Need replacement parts

I have this electronic gadget and need to replace the capacitors. I don’t really know what I’m looking for and the 2x blue things just have CTC all over them and nothing else. If you have the items or can work out what I need, could you please send me the sku numbers and I will order them thanks.

welcome to the core forum community…
they may not need replacing…what tells you that they do…??

i`m gathering that is a timer board of some description…or a 555 amp or tone generator…
they could be inductors …
can you power the unit down and meter across the solder joints of the components in question the 2 blue looking components… with a dmm meter and see if there open or shorted.

my money tells me there most likely bipolar electrolytic s, but they could be inductors…
i expanded the pic up size to the point that they may well be inductors… the value would depend on many factors if you have a schematic i could tell you what they are…??.
if there inductors or chokes or coils of some manner then they should be ok

the only other components are the timing caps the ceramic and the green cap and from what i can tell
the other larger electrolytic is just the input filter capacitor.on the power input .that is the one that you should be questioning if your really going to change the said components
…resistors usually go high under duress or having done a lot of work dissipating current…they dont look darkened or brownish

can you or do you have any more details about the cct board.

…the ctc markings are most likely tolerance markings if there bipolar electrolytic s.or other electrolytic s
if they are coils or chokes a as i said power it down am meter them to see if they are open or shorted…you dont need to remove them just meter across the solder joints…to see if there open or closed…??

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Hi Stephen
Looking at the pics, particularly 2, 3 and 4 there seems to be something funny with pin 4 of the LM555. Maybe not in the socket properly???
Very much doubt all the capacitors need changing.
I don’t mean to be rude or sarcastic but if you don’t know what these components are should you be attempting this without some assistance. Everyone has to start somewhere so do you have anyone you know who can give you a helping hand with identification and just as important soldering.
The big brown cap is 100uF 25V electrolytic. Looks like power supply filtering.
The 2 blue ones could be inductors but more likely electrolytic capacitors as I can’t think of much use for inductors in a LM555 timer circuit.
The green one is a “green cap”, polyester or mylar. Can’t make out the writing. 100V.
The little brown one is a 50V ceramic. Marked 103 which is 10000pF or 10nF or 0.01uF.
The resistor near the 555 is 10ohm, could be connected to pin 3 (555 output).
The other resistor near what looks to be a trimpot looks like 10k. A bit hard to make out the first colour but 10k is the only value in that series with the second colour black and third orange.
I do hope you can find some face to face help.
Cheers Bob


Hi Steven,

How are all those components connected, and what is this circuit actually supposed to do? If you draw up a circuit diagram for it, there’s a fair chance it matches one of the example application circuits from the datasheet for the 555 timer. Else you might be able to reverse engineer it.

LM555CN.pdf (388.7 KB)

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I think that he 2xblue things are inductor, they aren’t break down easily.


Hi Bob,
Thanks for your input and help. I really don’t know very much about electronics, but have been watching you tube videos on the basics as I am fascinated by what electronic components can do and would like to learn more. Unfortunately there is no one I can ask for help here but I wish there was, (it’s a small country town) so I’m on my own trying to learn this stuff. I do Fitting and Turning also welding and can oxy braze too, but I thought using the oxy might be a bit of overkill for this project… hahaha, so soldering is no problem.
I might just take the thing to the guys at Core electronics next week to look at and see what they think.
Cheers Steve.

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inductors of some description…if you blow up the pics take a close look at their legs there showing copper.
generally electrolytic caps don’t show this and the tops look more like ferrite and the bodys are more inductor not symmetrical cylindrical . but the guys at core-elec will throw some light on it for you with some luck.

Hi Oliver,
I’m not sure about drawing a circuit diagram or reverse engineering anything. I’m just a raw beginner at electronics. This thing makes a rather high pitched sound and has (I have unsoldered it) a 2" or so small speaker as well. In the pic the black mark is a texta mark showing where I unsoldered the 100uf 25v capacitor, it’s not a burn mark or anything.
Funny, I was thinking as a bit of a project I could just unsolder and resolder the new bits back on. Maybe it might be simpler to bring it to you guys to look at and give me some advice. Hopefully early next week.

Back of board|236x500

its a inverter /or converter of some description… the whistle your hearing is the coils or inductors when the field voltage/current is collapsing causing them to turn into what you would call a speaker without the paper cone the beads are resonating from the frequency generated by the 555 timer chip its most likely a square wave step up or down voltage converter…there are other outcomes this is just the noise made whilst trying to get rid of the spectrum of unneeded r.f
when the field collapses the whole spectrum is present…the coils may be just there to get rid of noise or unwanted spectrum… if its making noise the cct is not tuned thus it may have exactly what you wanted/set out to find..are the caps faulty. id replace the green cap and the ceramic…or the designer made a mistake.or the trimpot is not set correctly to the tuned frequency of the design.the trim-pot is most likely ten times the resistance or the set resistor of the timing cct so most likely 100k perhaps or a division of it depending on what output frequency you desire…but it is a divide network…
A tip if i may if your really into making this board run is the 555 timer cookbook… from jaycar it`s quite handy and almost out of print now though…browse astable oscillators…

Hi Brian, I will try replacing the caps that you suggested. There is an adjustment on the trim pot which i had previously adjusted. The thing was working ok but I wanted it a bit louder so I hooked up a powered speaker to it and now (whoops) it doesn’t work so i guess i blew something in it. But just what, is the question. I really want to learn how to test electrical parts to see if they’re blown or not. I guess making mistakes is how you learn sometimes.

