Author Topic: Need help with SMPS / MA3810 chip  (Read 11181 times)

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Offline flolicTopic starter

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Need help with SMPS / MA3810 chip
« on: February 24, 2012, 09:01:46 pm »
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, but
supply 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
 

Offline PeterG

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Re: Need help with SMPS / MA3810 chip
« Reply #1 on: February 24, 2012, 10:00:29 pm »
Any chance of some pics so people can see whats going on?

Regards
Testing one two three...
 

Offline flolicTopic starter

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Re: Need help with SMPS / MA3810 chip
« Reply #2 on: February 24, 2012, 11:40:27 pm »
Any chance of some pics so people can see whats going on?

Sure  ;)

This 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:




 

Offline Bored@Work

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Re: Need help with SMPS / MA3810 chip
« Reply #3 on: February 24, 2012, 11:58:27 pm »
Did C1 shit all over itself?
I delete PMs unread. If you have something to say, say it in public.
For all else: Profile->[Modify Profile]Buddies/Ignore List->Edit Ignore List
 

Offline flolicTopic starter

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Re: Need help with SMPS / MA3810 chip
« Reply #4 on: February 25, 2012, 12:09:05 am »
You mean C11? No, that is some kind of glue.
 

Offline Rerouter

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Re: Need help with SMPS / MA3810 chip
« Reply #5 on: February 25, 2012, 02:36:27 am »
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,
 

Offline SeanB

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Re: Need help with SMPS / MA3810 chip
« Reply #6 on: February 25, 2012, 09:35:22 am »
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?
 

Offline flolicTopic starter

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Re: Need help with SMPS / MA3810 chip
« Reply #7 on: February 27, 2012, 11:22:40 am »
First, thanks for all suggestions. But supply is still dead...

so have you been testing it with some kind of minimum load?
Yes. The rest of electronics is permanently connected to supply.

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?
Every 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.
 

Online Psi

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Re: Need help with SMPS / MA3810 chip
« Reply #8 on: February 27, 2012, 11:47:39 am »
Every 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.

Are 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.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline flolicTopic starter

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Re: Need help with SMPS / MA3810 chip
« Reply #9 on: February 28, 2012, 08:03:23 am »
He is right , all aircons need a logic signal / analog voltage signal from the indoor unit for the power supply to fire up .

Yes, 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.
 

Online Psi

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Re: Need help with SMPS / MA3810 chip
« Reply #10 on: February 28, 2012, 10:07:38 am »
Yeah, have a closer look, from the pic it appears the corner of it may have exploded.

« Last Edit: February 28, 2012, 10:13:01 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline nukie

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Re: Need help with SMPS / MA3810 chip
« Reply #11 on: March 03, 2012, 12:17:50 am »
sharp eyes you got people! makes tv forensic shows look dumb. is the PCB coated with clear conformal coating?
« Last Edit: March 03, 2012, 12:20:48 am by nukie »
 

Offline flolicTopic starter

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Re: Need help with SMPS / MA3810 chip
« Reply #12 on: March 03, 2012, 05:44:37 pm »
is the PCB coated with clear conformal coating?
Yes.

Rectifier (covered in white glue) is also ok.
 

Offline nukie

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Re: Need help with SMPS / MA3810 chip
« Reply #13 on: March 04, 2012, 12:19:10 am »
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.
 

Offline flolicTopic starter

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Re: Need help with SMPS / MA3810 chip
« Reply #14 on: March 05, 2012, 08:15:16 am »
That was the first thing I did, baking for hours at 80-90C...
 

Offline flolicTopic starter

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Re: Need help with SMPS / MA3810 chip
« Reply #15 on: March 06, 2012, 07:38:19 pm »
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?
 

Offline level13

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Re: Need help with SMPS / MA3810 chip
« Reply #16 on: July 03, 2013, 08:39:04 am »
did you found the problem with that IC? I have the similar board from daikin have same problem.
 

Offline peter.mitchell

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Re: Need help with SMPS / MA3810 chip
« Reply #17 on: July 03, 2013, 01:18:16 pm »
1) find out what voltage/current requirements are
2) find power rails on board
3) desolder existing components
4) attach external 3rd party isolated power supply
5) close the lid and forgeddaboutit
 

Offline nuno

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Re: Need help with SMPS / MA3810 chip
« Reply #18 on: April 09, 2020, 04:07:32 pm »
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 :palm:), (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 ones  |O

Unfortunately 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.
« Last Edit: April 09, 2020, 04:32:47 pm by nuno »
 

Offline nuno

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Re: Need help with SMPS / MA3810 chip
« Reply #19 on: April 09, 2020, 04:31:56 pm »
I'll take the opportunity to tell a tale of a pitfall  :D

I 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.
« Last Edit: April 09, 2020, 04:33:43 pm by nuno »
 

Offline nuno

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Re: Need help with SMPS / MA3810 chip
« Reply #20 on: April 23, 2020, 09:23:27 pm »
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 :D . 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 this post above.


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 :palm:), (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 ones  |O

Unfortunately 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.
« Last Edit: April 23, 2020, 09:31:17 pm by nuno »
 


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