Garage door opener-safety cutout faulty

[Cornboats]

I have vintage Slavedor garage door opener that has stopped closing the door. If I disable the up/down current control to the motor it works fine. I've attached the larger control board which is for everything and the smaller current control board.
Normally the current control is set slightly above the maximum current normally used. If the door exceeds this it should stop and reverse when closing or just stop when opening. Can someone please explain how the current control board works so that I can try and repair or replace the defective parts.
I see my self as an interested novice willing to learn.

Please note I've checked the electrolytics and they're all within capacitance and esr spec.
The rear side of the smaller board has been desoldered ready to pull components.

[stj]

maybe it's mechanical, is it all clean and greased?

[lotas]

What a strange soldering.

[stj]

interesting - braid and an oversized iron did that.

[redwire]

I think it's premature to desolder all of the components near the OPEN and CLOSE adjustments. I can see each is part of the simple (4538 IC) timer, I think 0.15uF timing cap and >500k. I would've troubleshooted a bit more.

Typically, garage door openers trip on high torque/jam by monitoring either motor current (using a large sense resistor) OR they monitor motor speed (using slotted optical encoder as a tach). Motor current going up/motor speed going down due to a jam or squished cat can false trigger if the mech is old and needs a cleaning, lube like the chain and rollers etc. or alignment if the building has settled and the tracks are crooked.

Are you sure these OPEN and CLOSE adjustments are for torque limits, or are they for position? The door open and close limits are typically done using limit switches with mechanical adjustment. I don't see those in the pics or a big current-sense resistor or some means to monitor the motor. I've never seen dual (open/close) adjustments for torque limits.
It's a swing up or down, or sideways or roll door?

[Cornboats]

Thanks for taking the trouble to reply
There was a black cover concealing the parts. I wrongly assumed this was a 1 piece component and so desoldered to lift off the board.The black cover prised off using a sharp trimming knife, but only after I'd desoldered the components.
I've serviced the operator for many years paying attention oiling to metal on metal parts. Alignment is ok and upper and lower limit settings are working. The limits aren't shown as close and open limits are installed on the chain track.
The door is one of 2 installed side by side on identical up and over tracked doors. I have substituted the other board just to see and everything works ok, so I deduced from that that it was the torque settings board. With the substitution fitted, reducing the setting the door stops and by increasing the door opens fully.
The torque settings are used on a number of older garage door operators. I can think of Chamberlain Liftmaster & Henderson, although these have included the circuits in only the one main board but I'm sure there are more.
Could you explain how the circuit works so I might be able to copy and make a replacement? I've attached some more photos showing the motor encoder you mentioned.

[stj]

did you test the 2 boards seperatly to narrow it down?
the small board i would test the film caps and maybe the pots end to end

[redwire]

Oh I see it has a tachometer. The CNY70 relective optical sensor on the little board.
Note it's common these (infrared LED) ages and goes weak, or dust gets in, so this might be what has happened. Are both OPEN and CLOSE needing to be cranked to max? The one sensor is used by both.

I would say this is how the torque sensing is done, it looks for tach pulses (motor speed) to be too long (slow). When the speed is too slow, the pulses stretch out and are longer and if they exceed the pulse width setting on the board, it trips. So the board you took apart is likely a (dual, open/close) pulse timer, if too long then trip and halt things.

The Piher trimpots I would also check if the wiper (middle pin) has gone open (oxidation) or works when you turn them. You can use a spray cleaner or move them around a few times.
What is the number written on the transistor, it has 3 legs.

[Cornboats]

No I didn't try the operator with the other main board, only the torque setting board.
The transisitor is ZVN 330 6A

To test your theory on the bench could I connect to an oscilloscope, (I have an old analogue) to see the pulse width setting?
I've sketched a schematic of the torque setting board which I'll upload today which may help.

[redwire]

I tried to make a schematic but couldn't make out the traces and the IC's pin 14 seemed to be a strange connection.
It appears the ribbon cable's far 3 pins are for the photosensor which comes in to this board.
ZVN3306A is a Zetex N-ch mosfet not a vanilla NPN like I expected. Likely the photosensor amplifier?

[redwire]

OP crossposted https://www.electro-tech-online.com/...faulty.164445/ and problem is the connector missing pin?

[Cornboats]

Les from electro-tech has pointed out pin 5 on the socket is broken. I'll resolder everything and once I've sorted out how to replace the broken pin I'll retest. 2 out of the 3 connections on the phototransistor are shorting aswell. The data sheet for CNY 70 shows I should be getting a diode test result so I'll check the known working operator to see if the result is the same.
I've attached my interpretation of the schematic for the small torque adjustment board. Could you explain how this design works to interpret torque of the motor?
I'm wondering if I can make this circuit up to protect other motors I have in use on other projects.