When I plugged unit in motor starts turning. Measure .2v @ C4. Pressed limit switch, voltage went up to 9v in ~2 sec. and then motor runs again.
I took these measurements with the 100uF cap installed

The 555 time is in accordance with a 22K+100uF capacitor. If the 555 can produce this timing, then the 555 is definitely OK.

There is something wrong with the PCB pads on the variable resistor or the VR itself. There could be a hair line conduction trace shorting the pads.

You cannot measure the resistance of the VR while it is soldered to the PCB as there are other conduction loops. However, you can measure correctly if you first remove the 22K resistor and measure resistance across the variable resistor.

Make sure that you can measure 100KΩ or whatever highest value you can get. Try adjusting the VR to see if the value changes.

 

I did remove the VR from the board before testing. I placed one probe across the center and one end leg and placed the other probe on the remaining leg I then rotated the adjustment and received readings from 0 ohms and as I rotated clockwise the reading went to 104.5K. I then placed it back into the board. I also made sure, although I know it is not necessary, to connect so resistance increased when rotating in clockwise direction. It almost seems tempermental in its operation. I checked all solder joints and board traces. found one trace with no continuity and repaired. I also reheated all solder joints and they are fine. Plugged in and motor runs imediately on power up. Shouldn't the motor always be off when plugging in until 555 times out? Now pressing lim sw instantly reverses motor rotation. I replaced C4, 555, and 2N7000 @ 555. Same problem. I always unplug prior to replacing any components. I am beginning to think the board is posessed!!

 

I also reheated all solder joints and they are fine. Plugged in and motor runs imediately on power up. Shouldn't the motor always be off when plugging in until 555 times out?

When you power ON, different things can happen. The 555 monostable can assume a triggered mode. In this case, the motor will not run. Or the 555 can startup in a reset condition and thus the motor will run immediately. But whether the 555 is triggered or not does not matter and will not cause the subsequent circuit operation to fail.

Now pressing lim sw instantly reverses motor rotation. I replaced C4, 555, and 2N7000 @ 555. Same problem. I always unplug prior to replacing any components. I am beginning to think the board is posessed!!

Have you done the measurement as I told you by removing the 22K and then measure the resistance across the VR after soldered it onto the PCB?

Also please measure the resistance from either ends of the VR to +Vcc.

 

Removed 22k measured across VR 104k @ full clockwise 0k @ full CCW. One leg of VR is connected to +vcc. Got continuity on +vcc trace to the VR. Got 104k across VR when full CW and 0k when full CCW.

 

Removed 22k measured across VR 104k @ full clockwise 0k @ full CCW. One leg of VR is connected to +vcc. Got continuity on +vcc trace to the VR. Got 104k across VR when full CW and 0k when full CCW.

Set the VR to max. 104K and soldered back the 22K.

104K plus 22K =126K and with 100uF, would give a 13.8 second delay with 555.

Power ON and check your timing again.

I don't know the reason if the timing is only a few seconds delay in this case.

 

Considering ther seem to be no other options I did the followig. I removed the dip socket from the board and soldered 555 direct to pads. Take a wild guess what happened. It works. I started @ full CCW = 2 sec. slowly turned VR CW and delay increased with resistance. The only strange thing was when rotated to full CW direction the motor stopped when press sw, but never restarts. Waited over 1 minute motor never started. The combo is C4 = 100uF, VR = 100k, and R2 = 22k

 

Just for kicks, I also removed the 4013 dip socket and soldered 4013 direct. Now all seems to be working fine. Weird right! I will test this unit for a few hours, changing the delay as I go. I will report back on results. I guess the less connections the less chance for trouble.

 

The only strange thing was when rotated to full CW direction the motor stopped when press sw, but never restarts. Waited over 1 minute motor never started. The combo is C4 = 100uF, VR = 100k, and R2 = 22k

These things happened all the time. One only has to take care of it.

Place a voltmeter on C4, what does the reading tell you?

If there is no voltage rise then the 555 will wait forever.

Why there is no voltage rise? The path via (22K+VR) is open(likely) or the capacitor/555 is dead(unlikely).

The VR could be in an open-circuit state if you keep turning it CW after it clicks. Normally this open-circuit should not happen but these days, I always expect the worst from component.

 

I wanted to assemble one control board into its enclosure. As I put together the C4 cap intefered with installation of one limit switch. To make a long story short, I removed C4 and moved to center of board. Unfortunately when I re-installed the cap I reversed polarity. Obviously the board malfunctioned. I removed and discarded C4 and installed new one correctly. Powered up pressed limit switch, motor stops, 555 times out but motor runs in one direction only. What other components might have been damaged because of installing C4 backwards? Should I just replace 555 and 2N7000?

