That makes sense and I usually try to avoid them in that situation as well but back when that board was built they may not have had a high enough value available in ceramic.

 

Thanks.

It is cheaper and more efficient to throw something away and build a new one with new materials.

Or is it? When we don't factor in the cost of cheap energy, priceless resources and long term environmental destruction, the price we now pay is greatly understated.

Our expansionist monetary system relies on ever increasing levels of consumerism and consumption. Almost everything we do today is non-sustainable. Sooner or later we will face the consequences.

Yes I don't disagree/I am not fundamentally opposed to that.
Most circuits nowadays are SMD, sub-SMD only, no re-use possible, in most cases also no repair possible.

What bothers me for instance countless cable standards for mobile devices. Put marketing/junketing in the first place, don't care about consumers/environment.

I hope you enjoy tinkering with the circuit, but as I wrote, don't put too much effort into it.

 

Depends what you mean by effort.
The more you do, the more you learn.
No task is too trivial or too difficult for me.

 

Mr Chips great work on the schematic and many thanks.

I wasn't convinced that turning Q1 round would resolve this but bowed to your knowledge, however once turned around the results are similar except know the LED fully switches off but TRIGGER is still allowed to be tripped without the RESET being pushed?

 

I am going to assume that you do not have an oscilloscope.
Perhaps you have a test meter of some kind, an analog or digital voltmeter?

The two transistors are probably in the wrong locations.
The 2N2222 has similar specs as BC142. Hence this should not matter.
(If the information you have provided is correct you could use 2N2222 for both Q1 and Q2.)

I suspect possibly Q1 and U2 are damaged.

To start off, remove Q1.
Connect a voltmeter between either side of R3 and GND.

Alternately press S1 and S2 and observe that the voltage switches from +V to GND.

What is the input voltage supply value?
What are the two voltage readings on both sides of D1?

Can you provide the values of all the capacitors to make the schematic complete?
What is the part number of the relay? I need to know the current draw of the relay.

 

Your right, no scope, sorry. but DVM I do have.

I have changed both q1 and u2 already, just in case without any change.

C1, C4 are .1uf
C3 is 22uf 16v
C2 is 3.3 (red, org, blk,red)
Relay is a National (assume semiconductor) HB1-DC12V

Input supply voltage is 12VDC

I'll be back in 10mins with the voltage readings, just waiting for the iron to warm up!

 

Input volts 11.71v
Q1 removed

R3 is 0v going to 11v when triggered, when falling back to 0v when reset, R3 to pin 1 of Q1 is 10.95v when triggered.

D1 is 11.71v and 11.00v (normal 0.7 drop expected with diodes)

 

Are you sure you don't have it backwards?

When S2 (TRIGGER) is pressed, voltage at R3 should be 0V.
When S1 (RESET) is pressed, voltage at R3 should be 11V.

 

Ok I was getting that result however I was going from S2 to S1 then S2 etc..

What is actually happening is when you first power it up the relay fires and the trigger LED goes on for the duration of the timer, while the LED is on there is 0v on R3. If you press S2 (trigger) the relay fires and LED illuminates but R3 stays at 0v.

Then pressing S1 (reset) R3 goes 11v,
Pressing S2 (trigger) and R3 falls to 0v,
once the timer expires this stays at 0v,
if you press S2 (trigger) again although the relay fires and the LED comes on R3 stays at 0v,
pressing S1 (reset) returns R3 to 11v.

Sorry for the confusion.

I also tried putting a 2N2222 in Q1 and replacing U2 this reacts in the same way as above.

 

Now I am confused. What you described above appears to be the correct operation unless I have misread something.

Let us go over a few things.
2N2222A should be fine for both Q1 and Q2. The relay is rated to operate at 16mA.
The 2N2222A is rated at 600mA, 625mW and should be fine.

Press S2 (TRIGGER), LED1 = OFF, LED2 = ON, Relay = ON
Press S1 (RESET), LED1 = ON, LED2 = OFF, Relay = OFF

Press S2 (TRIGGER), LED1 = OFF, LED2 = ON, Relay = ON
Wait for time out, LED1 = OFF, LED2 = OFF, Relay = OFF
Press S2 (TRIGGER) no change, all OFF.

