ZD-8915 (SS-331) conversion from 18V to 24V

[cybermaus]

Some 19 months ago, I bought a ZD-8915. In a local store even, but it is still China stuff.
And at first, I was very happy with it. Still am, despite what I am about to write, would buy again.

But I started to get small annoyances. Being:

- Very loud FAN. I thought it was broken.
   Like many others, I replaced the fan nearly instantly, but that did not work. Below I explain why.

- Power switch on the back
   Has been moved to the front a while back.

- Extremely slow heatup time. 10 minutes to 400C (which is really only 350C)
   Main mod for this post.

- Temp is off by about 50C (edit: now also fixed)

- Bad sleep mode. Handling does not keep it awake, I have to hit something with the gun

- I may eventually also add a delayed vacuum valve, as I have seen others also do.


So, it turns out the noisy fan and the slow heat-up time are related. The problem is, it has a 24V heating element, a 12V air pump, 12V Fan; But a 18V power supply.

So putting a 24V 90W heating element on 18V yields only 50W. And indeed, checking consumption that is what it takes.
That is the slow heating explained.


Furthermore, the 18V is dropped with 2 ceramic 1R5W resistors to 12V for the airpump. Very wasteful.
BUT, the 12V cooler fan is on the same resistively dropped 12V rail as the Airpump. Ergo, it is nearly always running on 18V !!
Only when you run the pump does it drop to 12V, but I never noticed the fan sounded better when the pump was running. You know, with the added pump noise.
And when the pump does not run, then voltage barely drops, so the full 18V over the 12V fan.

Yeah, that will make it sound as if it is about to explode alright....


And finally, not very critical, but also a bit silly:
The control board is running from a 78L05, is again from the 18V, but again resistively dropped to 15V.
The resistivity dropper is inside the PSU even, so it needs two extra leads out of the PSU. Not sure why. Maybe the 78L05 gets to hot from 18V, but not from 15V?

The Mod:

I modded the PSU from 18V to 24V by tweaking the resistor network around the TL431AA voltage reference.
Adding a 68K resistor parallel to the R8 resistor (24K Ohm) yielded 23.5V output. Which is good enough, especially as the capacitors are only rated for 25V


Next I added a cheap DC/DC board to convert the 24V to 12V, and will now feed all 3: airpump, control board and fan, without any resistive dropping.
I did test if the board could handle a continues 2.5Amp for the Airpump. Not that the Airpump runs continuously, but to be sure...


From the PSU, I removed the thin 15V red/black leads for the control board (the resistive dropper for that was inside the PSU), as well as the 18V thin black/white leads for the airpump. And instead added proper (thicker) Red/Gray wires. The reason for the odd  Red/Gray color combo is that the original colors were also odd.
For example: two of the black wires of the PSU were +18V, and one black wire was GND.... Go figure the logic of that....
So anyway, as I did not want/need to change the Black/White wires to the Iron, I kept Black as +V, and chose different colors for permanent 12V and permanent 0V

Code: [Select]

original       new     meaning
Black (thick)  Black   +18V (now +24V) for Iron (unchanged)
White (thick)  White   PWM switched ground for Iron (unchanged)
Black (thin)   Red     +18V (now +12V) for Airpump/Fan (now also Control board)
White (thin)   Gray    permanent ground
Red (thin)     --      +15V for Control board (removed)
Black (thin)   --      ground for Control board (removed)
Orange (thin)  Orange opto-coupler to Switched Iron ground
Green (thin)   Green  opto-coupler to Switched Iron ground


The power distribution board also was slightly changed. Basically, I removed the two large resistors, and re-used their pads to create a +12V and 0V point for the control board wire. Not too hard, see the images.


Now the device heats up much faster, draws the listed 90W while doing so. And the Fan sounds more reasonable.
I may still changed the fan for an ultra-quiet one.

Mods I may make in the future

- Replace Fan by more quiet one, and add internal shroud for more logical airflow
   (but the airpump is noisy anyway, so maybe not)

- Tune the pots on the control board to see if I can make the temp readout better
   (did not touch them yet) done

- Add small vacuum delay valve in the handle, so the suction comes in with more of an initial burst.
    Something like this: https://youtu.be/j8LMdIZuDyw but nicer looking)

- Put a relay for the AirPump, rather then running 3A over the tiny conductors and microswitch of the gun.

