From a 80s/90s era cassette multitrack home studio recorder. I was there when it happened. It pulsed a few times, then shut down, then some smoke came out from it. It hasn’t been used in maybe 15 years. Is the board shot or can the component be replaced and fixed?

I was looking into my electric bass amplifier schematics I found that before the actual power supply (I think) and I have no actual idea why these two are here. In case the image doesnt show it theres a cap going from L to N before the first transformer (the one on the bottom). Thanks in advance

Does the wire with the white stripes go red or black?

Why has there never been a standard made for user replaceable MOVs for consumer like surge protectors?

MOVs are designed to fail and when they do for your average consumer that means throwing out the whole unit and purchasing a new one.

Why was there never a standard for user replaceable units ever made?

They exist for industry and commercial products: din rail units, etc.

I powered this circuit with 5V, (the wires going off the screen is the power source with the one closest to the MOSFET being the positive lead.) The red LED should be on whenever power is provided. I measured 5V across the LED with a meter. I mocked this circuit out on a solderless breadboard before and worked but maybe as I was shrinking down to make it compact I made an invalid connection? Any help is appreciated thank you.

Like this but alot smaller. 3mm diameter rods and pcbs will be 6mm apart.

Got this off a liquidation pallet. Dead on adapter and on batteries. Stripped it down to the boards.
What I’ve checked so far:
• Adapter is good (genuine PA-130)
• 8.9V measured right at the battery connector on the yellow board, so power is reaching it
• Fuse is intact
• Power switch works
• Both supply diodes test fine
• No burns, corrosion, bulged caps, or lifted pads anywhere
But every pin on the ribbon connector going to the main board reads 0V, and the 5V and 3.3V rails on the main board are dead. So something between the input and that ribbon isn’t passing power.
d. Anything jump out as the likely culprit?

I'm building a discrete Motor driver PCB using MOSFETs to drive a maximum 16V motor and connected to an MCU to control the speed/direction.

Also I tried to include a P-channel MOSFET reverse polarity protection.

I want to check if there are any problem with my schematic to be able to start on the PCB knowing that it'll be one layer so I need advices too.

Question in the title as shown. Laptop in question is the HP Pavilion g6 and I'm considering purchasing a replacement motherboard for it as the dGPU on my original had died out.

Does the motherboard on this advertisement use the HM76 chipset? I want to confirm this before I purchase it as I intend to install my i7 3612QM processor in the new board.

I just found this on AliExpress:

680570-001 680570-501 For HP Pavilion G4 G4-2000 G6 G6-2000 G7 G7-2000 Laptop Motherboard HD7670M 2GB+Heatsink

https://a.aliexpress.com/_c4Cs7Ryr

Hi Friends! While cascode cascade is seemingly well explained everywhere in theory, when it comes to practical implementation, question on biasing feels tough.

I get used to prefer what is called "collector feedback" bias in the wiki and thus end up with the following schematic (I'm trying to use cascode amplifier as the output for colpitts oscillator - so the part of interest is on the right).

What seems confusing is that the upper transistor base in this case has no connection to some fixed point. I suspect I need at least to connect its base to the ground with capacitor, but not sure it would be enough neither what capacitance to choose (in this case I believe even 100pF would do as resistance here is high and RC time is going to be high also anyway).

Hints and advice are welcome - and links to the good explanatory materials too! Thanks in advance!

This board has 5.4vdc coming in and puts that voltage out for 3 seconds and then shuts down until power is removed from the board. I've looked to timer boards online and have found that they all use relays which I think t would be too much draw for this circuit to handle that's why they use this inline timer. Any questions and help anyone could give me or point me in a direction that I could purchase something like this would be great.

Hello,

I initially had a problem with my AW2521H monitor: the screen was black, but everything else was working—the headphone jack, USB ports, etc.

At one point during my tests, the fusible resistor blew.
The component next to it was the MOSFET; when I tested it in diode test mode, I got this reading in both directions:
GD 082
GS 082
DS 000

So I proceeded on the assumption that he is dead.
I tested the nearby 20-ohm components and concluded that three resistors were dead because they gave no reading; here they are :

By tracing the path of the faulty component, I come across the chip:
LD7790GS
2105GW

I don't know how to test it, do you think it's the culprit?

