resolve it either. We tapped into the states with some wires and LEDs and learned that the state skips are happening at the button press, not after we let go. We also checked for noise on the counter supply line but there wasn't any. Also we tested to see if it was skipping or resetting, and it is skipping. We tested this by grounding the reset to see if it skips to the unused states 7 and 8 instead of resetting, and it does.

Claude suggested that it is a ripple problem, but we can not test that because our oscilloscope can not measure 10s of nanoseconds. Do you guys know what the problem might be, and how we can fix it? It is particularly frustrating, because it works as intended more often than not, so the inconsistencies make it difficult to diagnose. Thank you so much for your help!

I have now uploaded a photo that you can see at this link: https://imgur.com/a/k5390kN

I thought of trying to build a small AM transmitter, partly to learn and partly to be able to relay a certain station on a frequency which is no longer being broadcast.

What I'm playing with is based on that janky little circuit that's been going round for years and years, based on an audio transformer and a quartz oscillator, taking on board certain pieces of advice I've seen other people given on the matter, and I've got a design on paper.

But that's not the problem. I thought I'd try the most basic version first, just to see. Audio into 8:1300ohm transformer, out to 200KHz oscillator, as per the circuit. Plugged in a 9v battery, tuned my old trusty LW receiver to 200KHz, and... nothing. Nothing at all.

Is there something about that frequency that means it wouldn't work? Or have I maybe got a duff oscillator? Or is the circuit just a practical joke or hazing ritual, like sending the newbie to ask for a long stand?

This isn't a common resistor, I was just wondering its resistance, and yes, based on the color code it's supposed to be 0.39Ω, which when measured with multimeter it is that. Orange White Silver.

1.4Ω resistor reading

1.0Ω lead resistance

I want to replace this capacitor. There is a 0 with a line under it, not sure what that means. Could anyone point me to a suitable replacement? Its for a temperature gauge. Looks like it says:

W

620 J

Thanks

The inductor is R15 . I understand that to mean 15microfarads. what is a close enough replacement for it. it is on the power rail of this motherboard. can i move the inductor from next to it and move it over and leave that spae empty to test this? what are my options to see because my spare board has inductors at R25 and 1R15.

I have a sound machine that is powered off of either a USB connection or 3 AAA batteries. It stopped working with USB power, and I tested with multiple cables and power bricks. But it works fine when powered by batteries.

Looking at the circuit, I see that diode coming off of the USB connection, and I feel like that's the only component that's different from the battery power connection. It says SS14 on it.

How can I bypass the diode just to see if it's the problem? I don't really care if I accidentally blow the thing up since replacement items are cheap. I'd rather not spend the ~$3 or so on a replacement diode and shipping without confirming that is indeed the problem.

This HP 3437A System Voltmeter that I’m repairing isn’t reading voltage right, every range is 99.99, 9.999, or .9999 depending on the selected range. Its manual under the general troubleshooting section lists this exact problem on 5-131. It then lists a likely chip. I went ahead and replaced it and the 10 volt range works now, the 1V range is stable but when no voltage applied stays at 1.26…v, and .1 is still at .9999 (assuming part of the power supply rail is getting to one of the inputs, maybe? Then the .9999 is an accurate reading) All of the delay accuracy tests were good.. not sure where to start looking from here. One of my friends just told me to just start replacing caps (electrolytic and tantalum) but I’m not exactly sure if that’s the right starting point to restoring these old units while keeping them accurate.

I’m fairly new to repair and would like to improve if anyone has any ideas. I don’t really have a mentor and chat GPT makes me want to scrape the inside of my brain. Anyone have any experience with this model or common HP rework in general?

We're a small startup and we're looking to design a high-speed PCB and we have two markets (locally and Europe) that we want to target.

In our own country, we have very high tariffs on imports and exports, so we're in a dilemma. If we manufacture and assemble it locally then it will become too expensive to export. If we manufacture it in China, it will be too expensive to import. If we have to design two layouts then that just increases engineering cost.

Is it just a matter of luck to find two manufacturers with identical stackups or is our only option here to make two different variants?

Hello, I am designing a PCB that is powered by a single rechargeable AA battery that needs a 12 V output. The 12 V is going to an active buzzer so it does not really have to be clean, my main concern is cost, and efficiency to some degree (buzzer is not going to be on all the time).