 

Powered up pressed limit switch, motor stops, 555 times out but motor runs in one direction only. What other components might have been damaged because of installing C4 backwards? Should I just replace 555 and 2N7000?

Don't change component before checking out what is faulty. This is not proper way to cure the defect.

You should be able to check why the motor is not changing direction by now. I have told you the CD4013 is responsible for motor direction changes and this depends on its pin#1 voltage, the 1MΩ + 0.1uF capacitor and the 2N7000 & relay.

If pin#1 voltage changes but motor direction don't, then check 2N7000 and relay. If pin#1 voltage stays at 0V or 15V, replace CD4013.

 

Also please measure the resistance from either ends of the VR to +Vcc.

I am confused. If one end of the VR is attached to +Vcc why do you say to measure the resistance from either end of the VR to +Vcc?

Also, what effect does changing from 330K to 1Meg resistor have on the 4013? Is this to increase the delay before coil 2 is energised?

 

I am confused. If one end of the VR is attached to +Vcc why do you say to measure the resistance from either end of the VR to +Vcc?

Because you could have a hairline crack on the trace so "you think" the end is connected to Vcc but in fact it hasn't. This is just to confirm the connection. Alternatively you could have both ends of the VR shorted to Vcc and these measurement would tell me exactly.

Also, what effect does changing from 330K to 1Meg resistor have on the 4013? Is this to increase the delay before coil 2 is energised?

The change has no effect on CD4013. The 4013 (pin#1)will change state immediately upon limit switch activation. It affects only the operation of the 2N7000. It adds more delay in the timing of energise and de-energise coil 2.

 

I truly appreciate all of your assistance and patience. This project has become a real challenge to get the bugs out. I spent most of today pulling out what's left of my hair to get this thing to work correctly. I have done continuity tests of all traces and found no problem. I measured both sides of the VR to +Vcc. O ohms anywhere along +Vcc trace. Measured VR pin connected to R2-22K. With meter on 200K scale the resistance read 0 ohms when VR turned full CCW. Set VR to 100K. Resistance rose steadily. It took about 1 minute for the value to go to 50K.
It is very important for me to get this thing to work. Unfortunately I will be out of town for a week. I imagine not having to deal with me is a vacation for you as well. I will have my laptop with me but not the board. Some minor additional information, I am using 1/4w resistors, if it matters, and all caps are rated min. 35v. I used the new 2N7000's and still have similar problems. Do you recommend a particular manufacturer of IC's, and what is a realistic cost for a quality 4013 and 555? I can't believe the wide range of prices. Perhaps the bargain priced chips I purchased were not such a bargain after all? Robust is a must!! A few extra dollars won't substantially increase production cost.
I know it seems premature to ask, but the next boards I will be producing will be from this template. I ask for you to review to ensure I have not missed anything as I did on the first. Could you offer any suggestions to increase the reliability of the circuit.
I decided to fly to my destination, instead of driving, giving me a few hours to tinker. I decided to play with the unit I had completely assembled, everything installed in enclosure, on Saturday. I plugged in motor runs, press sw. motor stops 10 sec. then started in opposite direction. Press other sw. with same result. After three or four correct operations pressing either switch caused instant reversal. Unplugged for a minute or so then powered up starts out correctly than same instant reverse. Unplugged and waited again then powered up motor turning. Pressed lim sw 1 and motor instantly reverses. Pressed switch 2 motor stopped timed out and restarted in opposite direction. Pressed switch 1 again and ckt. operated correctly. Let run for 15 mins. Press sw 1 motor stops, times out motor starts but no reversal. Press lim. sw 2, no effect. Press lim. sw. 1 motor stops, times out, but again starts without reversing. Pressed lim. sw. 2 motor stops, timed out, motor started again turning in correct direction for that switch. Press sw 1 motor stops, delay, starts no reversal of rotation. That's when I pulled the plug for today. I am offering this information in the hope it will offer some insight to the cause of the erratic operation.
View attachment compactboard.pdf

 

I plugged in motor runs, press sw. motor stops 10 sec. then started in opposite direction. Press other sw. with same result. After three or four correct operations pressing either switch caused instant reversal.