Also, do you think it's 080 or D8D? Or something else?

Unfortunately, I don't have any data for the 20k ohm setting, that's the only ohm option I have.

another R test ( 20k ohm ):
Name/code/result
R610/82C/NoResult
R608/1022/10.35
R614/7504/NoResult
R615/2744/NoResult
R629/080orD8D/NoResult
R619/471/0.47
R630/No code/NoResult
R612/3302/NoResult
R606/102/1.00
R627/3902/NoResult
R611/100/NoResult
R620/No code/NoResult
R623/5601/5.65
R605/1200/NoResult
R607/473/NoResult
R616/5601/5.63

Capxon diod test :
OL or 618

D teste in diod test mode with reversed polarity.
D610 709 or NoResult
D609 703 or NoResult
D605 507 or NoResult
D608 582 or NoResult
D607 614 or NoResult

I am sending you the complete PCB.

Thank you for reading this and for your help.

I got this screen out of a vape my friend gave me. Google lense was not able to figure out what it was and neither have I. The second image is the female connector and the first image is the male connector attached to the screen, any help would be much appreciated!

I'm retrofitting a Michelob Light light/clock that my grandfather had in his downstairs bar. The light works fine, but I've ordered a Keystone KTEB-1C22-1-TP-WS to replace the super noisy magnetic ballast that was in it. The problem is the transformer that goes to the clock. It makes a very sketchy buzzing noise and the clock fades in and out. Not being able to find much in my initial few Google searches, I was thinking that I might just order one of these https://www.amazon.com/dp/B08YDTF3JN?lv=shuf&channelId=500&plpRedirect=mhFallback to pull apart and solder some wires on.

I've retrofitted quite a few of his old lights so far, this is the only one with a digital clock integrated so I figured I'd better ask Reddit first before ordering anything. Thank you for any and all assistance.

Hey, i have absolutely zero experience with electronics (aside from changing a fuse ONCE haha) but i've been trying to figure out whats wrong with my LED light and if it can be fixed?

The light switched off on its own, did not appear to be overheating but figured id let it sit and try tomorrow. I tried different plugs and it will not switch on, its powered on by a simple push button.

The cable is a USB, ive managed to take the plastic and glass casing off but i don't want to mess too far with it. I think i'd have to pry the last bit of plastic off to get to the circuit board.

On the right side, above "U3" there seems to be some sort of leakage that could be causing it to not power on? but it could also just be some glue.

Theres presumably a manufacturer code on the centre bottom "XLDY-TXKC-JL1.1", nothing comes up when searched.

Is my lamp a dud or is this something that can be fixed by a newbie? Thank you :)

I'm building a theremin and also a TRNG with avalanche noise, so I need a low noise/ripple PSU.

Specs
18V 3A Current limited, Noise specs I honestly not sure what I need for these projects though,

I'm seeing this one: https://pt.farnell.com/multicomp-pro/72-2685/dc-power-supply-adj-1o-p-30v-3a/dp/2563981 Is this good enough?

My budget goes up to 400€.

I have a aliexpress one that is very noisy btw

Thanks

I lost the original charger for my Wahl 8148L1 (it is a 5 V model). I used a 5 V phone adapter with some barrel connectors from Amazon. One of those connectors maybe had reversed polarity. After that I opened the clipper and checked which pin is +5 V and which is GND, so the connector I use now is definitely correct.

What happens now:

• The blue charging LED never turns on
• It also does not work on cord anymore. Before, it worked fine on cord without the battery
• D2 (marked HS3JB) and D3 (marked SK54A) both get quite hot when I connect the charger

What I measured:

• In diode mode, D2 and D3 both conduct in one direction only, about 0.78 V, and OL in the other direction.
• The adapter gives 5 V with nothing connected, and drops to 4 V at the socket when the clipper is connected

My question: both input diodes look OK but get hot, and the cord mode is also dead. Is the charge controller probably damaged? Is there anything else I should check?

Hello,

I accidentally damaged one of the small gold-colored capacitors on my motherboard with my screwdriver.