- Link the sleep/shake input to the trigger switch


Or not. After all, it is working, and I do not need to wait 10 minutes anymore every time I want to use it, so I may loose interest.
Anyway, let me know if you have suggestions, of if you thought this useful.

Have a nice day.

PS: if someone knows why my inline images are not working, please reply or even dm me.

[Andy Watson]

There are some odd design choices in these units. I traced-out the circuit of my 331B version here:
https://www.eevblog.com/forum/testgear/using-a-proskit-ss-331h-on-110v/msg2283177/#msg2283177
It appears that all version use the ZD-P150 power supply module.

[cybermaus]

Nice schematic. I did in fact already found that a few days ago, and used it, thanks.

So does your SS331 also have a 24V element, or is there a special/unusual 18V element in it's gun?


Edit: also, your schematic has a 6-pin connector, my device has a 7-pin one. And I cannot find any wire for the shake sensor in your schematic
Now, it was mentioned by the seller (local shop) my device was a new version with sleep. So likely that is why I have an extra pin.
I did not focus on that while it was open, and the device is closed and back in its place now.
But it does indeed have sleep and wake. Be it I have to give it a rather hard tap to wake it.

but thinking about it, having a new version, new handle, who knows, maybe I also have a different heat element. It would explain why I see no-one else complain about the slow heating.

[sam_sam_sam]

cybermaus

I have several ZD-915 that do not have the sleep function on them so I do have that feature

But I have to ask you about the modification that you did to the switching  power supply

You know that it has a  +5 volt rail but did you know that it also has a -5 volt rail Zener diode with a 1 watt resistor how warm does this resistor get with the extra voltage to this device

How well does this modification work and how often do you use it  for hours at a time or a few times a week the reason I am asking is I might want to do this modification on mine but senses you have already done it I just wanting to know how well is holding up

How badly does the temperature over shoot or under shoot the set point

[mjongh]

I have opened up my ZD-8915 to do this great mod.

It has a slightly newer version of the power supply (V4), which uses different values for the feedback circuit resistors.
In this version you need to add an 6K8 resistor parallel to R8 to end up at roughly 23.5V.

[cybermaus]

Cool. Thanks for the feedback on the newer version.

It cursory looks like all your values (in this section) are divided by 10.
Maybe they done that to make it less susceptible to noise.

[cybermaus]

Sorry, I missed your questions. Not always checking every day.

cybermaus
You know that it has a  +5 volt rail but did you know that it also has a -5 volt rail Zener diode with a 1 watt resistor how warm does this resistor get with the extra voltage to this device

I am not aware of any -5V rail. Can you provide more details on that?

I do remember a input voltage divider, so the CPU knows the input voltage, probably as some sort of power-good signal. But I would not call that a rail.
In case you mean that one: It is now getting 12V instead of a varying 18V~15V, so any such resistor would get less hot.

How well does this modification work and how often do you use it  for hours at a time or a few times a week the reason I am asking is I might want to do this modification on mine but senses you have already done it I just wanting to know how well is holding up.

If I am honest, I use it sparingly.
When I do use it, I am happy to have it, but I am only an occasional hobbyist, and also nowadays more stuff is surface mount.
So if there is a 1W resistive dropper somewhere that I did not notice, and it is getting 24V instead of 18V, I may indeed not have noticed it breaking yet.
But as stated, I did not notice a -5V rail.

How badly does the temperature over shoot or under shoot the set point

Well, I have not done laboratory quality testing on that. Just a cursory check with my temp probe.

But when doing that, I noticed that even with the 24V, there is still a delay before the read-out temp reaches the tip.
I can already hear the regulator starting to modulate (you can hear the high pitch of the switched PSU), while the heat at the tip is still creeping up.
As a result, there is no real overshoot.

Undershoot usually happens because the gun goes to sleep while I am using it, which usually leads to me cursing and whacking the handle to my desk to wake it up.
But now at least it goes back up rather quickly.

The whole sleep shake sensor is rather silly. Unlike a normal soldering iron, this device has a usage trigger-switch.
The engineers messed up when they did not realise they could have used that instead of adding a shake sensor with wire and connector.

[cybermaus]

Additional note after checking Andy Watson's schematic:

I still do not see your -5V rail anywhere.
And additionally, the new 24V goes nowhere except directly to the Iron. So it should not matter unless if inside the PSU itself


However/Indeed: I do now see inside the PSU a Diode/Resistor combi D1/R1 (not a Zener) at 360 Ohm / 2 Watt
That indeed would get 1.6W instead of 0.9W. Should be OK, but had I seen it while I was in there, I may have modded it.
But still 2W is more then 1.6W, so should be OK.


