AEC chase circuit wont work

JohnInTX

Joined Jun 26, 2012
4,594
Can you post a photo of the soldered side?
Also, start with the pot in the middle and do not rotate it to the ends. At one end, the discharge transistor (pin 7) is connected directly to V+ and it won't like that.
 

Dodgydave

Joined Jun 22, 2012
10,082
Ok you can still check it with an ordinary meter, put the pit ib the middle, look at pin 3 of the 555 see what the voltage is, it should be pulsing, check pin 2 of 555 also should be ramping up down.
 

eetech00

Joined Jun 8, 2013
2,644
Hello

My guess is the 555 is not working. But this is a very poorly designed circuit.
If lucky, the first LED will be lit at power on, then then next LED should light at rise of each 555 clock pulse.

eT
 

SLK001

Joined Nov 29, 2011
1,548
My guess is that the 555 is in monostable mode and is only triggering once. I have yet to see a schematic of the thing. And when you post pictures, look at them - if YOU can't see anything of interest because they are too blurry, then what makes you think that WE can see anything of interest from the same photos?
 

Thread Starter

electricgeezer

Joined Oct 22, 2019
37
I got it working now, but I'll be darned if I know why. Here's what I did. On the 555 timer, I shorted pin 7 and 6 together, and it works...But I am not sure why it works that way, and if I order another, should I short it like this one. The weird part is that the other two do NOT work when pin 7 and 6 are shorted together. Huh!!!
 

JohnInTX

Joined Jun 26, 2012
4,594
It looks like some of the pins on the 4017 are poorly soldered.. Soldering is more difficult on a non-plated through board. That could explain why it suddenly worked after futzing with it.

FWIW, here's a schematic I got from tracing the board. Note that when the pot wiper is all the way up, the discharge transistor is connected directly to +9V - not good.

That's all I got..
All Electronics LED Chaser schematic
 

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Audioguru again

Joined Oct 21, 2019
3,821
The schematic shows an error and cannot be seen.

I agree that many of the solder joints look like they are not correctly soldered.

I solder perfectly with a temperature-controlled soldering iron (not one that gets too hot and not one with a light dimmer circuit which does not control the temperature) with a tinned tip and 63/37 tin-lead rosin-core solder.
 

JohnInTX

Joined Jun 26, 2012
4,594
The schematic shows an error and cannot be seen.
Hmm.. it loads OK on Firefox Windows but winds up in the downloads folder on Safari and Firefox on iPad. It’s viewable from there. Same on some other PDFs I the thread. Something new maybe?
It does require Acrobat 9.0 or better.
 

Reloadron

Joined Jan 15, 2015
6,204
Using your multi-meter, set to measure DC Volts with the unit powered up measure between pin 3 of your clock chip and ground. Does the meter bounce around or does it give a steady reading? The idea here is the clock chip, likely a 555 timer acts as a free running multi-vibrator. The polarized cap and the pot control the frequency (how fast the LEDs chase). Pin 3 of your clock drives what is likely a 4017 decade counter which counts up 0 through 9 and resets. Your images look like things are installed correctly. I can't imagine 3 of these things not working. We are missing something here.

LED Chaser.png

Ron
 

Bernard

Joined Aug 7, 2008
5,788
Post # 27, bottom view, looks like in photo. that 4017 pin # 15 does not connect to - ( ground ) which also supplies - to 555 pin 1?
 

Audioguru again

Joined Oct 21, 2019
3,821
I see the schematic today after registering to this website again (this site got new software last night) (I have a new e-mail address that did not allow me to login).

The kit is a mess. On another website Electricgeezer said it works with a power supply but does not work with a battery.
You know that a power supply has an output filter capacitor but this kit is missing an important supply bypass capacitor when powered from a battery.

I agree that the pot is missing a 1k resistor at each end.

Another problem is that with only a single resistor to limit LED currents then all the LEDs that are turned off have much more reverse voltage than the 5V shown on the LED datasheet as the maximum allowed reverse voltage.
 

JohnInTX

Joined Jun 26, 2012
4,594
Another problem is that with only a single resistor to limit LED currents then all the LEDs that are turned off have much more reverse voltage than the 5V shown on the LED datasheet as the maximum allowed reverse voltage.
You're absolutely right now that I look at it.
Mess.
Agreed. Kind of amazing how basic electronic principles are ignored over and over on the intertubes. You get so used to seeing it that you miss the easy ones. Good catch.

Glad your logins/downloads are working.
 