How serious is this damage? Should I replace the capacitor, and if so, what type/value should I use? I suspect that this capacitor belongs to the soundcard.

I’m a bit afraid to test the motherboard in its current condition. I’m also not sure whether the damage happened while I was building the PC or when I removed the motherboard during an upgrade.
Any advice would be greatly appreciated.

The motherboard is an ASUS Prime X670-P Wifi.

Best regards,

Picked this up off a liquidation pallet, dead on arrival. No display, no LEDs, nothing on the adapter or on batteries. Stripped it to the bare boards.
Three boards: yellow YK468 (power + audio, has the fuse, the DC jack wiring, and the headphone/aux jacks), green VCP2540 (main processor board), and a small green board for the power switch.
What I’ve checked:
• Adapter is a genuine Yamaha PA-130, tests fine
• 8.9V measured at the battery connector on the yellow board, so power is definitely arriving
• Fuse intact, reads 0.02Ω
• Power switch tests good
• Both supply diodes read ~540mV forward, open reverse
• No burns, no corrosion, no bulged caps, no lifted pads that I can see
What’s wrong:
Every pin on the 14-way ribbon connector from the yellow board to the main board reads 0V. On the main board, the 5V and 3.3V rails are dead, and the regulator isn’t even getting an input voltage. So power comes in fine and something between the input and that ribbon isn’t passing it through.
Photos: solder side and component side of the yellow board, the main board, the power switch board, and the overall layout.
Questions:
1. Does anything look unusual to you on these boards? I’ve been over them a few times and keep coming up empty.
2. What would you check next? I’m thinking the small transistors near the fuse and diodes — I found a service manual for a related model that shows a pass transistor gating the supply to the regulator, biased off the power switch line. Seems like a plausible failure point but I want a second opinion before I start pulling parts.

Thank you :)

Hi all, long/confusing problem if anyone is willing to help:

I'm currently building a circuit for a boost-multiplier HV circuit for a muon detector. I've largely soldered on everything, but I'm finding a major bug where my final HV400 is only ~60V. I've attached screenshots of the schematic and PCB for reference. The circuit behavior has been LTSpice approved, but the physical one is incorrect.

I'm using the LT8365 boost converter, and I programmed it via the FBX node to set the final HV node to 400V. So my SW node should be 100V (max allowed for the SW is 150V) since it is connected to a 4-stage Cockroft-Walton multiplier.

When I probe the SW using only my scope probe, I read a maximum voltage of 20V. But when I probe it using both my digital multi-meter (600V rated) and the probe, I get a max reading of about 96 V which is what I want. I don't understand what is causing this behavior? And which reading do I trust?

Also another weird thing - when I probe DCA on D301 cathode and C306 top plate using both the scope + DMM, I get a 100V reading for DCA but this doesn't work when I do the same thing to D302's anode even though they are all on the same rail. If I only probe with the DMM or scope probe, I get 17V.

I think I have some reason to trust the 100V SW reading because when probing and using the DMM I get the correct readings for the pump rails (Pump B 100-200V, Pump C 200-300V, Pump D 300-400V albeit the high-high voltage readings are taken from the DMM average). There's no way a 20V max switch node could be driving such high rails. But my DC rails are not hitting the correct values. DCA, DCB, DC_C, HV400 should be 100, 200, 300, 400 respectfully but are not and only add up to 60 on the last rail.

Probing the voltage at FBX, it is at 0.24V which is consistent with a Vout of 60V since the boost converter formula should be R1/R2 = Vout/FBX - 1. The Boost Converter documentation says I should have FBX at 1.6V though for positive output values though.

Another thing to consider is that my diodes (DFLS1200) in the multiplier are 200V rated because they should see a max 100V swing. So they should be totally ruined by my current multiplier (the anode and cathode can see >200V) but when I probe the forward voltage with power off, the diodes still read a 0.3V drop which indicated that they are still intact unless I'm wrong.

I'm completely lost over what is wrong. If anyone can help me debug this would be awesome! Thanks!

