Hello Electronics Fans,

Today I have an LG, LD651EBL, 65 Pint Dehumidifier that has suddenly stopped working. Up until yesterday, it worked well although occasionally it gave me the 24 error indicating the pressure switch malfunctioned. However, a few minutes unplugged and it worked again after plugging it back in.

Now, however, it is a total failure. here are the symptoms....

1). The Display Panel does not respond at all when plugged in. Nothing, no lights, no beeps. (With the exception that there is one quick beep just as it's plugged in)...but then nothing else at all. So it's as if power is not getting to the power panel. Even though a few quick tests showed that it is)

What I have tried or checked.....

1). The fuse. On the Control board there is a small, glass Buss fuse (3.15, 250v) so I replaced it. No change
2). On the Display panel I checked the wires with a VOM and found 12.56v at two of them (but not the Red and Black wires)
3). I tried cleaning everything. no change.
4). Carefully inspected the Display board with a magnified, lighted loupe for indications of overheating, swollen CAPS, broken or burned traces etc. Nothing obvious.

So at this point I'm wondering if someone could give me some assistance in diagnosing the problem. Even if the compressor was bad or the freon had run out, (which I doubt), the Display Panel should still light up, so I'm thinking this is more of a power supply issue.

Any suggestions appreciated. My intent is to try to trace back the power from the cord to the Main Control board, then from there on to the Display Board.
Somewhere there is a voltage buck board or some other means of converting the 120VAC to DC 12v to the panel. That's where I'll probably explore next. This dehumidifier is over $200 new and does a great job so IF I can repair it for less than $50 I'd be thrilled.

Thanks for any help!

Photos below.....if more photos are needed, just say so;

Here is a photo of the front and back of the Display Board panel

- The two larger rectangular IC chips are ULN2004L (high-voltage, high-current Darlington arrays )
- The small square chip in the center upper right is a 24CO1WP (appears to be an EEPROM of sorts) https://datasheet.octopart.com/M24C01-WDW6TP-STMicroelectronics-datasheet-17703652.pdf
- The larger, diagonally placed main IC chip is a TMP89FM42AUG (High-performance 8-bit microcontroller in compact package with On-chip oscillator and power-on reset circuit )


And here is a photo of the Main Control Board & HVAC control unit

 

A good place to start, as you mentioned, is to check for DC voltage. There are 4 diodes on the HVAC board ... two would be AC voltage connected, and two would be DC voltage, assuming the electrolytic filter capacitor is still good. Would you be able to investigate those diodes?

https://www.google.com/search?sourc...20i263j0i312.Iz1kPg8-gL0#imgrc=CdW59ylV2N5AqM:

 

all 4 tested good.

445ohms one way........Zero continuity the other

 

A concern I have is that if one of the IC chips have tanked, especially the TMP89FM42AUG, I'm not sure how I would determine that.

 

In particular, two opposing corners of the diode bridge should have AC voltage, showing that the mains transformer is operational ( a measurement to be cautious with ). The remaining two corners of the diode bridge should show a DC voltage, if things are working properly. The location of the AC connections to the transformer should be traceable to the transformer by inspecting the solder side of the board. If you measure a nominal DC voltage like +5, or +12 volts, then your DC supply is likely working. One frequent part that fails on older equipment is the DC supply filter capacitor, likely the black electrolytic capacitor in the photo. If you find that the measured DC voltage is unusual, you may have to de-solder that capacitor and see if there is a short through it. ... Assuming that you do not have a scope.
As far as the IC chips which you mentioned, you would have to identify them and determine their function. ... A quick search did not turn up a schematic diagram for this unit.

 

Pictured below is the Display Panel Board end of the connector cable from the Main Control Board to the Display panel Board (User controls)

I checked the output (or tried to) from the Main Control board to the Display panel Board.
Because of these tests, I'm inclined to believe the problem lies with the Display Panel Board instead of the Main Control Board or the other components in the Dehumidifier.
I say this because the voltages at the pins seem very reasonable and expected. If the Main Control Board were the culprit, I would have expected few pins to show voltage and even then, erratic voltages. These all seem well regulated.

