Elenco EK-12A Strobe Light Kit schematic

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,943
I have several pieces of an old Elenco strobe light kit. The PC board is marked:

EK-12A

Online searching indicates that the kit part number might be K-12A, K12, K12A, etc.

The pc board has reference designators (!!!), but I have no schematic, BOM, or anything else that assigns component values to the part references. Based on other strobe circuits, my guess is that the operating voltage is in the 4.5 V - 12 V range, but I have no data on that, either. I contacted Elenco over a week ago; no response yet.

Appreciate any help.

ak
 

MisterBill2

Joined Jan 23, 2018
17,719
I have seen two kinds of the cheap strobe flasher packages. The older ones used a half wave diode rectifier fed directly from the mains, and used a neon bulb relaxation oscillator to produce the trigger pulses for an SCR. They were very simple circuits. The slightly newer ones powered by a 12 volt wall wart have a simple oscillator-inverter to produce the high voltage, and they have a semiconductor trigger pulse generating scheme instead of the neon tube. There are quite a few published circuits that work, but don't bother with YOO TOOB.
 

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,943
The ones I have have a low voltage DC input, a 1-transistor flyback boost converter, and a neon bulb as the switch driving the gate of an SCR. The SCR dumps charge from a small cap into the trigger transformer.

ak
 

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,943
I found the "manual".
Of course you did. When have you not?

Please post a link to where you found it. As the bank robber said to Dirty Harry, "Ah gots to know."

The kits I have are an earlier, more "rustic" version. There are several differences. Mine having a TIP120 power darlington for the transistor, and a larger flash tube. But the transformer pinout is a match, so I think the circuit in this manual is close enough for me to sort out the parts.

Thanks.

ak
 

MisterBill2

Joined Jan 23, 2018
17,719
That "manual" has the appearance of an educational textbook. Certainly reading and understanding all of it would provide quite a bit of education.
Is the goal to build and use the device? Or what? The transformer, with the unusual pin-out, will be the hard to locate item if th plan is to build this and make it work.
 

MaxHeadRoom

Joined Jul 18, 2013
28,475
That "manual" has the appearance of an educational textbook. Certainly reading and understanding all of it would provide quite a bit of education.
Is the goal to build and use the device? Or what? The transformer, with the unusual pin-out, will be the hard to locate item if th plan is to build this and make it work.
Reading the manual, it is obviously a Kit of parts to put together .
e.g. "if you have a problem, consult your instructor!"
(or the Co.)
Soldering instructions are also included.
 

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,943
Is the goal to build and use the device? Or what? The transformer, with the unusual pin-out, will be the hard to locate item if th plan is to build this and make it work.
Let me restate my opening line. I have four old, unassembled strobe light kits. Each one has the pc board and all components. The problem is zero documentation. These kits are an early version of the one in the manual, but the manual schematic is close enough in some areas to give guidance.

The goal is to place these in basement areas and garage, and trigger them with the land line ring signals and the doorbells.

ak
 

MisterBill2

Joined Jan 23, 2018
17,719
OK, I had thought that some of the parts were missing, evidently that is not the case.
Given that the intention is to use them as indicators and not as entertainment, and at remote locations, they will need to be externally powered, the best choice being to not use battery power in each.
Instead of using an external DC supply powering the internal oscillator/transformer/rectifier string, which will demand close attention to polarity, there is another option.
Each strobe package could be powered from a low voltage AC source and be connected with common low voltage wiring that would feed the primary of the internal transformer of each strobe package. No "trigger" arrangement would be required to initiate flashing.
If the battery voltage is known, then the required AC voltage can easily be determined, probably a six volt transformer will be able to power all four devices.
 

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,943
Combining the schematic Bertus posted with the schematic from another similar kit, and tracing the PC board layout, I now have a complete and correct schematic for this kit.

I have four of these kits, picked up waaaay back at flea markets like the Dayton Hamfest. Three are clearly the first pass - the pc board has bare copper traces, no component legend, very slopily-sheared board edges that left the shear guide lines on the board, etc. One kit is newer; the board is solder-plated, and has a legend with reference designators; those are the reference designators on this schematic. The layout has different trace widths here and there, but electrically it is identical to the older kits. The electronic components for all four kits are identical.

If the power to the strobe part looks weird, that's because it is. I've verified that this schematic matches the pc board layout. It made sense once I figured out how to route the GND trace to show the *relatively* positive and negative power rails. Overall, this lines up well with what I have, although R3 is much higher than its equivalent in the current schematic for this kit.

UPDATE - the circuit requires a minimum of 10 V for operation.

ak


Strobe-EK-12A-1-c.gif
 
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MisterBill2

Joined Jan 23, 2018
17,719
It appears in the circuit drawing, that the base-emitter diode is part of the circuit charging the C1 capacitor , since D1 blocks the other charging path. That is a bit unusual.
 

Thread Starter

AnalogKid

Joined Aug 1, 2013
10,943
Agree, but the cap charges relatively slowly over time so the current is low.

Rough approximation - to charge the cap to 300 V in 2 seconds with a constant current, D2 current would be approx. 25 mA. Yeah, the circuit is pulsing, flyback, blah blah, but that gives a ballpark feel for the base current, which is not excessive. I might have to build up one of these puppies and scope it.

ak
 
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MisterBill2

Joined Jan 23, 2018
17,719
I did not intend to question the validity, only observing that it is unusual.

My thinking had been to suggest operating the strobes with perhaps six volts AC supplied to the primary instead of the oscillator circuit. But passing the charging current through the base-emitter junction might be a brilliant regulation scheme. Consider that as the cap starts charging the current is greater and so the oscillation is stronger. So it may serve to extend battery life. Rather a subtle trick, if that was intended.
 
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