If circuit starts to go wrong after several successful operations, then it is possible

a. the power supply voltage of 15~16V is too high. you'll need to reduce the voltage to 12V or below. For testing purposes, either buy a 12V regulated walmark adaptor(or use a 12V dc source) and remove the existing the bridge rectifier on the PCB. Connects the 12V DC regulated output to the circuit and see if the circuit now operates correctly. Or you can buy a 7812 and use it to reduce the voltage to 12V.

b. the 555 timing capacitor C4 (470uF) is too high for a 555. Although the 555 datasheet place no limit on the value of capacitor value at pin#7, it could be another possibility that the discharge of the 470uF into pin#7 has degraded the 555, causing it to fail eventually. You can eliminate this problem by placing a 1K resistor between 555 pin#7 and capacitor.

The failure sequent of event would seems to be:
1. at first the 555 fails, added: what is full part# marked on your 555 IC ?
2. the motor is not powered off the motor when limit switch is pressed.
3. the motor direction is reversed with power ON
4. the surge on the AC mains cause damaging of the 4013.

Regarding the last statement, you can add a varistor and a snobber to the existing circuit to reduce the chance of damage. Varistor is sold by DC rating so you will need to use one with 220V or higher because 120VAC power line has a nominal peak voltage of 170VDC and can be as high as 185V peak. V220ZA05 is a typical Metal oxide varistor rated at 220V DC.

I have reduced the gate voltage of one of the 2N7000 by half and also offer you the option to replace the 2N7000 by a NPN transistor 2N2222A and its your choice if you like to do the replacement. A NPN is supposed to be able to withstand more abuse than the existing MOSFET. I cannot replace the 2N7000 for the CD4013B output because I want a motor off sequence before changing its direction and a MOSFET is the easiest way to achieve this.

 

Now I am anxious to get back home to try mods. I assume all of these modifications are to be incorporated into the ckt., with the 2N2222A as an option. I included the data sheet for the 555 the chip is marked NE555N K46820. Also, what does the "E" represent off the 7812, and will the 7812 require a heat sink?
View attachment ne555.pdf

 

I assume all of these modifications are to be incorporated into the ckt., with the 2N2222A as an option.

Yes.

I included the data sheet for the 555 the chip is marked NE555N K46820.

The purpose of that question is to confirm that you are not using a CMOS version of 555 that can only provide limited output current. The NE555 or LM555 is fine. The added 1KΩ resistor at pin#7 is definitely needed. If you can use a 1MΩ variable resistor, you can reduce the capacitor values from 470uF to 47uF. A 1MΩ VR (not a multi-turn one like the existing 100K) is cheaper and the lower value capacitor is smaller in footprint. Surprisingly, a 47uF capacitor gives better timing accuracy because it "leaks" less.

Also, what does the "E" represent off the 7812, and will the 7812 require a heat sink?

The "E" means earth or ground. That means you have to provide a grounded connection along with the AC power supply. i.e. use a three-core flexible cable to provide power and ground to the controller and motor. The ground should also be connected to the metal rail and the motor casing.

The small voltage drop across it and light relay load on 7805 means that it is unlikely any heatsinking is needed.

 

I have been using an 8' 18/3 power cord. I have the earth ground to -Vcc trace, as well as a jumper wire to the motor frame. I will probably start using the 2N2222A, so I changed the value of the associated resistor to 10K. I will also go with the 1Meg. VR and 47uF C4 cap. If I go to an 8V TX secondary do you think I should still use the 7812 voltage regulator?

 

If I go to an 8V TX secondary do you think I should still use the 7812 voltage regulator?

These small transformers usually have high voltage regulation so manufacturers often rate their output voltage at full load. A 8V transformer without load could easily reach 10V.

This is the case with your 10V transformer which gives out about 12V AC unloaded.

With 10V AC and bridge rectifier, you can expect to get about 13V DC so no 7812 is needed.

 

If I change the VR to 1Meg., and reduce C4 to 47uF should I eliminate the 1K @ 555 pin #7? Also, is 16V adequate for C4? This combination with R1 changed to 47K should give me a 2-54 sec. delay right?

If OK with you I would like to post new board design for your review when it is completed. Based on your review I will modify an existing board with the changes to be sure it works before starting new board.

 

If I change the VR to 1Meg., and reduce C4 to 47uF should I eliminate the 1K @ 555 pin #7? Also, is 16V adequate for C4? This combination with R1 changed to 47K should give me a 2-54 sec. delay right?

I would suggest still using the 1K at pin#7 even if you use 47uF. You can use 25V or 50V rating for C4. 16V is too low. The timing range is correct.

If OK with you I would like to post new board design for your review when it is completed. Based on your review I will modify an existing board with the changes to be sure it works before starting new board.

Why don't you just incorporate the changes into the existing board by drilling extra holes, cutting copper traces and using jumpers to test out the final design before designing a new PCB?