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Advice on replacement power supply for Geemarc phone?

Discussion in 'Power Electronics' started by David B, Sep 4, 2021.

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  1. David B

    David B

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    Dec 29, 2017
    Hi, the power supply for my Geemarc CL1400 has packed up. I have a shoebox full of power supplies I have accumulated over the years. I found a few with the right voltage, polarity and connection that fits my phone BUT although they all work with the exception of one they are causing a loud humming on the phone line. The only one that does not cause humming is a universal power supply which gets quite warm (not really hot) but as this is going to left plugged in 24/7 I'm a bit concerned about a potential fire risk? So can anyone recommend a power supply that won't cause humming, get warm and be of a good safety standard to be left plugged in all the time? Or would I be better off getting a new phone that doesn't need a power supply to function properly? Also the back up aaa duracell batteries are almost flat, I was going to replace them with rechargeable ones but the phones instructions say not to use rechargeable batteries for some reason.
    Please advise. 20210904_111915.jpg 20210904_111809.jpg 20210904_115941.jpg 20210904_111915.jpg
     
  2. dave9

    dave9

    1,121
    303
    Mar 5, 2017
    You could crack open the original PSU to see if you can find/fix a fault in it, or observe the circuit to see if it has a unique design or added filtration, or possibly it is just a lower switching frequency.

    Your universal PSU might just be an unregulated linear type (despite being labeled "IC") that achieves the different voltages from different taps on the transformer winding, so only has 100Hz ripple for the phone to reject, and it would be normal for it to get hotter, and waste more power. I saw an online version of the owners manual but unfortunately it lists no power specs so all we have is the 500mA upper limit of the PSU to go by.

    If your universal PSU is getting too hot for your comfort then you might find a 1A, 12V linear PSU, or you could experiment with adding an LC filter in series with the Yamaha or another SMPS, or experiment with how low an input voltage it can tolerate and try a low dropout linear regulator in series between the SMPS and phone.

    For that matter you could even open up the universal linear PSU and drill more vent holes in the casing to help cool it. Odds are very high that it has a thermal fuse in the transformer that will disconnect the primary side winding if it ever overheats that much.

    And of course there is the last option, throw together your own PSU. While switchmode PSU design is a steeper learning process, a linear 12V PSU is not all that hard to construct, with mains AC - fuse - transformer - bridge rectifier - filter capacitor.
     
  3. David B

    David B

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    Dec 29, 2017
    Thanks for your reply dave9. Unfortunately I don't have the skills or time for repairing or modifying any PSU,s I have. Soldering a dodgy wire is about the limit of my "electronics skills". I was hoping someone could recommend a suitable PSU to buy online. I did try to find a new PSU online of the same make/model without success.
     
  4. dave9

    dave9

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    Mar 5, 2017
    You didn't tell us where you are located, to buy online without a long wait shipping who knows where. I took at guess at a UK location and searched amazon uk but didn't find any non-switchers in the brief search I did, so maybe some electronics repair place or a used goods thrift store might have something pre-EU regulations, something about getting rid of the linear type and mandating SMPS for everything? I don't know all the details about it.

    OR, just continue using the one that gets warm, that is expected and shouldn't pose a fire risk, but will waste more power, maybe a couple watts.
     
    Last edited: Sep 4, 2021
  5. David B

    David B

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    Dec 29, 2017
    Yes UK, I just tried my routers power supply with the phone and that one is much quieter but the connector is too short (it only just connects in the back of the phone) I could cut off the connector and join on the connector from the original broken psu but I cannot find any new ones the same make/model to replace the routers psu. I don't want to cause any issues with the router by using a different make/model. 20210904_213550.jpg
     
  6. dave9

    dave9

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    Mar 5, 2017
  7. David B

    David B

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    Dec 29, 2017
    Thanks, well spotted, I didn't see that one on ebay. I might go for that. The connector looks the same size as the one for my router (slightly too short for my phone). I might try to cut a bit off the sleeve around the connector so it goes further into the phone socket giving a better connection, if that doesn't work I can still replace the connector with the original one from the broken psu.
     
  8. David B

    David B

    22
    0
    Dec 29, 2017
    Thanks, I got that one from ebay. It works perfectly with my phone. The connector was too short to fit into my phone properly so I cut off a bit of the plastic sleeve around the connector so it would go in further.
    Interestingly I just went round my house putting an AM radio close to a few different power supplies and was surprised how much 'noise' and types of noise power supplies can emit :eek:
     
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