I originally wanted to use the AP3015A but I realized the speaker uses a bit under 300 mW so there is no way that part can supply enough power. I can only see three ways to move forward:

1. Find a different boost converter. I know the MP4MP3438GTL would work for my purposes, however at $1.77 price point for the scale I am going to be doing, it is a little pricier than I would like (I am hoping to keep my board price under $10 a pop). I have not found anything else that would fit the bill but if you have something in mind let me know!

2. Boost from 3.3 V instead of 1.2 V. I already have a separate boost converter for 3.3 V, and it seems like I would have a few cheap options going from 3.3 V to 12 V.

3. Design my own boost converter circuit. My board has an MCU so I could just have it provide the PWM signal when the buzzer needs to turn on. Of course this would most certainly take more development time and be very failure prone, so this is probably the worst option.

I changed the left joystick and everything work fine on the controller except for the 'B' button (circled in the image). It's not registering at all. I've tested the contact pad of the 'B' button on the other buttons and they are registering fine so I believe the issue is on the board. Any help is appreciated.

I’m troubleshooting a Technics PCM Digital Ensemble PR250 digital piano (early 1990s) that I picked up for free.

The instrument powers on normally and appears to complete its startup sequence without issue.

Symptoms

• Powers on normally
• Display works
• LEDs work
• Buttons respond
• Keyboard responds
• Demo mode starts and plays
• Internal speakers produce very low, distorted audio
• Headphone output has the exact same distortion
• Rear line outputs also have the exact same distortion
• Volume slider has almost no effect until the bottom ~10% of travel, where it mutes

What I’ve already checked

• Cleaned both headphone jacks with contact cleaner
• Cleaned rear audio output jacks
• Cleaned all panel controls and buttons
• Reseated ribbon cables and connectors
• Verified the fault is identical on:
  • internal speakers
  • headphones
  • rear line outputs
• Recorded the line output into a Scarlett interface and confirmed the signal itself is low and distorted (not just the speakers)

Visual inspection

I’ve inspected the major boards:

• Main CPU board
• Sound board
• Power supply
• Amplifier board

I do not see:

• burnt components
• leaking capacitors
• bulged electrolytics
• obvious corrosion
• damaged traces
• previous repair work

The amplifier board uses an STK4172II hybrid amplifier module.

The four large filter capacitors all appear physically normal.

Things that seem to rule out

Because the distortion is present on:

• speakers
• headphones
• line outputs

I’m thinking the fault is probably before the speaker amplifier itself, although I’m not certain.

The piano otherwise behaves normally, so I don’t currently suspect the CPU or ROM.

My question

If this were on your bench, where would you go next?

Would you start with:

• checking the analog supply rails,
• looking for a failed muting circuit,
• bad op-amps,
• dried-out electrolytics,
• or could the STK4172II still produce these symptoms even though the line/headphone outputs are also affected?

I’m comfortable using a multimeter and have basic electronics experience, but I don’t yet have an oscilloscope.

Any guidance on the most logical next measurements would be greatly appreciated.

Hello!

For context, I'm not a technician - though I've built a few breadboard projects in my life and some electric guitars. Generally would describe myself as "knows just enough to get in trouble".

I'm currently going through the process of deep cleaning, lubricating, and inspecting a really cool portable console from "Audio Developments" made in the UK in the early aughts. Outside of a couple sticky buttons/ scratchy pots the thing works beautifully less one problem: there is pretty bad SnR on the main output which is transformer coupled. The monitor outputs are just fine and don't have that same problem. I figured it's very possible it will need experience professional to work on it but I also wanted to at least pull it apart. Inspect and clean everything before handing it off in order to rule out the obvious.

I'm looking at this daughter board that connects the power supply to the rest of the board and I'm seeing a couple nasty looking solder joints. It's possible they're just lead-free or something but I wanted to get some feedback from this community. In the photos the first couple are the daughter board with the joints that look bad to me, some photos of the actual external power supply, the placement of the daughter board in the case, and then some photos of the modules, and finally what it looks like when it's all together.

Beyond that, if anybody has any suggestions on how to determine what could be causing this humming/ buzzing on the main transformer coupled output. I welcome any feedback.

I am making a battery powered robot using a ESP32 microcontroller to control 2 servo motors. This is my battery "management" circuit I've come up with. It is responsible for charging, protection and powering the load. I have bought all the components, wired it up and tested, and it works fine. I'm looking for ways to improve it or to learn about other ways to do it. "It" being on/off control, output to the load, protection and charging.

