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Thread: DM50 Strange "sleepy problem"

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    Default DM500 Strange "sleeping problem"

    I've got a DM500 clone that gave me restarts, even after having flashing it with a new image, (I was using the Gemini 4.10).
    I opened it and I noticed that the LT1940 was over heating so I changed all the electrolitics condensators and changed the LT 1940 and the LAN controler ASIX AX88796 as a precaution, but when I plugged the power nothing happen; no green led on the front panel but all the tensions on the main board are there: 5Volt, 3Volt, etc.
    I tried to flash it using the Jtag method but I never get a connection with the dream flash.
    What else can I do, besides buying a new one, to make my clone start working again?
    Thx



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    Well I found something strange.
    I've a DM500 to compare and I think there are two condensators missing, perhaps when I used the soldering gun to substitute de LT1940.
    But the bigger difference beteween the orib«ginal and the one "sleeping" is that the cristal is exactly the double; in the original I've got a 13,5Mhz cristal and on the "sleeping Clone" there is a 27Mhz one.
    My doubt is about the missing condensators:
    Shall I use the same value as the one on the original DM500 with a 13,5Mhz cristal, which are 150 (15pF) or shall I use condensators with the double value (30pF)?
    Please give me a hand, will you?
    regards
    Nagraeblanco
    Portugal

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    Senior Member gw1's Avatar
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    Default

    I guess you've tried a different power supply? Clone power supplies frequently fail so that's the first thing I'd suspect. See Z80's .

    If your regulator was overheating it's possible your power supply was giving excessive input voltage. That may have also damaged other caps around the input section. I don't have a DM500 schematic in front of me at the moment so I can't be more specific unfortunately.

    Replacing the ASIX is non-trivial. Is it possible you inadvertantly left a short circuit somewhere while replacing it? I've done it myself before so I know how easily shorts can arise beneath components, especially if you aren't fanatical about cleaning and flux. A short circuit on the data bus would obviously prevent it from booting even though the various supply rails are correct.

    There are at least half a dozen variations of the DM500 design around and there are some significant changes in circuit configuration and component values between some of them.

    Over the years I've seen several cases where crystal oscillator circuits had startup problems, usually due to overdriving the crystal or inappropriate load capacitors. I doubt that's the problem in your case though. Far more likely is you've created a short while replacing the ethernet controller.

    Others may be able to offer more specific help, but I have a gut feeling you'll end up needing to buy a replacement receiver. I own both genuine and clone receivers, and my general advice to people is to save up and buy a genuine model rather than a clone. There's a reason clones seldom have any warranty: clones are significantly less reliable overall, and if you know anything about switchmode or ethernet circuit design you'll understand why. Genuine DMM receivers aren't cheap, but since the clones use inferior inductors and capacitors (from what I've seen) it makes sense to pay the premium if you want reliability.

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    Thx GW1
    I'll follow your clue about asix shortcircuit because my real problem are the 3Volts which are around 2.4Volts and the flash, to wake up needs at least 3Volts.
    Once more thanks for your help.
    Anything from Portugal, just blow the wissel

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