ok a few things to note here…its a square wave output from what i can tell from the pics ... however it was meant to drive a 4000 type series flip flop for the basis of building a inverter..the two coils/inductors keep the signal clean .. im not going into inductors and efficiently etc…if a circuit has an inductor for the better part it smooths out ripple …but in a tuned circuit it …when the circuit is said to have the highest “q” or to be at 100% perfect…the current that flows trough the inductor will be as low as possible but still maintains the voltage the quality of the circuit…

ok now your bread board oscillator board…the lm555 has a max current out of 800 mA also its max input or output voltage is 16 volts…
most users would couple the speaker via one of those
there about 1cm square transformers come in mostly red type and blue type i think the red is 500 ohm and the blue is 1k on the input sides…and it don’t matter for your using a speaker on it…the cct just wont be efficient …matters not for what your trying to do.
there not that hard to get , or some decoupling method…i am guessing your powering up via 12 volts…

this is ok but it is also important that the chip is working properly… i will post a link later for testing them using a bread board and some discrete parts…

16 ohm speakers are common resistance 32 ohm if you have one…i`l post a link on a simple 555 tester using bread board proto typing board…

ok now if the chip is squealing or what ever is making that noise…as i spoke earlier there is a problem…get a few new chips…there around 2$ each …jaycar or online be cheaper…i buy 10 at a time…you can blow them easily…always socket them… and take note of the pin one dot on top of the chip put it in reverse will destroy it… i`ll leave it at that 4 now so you can digest it all…

q.r.t phase…

just google as well to find info

use a prototype bread board kit there around 10-15 dollars and come in very handy if your seriously getting into electronics…

Hi Steve, Brian
Just had a look at the back of the board. Now wish I hadn’t. There is some pretty wild soldering there. Wonder it does anything. Pin 1 (Gnd) seems to stop a bit short of the wire I think it should be soldered to so may be not connected. Nothing connected to pin 7 so how is the timing capacitor discharged. Looking at it I wouldn’t guarantee some of the other connections either.

Brian I think you are right about those blue things being inductors. They are both in series and fed from the 555 output (pin 3) via 10ohm resistor to that stray red wire. The black wire of this pair to Gnd. Now if this is a speaker connection the inductors are probably a filter of sorts to smooth out the square waves at pin 3 and sound a bit more pleasant.

But I still can’t see how it oscillates with no connection to pin 7.

A bit busy at the moment but if I get time I will attempt to draw some sort of circuit from the pictures. For my own curiosity as well. I have some 555s so might build it up just to see what it does.

Steven if you continue to connect and do things willy nilly you may experience a few more “blow ups”. You only really have to start worrying though when you get that greeny brown expensive smelling smoke. I got that out of the back of a brand new Tektronics Oscilloscope once many years ago. Fortunately not my fault and the component was guaranteed for life anyway so a replacement arrived the next day.

Cheers Bob

it`s running in astable mode …browse astable vs bistable lm 555

here is the link for a good book to get you started
if it was me toss that circut in the junk spares box

get yourself something like this ::

and this ::you can replace the trim pot with a standard 16 mm type pot if you like just hard wire it to the cct board mm makes for easy adjustments a linear type pot not a log type pot… eg…10kA and not 10k c or d…a: and :b type are linear…meaning that they have a linear scale adjustment…browse for a better explanation
one very handy book indeed

also to note a good multi-meter like this:

the out lay will indeed surpass the cost…and you will thank your self later on down the track …
you will find that most students started out with the 555 timer chip…there is so much out there on the web.just browse 555 and the circuit…e.g 555 tone generator…you will find plenty out there to choose from…

Hi Guys
Astable, Bistable and Monostable. Astable is the only one that will free run. The others need a trigger to change states. So Astable is a good call.

I have in front of me book I have had for many years. “IC Timer Cookbook” by Walter G Jung. A treasure trove of information on 555 and other timers (yes there are others). I could not recall ever having seen a free running circuit that did not use pin 7 to discharge the timing capacitor so I decided to try and find one.

Success. There is a very simple circuit called “minimum component astable” circuit. Requires only the 555 and 3 components. Pin 7 is not used. The charging and discharging is done with pin 3, the output. At first glance this looks suspiciously like the device Stephen has. The down side to this circuit is the timing (hence frequency) varies with supply voltage. This means you lose the nicest thing about the 555, the timing remains very accurate over a wide supply voltage variation.
Link (Result of a google search).

Stephen. What did you actually blow up. Your device or your powered speaker. If it was your device I would suggest the 555 would be the most fragile component on your board although if the powered speaker was hit with too much voltage who knows.

Cheers Bob


Thanks for all that info Brian, I’ll have to let it all slowly sink in. I ended up getting the parts from Jaycar.
I thought Core electronics was a shop (it’s just a warehouse) and I drove 4 hours from Coffs Harbour to talk to them and buy what I needed but when I arrived was told by a worker there, sorry you can’t buy anything here and I cant help you I really don’t know much about electronics, we just pick and pack stuff here. Fellow at Jaycar was really helpful, looked at the parts and just wandered off and got what I needed took 5-10 mins and cost about $10.

Hey Bob,
I’m not really sure what’s wrong. I thought if I replaced all the parts I couldn’t go wrong…lol

Thanks for your reply. Steve.

Hi Steve.
Ahhhh…Sometimes works and sometimes doesn’t. When I lived in PNG we maintained all the radio for Police, Ambulance etc and one model base station had an audio amplifier which was a real dog to trouble shoot. Direct coupled so everything affected everything else. When you are in a country with very little phone service (mobiles weren’t invented yet) and not even carrier pigeons the radio becomes all important. So the most expedient solution for the cost of half a dozen transistors at about 15c each and 20 mins work change the lot. Worked nearly every time and after checking the rest of the unit the customer had his radio system back working. Probably about an hour after arriving on site.
Didn’t matter that it might take 2 days to get there.
You haven’t said what test equipment you have. If it is not working after changing everything this could get a bit awkward.
Cheers Bob

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