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momaka
momaka
master hoarder
Last Activity: 11-05-2024, 07:22 AM
Joined: 05-04-2008
Location: VA (NoVA)
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  • momaka
    replied to 220v Led strip flickering
    in Troubleshooting Appliances and other Household Electronic Stuff
    Not really.
    The line is at relatively low frequency, so you would need a HUGE inductor (a few Henry's worth) to see any noticeable results. And moreover, that can cause some tricky stuff during high transients (sparking, inductive kickback, and etc.)

    Your idea does give me an idea, though.

    Take the abovementioned PWM circuit and add an inductor (with a free-wheeling diode) in series with the LED strip, and now you'll have yourself an actual buck regulator circuit that would be acting like a current driver circuit (sort of.) With this, the PWM should give...
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  • momaka
    replied to 220v Led strip flickering
    in Troubleshooting Appliances and other Household Electronic Stuff
    Going off of the idea with the rectified and smoothed (with large cap) mains... perhaps make a PWM driver circuit for the LED strip that's fed from the high voltage DC?

    In other words, you'll have: 230V AC mains --> rectifier + voltage smoothing (so about 340V DC) --> PWM driver (555 timer based?? or similar) + HV MOSFET switch --> LEDs

    So long as the LEDs are driven a little lower than what you'd get if they were directly connected to the rectified DC rail (i.e. around 230V DC on average), I imagine that should smooth things out. My guess would be that at 60-70%...
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    Last edited by momaka; 11-05-2024, 07:09 AM.

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  • momaka
    replied to Identifiing mosfet component - Replace with?
    in General Electronics Technical Discussion
    Just about any manufacturer that makes *13003 NPN BJTs should do. 13003, 13005, 13007, 13009 are all standard parts, so shouldn't matter which manufacturer you get it from.
    Whatever you do, just avoid the cheap China knock-offs on China mall stores on Amazon, AliExpress, eBay, and etc.
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  • momaka
    replied to Finding the wrong part at a loooong led strip, part works fine, part flickers, all parallel...
    in General Electronics Technical Discussion
    12V LED strips are typically made of small sections (about 5 cm long), wired with 3 series LEDs followed by a 120 Ohm resistor (in series) to limit the current. Thus, if an LED goes bad (open-circuit or intermittent die connection), you won't loose an entire meter-long section. You would just loose the 3 LEDs that make up the small 5 cm section and the rest would be working fine.

    So I concur with STJ - you probably have a wiring issue somewhere to the section that is flickering. Try using a multimeter to check the voltage in the flickering section... though I suspect you'll likely...
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  • momaka
    replied to EVGA NEX650G power supply detecting a fault on startup.
    in Troubleshooting Power Supplies and Power Supply Design
    Maybe there's a large AC current across it? Tried measuring the AC voltage? Probably going to be a bit tricky too with just a regular multimeter, as any high frequency may not be measured correctly, depending on the meter.
    Me thinks this needs to be looked over with an oscilloscope (if you have one.)
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  • momaka
    replied to Samsung Syncmaster 740BF repair
    in Troubleshooting Computer Displays
    There are 2 very important power rails on the T-con board used for driving the transistors in the TFT screen to change the opacity: V_GH and V_GL. When you disconnect the T-con board, these two rails become "missing". As such, most LCD screens assume a state where the TFT matrix is left mostly transparent... hence getting a white-gray-ish screen when the backlight turns on. This allows more easily to see if the backlights are turning On or not or whether a CCFL has any issues (pink or orange-tinted light coming from the affected CCFL.)...
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  • momaka
    replied to Samsung Syncmaster 740BF repair
    in Troubleshooting Computer Displays
    OK, sounds like the backlight indeed isn't working then.

