r/AskElectronics

Edit: Thanks for the help, it's working now

I bought this USB pd module from AliExpress. The first thing I noticed is that the module I received isn't exactly the same as the one in the image. According to the description, the output voltage can be selected by bridging the pads next to the voltage label. I have tried 2 usb c chargers that both support 20v output, but I cannot get it to output 20v. It currently outputs 12v. Has anyone had this problem before, or is this just a bad board?

tried making a direction controller by myself can someone pls tell me why the voltage across load is so low?

CAD model on Digikey shows a notch on the chip, datasheet shows a dot. What arrived has neither and I have looked under it as well, I don't see how I can physically determine pin 1. I hope someone can point out the obvious and help. Can I determine it using a multimeter?

Digikey: https://www.digikey.com/en/products/detail/stmicroelectronics/VNLD5090TR-E/4552573

This is an aquarium light that stopped functioning properly and I wanted to fix it rather than buy a new one. I really dislike putting things in landfills.

I purchased a pretty basic multimeter from harbor freight, but I already own a pretty decent soldering station. I just don't know where to start. Any help would be appreciated.

Hi,

Could someone sanity-check this small high-side switch block?

I’m using an ESP32 GPIO (12V_EN, 3.3 V logic) to switch an OLED supply rail. The input rail is currently named +12V, and the switched output is 12V_OLED.

The net names still say 12 V, but the final rail may be higher, possibly up to around 15 V. Because of that, I added the resistor divider on the P-MOS gate instead of pulling it directly to ground, to keep Vgs within a safe range.

The intended behavior is:

• 12V_EN low → OLED supply off
• 12V_EN high → OLED supply on

Could you check whether this topology is correct, especially the P-MOS source/drain orientation and the gate divider?

Schematic attached.

Hi,
I’m currently studying some designs and my tutor asked me this question : « should switches be put before or after resistors ? ».
I do have an idea that it has to do with MOS parasitic caps (my case uses a NMOS/PMOS switch) but I don’t know where to start to prove it.

I’m not necessarily looking to have the solution totally given to me but if I could have some help to start on how to prove which one is better (for gain, BW, phase margin, noise …), I’d be very happy.

Thanks !

TLDR: there's an intermittent issue where there's no effected signal, but if I turn it on/off a couple times and/or probe the Reticon output, then it functions totally fine. When it is in it's non-functioning state, if I probe the Reticon input I have signal, but when I probe the output I get static. I'm wondering if this is what happens when a BBD chip starts going bad, or if it just means that some other component connected to the BBD chip has an intermittent problem? And if the Reticon chip is okay, but something else around it is bad, do I risk damaging it by continuing to use/test it with power connected

More info:

I got this in a non-functioning state, converted from AC to DC, and then I'd get a couple seconds of effect before I'd get a "windy/staticy" noise (more like brown noise than white noise) and then the effect would cut out and I'd just have a clean signal. Bypass signal is always okay.

I tested voltages on the Reticon 5105, clock chip, and other op amps/transistors, and everything seems reasonable, except I had a lowish voltage on the Reticon output. I was thinking maybe it was a bias thing, so I tried adjusting the trims, which were all seized up, but I eventually, carefully, I got them unstuck. Moving the Reticon bias trim back and forth some brough the voltage up on the Reticon output, but where the trim was set initially seemed right judging by ear. Could whatever build up that was making the trims stick also have been making the bias connection faulty? Should I hit all those trims with some deoxit or something?

When it is working properly I get modulated signal on the output and can trace that modulated signal through the rest of the circuit with my probe.

Also weird and worth mentioning: it seems to work more reliably when I'm testing it with a sine wave and probe than when I actually have it connected to a guitar and amp. I assume it's just a coincidence, but could there be something about differences in voltages/impedances that's "jump starting" it or killing it?

Thanks!

It's a terminal block that I want to use as a bus bar for common GND. I won't be using much current, only up to 9A.

I’m aiming to remove the limiter circuit as it’s apparently a bit hyper active and impacts the performance of the HS8 monitors. A pretty common mod. I can’t find any info on the latest board revisions though!

Have included photos of everything I think is related and the other board just in case. And the latest service manual that shows the limiter circuit with all the wrong labels (R417 etc. )

Image 1: is the first thing that went out. Just a blank. Do I use a multimeter on the other one to measure it? But I also don’t know the name of it.

Image 2/3: Barely noticeable but it’s a SMD 4380 resistor that I can only find on alibaba and surprisingly not eBay. Is this for sure before I buy?

Also what kind of battery should I use to test this once it isn’t fixed? I used my drill battery and it was fine when I first got my tail lights but fast forward a year I did it again and blue the first one.
I desoldered it and put it back on just to keep testing the wires cause I forgot what did what and I need up blowing the 4380s the go on the LED strips.

Please I would really love some help with this. I’m not super into electronics like this. You can say I’m like one of the “mechanics” who doesn’t know how to diagnose a car and just knows how to sketch out parts. The most I do is solder wire or first project was replace my joysticks on a controller.

Hey, was cleaning my robot vacuum and pulled one connector off. Ordered a new robot but since i recently got a soldering kit to add back paddles to my ps5 controllers figured I should give it a try and if I even manage to get it back working, oh that would feel awesome!

7 pin connector came off the board and 5 pads are left, but two came off the board. Could someone please walk me through on fixing those two pulled pads, where to solder them to? 5 should be easy desolder and solder pins back to pads, but I'm not too sure about missing pads, watched some videos on repairing pads but this is my second solder project so my hopes are not high as not really savvy on this yet but would like to try this if someone could please give clear directions for me on where exactly to connect them to here.

If i understand correctly the first pin needs to be reconnected to the left and top and the 6th pin to the top there?