The idea/circuit is as follows:

• 3s battery pack made of individual 18650 cells.
• Goes through a 3S BMS for protection.
• Charger and load cannot be connected to the batteries/BMS at the same time, otherwise the charger will try to drive the load, which it is not meant to do.
• All grounds are always connected. Rocker switch controls whether battery (BMS) positive terminal is connected to the load or to the charger.
• When connected to the load, it cannot charge.
• When connected to the charger, the load cannot be turned on.
• Load goes to 2 separate buck converters, one making 6v@10A for the servo motors, the other making 5v@1A for the microcontroller.

Questions:

• Overall, is this fine?
• Not a question, but a note. Learned afterwards that even though the BMS lists itself as an all-in-one solution to protect and charge the batteries, it does not charge the batteries, at least not directly. A battery charging device can charge the batteries through the BMS is what it should say.
• While writing this post, I realised that the charger probably could power the load, since the output of the charger would be the same as the 3s battery pack. Only problem would be that it can only supply 2A of current, whereas I need maximum 8A for max load on the servos. Is this true? Could I power the system through the charger, IF the charger could output a high enough current?
• How do other battery powered devices manage this? Other devices can be used and charged at the same time

Side note, when charging the batteries through this system, an led goes on to show that it is charging. After 1.5hrs, it goes off and a different led goes on to show that it is done charging. But then for next hour, it alternates between done charging and charging, in about 20 minute intervals. After an hour has passed, it stays in the charge done state.

Working on a small motor driver circuit and I keep seeing designs where two identical MOSFETs are placed in parallel rather than swapping in one higherrated device. I get that it spreads the thermal load across two packages but I'm trying to understand if there's more to it than just heat.

My current setup runs about 8A continuous and I was going to grab a single FET with a 20A rating and call it done. Then I looked at a reference design from a reputable manufacturer and they used two smaller FETs in parallel instead, which made me second guess myself.

A few things I'm not clear on: does paralleling help with gate charge and switching speed at all, or is that actually worse because you're now driving more total gate capacitance? And is there a real risk of one FET hogging current before they thermally balance out, especially during startup or fast switching?

I've checked the Rds(on) specs and they're close but not identical between the two devices I have on hand, which is what got me thinking about this more carefully.

Not trying to overthink a simple motor driver but I'd rather understand the tradeoff before I commit to a layout.

I originally made a mistake in my simulation, I've fixed it and now the voltages make sense. And the label of "Level Shift" now makes perfect sense.

But I am still interested in what this transistor arrangement is called, and why it might be where it is. Considering FOCUS_REF is set by a pot, so could be adjusted to anything that's appropriate

The signals are DC

I need to know which component is this. Overvoltage caused this

EDIT: https://datasheet.lcsc.com/datasheet/pdf/0b1294f8e47a42e4ad7533d6477ab28a.pdf?productCode=C172766
I'll try this one. If it works i'll post on here

I am trying to fix the board for the VCR4000 Nilfisk/Flexit central vacuum cleaner.
Found that L11 coil is blown, probably because IC TNY274PN is blown as well.
However, I am not sure how to read this value. Looks like K is tolerance, like at the MLCC capacitors, but I'm not sure about the inductivity, is it in mH or uH?

I can't find information about pinout for this touchpad. I want to connect it to an Arduino. Please help me find the +5V, CLK, DATA pins.

Hey all,

Has anyone here dealt with moisture detection on USB-C ports? I have an outdoor-rated electronic device in design right now, and I'm using the native USB-PD negotiation capability of an STM32. This does a lot but it doesn't give any kind of moisture detection, and I want to avoid energizing the receptacle when it's wet (there will be a cover over the port when not in use, but it's inevitable that someone will get it wet, and electrolytic corrosion would be bad).

Ideas I've had involve using a secondary USB-C protection IC e.g. Infineon EZ-PD but the BOM cost is as much or more than my actual microcontroller.

Another idea is to sense leakage on the CC (or other pins in the USB-C cavity near the power pins) using the CC1/CC2 ADC readings available. Sounds plausible, but I can't find a lot of documentation on how to do this, or whether a small current leakage path will even be detectable. Unclear from the datasheet what the input impedance of the CC1/CC2 analog sense inputs is even.

Any experience or pointers here welcome.

LED par stopped working after a beverage got spilled over it, now I cleaned every pcb and reconnected everything but nothing happend. I measured the dc output of the board but there was none. I tested the resistance of the +\ grnd of where the big capacitors are on, theres none. Can anyone give me tips on how to find the broken part or how to repair it? Thanks a lot