Modification of chip in UVC lighting timer circuit - Page 1
Forum section: electronics / projects

author: perthm
author_rank: Newbie
timestamp: November 04, 2022, 08:18:59 am
content: Hi allI have a 40W UVC globe for pond sterilization, with an electronic timer built in. After powering up, the button on the front selects either a (one off) 2 hour or 6 hour operation.I would like to bypass the timer, so the unit comes on and stays on. I know how to short across the actual switch, but do not know what to do to bypass the timer chip. This way I dont have to press the button every day, which is not practical!Thanks in advance for any help.Allan

author: jpanhalt
author_rank: Super Contributor
timestamp: November 04, 2022, 09:09:37 am
content: I only detect 2 chips on that board. One is obviously 8-pin. The other chip (?) above it looks like 3 pin and may be a transistor or voltage regulator.Otherwise, not much else can be identified. Try to read what's on the 8-pin chip. Circuit trace and find which pins go to ground and positive supply. If you can get a decent part number off the chip, then circuit tracing will not be necessary. It is possible that chip is just an NE555 derivative.

author: ledtester
author_rank: Super Contributor
timestamp: November 04, 2022, 12:51:49 pm
content: What's the make/model of the unit? It can help to find more information about it online.Also, can you post higher resolution pics? And a pic of the UVC lamp itself would help to find more info.Here's some things to try:1. What happens after 6 hours if the button is permanently pressed down?2. What happens if the unit is powered up with the button pressed down? If it starts up then you can keep it going 24 hours a day with a programmable mains timer (like a light timer).

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 04, 2022, 01:02:16 pm
content: The 8 pin chip is almost certainly a microcontroller, figure out which pin controls the output and rewire it to always be active.

author: perthm
author_rank: Newbie
timestamp: November 04, 2022, 01:09:16 pm
content: Thanks. Unfortunately the chip is blank.

author: perthm
author_rank: Newbie
timestamp: November 04, 2022, 01:15:53 pm
content: I shorted the switch and when powered up it goes straight to the 2hr timer then turns off. Then I used a mechanical timer and pushed down a tag every 2 hrs. This keeps it going but I would prefer the correct way however.

author: jpanhalt
author_rank: Super Contributor
timestamp: November 04, 2022, 01:53:21 pm
content: If you can trace where power (aka VCC or VDD) and ground to the chip goes, it might help identify it. PIC 8-pin MCU have Vdd on pin1 and Vss on pin8. A 555 derivative has those pins reversed, i.e., pin 8 is Vdd/power.On both types of devices pin4 goes to Vdd, but on the PIC there should be a resistor between the pin and Vdd. The attachment shows how pins are typically numbered on 8-pin DIP IC's.EDIT:If you have a voltmeter, you might do an experiment. With the circuit powered up but the UVC lamps off, measure voltage from every pin to ground and write them down. Then initiate a one-shot on, and repeat those tests. That may tell you which pin is actively turning the lamps on and off. Note, active can be from low to high or high to low.