Then again, not even sure what this diode/resistor is supposed to do?
Provide some minimum load when the Iron is not driven, so the PSU does not over/undershoot every time the FET switches?

[sam_sam_sam]

This is a Zener diode setup and it is used for the controller board which when I saw this I thought it was a odd but I know this because I am going to run this until on 24 volt battery pack and when I tried to use this way the temperature part of the  controller would not work and you have to have this circuit for it this purpose

But you also have to use a SCR setup for a 3D bed table heaters and a PWM controller for this to work correctly I just have to use a computer battery pack module and reconfigure it for 24 volts and this project would be finished

The temperature over and under shooting is a lot better but you do give some speed to how fast ( the results are not bad ) it gets to the temperature that it is set to but on battery power you do not want the overshooting to be at a minimum to conserve battery power  because it runs at lower current

I have read that these Desoldering Gun have a life of about 500 hours but I seem to get more hours than this but when they get to about 1000 hours of use they have tendency to clog more often and the wire cloth covering turn black and when this happens you running hours left are very limited time for a new gun

One note about running it at 24 volts the heater element will not last as long because the more current it pulls and not a good option when running for hours and hours at a time I have thought about running this unit on an external switching  power supply before and might still do but I have a selector switch to switch from 12 volts to 24 volts for turbo boost but only use this when doing double sided circuit boards with wide ground planes but so far I have not found the right switching power supply for this purpose yet

One note that this is a failure but does not happen very often at least with my experience is temperature sensor failure and you will know that this happen because you will see — — for the temperature reading results but the heating element will still get power and destroy the heating element there is no fix for this failure as far as I know I have even tried to remove the temperature sensor wires from the gun but have not been successful in doing this

[SergeDr]

Thank you Cybermaus,
Thank you Andy,

I got hold on this desoldering station a few days ago and changed it according to your info.

Just one thing: has anyone noticed the U09 status on the display at power on?
This is probably normal since my device is working normally. Just to be sure.

B.R.

Serge

[cybermaus]

Just checked. Indeed.

First a all-elements-on screen test, then u09 for a second, then displays the temp.
I am assuming it is all as it should be.

[giovannirat]

Same behaviour on my station.

Probably indicates a firmware version.  v09

[SergeDr]

Nice, Thanks.

[cybermaus]

Since someone is making this topic active again form me via PM's, a small update:

Eventually I did get a few clogged nozzles. Not too bad, but still.
Once the solder oxidises, no heat or prodding moves will move it.

I find that a long thin drill however still makes short work of it.
So I advise getting one of these (from here, or ebay, or whereever):


https://www.eleshop.nl/reserve-reinigingsboor-voor-nozzles.html

[HumbleDeer]

Let me revive this one while I do some mods too!

The newer units branded ProsKit no longer have the zener/diode installed nor the -5 0v +10v used as neg/pos. The red-black wires that feed the LDO on the mainboard are now connected to the -5v (black) and +10v (red).

The motor on my pump is actually a 24v motor (1*). But as the manufacturer has measured, the increase in vacuum from 12v to 24v is marginal, especially given how low quality the pump is inside. Still, I decided to do some silencing mods to the pump.

The pump is no longer run in reverse, red being red this time around. But for some reason they run the tubing realllly far. That puts the vacuum "pull" at the rear of the unit and requires a tube going to the front. While the 'out' is just bare, causing a LOT of noise! Presumably this is to space the tube from the front, so it doesn't have to kink upwards. But the rubber mounts of the pump are flexible enough that you can shift it backwards quite a bit. Then, you can reverse the pump too, putting the exhaust at the rear and intake at the front. Cut the tubing to length, and use the remainder on the outlet, then coil it as much as possible (or use another piece of tube.) This acts as an acoustic transmission line, dampening at least some of the noise.

Here are some pictures so far as well as some pictures of the main board while I'm at it.

*1: There is a SKU label from ProsKit, and a Mfr label underneath. In both cases, 20200825 is the date of production; 25-08-2020. The common "555" gives me clues about the motor used; it's likely just a standard "555" motor, like an RS555. I wonder how much quieter it'll be when I eventually end up modifying it with a brushless motor or just make my own controller/driver entirely.

