Transistor replacement

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  • Haaheim
    Bias matching replacement transistor - Parasound 2250
    by Haaheim
    Hi guys!

    I am currently working on a Parasound 2250 (class AB), which had one defective channel. Components in the signal paths have been replaced, including an output transistor (2SC3519).



    According to the manufacturer, bias is adjusted by measuring 1-3mV across the output resistors. The original ones are completely fine around 1.5mV, but the replacement is not. Initially, I got a couple from eBay, assumed they were fake (they were) and was able to source a replacement locally. This exhibits similar behaviour, being around 0.6-0.8mV on its emitter resistor....
    05-13-2022, 12:45 PM
  • acedogblast
    Guide to transplant MEC1503 EC chip and EEPROM reprogamming for T14s gen 2 and X13 gen 2
    by acedogblast
    This is a guide that I am writing for helping others to replace their MEC1503 EC chip if it breaks (or to get around an inconvenient prompt to the BIOS). This forum has been extremely helpful to me so I would like to contribute to help others. I will tell you right now that this task is very difficult to do. You MUST have experience and tools to do precision micro-soldering, BGA reballing, trace repair, and general laptop repair skills.

    There are some specialty tools needed to do this task. The replacement MEC1503 chips can be acquired from Aliexpress. Do not buy the bare chips as...
    11-02-2024, 05:13 PM
  • BMCappelletti
    Lenovo Thinkpad E14 Gen3 stuck on "To interrupt normal startup, press Enter" screen
    by BMCappelletti
    Hi everyone.
    Lenovo Thinkpad E14 Gen 3, stuck on the "To interrupt normal startup, press Enter" screen.
    Found a lot of people with this issue, but with no definitive answer. Some people managed to get away accessing BIOS, going to Startup and turning off "Option Key Display". For me that only removed the interrupt normal start up message, leaving only the Lenovo logo.
    Most people say hitting Enter does not work. It's true, if you wait a few seconds. But if you hit Enter right away you get the options to enter BIOS (which works), run diagnostics (goes to a...
    02-18-2025, 12:22 PM
  • karatzdi
    Denon AVR 1908, High pitch noise on Surround back Left channel after long overhaul
    by karatzdi
    Hello,

    I know some might say... just buy another one. Sell it as parts..!

    So had this AMP for quite some time. Recently I saw light smoke coming out of the AMP. Had my fire extinguisher close by. Just kidding. Turned immediately all devices off from mains.
    Let things cool a bit, and opened up the amp device. I clearly saw on the main board which hosts the 5X amp (5.1), 3 10 ohms 1W resistors had their leads looking black, while the rest of the remaining 2 x 10 ohms were brownish as being installed from factory.

    Spent some time downloading the Service...
    06-11-2024, 08:38 AM
  • the_rem
    Unknown transformer : how to find a good replacement part ?
    by the_rem
    Hello guys,

    I would like a quite old but still good 800 W ATX PSU to be repaired. The problem was an extremely heavy coil whine coming from the small secondary transfomer on the PCB.

    I desoldered it hoping the references on the upper side would allow me to find a adequate replacement part. Sadly the written references drove me nowhere but to the manufacturer (I-MAG). I sent them a message like a bottle in the see asking them to send me a datasheet of the transformer. And... They responded ! I received a kind of datasheet (see attachment) but my competencies do not allow...
    04-23-2025, 01:48 AM
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