Need help with SMPS / MA3810 chip - Page 1
Forum section: electronics / projects

author: flolic
author_rank: Frequent Contributor
timestamp: February 24, 2012, 09:01:46 pm
content: I am trying to repair old Daikin air conditioner inverter board that is damaged by water. It has small SMPS driven by MA3810 chip.Original chip is fried, and also one power resistor (50 ohm/ 6W) in series with rectifier, on the primary side. I replaced that resistor and put new chip, butsupply is still totally dead. Every other component, and there are only few on the primary side, and few more on the secondary is tested ok.I can't test the transformer but it looks ok (no shorts between different windings and no breaks). IC gets lukewarm after minute or so.I connected my scope to the transformer but there is nothing, supply does not even try to start on power on.I don't have schematics. Datasheet for that MA3810 IC is useless (http://dl.dropbox.com/u/21387397/MA3810.PDF)I would appreciate any help.Filip

author: PeterG
author_rank: Frequent Contributor
timestamp: February 24, 2012, 10:00:29 pm
content: Any chance of some pics so people can see whats going on?Regards

author: flolic
author_rank: Frequent Contributor
timestamp: February 24, 2012, 11:40:27 pm
content: Quote from: PeterG on February 24, 2012, 10:00:29 pmSureThis is the whole board, with supply circled in red:This supply generates voltages for MCU and adjacent circuits (5V/12V), and three separate voltages for compressor opto IGBT drivers.Close ups:

author: Bored@Work
author_rank: Super Contributor
timestamp: February 24, 2012, 11:58:27 pm
content: Did C1 shit all over itself?

author: flolic
author_rank: Frequent Contributor
timestamp: February 25, 2012, 12:09:05 am
content: You mean C11? No, that is some kind of glue.

author: Rerouter
author_rank: Super Contributor
timestamp: February 25, 2012, 02:36:27 am
content: so have you been testing it with some kind of minimum load?. also you said you measured no voltage on the transformer, that would sound like a dead transformer or a dead short on its output, i would be looking at that tantalum and measuring resistance across system ground and the voltage outputs of the chip,

author: SeanB
author_rank: Super Contributor
timestamp: February 25, 2012, 09:35:22 am
content: Change R34 and R8, they are likely to be open, and R8 is a fusible device, so will have gone up with the chip. Check the optoisolator OIS20 by replacement as well. Normally if the resistor R4 has died I would change both the bridge rectifier and C11 as a matter of course. Check all tracks for continuity, they can break near invisibly.Can you not get the board from Daiken as a spare?

author: flolic
author_rank: Frequent Contributor
timestamp: February 27, 2012, 11:22:40 am
content: First, thanks for all suggestions. But supply is still dead...Quote from: Rerouter on February 25, 2012, 02:36:27 amYes. The rest of electronics is permanently connected to supply.Quote from: SeanB on February 25, 2012, 09:35:22 amEvery component is tested, all are ok. No broken tracks. I tried another IC but it is the same. I replaced optocoupler.I can get replacement board from Daikin but it is very expensive.

author: Psi
author_rank: Super Contributor
timestamp: February 27, 2012, 11:47:39 am
content: Quote from: flolic on February 27, 2012, 11:22:40 amAre you sure that it doesn't require some logic signal on one of the connectors in order for the powersupply to start up.Often if you power up a pcb on the bench with all the connectors unplugged you have to find the pin that enables the board to powerup.

author: flolic
author_rank: Frequent Contributor
timestamp: February 28, 2012, 08:03:23 am
content: Quote from: Dave.S on February 27, 2012, 08:20:09 pmYes, that's true. Signal from indoor unit is needed to turn on aircon. But this supply (in outdoor unit) is always on. There is no "enable" input or something like that. In fact, whole this board is always on, and just waits for a command to start compressor, fan and valves.I had another board just like this one, and I know that supply should start as soon power is applied.

author: Psi
author_rank: Super Contributor
timestamp: February 28, 2012, 10:07:38 am
content: Yeah, have a closer look, from the pic it appears the corner of it may have exploded.

author: nukie
author_rank: Frequent Contributor
timestamp: March 03, 2012, 12:17:50 am
content: sharp eyes you got people! makes tv forensic shows look dumb. is the PCB coated with clear conformal coating?

author: flolic
author_rank: Frequent Contributor
timestamp: March 03, 2012, 05:44:37 pm
content: Quote from: nukie on March 03, 2012, 12:17:50 amYes.Rectifier (covered in white glue) is also ok.