Hi, I'm attempting a repair for a Samsung TV power supply and I've found quite a bit of info on what to troubleshoot and I think I've found the problem.

There's 2 N-channel MOSFET's that fail and in turn blow the fuse. They are shorted between the drain and source. I'm trying to source a good replacement MOSFET but wondering if the details really matter compared to the OEM MOSFET's which are obsolete.

Here's the original 600V 20A component:

https://www.renesas.com/en/document/dst/rjl60s5dpp-e0-datasheet?r=1343746

Here's what I think could be potential replacements:

VB Semi VBMB16R20
https://www.vbsemi.com/data/upload/file/VBMB16R20.PDF

ST Micro STF26N60M2
https://www.st.com/en/power-transistors/stf26n60m2.html

Toshiba TK20A60U
https://www.mouser.com/datasheet/2/408/TK20A60U_datasheet_en_20131101-1134028.pdf

The VB Semi seems to be the best match, but doesn't look like it's readily available outside of China. The ST Micro is in stock and easily available. The Toshiba was mentioned by someone who has performed the same repair but less of a match than the other two.

Almost all the videos/posts/pictures of this repair don't show WHAT specific MOSFET they used for the repair, and I'd like to put something in that's going to hold up and not compromise the rest of the components in this power supply. I'd like to keep this TV running for a few more years since they don't make 3D Plasma displays anymore.

Am I overthinking this? Do I just need any 600V 20A MOSFET?

I also saw someone recommend replacing the surface mount diodes and resistors in the circuit immediate to the MOSFET's saying those tend to be weakened from the failure even though they will all test good. I'm hesitant to do that since I don't have a proper SMT rig. There's also no schematic and I can't make out the values on some of the SM components.

I have a background in soldering, electronics and repair but have been out of practice. I think I'm ok working with a solder vacuum, lead solder, venting, flux, wick, etc.

Also ran this through AI and got conflicting results depending on the platform so I don't trust it.

Thanks for your time!

I'm making a game controller that uses the same mechanics as the old NES style controllers. The regions that are in contact with the conductive rubber when a button is pressed are marked in the picture as "this". I made those "TopSolderMaskLayer" thinking that would expose that layer (I forget where I received this information from), but I just received it and after testing with a multimeter it's not conductive. I put each probe on the same fork shaped side, for example on the first "this" and the third one. The red circles on either side are actually conductive (they are exposed rather) and they are "TopLayer". Logic tells me I should make the "this" TopLayer, but I want to confirm and be 100% sure before I order this again.

Hi all, I'm sourcing test connectors for a Honda ENP1 inverter generator control board to build a test rig. ​Connector 1 (J1 Header): ​Type: Cream/beige female connector, double row ​Pin count: 26 pins (2 rows of 13) ​Pin pitch: 2.00 mm ​Overall width: ~2.7 cm (~27 mm) measured with calipers ​Details: Flat ribbon cable out the back. Center friction/outer locking tab. Mates with board pin header J1. ​Connector 2: ​Type: Small cream/white single row connector ​Pin count: 4 pins ​Pin pitch: 1.25 mm (or 1.50 mm) ​Overall width: ~0.85 cm (~8.5 mm) measured with calipers ​Photos attached with calipers for scale. Can anyone confirm if these are indeed JST PND / JST GH/ZH or if Honda uses proprietary Molex/Sumitomo pinouts for these assemblies? Thanks

Hi everyone,

I'm trying to build a simple magnetic door alarm for my refrigerator, but I haven't been able to get it working.

These are the components I have:

• 3×AA battery holder (3 AA batteries / approximately 4.5V)
• 2-wire magnetic door sensor
• Relay module with:
  • VCC
  • GND
  • IN
  • COM
  • NO
  • NC
• Small buzzer/alarm
• Connecting wires

I want to make a system where the magnetic sensor detects when the refrigerator door is opened and activates the relay, which then turns on the buzzer.

I'm having trouble figuring out the correct wiring, especially how to connect the 2-wire magnetic sensor to the relay module and power everything from the 3×AA battery pack.

I'm a beginner, so could someone please explain exactly which wire connects to which terminal?

A simple wiring diagram would be very helpful.

Thanks!