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Power Recliner controller

Tinkerer2

Jan 21, 2021
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My experience. I've checked and replaced capacitors, as well as, burnt resistors and relays before in a few electronics and managed to get them working again. I'm not an engineer.

The controller has a 120v to 24v ac transformer and a circuit board. The circuit board has a fuse which blew. Other components physically look ok. Replaced the fuse plugged the unit back into 120v without the chair attached and the fuse blew again. So something is shorted and it isn't the motor powering the chair.

The circuit board has resistors, capacitors, transistors, diodes, 2 relays and a rectifier. The relays are used to change the direction of the DC current to operate the chair into recline or upright.

I've checked the transformer and the rectifier. 23.9 v AC from transformer and 21.2v DC from rectifier. All of the resistors appear good, measured in circuit, they have the correct resistance according to color bands except that 2 are identical and read 740 ohms but the first 2 bands are not violet/purple and yellow. All of the resistors are blue and the colors of the bands are difficult to determine. They aren't burnt or anything. Maybe it is just my eyes (getting older). Since the 2 resistors are identical and the resistance is identical, I assume they are good. I also wouldn't think that if they were bad, they would be shorted and causing the fuse to blow. But, I'm not an expert.

If I get a photo attached here are the resistor measured values.
R1 0.99
R2 4.65
R3 0.74
R4 0.74
R5 4.64

I checked the capacitors with an ESR Meter. Meter says they are all good. They are not swollen or leaking.

The diodes. They all checked good except 2 showed voltage in both directions. I removed them and tested our of circuit. They only passed voltage the correct way when they were out of circuit. Maybe the test passed voltage back through the circuit and was read by the meter? I checked them multiple times in circuit and got voltage both ways so it wasn't user error.

Now to the transistors. This is the first time I've ever checked transistors and I'm not understanding my results.

First letter was red lead and second letter is black lead

1st Transistor
2N551 B 331
C and B Meter had a blinking 3 and then .000 so I think that was equiv. to OL
E and B 0.745
C and E 1.083
B and E 0.751
B and C 0.748

2nd
BC547 B 011
C and B 1.539
E and B 1.106
C and E 0.751
B and E 0.704
B and C 0.700

3rd
BC547 B 011
C and B 1.435
E and B 0.909
C and E 0.752
B and E 0.687
B and C 0.684

It should be noted that pin C of transistor 2 is connected to pin B of transistor 1 by solder on the back of the board. Looks original but I don't know why that would be.

Any help is appreciated. I'm going to have to order the 2 diodes I removed and not sure what else I may need to fix this. Oh, the rectifier and fuse were removed in these photos. I have a new fuse.
 

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  • Back of board (partial).jpg
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  • Front of board.jpg
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Tinkerer2

Jan 21, 2021
9
Joined
Jan 21, 2021
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I just checked a new rectifier and got 23.87v AC from transformer and 20.9v DC from the rectifier. All measurements were under no load conditions.

Shouldn't there be a voltage drop across the diodes in the rectifier?

Photo isn't exact one in the circuit but it looks like this one.
 

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Tinkerer2

Jan 21, 2021
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Jan 21, 2021
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OK, actual part# is KBPC1010. If I should be getting 32v dc, why is it that new ones don't output 32v?

It seems the transformer is doing its job since it outputs 24v AC. So if the rectifier should output 32 why isn't it? And would low voltage blow a fuse? Fuse is T5A 250V.
 

Bluejets

Oct 5, 2014
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OK, actual part# is KBPC1010. If I should be getting 32v dc, why is it that new ones don't output 32v?

It seems the transformer is doing its job since it outputs 24v AC. So if the rectifier should output 32 why isn't it? And would low voltage blow a fuse? Fuse is T5A 250V.

You don't say how or where you are measuring the dc.
 

Tinkerer2

Jan 21, 2021
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With the rectifier off the board, I connected the transformer outputs to the ~ inputs on the rectifier. Then I measured voltage across the + and - legs of the rectifier.
 

Martaine2005

May 12, 2015
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24v ac * 1.414 - 2 (actual diode v drop) approx = 32v dc
Agreed, but that is only after multiplying the RMS to find peak. Not measured voltage.

The bridge will have a voltage drop of two diodes.

Martin
 

Tinkerer2

Jan 21, 2021
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Well, after further testing (and removing and checking components), I found that one of the relays is actually shorted accross the NC and NO terminals. It is the one closest to the center of the board. I don't see how a relay can fail shorted but a google search about relays says that out of relay failures, 19% are shorted.

So, I'll need to replace at least 1 relay. Will probably go ahead and do both.
The relays I have will fit the board but are a lot shorter. Specs are:
TRD-12VDC-FB-CL
6A/250v ~ 12A 120VAC
12A/28v 12A 28VDC

The one on the board is:
SRU-12VDC-SL-C
10A/250vac 15A 120vac
10A/30vdc TV-5 120VDC

Per data sheets they are both normally closed with the closed pins in the same position. I have no idea what the TV-5 means. But is what I have a good replacement? I can not find a US supplier of the SRU-12VDC-SL-C but I have found some SRD-12VDC-SL-C in the US. Looking at the US because of faster shipping. If what I have is not a good replacement, would the SRD version be a good one?
 

Martaine2005

May 12, 2015
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TV-5 is probably just general purpose.
The TV rating (transient voltage) is for current inrush. This should be in the data sheet.
You can probably ignore the high voltage AC and DC ratings as your circuit is 24VDC.
As for the SRU vs SRD, check the data sheets for coil power consumption or similar. There will be a difference but probably not going to make any difference to your circuit.
Use the relays you have. They will be fine if the pinouts are the same. Double check with the data sheet.

Martin
 

Martaine2005

May 12, 2015
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Sorry, I made a silly statement in my last message.
What voltage are the motors on the chair?

Martin
 

Tinkerer2

Jan 21, 2021
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Great question. There isn't a label on the chair motor. Any way for me to know/find out?

"As for the SRU vs SRD, check the data sheets for coil power consumption or similar."

They are both low power (0.36 W) and is what the "L" signifies in the part #. The SRU/SRD part of the part # indicates the Model of Relay which I can't find any info on as to what the difference is or what Model of Relay means.

Mine is rated 12A at 28vdc and the original one is rated 10A at 30vdc. So I assume mine is rated at 12x28 = 336w and the original would be 10x30 = 300 watts. Would that make mine slightly better than the original? Or does it work that way?
 

Martaine2005

May 12, 2015
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Would that make mine slightly better than the original?
On paper it does. Your calculation is absolute max wattage rating.
Never use components at max ratings, always leave plenty of head room. A rule of thumb is 75% or lower.

I presume the relays are for the motors.
You could remove the faulty relay so the short has gone, then measure the good relays switching voltage. The red capacitor beside both relays is more than likely a suppressor and will also have the same voltage across it.
That voltage will be powering the motor.
My silly statement was about the high voltage ratings. If they are switching high voltage then those ratings matter too.

Martin
 

Tinkerer2

Jan 21, 2021
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Replaced both relays with my TRD-12VDC-FB-CL and all is well. Thanks everyone.
 
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