AEC chase circuit wont work

Thread Starter

electricgeezer

Joined Oct 22, 2019
37
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
3,829
Since pin 3 of the 555 is pulsing then the problem must be with the 4017.
With the circuit not powered, use an ohm-meter to measure that pin 8, pin 13 and pin 15 are connected to 0V and that pin 16 connects to the positive battery terminal.

Add a capacitor between the + and - of the battery wires. A value from 0.1uF to 10uF will be fine.

Check that there are no solder shorts on my attachment here.

Use a temperature controlled soldering iron and 63/37 rosin core solder then re-solder all the pins that look like poor soldering here:
 

Attachments

Thread Starter

electricgeezer

Joined Oct 22, 2019
37
ok thanks, will check that when I get a chance. On the off chance that it was a bad 555 or a bad 4017 I ordered three new ones from jameco electronics, and in addition got three new chasers also. We will see what happens. Hehehe
 

Thread Starter

electricgeezer

Joined Oct 22, 2019
37
Thanks Ron, don't know if this helps but here is the circuit board NEW before anything is done. On the off chance that the 555 and the 4017 are junk, I ordered three new of each from jameco electronics, and also ordered three new chasers to assemble when they finally arrive, in a week or so.

[/QUOTE]
 

Attachments

Reloadron

Joined Jan 15, 2015
6,204
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:
Now that you mention it those are well worth a second look.

Ron
 

Tonyr1084

Joined Sep 24, 2015
6,452
OK, here's what I got from your photographs: This is an x-ray view through the board. I've slightly modified the traces to present it more as a schematic. Black is ground, Red is power, Orange and Salmon are control and Blue is clock. Green are the outputs. Parts count: Capacitors (2), Resistors (1), Potentiometers (1), LED's (10), 555 timer (1), CD401 7 (1).Chas Board 2.png
 
Last edited:

Bernard

Joined Aug 7, 2008
5,788
The CB has not changed from mine, about 2004, until now but I see that mine has some different parts, pot 1M with 27k to + 6V supply, & several attached test leads to attach to bread board. Never had problems except replaced one bad red LED.
 

eetech00

Joined Jun 8, 2013
2,644
The CB has not changed from mine, about 2004, until now but I see that mine has some different parts, pot 1M with 27k to + 6V supply, & several attached test leads to attach to bread board. Never had problems except replaced one bad red LED.
Hmmm....seems like this board would have a better chance at working with a +6v supply, 74HC4017 chip, 1M pot, 1u Cap, and 430 ohm limiting resistor.

eT
 

Audioguru again

Joined Oct 21, 2019
3,829
In those old days, a circuit like this was designed by a 10 years old kid who knew nothing about electronics then it was posted as an Instructable. Or it was a copy of a copy of a copy..... and some parts were lost.
 

Thread Starter

electricgeezer

Joined Oct 22, 2019
37
Thanks EE, I am not sure and far from being an expert. Here's what I am doing so far. I have one that's working and two that are NOT. Ordered three more brand new ones and also...just in case the 555 and the 4017s that came with it are china junk, I ordered new 555 chips and 4017 chips from jameco electronics also. I will eventually get two of these working.. Hehehe. Today I am going to take one of them, and completely desolder, and resolder the whole thing and see if I can get it to work. When the new ones arrive, will take it step by step and show folks on here the soldering as I complete it.
 
Top