SKU label: QJT-555SPH 20200825

Manufacturer label: www.cdmmotor.com CDM-555-37040 DC24V 20200825

[HumbleDeer]

Update to what I ended up doing:

• Did the power supply voltage mod on the TL431 circuit to bump the voltage to a solid 23.8v
• Created a trigger exclusivity circuit that halts the heater during pump action. The unit shuts down without. It's simply a BJT stealing the current from the LED in the phototransistor that drives the mosfet. On the drive side (on the blue pcb) I added a BC NPN w/ 10 ohms base resistor, resulting in just enough current flow through the original currenet limit resistor, that the voltage drops below the opto's Vf.
• Broke the Sleep Mode trigger to where before it would never go into sleep after the first time soon after turn-on, it now goes to sleep and never wakes up. Methinks adding a trigger-tied Sleep Release wouldn't be bad, so that the handle trigger also signals to the unit that the handle is used (instead of the sensor in the handpiece, which seems to awfully squeel along with the PWM of the heater mosfet!) I haven't investigated what broke the trigger but it's likely to do with either a loose wire, or that I fiddled around in the handle in the search for where the squeel came from (which turns out, doesn't come from there as a source!) I did swap two wires that were reversed according to the manual in terms of thermocouple reference ground used. But that may actually have been intentional in the first place, who knows. I also don't.... really at all remember what the config was before I fiddled. D'oh!

[GrievousAngel]

This is an older post, however is an excellent source of ZD-915 electrical (the best I have found).

I noticed this post during my ZD-915 gun and power supply replacement project. Wish I had seen this earlier. Anyways ...

I have a 120VAC to 24VDC @ 6A switching power supply (AC-DC2406) and a DC-DC 24V to 12V @ 6A converter (adj Step U/D & constant I). I also have a new 24V desoldering gun (948) w/ proper 6 pin plug. My plans are to feed 24VDC to the new 948 gun w/ a 24VDC heater element), then feed 12VDC to fan and pump and front panel. My concern is what to do with C+ and C- wires (GRN & YEL) and the +10V and -5V wires (RED & BLK) as their PCB markings are not real clear other than they go to the front user interface PCBs! I also purchased (2) small adjustable DC-DC converters (set to 12V to 10V) and a (set to 12V to 5V) if needed. Understand that the OEM power supply will be replaced as in gone.

After reading the post, it becomes apparent that I need to reach out for assistance and suggestions.

I am also considering adding an 24V mini air valve to create a pulse of vacuum when trigger is activated (using the internal vacuum hose as an accumulator). Has anyone installed the impulse air valve with satisfactory performance? How do most get around the negative of running the pump all the time? I do not want to run the pump continuously, however ~1 sec of 'spin-up' time would be OK. Suggestions?

Hoping to get this thread going again ...

By the way . . . I am new to EEVBlog. This is an awesome EE and DIY forum! Happy to be here.

GrievousAngel

[cybermaus]

I have a 120VAC to 24VDC @ 6A switching power supply (AC-DC2406) and a DC-DC 24V to 12V @ 6A converter (adj Step U/D & constant I). I also have a new 24V desoldering gun (948) w/ proper 6 pin plug. My plans are to feed 24VDC to the new 948 gun w/ a 24VDC heater element), then feed 12VDC to fan and pump and front panel. My concern is what to do with C+ and C- wires (GRN & YEL) and the +10V and -5V wires (RED & BLK) as their PCB markings are not real clear other than they go to the front user interface PCBs! I also purchased (2) small adjustable DC-DC converters (set to 12V to 10V) and a (set to 12V to 5V) if needed. Understand that the OEM power supply will be replaced as in gone.

Replacing the power supply completely is not entirely so trivial because (as you noticed by the GRN&YEL wire) it is not only a power supply, but also the high-current switch for the iron.
They mostly likely combined the two so that they could do with only one heat-sinc. So if you replace the power supply, you'd have to build your own high current switch.

It there a reason you plan to completely replace the power supply? Is tweaking the pre-existing one to 24V not sufficient?

I am also considering adding an 24V mini air valve to create a pulse of vacuum when trigger is activated (using the internal vacuum hose as an accumulator). Has anyone installed the impulse air valve with satisfactory performance? How do most get around the negative of running the pump all the time? I do not want to run the pump continuously, however ~1 sec of 'spin-up' time would be OK. Suggestions?

