Upgrading a cheap desoldering station (ZD-915)

Discussion in 'Electronics & Electrics' started by Thalyn, Apr 21, 2019.

  1. Thalyn

    Thalyn Member

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    Following a disappointingly short run (though probably not bad for the price), my ZD-915 (purchased as a now-discontinued TS-1513 from JayCar, but also available from RhinoTools and many others) has developed a fault. I suspect it's just the heating element which has failed, so it's (hopefully) not an expensive or difficult fix, but it did get me wondering about improving it.

    The most obvious change would be the gun itself. Since Zhong Di seems to base their units on Hakko gear (or else they coincidentally fit the same accessories), I'm wondering whether it would be feasible to switch out the heating element for a Hakko unit. This would naturally be a higher quality unit and should provide a much longer service life. Further, would it perhaps even be possible to switch out the entire gun for either a Hakko 802 or 809, depending on which would actually fit, and get all the other benefits such as the revised heating assembly.

    Has anyone tried such substitution before, or is it even likely to work at all?
     
  2. Technics

    Technics Member

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    While I can't speak for that specific unit as far as I'm aware some of the knock off Hakko 936 soldering stations were not compatible with the genuine heater because they used a thermocouple while the original (and some clones) used a PTC thermistor.

    Given you unit is broken anyway there's no harm in tearing it down for further investigation. It looks like the ZD-915 has a temperature sensor in the element for closed loop temperature control while the Hakko units don't sense temperature and only provide open loop heat adjustment. So I'd say it's unlikely to be an easy swap.
     
  3. aXis

    aXis Member

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    You should be able to test the element to see if it's failed.

    I had a Hakko clone fail on me and the culprit was the SCR that modulates the low voltage AC power. It was quite easy to source and replace (with a spare soldering iron).
     
  4. OP
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    Thalyn

    Thalyn Member

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    Dang. I was afraid of that. I had looked to see if I could find pictures to tell how viable it is, and they did appear to have a different number of wires on the heating element. I guess if that's why it's going to make it a far larger task than I'd thought, to the point where it's probably not even worth bothering. Of course, I've learned never to trust "stock" pictures since they have a habit of being incorrect models, prototypes, or just mysteriously missing pieces, so I figured it was better to ask.
    That's something I'm going to have to look into, in that case. It's at my brother's house at the moment (that's where it's being used for now) so I can't investigate just yet, but I'm assuming that's something I'll have to look for on one of the two PCBs behind the front panel, yeah?
     
  5. aXis

    aXis Member

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    Yeah there were very few components in mine - a transformer, a basic controller board and then one main power element (the SCR).

    Maybe I've just had a bad run of counterfeit over-specified parts, but it seems like SCR's are quite fragile and will just blow from electrical stress.
     
  6. OP
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    Thalyn

    Thalyn Member

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    Cheers. I'll break it open again on Thursday if the new heater doesn't do the trick. More I know about fixing it the better, especially if I can't slowly sub out parts for better variants.

    *ed: Just to check, since I want to have an idea of what I'm looking for ahead of time... is the SCR inside the power supply? I can't find any good pictures of it, but the descriptions which accompany suggest that there's three TO-220 packages in there. Two are side by side - one is a mosfet (N1), where the other is a "rectifier" (D2). The other (on the same side of the case) I can't find any info on, nor can I find anything silkscreened in the pictures, so I'm leaning towards this being the SCR.

    Would a triac also be a suitable replacement for this, in the event I can't find (or am too impatient to wait for delivery of) an SCR?
     
    Last edited: Apr 23, 2019
  7. aXis

    aXis Member

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    I used the word SCR but it was probably a TRIAC, you would want to search the exact part though. That said sounds like your unit is rectified to DC and then switches a MOSFET, not a TRIAC.

    First things first, you really need to diagnose the type of fault you have. Is your unit not putting out a (low) voltage, or is the heater cartridge busted?
     
  8. mtma

    mtma Member

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    If it's this, it has switchmode front end and not based on a transformer + triac control.
     
  9. OP
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    Thalyn

    Thalyn Member

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    Well, it looks like fortunately it was just a dead heater. I haven't done any thorough examination of it, but a quick inspection has what appears to be a short on the earth line (it could just be cooked) and some noticeable corrosion where the wires attach to the element itself. Plus what appears to be a crack in the white stuff coming out of the back of the barrel, but I've no idea whether that's adhesive or the ceramic itself. A new heater installed and it's working just fine, so I may need to pick up one or two spares while I still can.

    On the down side, though, I guess there's not really much I can do in the way of substitution for better parts or otherwise upgrade the unit. I mean, sure, I could fit a relay or transistor so the trigger doesn't have to carry the full motor current (assuming it does that - haven't investigated). And I have heard of people adding a separate pressure tank with a switched valve to apply more instant suction. Could also change out the resistor-based voltage regulator for the fan and motor to something more efficient. But that's neither here nor there, since those parts are still working.
     

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