Help with an Omax PCB/Driver? - Page 1
Forum section: electronics / repair

author: pdtiger2015
author_rank: Newbie
timestamp: May 13, 2020, 10:54:48 pm
content: Soooo I messed up good. When I was cleaning my desk I unplugged both an electric picture frame and my Omax microscope. When I was putting everything back, I must've gotten my cords mixed up and instead of giving it 5 volts I gave it more like 12. Believe I burned up the chip/board that controls everything in the microscope. After light wouldn't come back on, I turned it over and removed cover to find this control PCB had a burnt electrical smell to it.Saw on another site post where someone did the same thing. They suggested going back with a "Buck Regulator". I think this might work, but this damaged chip/board/driver has an additional input (2wire green clip) that controls the brightening and dimming of the light. Not just power in and power out.I included a picture of the .1w - 5w PCB control chip that was damaged. The red and black 2 wire clip in the back supplies power to this chip(driver?). The middle 2 wired red and black clip supplies power to the light. The 2 wire green clip i mentioned controls the dial that adjusts the brightness. I believe this dial varies the light by varying the voltage supplied to the led light.Im still tryna understand how a buck control works, but I believe it allows me to set the out going volts to the desired range. But would I be able to somehow solder on/incorporate this 2 wire green clip that controls the dimness of the light. If im understanding everything right this buck control would only allow me to set the voltage to 5 volts (brightest setting for light)? Would I be able to tone it down to maybe 2 volts when I desire a more dim light.Or even better yet, does anyone know where I might can find a replacement to this damaged 5w control PCB so I can avoid modifying the scope with the buck regulator? The numbers on the back of the PCB/driver are (DXL80D 160513).Thanks in advance for all the help. I apologize if this post is at all confusing or I rambled and repeated myself. I tried to include as much info as i could think to add

author: pdtiger2015
author_rank: Newbie
timestamp: May 13, 2020, 10:57:53 pm
content: Didn't add photo to first post for some reason*

author: pdtiger2015
author_rank: Newbie
timestamp: May 13, 2020, 11:00:15 pm
content: Just thought might as well add a photo of the back*

author: KX4QC
author_rank: Newbie
timestamp: December 01, 2021, 01:35:12 am
content: Solved. OMAX microscope good again! -And working without trouble on 12v!Disclaimer:This repair saved me, but will almost certainly invalidate your warranty. If you fried your PCB, it is probably not covered anyway, so what are you going to do?Yes, I too got the booby prize for plugging in 12v and fried the PCB, the LED and the potentiometer! Couldn't find a replacement DXL80D so decided that this is a simple LED dimmer project, and started over, using LM317T, a cheap part detailed athttps://circuitdigest.com/calculators/lm317-resistor-voltage-calculatorand available fromhttps://www.amazon.com/gp/product/B07VNNHWF9/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1. Details that might be useful: R1 470R, R2 the dimmer control (replaced with 4.7k 3W)https://www.amazon.com/gp/product/B017LBAWIA/ref=ppx_yo_dt_b_asin_title_o06_s01?ie=UTF8&psc=1. This control is heaver, but fits with a little reaming out of its mounting hole; the 4mm shaft rits the original wheel knob. I bridged a 1k multiturn between the two blue wires on the dimmer to calibrate the LM317T output voltage to the LED forward voltage spec. Anything else? Not really but a heat sink is advised for the LM317Thttps://www.amazon.com/gp/product/B081GRZB6S/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1. The silicone mat and insulator were omitted.Ah yes, I blew the LED too!Replaced with same spec 3W LEDhttps://www.amazon.com/gp/product/B01DBZICDC/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&th=1applied with silicone cooler paste to heat sinkhttps://www.amazon.com/gp/product/B06XKTRSP7/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&th=1.Calibration: (important) Turn the dimmer to minimum before applying power. Measure voltage at LED+ and LED- slowly increase the dimmer , adjusting the 1k preset to keep the voltage 2.8 - 3.0v. Eventually the dimmer will be at maximum, time to adjust the preset to exactly 3.0volts, the specified forward voltage for this LED.Tidy it all up and enjoy, safe in the knowledge that everything that can be broken, fried or just die is now replaceable quickly and easily.Yes, I know this is a cheap and dirty solution to the problem but it does restore full functionality and it's an inexpensive repair to the fine microscope.I suspect that this simple LM317 "hack" might be a prctical starting point for any other LED dimmer projects?(If we wanted to be "respectable" we wouldn't use variable voltage, we'd use a constant current source and PWM dimmer for much more moolah and complexity. This li'l LM317 is robust and easy and works.)the repair with LM317TThe LM317 dimmer board. That's all there is to it!The dimmer potentiometer bridged with calibration multiturn preset.Fried original PCB. Good riddance! The microscope is better now than before.

author: KX4QC
author_rank: Newbie
timestamp: December 01, 2021, 04:34:04 am
content: A welcome bonus - I should have mentioned that the LM317 repair described now makes the microscope almost impossible to damage with the wrong wallwart.It should now tolerate and function well with correct polarity DC 5v - 35v power adapters.Why the F didn't Omax use this solution originally? It would have saved many people a lot of trouble....Maybe a little off-topic, but this LM317T solution also controls LEDs in our RV. Give it a try!

author: KX4QC
author_rank: Newbie
timestamp: December 03, 2021, 02:51:55 am
content: A small update:A polarity guard diode has been added to the +v power in.The adjustment has been moved to the board. Neater and easier all round. The fix continues to work well, and seems vastly superior to a hugely expensive dealer repair to restore function but also future vulnerability to wrong voltage or polarity. Seems widely applicable to many Omax microscope models, maybe many others that use a 3W LED illuminator.-And yes there is now another such board dimming a LED in our RV. Not bad for under $5 in parts.

author: mcovington
author_rank: Regular Contributor
timestamp: December 20, 2021, 11:41:28 pm
content: I am facing the same problem and will probably do my own design. Shouldn't we be focusing on current regulation rather than voltage regulation for an LED? And can you share your schematic?

author: mcovington
author_rank: Regular Contributor
timestamp: December 20, 2021, 11:45:40 pm
content: Also, looking at Amazon, I am wondering why they call it a 3W LED when specifying 3.0 V and 600 mA. That would be 1.8 W unless I've missed something... 3.4 V and 700 mA (their absolute max.) = 2.4 W.

author: fzabkar
author_rank: Super Contributor
timestamp: December 21, 2021, 12:00:29 am
content: Here is a simple current source using the LM317:https://www.circuitsdiy.com/lm317-constant-current-source/

author: Durghan
author_rank: Newbie
timestamp: August 26, 2022, 03:20:22 am
content: Hey, so, I've gone and done the same dumb thing. I would like to fix my microscope but I'm a complete idiot when it comes to electronics in this way and I'm practically blacking out trying to understand what I need to do. I'm sure in the grand scheme of things this is actually pretty simple, but you wouldn't by any chance have made a complete idiot's guide to doing this somewhere have you? I've come back here a few times since someone sent me here a little over a month ago and I don't feel like I'm getting any closer to understanding exactly which parts to buy and how they should be assembled. Thanks!