Identifying Capacitors

Thread Starter

Tasp

Joined Aug 10, 2008
45
Sorry, I was confirming all is correct, but was querying because if all is right why isn't it working!

Let me clarify.

The original problem was, the unit didn't work at all.
I repaired a burnt out, track it still didn't function, I replaced Q1, Q2, U1 and U2.
The unit began to work but LED1 would dim and the issue where you could trigger it over and over without pressing reset would occur.

When Q2 was replaced I think it was fitted backwards because LED1 wouldn't switch off completely, after turning round LED1 now turns off completely when S2 (trigger) is pressed. (With Q2 the middle pin (base) was tucked under so I just replaced like for like, see attached picture for clarification, this picture is off a different unit which I have successfully repaired, hopefully this will show how Q1/2 are fitted, when I fit them to the 2nd non working board in the same orientation I still have the multiple triggering problem.).

Q2 is currently disconnected, but the circuit still doesn't work correctly, S2 (trigger) can be pressed multiple times which trips the LED2 and Relay without the need for S1 (reset) to be pressed.

I have replaced Q2 a couple of times, 90% correctly orientated. But isn't Q1 and R3 just for illuminating LED1?

I have uploaded a video to Youtube to show the problem.http://youtu.be/K0afvM59X04
 

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MrChips

Joined Oct 2, 2009
30,712
According to the photos, Q1 is still connected backwards.
The tiny metal tab on the transistor can indicates which lead is the emitter. This should be connected to GND, not to the LED.
 

MrChips

Joined Oct 2, 2009
30,712
I believe what you are saying and what I see in the video.
And we both agree that that is not how the circuit is designed to work.

After the circuit times out, what is the voltage at pin-3 and pin-5 of the CD4011 (U2) chip?

Measure the voltage at the top side of the IC, directly on the top of the pin with respect to GND.

I suspect pins 3 and 5 are not connected.
 

Thread Starter

Tasp

Joined Aug 10, 2008
45
Right I've clouded the issue again, I have 2 units the last pic (unit1) in post #41 has the transistors labelled the wrong way round to the board I'm having issues with (unit 2). I will update now.

(unit1) post #41 is working correctly, but how if the transistor is round the wrong way?

I will test U2 tomorrow, thanks for your help so far most grateful.

Post #41 has been updated with the correct part identifiers.
 
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MrChips

Joined Oct 2, 2009
30,712
Finally, Thank You!

So go figure.

Now, have you determined why pin-3 and pin-5 are not connected?

My bet is the contact at pin-5 at the IC socket is not making contact with the pin.
Either the contact is bad or the pin on the chip is bent under the chip. I've seen the latter many times.
 
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Thread Starter

Tasp

Joined Aug 10, 2008
45
Right, replaced IC holder and resoldered joints on the lower half (incase of dry joints), reinstalled 2N2222 with the emitter (sticky out bit) facing LED1.

Same problem still exists. Trigger can be pressed multiple times.

I do notice that it appears that if I press my thumb under the S2 switch when pressing the switch the board functions correctly, only being able to trigger once and requiring a reset.
I thought this was a dry joint hence resoldering, the switches are 0.1-0.2 ohms to Mohms when open.
 

MrChips

Joined Oct 2, 2009
30,712
Did you measure the voltage at the top of the IC pin directly?

If pin-5 is 0V there is no way that S2 would be operable.
 

Thread Starter

Tasp

Joined Aug 10, 2008
45
Yes measured by putting the probe directly onto the top of the IC leg adj to the top of the IC. Not from underneath.
 

Thread Starter

Tasp

Joined Aug 10, 2008
45
Pins 3 & 5 are still 0v after timeout. Measured from the top of the IC.

The only other thing I notice is that this works (requires reset), if when I press the button, if my finger is shorting out the pins underneath.

What am I missing here?
 
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