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Need some help building a circuit involving switchs and relays
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Shaydzmi:

--- Quote ---If the full 24 VAC was across them it would be 1/2 Watt dissipation.
Since those are 1/4 Watt, that's not what is happening here.

--- End quote ---
I didn't understand, can you explain this to me?


--- Quote ---Tell me, from your experience, or actually testing now:
Stick a finger on a switch and make a bulb go on.
Stick a finger in another feeder switch and make another bulb go on.
Did the bulbs get dimmer when you put another switch on?

--- End quote ---
Yes, they get dimmer and dimmer until they bacome off when 5 or 6 are triggered.


--- Quote ---See, if there are no more resistors anywhere then all the bulb current goes through that 3.3 k ohm resistor on the board.
That would mean that the bulb is running on much less than 24 VAC.
--- End quote ---
Look, those 168 bulbs/resistors aren't going to the 3.3k ohm, they are going to the 3 big ceramic resistors (you can see them on the board).
The 3.3k ohm is handling just 3 big leds (I assume... tomorrow I'll take a picture of one of them).


--- Quote ---Do you have a replacement bulb number?
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When they burn out, usually I replace them with this:
https://www.narva.com.au/products/47508


--- Quote ---Do you have the service manual for this beast?

--- End quote ---
No.


--- Quote ---Note: I've updated again the drawing above.
--- End quote ---
Correct.
Thank you.


Renate:
24VAC ^ 2 / 1200 ohm = 0.48W
I guess that they always presumed that there would never be full 24 VAC there.
17 VAC ^2 / 1200 ohm = 0.24W

Ok, that control board has been all screwed up.
As I said, the stacked power resistors are bypassed.
There is only the 470 ohm resistor actually doing anything.
But it looks like one end is ground as it goes to the minus side of the big cap.
The AC comes in on a 2 pin connector and each side wraps around the board with screw holes!

The 3 sensor circuits seem to be designed for 24 VAC vs 0V.
It doesn't seem that they would work very well for working with a voltage over a drop resistor or a load.

Can you measure continuity between the feeder cable and the plug that goes into the control board?
Can you see where somebody shorted the two conductors of the feeder cable?
Renate:
Ok, I figured it out.
The 3 rectifier bridges: Those are for regular 24 VAC signals like broken needle detector, door open, etc

The control board is only designed for a single feeder bus.
The 470 ohm is the 24 VAC supply.
The detection is done by the ST BTA16 triac.
It triggers on the voltage drop across the 470 ohm.

You know the good thing about these forums? It gives you a lot of chances to be wrong!  |O

So, the big triac, the 47 ohm, the two zeners and the big yellow thermistor are there to trigger and provide the full 24 VAC to all the light bulbs.
It is an independent, self-contained sub-circuit that bypasses the 470 ohm.
Since it triggers late in the AC cycle there will be some spikes across the 470 ohm resistor if a light bulb is on.
It's the TO-92 transistors that are further along that do the actual detection.

There's no reason that the bulbs should dim if 4 or 5 of them are on.
The triac/thermistor bypass could be broken.
Shaydzmi:
Yes, the 3 bridge rectifiers are for: 1- Needle detector. 2- Open gate. 3- Revolution counter.
FYI: Only the revolution counter is working, the rest are broken.


--- Quote ---You know the good thing about these forums? It gives you a lot of chances to be wrong! 
--- End quote ---
That is you, me I'm always wrong.
The ceramic resistors ARE NOT bypassed, you can look at the board again.


--- Quote ---So, the big triac, the 47 ohm, the two zeners and the big yellow thermistor are there to trigger and provide the full 24 VAC to all the light bulbs.
It is an independent, self-contained sub-circuit that bypasses the 470 ohm.
Since it triggers late in the AC cycle there will be some spikes across the 470 ohm resistor if a light bulb is on.
It's the TO-92 transistors that are further along that do the actual detection.

--- End quote ---
I didn't understand any of this.


--- Quote ---There's no reason that the bulbs should dim if 4 or 5 of them are on.
--- End quote ---
There must be a reason though.


Shaydzmi:

--- Quote ---Can you see where somebody shorted the two conductors of the feeder cable?
--- End quote ---
The two conductors are twisted right at their end, you can see where by looking at one of the previous photos.
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