    In that case, check the small brown cylindrical fuse on the power supply board near one of the inverter transformers. It has the text "T3,15A250V" written on it. If it's blown, then the inverter for the backlights won't work. If it's not blown, then it's possible the inverter is detecting an issue with one of the backlight tubes or the associated transformer driving them and shutting down. The transformers can be checked fairly easily - at least their secondary sides (the pins connected to the blue caps that then connect...
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  • momaka
    replied to TDA2030A Audio Power Amplifier Question
    in Troubleshooting Audio Equipment
    OK, as we suspected, there's not much difference between the two, other than one being Pb-free. So just get the cheapest one.
    BTW, it might be worth investigating the output voltage of the power supply in the speakers. Perhaps it was close to the absolute maximum rating limit of the IC, and that's one possibility why both may have blown.
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  • momaka
    replied to Fender Mustang non valve guitar amp - owner connected 110v amp to 220v.
    in Troubleshooting Power Supplies and Power Supply Design
    By the way, forgot to mention... once you replace all parts and are ready to power up the amp, it may be a good idea to do so through an incandescent or halogen lamp in series with the AC line to limit input current, should something still be very wrong with the primary circuits. 100W incandescent or 72W halogen is usually OK for testing PSUs, IF their output is disconnected from the rest of the device. But if that's not possible or you want to test the rest of the device too, then a 100W incandescent may not be enough. In such case, going up to 150W or 300W halogen may be needed.
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  • momaka
    replied to Samsung Syncmaster 740BF repair
    in Troubleshooting Computer Displays
    Hi soopacrucial and welcome to BCN forums!

    Looks like you already did some key troubleshooting already, particularly with the recap on the power supply board, so that's a good start. Only thing I would advise for next time is to use better quality capacitors, seeing that you have use ChongX and probably other no-name brands. That said, I doubt this would be the cause of the issue you were seeing originally. So let's continue with more troubleshooting.

    For starters, let's determine if the backlight is working. You mentioned you could kind of see it turn On but aren't 100%...
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  • momaka
    replied to Hot Water Rad - A Few ECU Fans and a Timer Switch
    in General Electronics Technical Discussion
    IIRC, timer delay devices (both for ON or OFF delay) do exist. I actually have one... but it's somewhere in deeper storage, so may take a while before I can get a part number for you. All I remember about it is that it is a delay OFF timer (i.e. can disconnect a contact after a certain time has passed after power is removed) and has configurable time settings from a few seconds to a few hours.

    That being said, you would need to know what type of signaling the furnace and zone pumps use (i.e. AC or DC and the amplitude of the voltage) in order to determine if there is even a time delay...
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  • momaka
    replied to 1029A Genelec speaker, transformer help please
    in Troubleshooting Audio Equipment
    Yes, sometimes they do.
    All depends if the manufacturer was ordered to do so for the customer / design of the device.
    There could also be just a regular time-delay fuse in there too (on the primary winding.) In fact, that's more likely to be the case.
    My experience so far with transformers with 220/230/240V primaries is that you just can't use fast-acting / quick blow fuses, as the primary startup current can be extremely high in some cases (depending on what voltage the AC supply is at that particular moment - i.e. if the AC is at the peak of its amplitude at that instant......
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  • momaka
    replied to TDA2030A Audio Power Amplifier Question
    in Troubleshooting Audio Equipment
    The above 2 links are not working for me - I get an "Access Denied" error. IIRC, this is the 2nd time I get this problem now with farnell. Looks like their website uses a shitty design where if links are viewed from a different country, it just doesn't work.
    With that said, instead of links, can you post the manufacturer part numbers instead? (These are usually the same regardless if looking up on farnell or Mouser or Digikey, so that way we can see what you are seeing.) As for the output power to the speakers, that is usually limited by the output voltage (and sometimes power...
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  • momaka
    replied to Fender Mustang non valve guitar amp - owner connected 110v amp to 220v.
    in Troubleshooting Power Supplies and Power Supply Design
    Primary MOSFET most likely has survived, since it's rated for 700V, and also the primary caps very likely did not allow the voltage on the primary to double before they started conducting severely / shorted out.

