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

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Beau Geste:

--- Quote from: alxtr1bal on February 15, 2023, 09:00:48 am ---
--- Quote from: Beau Geste on February 12, 2023, 05:09:30 pm ---
--- Quote from: alxtr1bal on February 09, 2023, 07:03:57 am ---Hello guys;

I did this cool modification on my old station i bought some years ago , the PSU is the same version as OP. So i now have a steady 12v (from 23.5 to 12v with the converter) that powers the board with the switches for fan, display and pump.

My problem is that the temperature of the heater never stops ! it goes over 500, then the display says "Error" , but the heater continues to heat (even becomes red !!) ...

What could this be related to ? psu (opto isolator ?) , or the control board part ?

--- End quote ---
Hi,
I had the same problem. I solved it by buying another control board. Probably the fault is in the TL7805 and TL431 voltage regulators. Check them with the multimeter if they are OK or not .However, the control board does not cost more than 30 euros.
Ciao :)

--- End quote ---

Ciao there :)

Thanks for the suggestion, i'll check that !

Do you remember where you bought the control board replacement?

Thanks again ;)

--- End quote ---
Sorry for the late reply. Yes, I bought the control board on Allegro.pl. :)
https://allegro.pl/oferta/plytka-sterujaca-wyswietlacz-lcd-niebieski-zd-8915-11026793876?reco_id=17400eef-221e-11ec-9f46-0c42a1097bde&sid=041047f9c36843e364ecb91b45c568a2755aa386fe7

Beau Geste:

--- Quote from: alxtr1bal on February 18, 2023, 03:32:34 pm ---Hello guys, just to let you know, i replaced on my PSU the double schottky diode mosfet (that was shorted) (by a FQP50N06) , and the optoisolator for the temperature (that was shot) (by a pc817). 

:phew:

Working again.

--- End quote ---
Great! You can't go wrong. When the temperature is out of control it's either the Mosfet on the PSU or the TL7805 and/or TL431 on control board  :-+

cybermaus:

--- Quote from: Spawn on March 13, 2023, 07:29:48 am ---@cybermaus thanks for posting this information.

I ordered a ZD-8915 couple of weeks ago from Eleshop, but it was in backorder and I had to wait 2 weeks before it get delivered, meanwhile I came across this topic and I also planned to do the modification.

Yesterday I opened up the ZD-8915, and it has (again) a newer version power supply (ZD150-PQ32/15) and it is still a 18V power supply.
Took a picture of the resistors around the TL431A, but it was hard to get a nice picture, it is buried between higher components, so far I can see it is now R20 which needs a parallel resistor on it, the value is 2K4 and I think it needs a 6K8 resistor parallel on it for +/-24V

I am not that great with this kind a stuff, can somebody please check for me if I got it right with the R20 and the parallel resistor?
The other problem is getting in there with a soldering iron to solder another resistor, since there is no room at all for the iron.

I hope that my picture is clear enough.

--- End quote ---

Hi SPawn. No one got back to you? Sorry, but I have been busy, not paying attention to eevblog.
Anyway, the picture is really too fuzzy. If you want some advise on which resistor, you'd really have to try and get a clearer picture, where we can see what is connected to what.

vdtoorn:
Hi, just getting back to the subject of the intermittent startup, that appears to be fixed!. Briefly, the ZD-8915 was not starting immediately but instead switched on/off all the time with a time interval of about 1 second.

It turned out it was due to the VCC of the FSCQ1565RT (the 5-pin chip PWM chip attached to the heat sink), that starts up with power from a capacitor to begin with, but later gets its power from a winding of the main transformer. The transition to that second state failed because of a cold/damaged solder joint of capacitor E5, in my case.
Apparently the capacitor got warm during the startup attempts and made contact so operation would resume after 20 times or so. A power cycle of the device would switch on immediately but the fault returned when everything cooled down.

Sorry to say that didn't actually fix it, admittedly I tried without the gun attached. I think I'll just reverse the voltage mod, but at least the fan and front-end are now running off a stable supply. Guess the high voltage took some part of the power supply out of spec

Kudos to Andy Watson working out the schematic, for the 8915 there is one difference I found for my version (v4): the bridge rectifier is not 4x 1N4007 but 4x 1N5399, which are rated 1.5A instead of 1A.

radiofan:
FYI, I recently solved the intermittent startup problem on my ZD-915. I replaced E6 and D9 with a fast recovery diode (1N4937) and it is working again. I increased my heater voltage a tad, to 20V.

Much thanks to @Texmisure for the circuit diagram.

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