I never did get around to that. Still think it would be a good idea.
However, I would not have the pump run continuously. Instead, I'd add a small buffer-vat (10 cc of air or something, and a dual action trigger to the gun switch.
So if you press the gun switch half way, the pump starts, "fills up" the buffer with vacuum, and then you press the switch further and the "vacuum is released"


The way I plan to do it was even mechanical, not a electrical. Have a small pneumatic valve hooked the trigger, making it an mechanical air trigger, more then a electrical switch, however have a microswitch hot-glued to it for the dual action.

My reason was not even the wear of the pump, but the noise. I do not want that thing blaring all the time. But I guess wear is also a good reason.
Mind you, if you do run it continuously, you do also solve the GRN&YEL wire problem, as it means you do not need to switch the pump, just have it on the whole time.
Still, I would not recommend such.

[GrievousAngel]

Well ... After installing the new PS, it became apparent that C+ & C- is the TC feedback to the PS in order to control iron temperature. I am at the point of (just for kicks) trying locate a TC control module that could placed between the new 24V PS output and iron heating element, using C+ & C- to control the new module that drives the iron. leaving the front panel as is. Does this sound reasonable?

What type / class of signal is passing via C+ & C- (between the PS and the front PCB) to control tip temperature?

I had plans of using the mod'd ZD-915 as my 'other' desoldering station, since I located a good used Quick 201B desoldering unit. Has anyone compared the Quick 201B to the ZD-915 w/ 24V/12V mod installed?

Thanks for the feedback.

[cybermaus]

What type / class of signal is passing via C+ & C- (between the PS and the front PCB) to control tip temperature?

As you can see in the schematic by Andy on the 2nd post of this thread, the C+/C- wires as you call them drive a optocoupler, which drives a big FET.
Best duplicate that part of the schematic.

[vdtoorn]

Hi, I did the modifications and they appear to work fine, at least the voltages are OK.

But, when I attach the gun though, the machine is starting up and shutting down in a regular pattern every second or so. I managed to get it to work by running the pump during this time, after a while the machine just stayed on continuously and I could do some desoldering without problems. Unfortunately, the problem came back the next time I powered the machine on.

This makes me think something tries to detect the voltage, and because of the modified voltage, it shuts the system down. I have no idea where I should be looking for the problem though. Could you give me some hints on how to troubleshoot this?

[cybermaus]

That is a bit weird.

Powering on/off like you describe most likely would come from the logic pcb.
The 18-now-24 V goes to the logic board.

The logic board in my case was fed from a 15V separate wire from the PSU that was also resistance dropped from the 18, but on the board itself dropped to 5V with a &*05
Is this still the same in your more recent model? Can you check what voltages you are feeding the logic board, and if indeed the input goes directly to a 7805?
If so, feeding it 12V should be completely fine. Maybe your 12V is not stable enough, measure it continuously while you are using the device.

[vdtoorn]

Hallo Cybermaus,

Thanks for the response! I will do some measurements to see if the 12V is good, the front panel did work on 12V from my bench supply. Would the the front panel logic be switching the whole unit (including itself) off?

Interestingly if I leave the machine flashing (switching on/off) for a bit (20 times or so), it will end up working continuously, and switching it off and within minutes on again, it will work well immediately.
Only after leaving it to cool down (or drain some cap somewhere) it will restart with the self-on/off behavior.

I'm starting to think the PWM module is tripped to do an automatic shutdown for some reason, there are some voltage/current safeguards on the chip (according the the datasheet, if it is the same chip as in the linked schematic)

Anyway, I have some probing to do! I'll report back  if I find a fix.

[cybermaus]

To repeat, I would suspect the 12V rail, and its stability, more then the logic board.

How are you generating the 12V? What device/module are you using? Is it powerful enough?
Afterall, the PSU itself only does 18V. Now that you modded it, 24V, so you must also have added some sort of step down to 12V right?

[vdtoorn]

You're probably right, I've used a "Buck Converter XL4015 5A" to be sure it would be up to the task (from an online shop in NL). In operation it shows up as 12.0 volts on the meter. It has 3 lights, 'green' is on all the time meaning there is less than 400 mA output current, so probably no problem there.
This device has a variable amp limiter, I've now tried to increase that threshold with the potmeter a lot, preliminary results indicate this may be the culprit.

Ok that didn't help...