author: nukie
author_rank: Frequent Contributor
timestamp: March 04, 2012, 12:19:10 am
content: then beware of moisture trapped in between the conformal coat and PCB. preheat the board for a few hours at 60-70c before powering up.

author: flolic
author_rank: Frequent Contributor
timestamp: March 05, 2012, 08:15:16 am
content: That was the first thing I did, baking for hours at 80-90C...

author: flolic
author_rank: Frequent Contributor
timestamp: March 06, 2012, 07:38:19 pm
content: I tried everything and only thing that can still be broken is transformer.It looks perfectly normal, no funny smell and no breaks in windings.But I think it must have shorted few turns in primary winding.I connected primary winding to my FG through 50 ohm serial resistor.FG is set to pulse mode, pulse width is 1us with 10V amplitude.Scope is connected directly to winding.What do you think?

author: level13
author_rank: Newbie
timestamp: July 03, 2013, 08:39:04 am
content: did you found the problem with that IC? I have the similar board from daikin have same problem.

author: peter.mitchell
author_rank: Super Contributor
timestamp: July 03, 2013, 01:18:16 pm
content: 1) find out what voltage/current requirements are2) find power rails on board3) desolder existing components4) attach external 3rd party isolated power supply5) close the lid and forgeddaboutit

author: nuno
author_rank: Frequent Contributor
timestamp: April 09, 2020, 04:07:32 pm
content: Same problem here, also by water damage. PSU doesn't come up.Everything looks ok except an apparently damaged (open) diode inside the PSU IC (VD1 in the attach). I bypassed it with an external diode but it still doesn't "convert". Voltage gets there. Anyone with further information?I found the internal schematics of MA2810 and I assume the MA3810 is similar just different power handling (similar datasheets; datasheets are incomplete, no pinout nor internal diagram), (reverse enginneered) schematics makes sense with such internals, see MA2810 internal diagram attached. Can't find any manual, schematics, whatever for this A/C model; can find for the newer models but not for these older onesUnfortunately this PSU has also several outputs with other voltages and opto couplers and other stuff, I haven't looked into it in detail, which doesn't make the task of replacing it with something "off board" easy.By the way, I have fixed this board before (another totally different problem, track corroded), and it can be powered up by 62VDC into the mains AC input, so it's an easy test. I didn't try lower voltages to see what's the minimum. Plug-in the LEDs board's 2 connectors, as one of them (the big red one) is for a mains fuse which lives in the LEDs board. The board consumes ~30mA with nothing else connected.

author: nuno
author_rank: Frequent Contributor
timestamp: April 09, 2020, 04:31:56 pm
content: I'll take the opportunity to tell a tale of a pitfallI use 2 series ungrounded 31V max lab DC power supplies to get the 62V. In my naiveness, I set and forget one's limit to 1A and then controlled the limit on the other (much lower, 50 - 100mA). In the test (the one with the bypassing diode I mention above), there's almost a short on the input supply. Fact: these lab PSU settings don't provide protection... because the 100mA limited PSU forces zero voltage, but the other PSU's current can still pass through the 0V source, so I provided 31V 1A to the equipment. Gladly I am always on alert and act quiclkly.

author: nuno
author_rank: Frequent Contributor
timestamp: April 23, 2020, 09:23:27 pm
content: Ok, just to let you know I've able to fix the board. There was a open 1.5M resistor on the PSU, R34. In the circuit it measures much lower than this, so it's not possible to test it without isolating a leg (I usually do it by cutting a track). This resistor biases the power switch (MA3810 pin 3) to V+ (rectified mains, so, where I live, some 330V). These A/C boards have been beaten to death by the weather, so I try hard not to remove any components for testing or doing any hard intervention. When everything else fails, I start using the physical test; I slightly bend the board in several directions, I pull and push a bit on some components, trying to find an intermittent fault. That's when R34 made contact and the PSU came up. Replaced it and it's back to work. The resistor is visibly corroded at the ends, although still mechanically stiff.In attach my partial PSU reverse-enged schematics; sorry about the hand-cad. Don't trust your live on it.The V+ node then goes to a 7812, etc. See what I believe (from part datasheet and my measurements; still don't know why doesn't seem to be a diode at pins 1-2) to be also the internal diagram of MA3810 in thispost above.Quote from: nuno on April 09, 2020, 04:07:32 pm