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trying to fix a small board with few parts from an arcade game, and can't

doeby

New Member
120466

schematics, i tested all the resisters and the bridge rectifier. the diode. what it is doing is all messed up, so i think something is back feeding somewhere.
How it is supposed to work, the motor will run, until 1 of the OP gets broken, (by a hole in a spining piece attached, so the light doesnt get reflected back to sensor). So if OP1 and OP2 both are recieving light sighnals the motor will run, and when 1 of the OP doesnt recieve sighanal(motor moved piece into position) it should shut off. What it is doing, is running constant, as long as either of the OP get light. What i find really strange, is that it will run, no matter which part of the opb742(OP1 OP2) gets light, i thought it was 1 side emitting light, the other side recieving it. i did order 2 opb742, because they would only work if i shinned light from a flashlight directly into them(not by themselves, like they should) Any ideas on what could be broke that is allowing it to run constantly.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
The logic function is that it will only turn the motor off if both signals from the opto sensors are high.
That needs light blocking from both, so it will continue to run with either one alone unobstructed.

The outputs of the optical sensors should be low (or less than 1/3 +VCC) if the LED is on and nothing obstructs the light path,

They should turn off and the output be pulled up to near +VCC if the light path is obstructed or the LED is off.


The LEDs are driven from the AC side, which means they will be on only half each cycle or less. With both obstructed, one or the is low most of the time so the motor will run full speed.

With either one blocked, the motor will rapidly be switched on and off, like 50% duty PWM - possibly for a "slowdown" effect as it gets near whatever point both sensors are blocked and it stops.

That will cause odd readings with a multimeter, an oscilloscope would be more appropriate for faultfinding on that circuit.


Overall, both sensors unobstructed should give full speed, either one obstructed a lower speed and both obstructed stop the motor.
 

doeby

New Member
thank you for your reply, and please don't take offense, but it is working some other way. i have one that is working right next to this one, and what i can see, the motor stops when 1 of the sensors doesn't get reflected back. i took a picture of the wheel that is hooked right in front of the OP sensors. You can see the shaft hole, and 1 hole below it, and the cutout for the other sensor at the top. there is no way with this in front of the sensors, that both sensors ever have both of them not reflected back.(if i am right, this when you say the schematics says its the only time it will stop) When the motor if moving, then both sensors have the wheel reflecting back. On the working one, it rotates the cirlce half way, and it seems like 1 of the OP sensors loses reflection by the hole, and it stops. then when it starts again, it rotates half way, and the cut out at the top lets the other OP sensor not get reflected and stops.
When i test the board with a flashlight and no wheel attached, it does operate just how you stated it should, only stops running when no light in both sensors, but not possible with the wheel attached. could the main board be cutting power, switching power. whats causing the motor to stop, as 1 OP sensor is always getting reflected light, and the schematics show that should be keeping the motor running..



middle hole is for shaft---how it was set up when working, and others in the game
WHEEL.jpg
 

doeby

New Member
here is the main board schematics, i couldnt really follow it to find the In+ and In-. they are in the upper right listed as motor(goes to little board with motor attached)
(i did hook the IN- IN+ to another board, and it worked fine. so i assume the input from main board isn't problem. )but i still dont know what sighnal or length the main board is putting out to the "not working" board


main board.jpg
 
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Pommie

Well-Known Member
Most Helpful Member
If the input is AC then both LEDs will be off when both signals are zero or a zero crossing detector. However, that makes no sense looking at the rest of the circuit. As it's socketed I'd start by replacing the 4093. Are you able to scope pins 1, 2 & 3 of the 4093?

Mike.
 

doeby

New Member
i understand the leds will be off part, i just dont understand the zero or zero crossing detector.(is that the OP sensors). unfortunatly i have no way to scope 123 of the 4093. is it possible to just buy a new chip and put in, or is it a programmed chip.
there are no other inputs to the little board, and the main board tells it when to operate, so i am assuming it either switches ac between INs. would that trigger it to operate.
 

Pommie

Well-Known Member
Most Helpful Member
The 4093 is a simple quad schmitt trigger input NAND gate so can be simply replaced. Make sure you get the correct letters before the number (CD, HC etc.).

Mike.
 

doeby

New Member
every where i look, they dont have the one 4093 i need, says its obsolete, or quanity 0. could somebody let me know what an equivalent to it
mc14093bcp
ffec9045
link to it would be awesome.
 

Pommie

Well-Known Member
Most Helpful Member
What is the exact number on the chip and can you measure Vcc? Do you know how old the board is?

Mike.
Edit, are you able to measure the voltage on the left most pin (pin 1) of the TIP120 when the motor should be off.
 

doeby

New Member
numbers for the chip 4093
mc14093bcp
ffec9045
board from 1991.
i dont know how to test vcc

edit: think i found the right one
is this correct.