I assume your LEDs are now working properly, no dim LEDs?

 

The relay coil draws ~100mA. National was one of Matsushita's old brands.

 

I only just noticed. R3 is shown as 47kΩ. This seems rather high.
Change this to 10kΩ.

 

Press S2 (TRIGGER), LED1 = OFF, LED2 = ON, Relay = ON
Press S1 (RESET), LED1 = ON, LED2 = OFF, Relay = OFF

Yes above works fine no probs. However.

Press S2 (TRIGGER), LED1 = OFF, LED2 = ON, Relay = ON
Wait for time out, LED1 = OFF, LED2 = OFF, Relay = OFF

Works, But after time out..

Press S2 (TRIGGER) LED2 = ON, Relay ON (Should ignore button press, no LED, no Relay, until reset is pressed.)

I can change R3 to 10k, as it was in from start I assumed it was correct.

 

Not possible. Of course unless something is wrong.

After time out, LED1 = OFF, LED2= OFF, Relay = OFF.
Measure the voltage at U2B, pins 4, 5 and 6.

Pin-5 should be 0V
Pin-6 should be 11V
Pin-4 should be 11V

Since pin-5 is at LOGIC LOW, pressing S2 should have no effect.

 

So hang on, once the unit has gone through it's cycle,

ie.
Reset
Trigger
Relay On
Time out
Relay Off

So your saying you SHOULD be able to press Trigger again and get the relay on?
I was always led to believe that it wouldn't trigger again until the reset had been pressed? Which is what I'm trying to make it do.

 

No, I didn't say that.

Once the trigger is pressed, trigger no longer has any effect.
You have to press reset in order to trigger again.

 

Works, but after time out...

Press S2 (TRIGGER) LED2 = ON, Relay ON (Should ignore button press, no LED, no Relay, until reset is pressed.)

Timing out IS a reset. The manual reset button is only used to terminate timing early.

 

NAND gates U2A and U2B constitute a SET-RESET flip-flop.

TRIGGER sets the flip-flop and RESET resets it.
Once the flip-flop is set, nothing else will reset it except RESET, not even the 555 time-out.

U2C and U2D is a monostable pulse generator. It generates a negative going pulse on the leading edge of the flip-flop signal when the TRIGGER button is pressed for the first time. Once the flip-flop is triggered any subsequent pushes on S2 (TRIGGER) will have no effect.

 

Not possible. Of course unless something is wrong.

After time out, LED1 = OFF, LED2= OFF, Relay = OFF.
Measure the voltage at U2B, pins 4, 5 and 6.

Pin-5 should be 0V
Pin-6 should be 11V
Pin-4 should be 11V

Since pin-5 is at LOGIC LOW, pressing S2 should have no effect.

All above is correct?

 

All above is correct?

Now you're confusing me again. Are you asking a question or confirming the above is correct?

Let's back up for a second. You started off with the following problems:

1) LED1 (RESET) is dim.

Does that problem still exist?

2) The board did not function as expected.

One would expect that TRIGGER would be ineffective after pressed for the first time. The only way to trigger on a subsequent time is to press RESET before pressing TRIGGER.

Has this problem been resolved?

My assertion is that Q1 is either faulty or installed incorrectly.

How to test:

Disconnect R3 or Q1.
The circuit should now function correctly (except LED1 will always be OFF).

How to test Q1:

Install Q1 but disconnect R3 from U2A (keeping R3 connected to the base of Q1).
Connect the disconnected end of R3 to GND. LED should be OFF.
Connect the disconnected end of R3 to Vcc. LED should be ON (bright).
Try the original R3 value of 47kΩ and compare with 10kΩ.
Is the brightness of the LED the same in both cases?

If the LED does not go OFF and ON with acceptable brightness, check that the pin-out of Q1 is correct. If you are certain that the pin-out is correct, replace Q1 with a working transistor. 2N2222 should work but watch the pin-out.