negative ion generator with UC.3843 - Page 1
Forum section: electronics / repair

author: frantal
author_rank: Contributor
timestamp: April 27, 2020, 05:41:20 pm
content: A long time ago I made a kit from an electronics magazine, of which I attach the schematic and components. I detect the 311Volt from the rectifier and the 5 Volt on pin 8 of the integrated UC.3843. I am unable to supply power to both the high voltage, through the L3 winding of the transformer T1, and to the fan and LEDs that are on the L4 winding. I tried to remove C10 and DS9 by putting a 10 MΩ resistor and in this case the fan turns, the LED lights up and I have 16.9 Volts on pin 7, but I don't have high voltage on the needles. If I reset everything as it was originally (removing the 10 MΩ resistor) the fan stops turning and the LED does not turn on either (on the fan terminal I measure 0,9 Volt !!). What could I do to make IC1 and MFT1 deliver a little more current sufficient to make both parties work? Thanks for help....

author: Manul
author_rank: Super Contributor
timestamp: April 27, 2020, 07:54:03 pm
content: I'm quite sure it is not because of little power, but because some HV diode (DS9-DS18) or capacitor (C10-C19) is failed.

author: nicknails
author_rank: Regular Contributor
timestamp: April 27, 2020, 08:52:24 pm
content: Most likely the multiplier. Are you able to measure the diodes for shorts or opens? You can measure the caps in-circuit and see if any are in the low-ohms indicating a short or a damaged cap.

author: frantal
author_rank: Contributor
timestamp: April 29, 2020, 03:32:51 pm
content: I tested all the diodes with a a 9 Volt battery and a multimeter and all gave me 4,6 Volt if conducting sense. Then I tested all the caps with a multimeter on Ohm position and all gave me non visible resistance, except one that showed 14 MOhm. I replaced it, but the result was the same. I have HV at the nails, but the fan and the led didn't work. The led gave a flash of light at the shutdown, nothing more and the voltage to the fan was 1,09 Volt. I had already tested the fan with an external power supply and it worked with 12 Volt and 65 mA of absorption.

author: Manul
author_rank: Super Contributor
timestamp: April 29, 2020, 04:27:35 pm
content: It is not easy to test high voltage capacitors without special leakage testers.I would try like this:Remove C14, if still bad (fan not spining) remove C13, if still bad remove C12 and so on. In that way you will at least isolate which section of multiplier is bad.

author: frantal
author_rank: Contributor
timestamp: April 30, 2020, 10:04:13 am
content: Many thanks for your suggestion!I removed the capacitors one by one, starting from C14 and going down to C11 (only on that row).At that point the fan started spinning.At this point I put the capacitors one by one, excluding C11 and it works! Now I have to find a capacitor to replace.

author: Manul
author_rank: Super Contributor
timestamp: April 30, 2020, 12:08:27 pm
content: In that case can be bad:C11, C16DS11, DS12You can remove C12 (isolate everything after this bad section) and for example try to change C11 with C14, or DS11 with DS16 (lets assume they are good) to find which one of these 4 parts in that section failed.

author: frantal
author_rank: Contributor
timestamp: May 01, 2020, 08:19:47 am
content: I had celebrated victory too soon!!I took away C12 and replaced C11 with C14: fan no more spinning... Then I replaced DS11 with DS16: no changement. Then I took away C11: the fan restart. I ordered 10 caps 4700 pF 1000V to replace, but it seems a defect of too much current absorption of the HV sector despite fan and led circuit.

author: Manul
author_rank: Super Contributor
timestamp: May 01, 2020, 05:06:12 pm
content: Did you try changing C16 and DS12? There may also be not one part damaged. Some capacitor(s) or some diode(s) is breaking down on high voltage. Actually this design is somewhat marginal if we look into voltages. Especially because it was designed for 220V mains voltage, but these days it is often more close to 240V.

author: frantal
author_rank: Contributor
timestamp: May 02, 2020, 08:35:32 am
content: Could help to have a High voltage HV probe, multimeter attenuator (self made, not so precise...) to test some of these components?

author: frantal
author_rank: Contributor
timestamp: May 05, 2020, 06:16:08 pm
content: I found some caps of 4700pF/1 kV. So I replace C11, C16 and others. Now it works...! but I noticed on the PCB solder side that sparks arise between the tracks where the power cable is soldered. Do you have any idea?

author: Manul
author_rank: Super Contributor
timestamp: May 05, 2020, 06:39:57 pm
content: Power cable? You mean mains power, 230V? Between live and neutral? Or you mean high voltage output cable?

author: frantal
author_rank: Contributor
timestamp: May 05, 2020, 07:12:06 pm
content: Yes I mean between the three points where the Power cable is soldered on the PCB (230 V)

author: Manul
author_rank: Super Contributor
timestamp: May 05, 2020, 07:32:44 pm
content: So it seems that high voltage ground is connected there. Is mains ground connected? Do you have grounded mains socket?

author: frantal
author_rank: Contributor
timestamp: May 06, 2020, 11:37:32 am
content: It was!I forgot that the power strip to which I attached the device did not have the earth pole! connected.Thanks again for all the help