ZD-915 Mysterious Fault

[axeman]

Hi Guys,

Hopefully someone can help me as I have swapped the psu caps , the switching IC, the soldering gun heating element, the M7 diodes on the psu and the display board. checked all caps and diodes for shorts and still I'm getting the U3 error with constant reboot. The unit stays on without the gun connected.

A strange symptom is that when turned off the unit flicks on the display and fan only for an instant every 10 seconds or so.

There is a ticking sound coming from the PSU when turned on with and without the gun attached. Can't remember if this is normal or not.

There are no scorch marks or any signs of failure on either side of the boards.

Any help much appreciated.

[petehall347]

Re: ZD-915 Mysterious Fault

https://www.badcaps.net/forum/showthread.php?t=51202

[axeman]

Re: ZD-915 Mysterious Fault

Thanks for getting back Pete,

Already swapped the M7 diodes twice

[petehall347]

Re: ZD-915 Mysterious Fault

do they measure ok in circuit ?

[axeman]

Re: ZD-915 Mysterious Fault

Just checked diodes in circuit and D8 looks suspect. So will remove and check.

[axeman]

Re: ZD-915 Mysterious Fault

D8 checks ok removed.

[axeman]

Re: ZD-915 Mysterious Fault

If the unit powers on ok with the soldering gun removed does that mean the problem is most likely on the display board side?

[sam_sam_sam]

Re: ZD-915 Mysterious Fault

Replace the switching power supply regulator because this can cause it to this as well but first replace the small value capacitors around the switching power supply regulator and see if this makes a difference

I see that you have already replace the capacitors and you still have these issues then try this what I have below

One note test the switching power supply with two MR16 incandescent light in series and see if it will stay on or not if it does then use two sets of them and see if it still does on the two wires that goes to the heater element not the temperature sensor wires you want the heavier two wires now you will still see the error message but it should stop the restarting issue unless it is a defective controller board the light bulbs should stay on continuously and not cycle on and off

If it does then re-hook the Desoldering Gun if it does not stays on then the issue might be a shorted heating element

I also see that you have tried another gun and this tell me that either the switching power supply board still has an issue or that the controller board might have some type of issue but not staying on and restarting might be more of a switching power supply board issue try replacing the optic sensor or at least measure the LED side ( the input side of the device ) you should get about 1.5 to about or even a little bit more than 2.0 volts and it should be steady not jumping around when trying to load up the switching power supply board

I have about 8 of this type of units and I seen different failure issues with these units

Now you can try to power the Desoldering Gun Station but you will have to do the following depending what version you have there is a -5 volts power supply rail that has to used for the controller board power supply rail you will have to find the Zener diode and a 1 to 2 watt resistor on the switching power supply board has to used or the temperature controller part of the controller will not work correctly anymore

The reason I know this is that I try to build a battery operated desoldering station and it does work however you have to use a PWM controller on the heater element if use it on battery power because the controller portion of the controller will not work correctly anymore if you try to use battery power

If I were to power ( with a computer switching power supply) the desoldering station here is what I would do is remove all of the switching power supply components and where the low voltage filtering capacitors are this is where I would put the power supply wires at this point on the switching power supply board and everything should work unless you also have a controller board issue as well

The reason I think you might have a issue with the controller board is if the diode shorted on the controller board I also had this happen and the controller board did have an issue with controlling the temperature correctly after that

I hope this helps you

[axeman]

Re: ZD-915 Mysterious Fault

Thanks for response Sam et al. Just back from hols so will try suggestions over next couple of days and report back.

[eradiofan]

Re: ZD-915 Mysterious Fault

I had this fault with mine. I purchased it in 2020 and despite restarting from time to time, I managed to use it for over 3 years before it finally packed up. Constantly re-starting.

Took me a whole day to track it down, using a high-votage differential probe. The continuous restart is caused by a switching regulator error condition and there are many types. In my case, the FSCQ1565RT switching regulator was losing VCC after a short time, causing a reset.

The circuit (from eevblog) is supposed to charge E6 via R13+D9 but this was not happening. I replaced E6 and D9 with a fast recovery diode (1N4937) and it is working again.