At this point, my primary objective is to get the Display panel to come back alive (lights turn on)

Pin 1 - 4.5v
Pin 2 - 4.5v
Pin 3 - 4.5v
Pin 4 - 1.8v
Pin 5 - 0v
Pin 6 - Ground
Pin 7 - 12.5v
Pin 8 - 5v
Pin 9 - 12.5v
Pin10 - 12.5v
Pin11 - 2 volts
Pin12 - 12.5v

 

Try to locate a schematic diagram, if one is available ... just guessing otherwise.

 

Try to locate a schematic diagram, if one is available ... just guessing otherwise.

After an exhausting search, there doesn't seem to be one available.
Have contacted LG but they probably have nothing to gain by providing one. Very long shot at best imo.

 

... can't help but wonder if the original pressure sensor error might be involved somehow. The problem with that is that removing it or even replacing it would require a Freon evacuation and refill ... no guarantee included.
... take something and tap on it a few times.

 

what I planned to do was to connect the compressor directly to 115v just to make sure the compressor is still working. I may have to utilize the capacitor, not sure yet. But IIRC, many of these pressure sensors incorrectly detected low pressure. The switch itself was the problem. I may bypass it. I don't think it's a freon issue. The thing worked great for over a year right up to the failure of the board.

 

Check the bucket switch for continuity operation ... seems to be a frequent problem that can disable operation. ... It would be subject to water vapor and possible sticking or corrosion ... not too difficult to check.

 

Check the bucket switch for continuity operation ... seems to be a frequent problem that can disable operation. ... It would be subject to water vapor and possible sticking or corrosion ... not too difficult to check.

Carefully checked that....working normally. I don't think that switch would completely stop the Control Board or Display Panel from activating.

except for one quick beep when I first plug it in, the Display panel is completely dead.

I was thinking.....the dehumidifier doesn't necessarily have to have a humidistat, fan speed control and all the other things on the Display panel to operate. All it needs is for the compressor to start and the fan to blow. Those two things alone would make it "work". So, while it wouldn't turn itself off, that could be done manually.

So I'm thinking if I cant get the Main Control Panel and Display Board working, I may just rig up the unit with an On/Off switch to just turn on (and off) the compressor and fan manually. Bare bones dehumidifier. Heck, for that matter, I can rig up the bucket full switch to interrupt the power so I could still make the bucket full cut off work.

Features I'd lose.....
1). LED humidity percent display (no biggie)
2). Humidity setting (no biggie, I have a humidity meter in the room anyway)
3). 2 hour or 4 hour run cycle timer (no biggie there, just turn it off when the room is dry)
4). Fan Speed (big deal.....set it to one speed all the time)

NONE of these are really all that important.

We get so used to the luxuries of electronic control that we forget that most of it isn't really essential for basic operation.

This has me thinking....I have DHT22 humidity sensors on hand because I'm into the Arduino stuff. I have so much electronic gadgetry and IC's and buttons and components etc, I'll bet I could use Arduino to replace Most of those functions listed above. essentially replacing the Control Board with Arduino.

Of course, I could order a new Main Control board and/or Display Board, but there's no guarantee it would solve the issue. It would be SO much easier just to buy a new Dehumidifier....but where's the challenge, fun and learning in that?

 

The source here states that a defective control board will cause the unit not to run:
https://www.repairclinic.com/Repair...616-/new/LG-Dehumidifier-not-working-LD651EBL
...
It says that they are available ... replacing it might account for the lights out condition as well as the error code.

 

... ok ... sounds like a project .... post it on the forum if you get anything working.

 

Thanks for the assist DRC, I will

 

Called LG and to my surprise, they pointed me to a service manual that had a circuit diagram. However, SCHEMATICS are not available.
There isn't one for the Display board, but this helps
Notice in my test of the connector above, I had identified ORANGE as the common....and this Circuit Diagram supports that.....(See MOTOR connections, OR(Com))

 

As far as the DISPLAY BOARD is concerned......

It occurred to me......

Electronics manufacturers have the "capability" to program a wide variety of hidden commands into their devices today.
This unit has a micro processor and a EEPROM chip.
Is it "possible" they program the EEPROM so that after "X" number of events the unit totally disables itself programmatically?
Could there even be an onboard hour-meter that can count how many hours the unit has run in it's lifetime?