-14.5 1st pin on tip 120. used ground from motor(black probe in case you think i reversed them), my meter actually read minus 14.5
pin 3 of tip 120 also had -14.5 volts. i assume since i got voltage, the ground was good to use...
collector pin 2 had 0 volts

i did test the motor while it was running, and its a 12 volt motor

33.5 ac into the board. at IN+ and IN-(actually +to red probe -to black 33.5ac... but black probe to + and red probe to -, got 0 voltage.)
 

rjenkinsgb

Well-Known Member
Most Helpful Member
I was basing the mechanical side on the sensors being slotted opto switches, which is what the appear to be on the drawing. Going through the original question again I see you mentioned "reflective" but I missed that...

Reflective switches have the opposite output, low when the reflector is present and high when there is a gap.

With that arrangement, the motor should have full power if both sensors are seeing the disc, half power of one is at a gap and no output if both have no reflection.

It may be that the system is deliberately "stiff" mechanically and adjusted so half power is not enough to overcome drag. That would allow it to stop when either sensor sees a gap.


Look at the voltage between the output of the 4093 (pins 10 / 11) to its ground (pin 7) and see what readings you get with both sensors open, each on its own with a reflector present and the reflector over both.


Note that if the opto detectors are sensitive enough, any ambient light may keep them turned on and force the motor to run. It may need shading with something at a far enough distance to avoid reflections.


The 4093 is a very common IC, we use them in production items.
Examples:
 

Pommie

Well-Known Member
Most Helpful Member
I see you mentioned "reflective" but I missed that...
Missed that too. If IN+ and IN- are AC then the LEDs are ON/OFF on opposite phases. So either seeing a slot would cause it to stop (or run half speed) as the first NAND would see one one 50% of the time - rather confusing. Personally, I'd simply replace the TIP120, the 1N4002 and the 4093 unless you have someway to test them.

Mike.
 

doeby

New Member
i think you both have the circuit figured out correctly. the motor is attached to a gear box, that is hard as hell to move. So the half power motor not enough to move it, is i am sure correct. so if i could just recap, and hear what you think i should do next.
if i use a flashlight, i can activate the op sensors, but neither one will work if i just try to use the disc to do the reflection(so both led emitter lights are off, or they are broke) the motor does turn on, with direct flashlight in either OP sensor.(just room light doesnt turn the motor on) So it seem the circuit is running correctly, with me overiding the OP sensors. So i would think its the OP sensors that need replaced?
so how does the main board call for it to move, as 1 sensor would be in a gap, and motor would have half power. does it switch ac input, and bypass that sensor to give it the power it needs to move past the gap. then when the other sensor comes to the gap, it again gets half power, and stops.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
There is nothing in the circuit to start it...

Is there no mechanical trigger of any type? I have no idea of what mechanism it works with, so I don't know what to suggest re. that side of things.
 

doeby

New Member
nothing, there is the 2 inputs and that is it. i tested them, and i dont know if this helps solve anything, it looks like 33 volts ac to 1 wire, and nothing to the other, then when main board calls, it switches 33 volts to other input, and nothing on other.. does that mean that only 1 of the eye sensors has power at a time? just throwing it out there.

I never before read schematics, so please correct me on anything i have wrong.
looks like ac comes in, the bridge rectifier, sends dc voltage to motor positive, and thats is it from the diode diagram. so ac voltage continues to OP1 sensor. (no power to OP2). Then if it makes a connection, sends the ac voltage, on down to the 4093(which is really just relaying a sighnal whether it comes from OP1 or OP2). [i dont know is the 4093 would flip voltage from ac to dc]..which then goes to the tip120. ac voltage activating the relay, (emitter ground) sending the ground to the negative of the motor.
moves until the light sensor on OP1 had a hole, loses connection. then main board switches IN to 2nd wire, rectifier does same thing, everything else same, but it moves motor until OP2 has a hole in disc, and loses connection. this would leave the motor with no power in off cycles. and allow the main board to know which position it is, by whether IN1 of IN2 has power to it.
 
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rjenkinsgb

Well-Known Member
Most Helpful Member
t looks like 33 volts ac to 1 wire, and nothing to the other, then when main board calls, it switches 33 volts to other input, and nothing on other..
If it is fed from DC and the polarity is reversible, then it would work with only one or the other sensor!
One would be powered continuously and active, the other off (high) so inactive. It would run until it found either the outer or inner cutout.


With the bridge rec at the input & no other context, it appears to be an AC powered unit, without any external context. Knowing how it is fed makes all the difference.
 

doeby

New Member
in between i edit the above post.
i feel i should know this, but how am i sure whether its ac or dc
if i use AC setting, between the 2 wires, 33 volts 1 way,,, 0 the other
if i use DC setting, 15. volts between 2 wires, and -15 the other way..
 

doeby

New Member
sensor.jpg

how does this opb742 work in this schematic. i know the left side is the LED, the positive and negative turn it on.
On the right, is it a collector and an emitter. but if thats the case, isnt this sending a ground out, that is intersecting with positive voltage. shouldnt that cause a short. isnt this schematic showing that the vcc+ is going out the trace to the right. whether the sensor is on or not......
 

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