TV lift board replacement

[Johnrobbinsjr]

I need some help finding a board to replace the one that burnt out on my TV lift in my travel trailer. It operates off of 12v and drives a motor to raise and lower a tv using a screw gear. There is a momentary rocker switch that you press once to raise the tv and press the opposite side to lower the TV. The board recognizes the limit of travel by measuring the current. So you press up and the tv rises to the upper limit when the motor current increases at the top the motor stops. Some for going down. The label on the board says H-bridge motor control w/current monitor. I have looked at several H-boards, but can't find any that meet the same functionality. Any help would be great. I will contact the original manufacturer, but I doubt they will be helpful, and it is a holiday weekend.

 

[kellys_eye]

If a replacement board is easily available (and affordable) then obviously sourcing one is the simplest solution as repairs, whilst fairly simple to do, require soldering skills and, potentially, some test voltage measurements with a meter.

Can you post a picture of the board (both sides). We might be able to determine if the unit is easily fixed.

 

[73's de Edd]

Mega-ditto . . . .
Can you post a picture of the board (both sides). We might be able to determine if the unit is easily fixed.
OR . . .if it is a Lift It brand. . .it has a 5 yr warranty .

 

[Johnrobbinsjr]

Well if we are going to try and repair this one, I should give you more details. This board powers on, but immediately falts when the button is pushed. Red LED comes on when it falts. Wait a minute and it goes off, push the button again and it falts. Do this enough times and you might get it to raise the tv once. This board has an optional remote board (green) on it. I don't have a remote for it (was never given one). Thought about removing that sub board to see what happens. The board gets very hot when plugged in. Specifically U4. I believe this is a mosfet. I know a few things about board components, but more on the noob level of diodes and resisters. I can solder very well I have no doubt that if I could identify a component that needed to be replaced I could do it. Unless it is a microchip. My best guess is the board is reading an incorrect current draw and shutting off as if the motor has reached the limit. I have not checked current draw of the motor, but it seems to be operating fine when 12v is directly applied. Hope this information helps and thank you for your help.

 

[kellys_eye]

U4 is a voltage regulator to provide 5V to the daughter board (wireless receiver) and is unlikely to be the cause of the problem - they do tend to get 'warm' (sometimes hot) to the touch - but it shouldn't get too hot to touch.

You should be able to power the board without a motor connected and still hear the relay click in/out as the relevant up/down function is ordered.

If there is a mechanical issue (have you checked for physical obstructions of the motorised parts?) then the over current situation will shut the motor down but without a motor connected this can't happen and 'normal' operation should be possible (measure the volts at the motor terminals to determine if power is being fed out of the board).

 

[Johnrobbinsjr]

Thank you for the information. I will check as you are suggesting, but I have checked for obstructions and I tried to operate with no load on the motor. It was doing the same thing. The voltage regulator or other parts in that area get super hot. Hot enough to melt the hot glue used to hold the board in its case. I will test voltage on outputs.

 

[kellys_eye]

U4 will have 12V, zero volts and 5V on the pins (not sure which order but providing you measure those voltages then the regulator can be considered 'ok'.

With no load connected there shouldn't be much in the way of power dissipation in that device. You could snip (temporarily) the +5V link to the wireless board to remove that as a potential cause of overload.

Then I'd be looking at the diodes D5, D6, D7 and D8 for a short circuit.

It's somewhere to start!

 

[Johnrobbinsjr]

Thank you again for the help. I checked the voltage regulator and I got 12, 0, and 8.5. 8.5 sounds a bit high and makes me feel that this is my problem.

 

[Johnrobbinsjr]

Can I completely remove the voltage regulator since I don't use the daughter board?

 

[Johnrobbinsjr]

I lifted the 12v pin removing power to the daughter board. There is no more heat from the voltage regulator or from the chips on the daughter board. The board still seems to function properly, I don't have the motor with me to fully test, but I have a good feeling this fixed my problem. I will update when I reassemble.

 

[73's de Edd]

Sir Johnrobbinsjr . . . . .

Tested motor with 12VDC and adequate current ?

Tested motor mounted in mechanics and reversed battery polarity to test in both directions ?

You say that you never had the RF remote . . . so did you hit the center photos white (RED rectangle around it ) pushbutton . ..or did it have to be extended outwards mechanically ? .

If that was the case, since the daughter board has been powered down, I think that it will be necessary to put + 5 VDC, temporarily, to either the left side of resistors R11 or R13 to initiate a motor lift cycle manually.
I certainly have enough mark ups below here to fully further explain system functioning in detail . . . . if so needed.

TECHNO REFERENCING:

73's de Edd

 

[Johnrobbinsjr]

Edd, thank you for your help and information. I did lift 12v pin from U4 and I have reassembled the lift and everything is working properly. It is absolutely brilliant that picking up one pin seams to fix my problem, I was going to buy a new board, but with everyone's help I was able to fix with a workaround. Edd, after looking at your comments about supply 5+ to R13 & R12, I am confused to why it does work properly as it is. Currently to initiate a motor lift cycle manually you ground Q3 or Q4. Love all the work everyone has put into this and I am learning more than I expected to about this type of circuitry. Thanks everyone again.