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Thread Starter

electricgeezer

Joined Oct 22, 2019
37
Using your multi-meter, set to measure DC Volts with the unit powered up measure between pin 3 of your clock chip and ground. Does the meter bounce around or does it give a steady reading? The idea here is the clock chip, likely a 555 timer acts as a free running multi-vibrator. The polarized cap and the pot control the frequency (how fast the LEDs chase). Pin 3 of your clock drives what is likely a 4017 decade counter which counts up 0 through 9 and resets. Your images look like things are installed correctly. I can't imagine 3 of these things not working. We are missing something here.

View attachment 189459

Ron
 

Thread Starter

electricgeezer

Joined Oct 22, 2019
37
Thanks ron, will check pin 3 with multimeter and see what happens. Yes, I built three and only one is working. Since they are only $6.95 a piece, it's not a problem to buy 3 more. But I hope to have this figured out soon. In addition as I work on this, I am trying to figure out how to get two of them to work together, so I can use fiber optic cable to run a marquee theater sign in HO scale.
 

Reloadron

Joined Jan 15, 2015
6,204
In addition as I work on this, I am trying to figure out how to get two of them to work together, so I can use fiber optic cable to run a marquee theater sign in HO scale.
Adding more should not be too difficult. You have as mentioned, a clock signal generated by your 555. That clock signal is passed along to a 4017 CMOS Counter Divider. This allows a visually appealing LED chaser effect. The 4017 does have a "carry out" pin which can be used to drive another 4017 resulting in what is known as "cascading 4017 counter/divider chips". The downside I see is as the first chip increments up once it provides a carry out it will start counting up again and the second chip will increment up one count.

Ron
 

Tonyr1084

Joined Sep 24, 2015
6,451
Don't know why I'm not seeing the diagram (schematic). Here's what I know of chase circuits - the 555 has to be clocking (Pulsing from zero volts (ground) to positive (near the full voltage of the battery), unless regulated somehow). First thing I wondered was if the circuit is correct. The 4017 has an enable pin that must be held either high or low (not sure off hand). If it's not held properly then the chase lights won't chase. Those are my first two suspects, a non-pulsing 555 (non clocking) and an incorrectly wired enable pin.

Another possibility is the voltage supply. It may be higher than what the 555 can handle. I don't recall seeing a stated voltage for the power supply. IF you've over-voltage(d) the 555 it could be blown. (not clocking). And one last possibility I can think of - ESD (Electro Static Discharge (or Damage)). Remotely possible is an over-heating condition caused by too much dwell time with the solder iron on any given leg of any given component.

If you don't have access to very many test tools, you can build a simple LED Pulse detector. It simply connects to pin 3 of the 555, through an appropriately sized resistor, through a properly oriented LED. If the 555 is pulsing slow enough you can see it visually. If it is pulsing too fast to detect with the human eye (typically 27 pulses per second [PPS]) then moving it rapidly across your field of vision will reveal the pulses individually. Unless you're pulsing at such a high rate you can not see them even when you pass the LED through your field of vision. IF it is pulsing then you should see the same pulses at the clock pin of the 4017. If you have pulsing going on there then the problem is located in the 4017 chip. If you're NOT getting pulses at pin 3 of the 555 then the problem is there somewhere. You could be using the wrong value capacitor. Or your pot may be defective - or fully turned to one full end or the other.

I'd start there - determining whether the problem is with the 555 or the 4017. From there you can further diagnose the issue. If it's the 4017 it may either be a faulty circuit design, bad chip or an ESD related issue. In my 35 years I've seen plenty of failures due to ESD. Working at an ungrounded station while sitting in a cloth chair on a plastic floor protector and you're in your socks - BOOM goes the chip(s). My wife had a plastic floor protector at her computer station. Time and again when I'd sit there in socks (and other apparel), sliding my feet around I'd get a heck of a shock from ESD.

Like I said, it could be the chips themselves. They may have been exposed to an ESD event during shipping as well. Did they come in a metalized film bag? Were they stuck on black (conductive)foam? Were they stuck on PINK foam? (the pink foam is NOT static protective). Did they come loose?

I'll continue to follow this thread to see if I can at some point access your schematic diagram. Then I may even de-construct the PCB and reveal the traces to see if they follow the schematic. If I find an issue I'll speak up.
 

Audioguru again

Joined Oct 21, 2019
3,821
Since the soldering is so poor then by shorting pin 6 to pin 7 of the 555 makes one circuit work, maybe because that pin 6 or pin 7 now is soldered but it was not soldered well before.

Leadless solder or plumber's solder don't work well. A cheap soldering iron that gets too hot incinerates the rosin in the solder.

Also I notice two solder shorts in the fuzzy photo:
 

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