flashlight pcb suspect - Page 1
Forum section: electronics / repair

author: brent
author_rank: Newbie
timestamp: May 15, 2016, 06:49:08 pm
content: I have a 3 m candlepower re chargable flashlight. Battery is fully charged however the switch only allows power to the bulb for about 8 seconds then cuts off.I have disassembled and find no corrosion nor any dirt. the switch seems solid. all wires appear unbroken. I have moved all the wires to check continuity but no change. I still get about 8 seconds. Now I fear that one of the pcb's is the problem. There are two - one for a bulb intensity reostat, and another that appears to be tied to the re charging circuitry. I'm not sure if pcb is the correct term but it is a board where tiny resistors and such are connected and the wiring goes to solder bits on it.Is there a simple way to know if this is junk or can I repair it?Thank you.

author: tautech
author_rank: Super Contributor
timestamp: May 16, 2016, 02:45:58 am
content: Welcome to the forum.Is this a LED, HID or incandescent unit?Some pics will help.

author: TheMG
author_rank: Frequent Contributor
timestamp: May 16, 2016, 03:40:24 am
content: I'd suspect the battery before anything else. How old is it and what type of battery is in it?Since you mentioned it uses an actual bulb, is this one of the older style halogen flashlights with a rechargeable lead-acid battery inside? If so, the battery is probably toast and needs to be replaced.It sounds like the circuit is just doing its job and turning the flashlight off once the battery voltage drops too low.Check the battery voltage when powering on the flashlight and until it shuts off.

author: brent
author_rank: Newbie
timestamp: May 16, 2016, 01:16:24 pm
content: Thank you. It is a non LED, blue incandescent bulb. The battery is a LONG WAY re chargeable lead acid, and about 8 years old. I took a closer look at the meter and batt voltage and it appears to be sitting around 5 volts, so perhaps it is the battery, as suggested. I checked the resistance across the battery terminals and get about 3 or 4 ohms when it stopped decreasing. no load.It was charged overnight, so should have been ok. It is a lead acid re chargeable type that says 'cycle use: 7.25-7.45v' and 'standby use:6.8-6.9v'.As I watch the voltmeter and press the switch on the light, the voltage at about 5, waggles about a volt or so down, then up, and continues to do this while sw is held. when I release the sw, it steadies out at about 4.5 to 5 volts. here are some pics. I'm thinking you are correct regarding the battery being toast. Do you agree?Many thanks for the assistance!

author: tautech
author_rank: Super Contributor
timestamp: May 16, 2016, 03:07:54 pm
content: Quote from: brent on May 16, 2016, 01:16:24 pmTheMG may have nailed it but there are other checks you could do.With your voltmeter set to the 10V range for better resolution you could repeat the tests to check the battery voltage when the light fails is of a repeatable value.As we can't see the underside of the PCB we can't be sure if there's battery monitoring circuitry present or if it consists of only charging circuitry.Otherwise another 6V supply instead of the battery could confirm if the battery is toast.That mightn't be too easy as it'd probably need to supply ~5A.Images can be inserted (not pdf) by inserting the uploaded image file link address like this: imgimage address/img (brackets missing)You can edit a post after copying the link address, paste the link, highlight it and click on the Insert Image button.

author: brent
author_rank: Newbie
timestamp: May 16, 2016, 09:14:41 pm
content: I hooked up a 6 volt 6amp charger to the terminals and the light works perfectly. So I guess I'm ordering a battery.Many thanks for the help folks!

author: tautech
author_rank: Super Contributor
timestamp: May 16, 2016, 09:28:32 pm
content: Quote from: brent on May 16, 2016, 09:14:41 pmGlad you cracked it, 8 years usage is pretty good for SLA regardless of brand.

author: TheMG
author_rank: Frequent Contributor
timestamp: May 18, 2016, 12:20:14 am
content: Quote from: brent on May 16, 2016, 09:14:41 pmYep, at 8 years old and the fact that it drops to 5V when you turn on the light, that battery is definitely past its useful life.