    I agree with STJ in regards to the omitted balancing resistors across the two primary caps - they really should have been there. If you do replace the two primary caps with 2x 200V ones again, it would be a good idea to add those resistors (one resistor across each cap). Commonly used values are 270k, 300k, 330k, 390k, and 470k (with 300 and 330k being the most common), 1/4...
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  • momaka
    replied to Roland vg-8
    in Troubleshooting Power Supplies and Power Supply Design
    Interesting.
    So the secondary side has gone open-circuit and the primary is still fine?
    If that's the case, I suspect there may be a thermal fuse on the secondary side that has also gone open. Normally thermal fuses are on the primary side... but I had a subwoofer TX that had it on the secondary only, and the primary was protected via external fuse.

    Get a multimeter and try measuring the resistances of the primary and secondary sides.
    It's OK if the secondary is reading low-resistance - that's normal due to the thickness of the wire and the (relatively) low number...
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  • momaka
    replied to XFX GeForce 6800 XT AGP [PV-T42K-UDE3] – recapping and mods
    in Troubleshooting Desktop Motherboards, Graphics Cards, and PC Peripherals
    Hi Ziemax,
    Are those pictures of your card? If so, which one is it? It appears the pictures are of two different video cards. I can only assume the 1st picture is a crop of my card and the 2nd one is yours??

    Either way, on the 2nd picture, the "missing" components look they were never installed from the factory. This could be due to a number of reasons - one of them (and most likely) is if you have a slightly different model with either less VRAM (128 MB) or just different VRAM chip configuration. So check that first or post a picture of the top-side of your card with...
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  • momaka
    replied to cheap but good thermal paste?
    in Equipment Usage, Soldering, Techniques, and Reviews
    It does indeed... or perhaps it's very slightly conductive? Either way, I found out the hard way - replaced the HOT on a CRT monitor and added a tiny bit of MX-4 to both sides of the old silicone pad (so little that none pushed out from the sides), thinking it would help the transistor run cooler. Upon power up, I heard and smelled arcing and the CRT didn't turn on. I thought the HOT had shorted again, but nope - the MX-4 compound that got too close to the transistor screw arced over and created a conductive carbon path. Transistor itself survived and was fine.
    So lesson learned there. ...
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  • momaka
    replied to XBOX 360 Jasper
    in Troubleshooting Game Consoles & Other Weird Devices
    It very likely won't be a missing/shorted voltage rail. Like a computer / PC motherboard, the Xbox 360 motherboard checks if all of the DC voltage rails are present and correct at boot time. So if any rail is not there, the board won't boot.

    Try stj's suggestion of removing the SATA cable from the ODD and see if the issue disappears. If it does, then the issues is with the optical drive somewhere.
    My guess would be the eject button on the optical drive is marginal and making partial contact from random room vibrations. You won't be able to see this with a regular multimeter,...
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  • momaka
    replied to sound blaster Z SE ,How to check these caps?
    in Troubleshooting Audio Equipment
    Traces on the back of the card looks OK-enough to me. Scratched a little - yes... but doesn't looks like the scratches are that deep to have cut them. Could/should check for yourself, of course. However, I suspect none are that deep. Also, most of them look repairable.

    That said, did you try the card out in a PC? At worst, it just shouldn't work. At best, it could be working OK.
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  • momaka
    replied to ASUS P4P800SE/P4C800-E recap (polymod?)
    in Troubleshooting Desktop Motherboards, Graphics Cards, and PC Peripherals
    What caps are originally installed on these boards?

    The erratic POSTing could be caused by many different things.

    Is the RAM known good and stable on any other PCs of that era? Passes MEMTEST at rated SPD frequency??

    How about the PSU? What brand and model is it? Known to be a model with non-Japanese capacitors? Pictures of the insides and label if it's not a universally known brand would be good to have to determine its solidness (or lack of, possibly.)

    As for the motherboards, I don't recommend going for a polymod right away. Some ASUS boards...
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