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Sparks Flew -- Garage Door Opener Sequencer Circuit Board

whiteoutage

Jul 20, 2017
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While replacing a nearby motor bearing my screwdriver drew a spark on damaged area of board -idiot forgot to unplug mains. Now when i press the garage door remote control, the door only wants to go up -a 2nd press stops door as usual, but the third press now resumes upward. )-:

The 3 tantalum caps on the left are all darker/burned way out of range in both capacitance and ESR values. The markings on the 5 similar tantalums are 103-TQ8 - the smaller one in middle says B-102K. The two I think are good both measure about 50 picofareds. Wondering if I can swap the 3 bad ones with 50pF and at what voltage? The nearby resistors all test good as does the large cap at the end left. Will test the nearby transistor out of circuit tomorrow. Any other tests/advice would be greatly appreciated. Note: I am an electonics knob but always give it my best.
 

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Harald Kapp

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The 3 tantalum caps
These are not tantalum but ceramic. Tantalums don't come in pF range.
102 = 10 × 10^2 pF = 1000 pF = 1 nF
103 = 10 × 10^3 pF = 10000 pF = 10 nF
Voltage is also coded, see e.g. here.

No visible damage to the board, but sparks are a bad sign. I'm afraid you'll have to check all the semiconductors.
The controller chip Micrel Y30442B is a custom programmed part. Not freely available, I guess. If the defect is therein, you'll have to order a new board.
 

73's de Edd

Aug 21, 2015
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Sir whiteoutage . . .

Are you able to find the burnt spot on a pin that you grounded . . . . to pinpoint what parts were involved ?.
On a power up . . . check for how much DC voltage presence is on the axial leaded corner gray E-capacitor.
Also the black radial closest to it, is pwr supply related also.
Also, check for voltage across the two black ones at the opposite end of the board also.
Moreover, let us see a like size photo of the foil side of the board, as the receive portion is probably being built with SM discretes at the extreme corner near the Micrel decoder chip.
That will also let us see the wiring connections of the 24VDC being fed to the 3 mechanical relays and their nearby driver transistors as well as the one opticalisolator used..
There is a transformer that feeds into the (4) 1N4007 at the gray cap corner, you may have blown a fuse within or associated with its primary winding..
Otherwise, dc upply voltage should be present across that gray cap.

73's de Edd . . . . .
 

whiteoutage

Jul 20, 2017
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Sure is a treasure to be able to get such no-nosence professional advice here!

Sorry for the delay. Found out the motor was not repairable due to a propietary bushing so had to buy a whole new head unit. I would still like to repair the board in case a good motor pops up somewhere in the future.

Pictures of foil side of the board, and the missing transformer are attached. Have not done any voltage measurements as advised yet but will try tomorrow. Even though there are no obvious burns on the board, there are some suttle burn marks on frontside of board, but will check the transformer area for burns as well tomorrow. The quilty screwdriver spark was a glancing blow and had the garage not been so dark I may not have noticed it out of the corner of my eye.

I did desoldered the 3 burntish ceramic caps mentioned. Two tested at about 500pF (not nearly as bad as my previous on-board measurements indicated - rather than 1000pF as marked),. so I replaced those two with some salvaged from old TVs, the third one tested fine so I just soldered it back in place. It was a struggle for me but I managed to desolder the transistor with some crappy braid and it tested good. For the record it is a PNP marked KSP55.

Regarding voltage measurements any advice on how to best go about would be much appreciated... Also, after sparks occured I did test and that is when the problem "no down door" started so I am thinking it is probably ok to test again after replacing the two caps?
 

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73's de Edd

Aug 21, 2015
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Well there is no receiver built on this board so, it has to be on another board / portion being plugged into the kazillion other connector stakes being on the sides of this board.
As for your suspect of those 5 disc ceramic capacitors of 0.01 and 0.001 ufd values, and also a small axial leaded ceramic one that is mostly pale green colored and located beside a transistor and power diode.
I would be having all of those on my suspects / or / need to test priorities list, just before the 3 jumper wires used on that unit.
I am suspecting that your "no down door" syndrome will be associated with one of the driver transistors associated with each of the relays adjunct to them. Or the photo optical sensors at the sides of the doors that feed to circuiry to tell the door to go to open door position if detecting an obstacle. If you can still get the other door movements.and I assume that your remote still trigger the unit, so that Micrel decoder chip is working, as is your power supply portion..
 

whiteoutage

Jul 20, 2017
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Changing those two caps had no noticeable effect (still just wants to go up). The (4) 1N4007 diodes all tested good in circuit. With the garage door opener plugged in the transforer reads 120v on input and 21v on output so that also seems good; however, on the large grey axial capacitor I could not get any readings in either the on or off position. On the other two caps right next to each other that you asked about, I got 7.5 and 7 volts in off. Hanging precariously on a ladder may be giving shaky measurements. When I take the opener down tomorrow I will do some further tests with that big cap. colored cap, and the adjacent transistor as you suggest - thank you!

Note: During testing I probably pressed the remote button about 30 times or so. During one sequence of about 5 presses in succession, the opener rail actually went down once but unfortunately I could not duplicate that again.
 
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Harald Kapp

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During testing I probably pressed the remote button about 30 times or so. During one sequence of about 5 presses in succession, the opener rail actually went down once but unfortunately I could not duplicate that again.
Just to make sure the issue is with the opener and not with the remote control: Do you have access to a second remote control for testing?
 
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