Fixing A Defect Dual Motor Bedspring Unit
This repair is about a dual motor unit for a boxspring bed that suddenly short circuited. After which the copper tracks of the remote control were severely damaged and both motors no longer worked. Below photo shows a similar new unit that can be bought for around 104 Euro although it is uncertain if specs and size are the same compared to the now defect unit.
My brother, who’s motor unit it was, phoned me about this unexpected problem and emailed following photos to me.
Later that day I picked the heavy unit up at his house went home on my bike and started examining why it no longer worked.
Above photo showing the solder side of the by a 5 pin DIN wired remote clearly was missing some of its 3 lower copper tracks. They were partly gone and because there was no fuse or safety resistor anywhere in this unit it had destroyed the remote and most of its single pole changeover switches too. Which is a bad sign for the German manufacturer of this OKIMAT 3H4/6 dual motor control unit.
Following photo shows the top side with the 4 micro switches of this remote.
These DB2 marked 3 pole changeover switches have a make contact in the middle and a break contact on the 2 outer pins as below photo shows.
Previous photo showed the mainboard with simple 28V dc voltage power supply without any fuse or over current safety measure! Notice the 12 wires that made finding the culprit a little more difficult.
So before I could diagnose the problem I had to make a quick overview of the entire circuit with all its connections. With next drawing of the mainboard as result. Also to make sure no error escapes my attention.
Next photos show all internal wiring and motor switches that made examining the problem a little more complex. Both motors on each side of the unit with the transformer in the middle. Here the mainboard is shown turned upside down to show all wires. Normally the DIN plug is upward with the wiring downward. As the photo after following snapshot shows.
Previous photo also showed both micro switches that are side mounted on each of the moving motor blocks. And next photo shows more closely the right motor block with also 2 side mounted microswitches.
Previous photo again showed the simple mainboard on its solder side as said without any safety fuse or controller chip.
After all connections were examined following circuits made everything clear and simple. With first the mainboard circuit. And second drawing is from the now heavily damaged remote controller circuit.
Both top single pole changeover switches P3 and P4 connect both motors to the 28V DC voltage on the blue wire. While their black wires are grounded.
And with bottom changeover switches P1 and P2 the motor polarity is inversed. The on the motor blocks side mounted microswitches are break contacts that limit the maximum motor block movement possible.
Conclusion: The right motor under the mainboard was defect with only about 10 ohm resistance and had overheated the remote controller copper tracks with a large over-current. Burning away the copper tracks. Why the dual motor unit afterwards no longer worked. The left motor in the unit was fine measuring about 196 ohm. And after the still short circuiting right motor was removed from the mainboard connector that left motor was working splendidly.
All now depends on the availability of such a replacement motor and its price.
But clear is that the manufacturer made a wrong decision not to use any over-current protection in this design. Or any over-voltage protection either for that matter! That could have caused a fire or worse and certainly would have saved the remote!
Anyway hereby now is a complete matching service manual for this Okimat dual bedspring motor unit and probably many similar units.
Albert van Bemmelen, Weert, The Netherlands.
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Note: You can read his previous article on Completely Dead Original Wireless Xbox 360 Controller Fixed
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Parasuraman S
August 19, 2023 at 9:17 am
Vow! Excellent article! I am hearing about this device for the first time! What an effort taken to compile this article with excellent manually drawn circuit diagrams! There cannot be any match for you, dear! Excellent explanation too! Very informative! Many, many thanks for sharing!
Waleed Rishmawi
August 19, 2023 at 12:33 pm
Wow, impressive detailed repair. I hope you will find the right parts with the right price to finish the repair. Have a blessed day and thanks for sharing
Albert van Bemmelen
August 19, 2023 at 2:22 pm
My brother bought a complete new unit because the price of a new motor unit was almost as high as a new replacement motor. And he didn't want to wait 1,5 month on a new motor either. And only a new motor unit comes with a new 2 year warranty time. He now at least has a good spare motor.
The new motor unit came with a single 9V block battery extra. Apparently for unlocking the motor movement to be able to lower the bed unit even when there is no 230V AC power. Which the old unit didn't have.
And I ordered 4 new changeover DB2 pushbutton switches for about 8 euro so my brother also has a spare 5 pin DIN remote controller. But I am still waiting on the seller to ship those that apparently are German brand and now maybe first have to be send to China after they can be shipped to my country?
Yogesh Panchal
August 20, 2023 at 12:09 am
Albert,
Things are common now, after giving time & efforts you come to know parts not available or not worth to buy....
Albert van Bemmelen
August 21, 2023 at 1:47 am
Yes true. Recently I received 4 cheap brandnew China made Arduino Nano v3.0 modules with ATmega328p processor and incompatible CH340G usb to ttl chips on them. But none worked in Arduino IDE. Not over USB, and neither on the ISP connection!
Did cost me a whole day with many wasted hours of trying to program them with my Pololu programmer, my TinyUSB programmer, and even my TL866II and I gave up for now! Apparently it is a known fact of these clone modules with bad CH340G interfaces. Cheap always has its price!
Albert van Bemmelen
August 22, 2023 at 12:44 am
luckily I found and solved the problem today. With my TL866II I flashed the new optiboot Arduino 328p bootfile from ARDUINO IDE over into the bad not communicating only flashing L led and lit PWR led NANO 3.0 defect looking boards. That were not communicating over USB and neither on ISP!
BUT WHILE AND DURING THE PROGRAMMING the button on the NANO 3.0 module must be pressed in all the time! Else the Nano 3.0 boards are completely dead and are wrong read as being some strange $FFFFFFFF processor! Now the modules are working and correctly read as Vid: 0x1A86 processor and Pid:0x7523 boards! And can without any problem be used in any ARDUINO IDE program.
Albert van Bemmelen
August 26, 2023 at 7:53 pm
Update: after further opening the unit and after removing both DC motors they were German made type OKIN 24V - 011 VP 24V 10-04/C.
And in the drawing with the micro-switches to the blue wire of both left and right motor, only the top switches (parallel to D5 and D7) were break contacts. The bottom switches (parallel to D6 and D8) each were make micro-switch contacts.
No components were defect and even the short circuit on the right motor was now gone! So it appears that the shorting right motor was only temporary. Because now both motors perfectly worked when tested on my regulated power supply set at 24V upto the 28V as they also worked at in the circuit. Drawing only 0.183A (4.3W) at 24V and 0.189A (5.3W) at 28.14V DC. No doubt that only the previous short circuiting right motor had caused the burning away of the copper tracks of the remote controller board because nothing else is defect and the previous 10 Ohm was only measured on the blue and black wires of that motor!