It should be dropping a maximum of 0.8V. Datasheet

If it has 12V+ on the anode, and virtually none on the cathode, something isn't right.

it has 12V on the Cathode and nothing on anode, i just test that diode and it's fine (i lifted a leg)

 

Ok, I'm confused then.

The resistor, 820, what is the voltage across it? This allows finding current through it.

The 3V on D8 is a problem, as Zeners aren't made that small.

If the speaker has output, and there are pulses on the other lines of the NAND gate, that should be switching the transistor on and off as well, unless the pulses never overlap.

 

Ok, I'm confused then.

There is only a wire between D7 and D8 on the schematic, a wire can only have one voltage at any given time, but it's shown as 3V@D8 and 12V@D7.

let me check....what about the resistor in between D7 and D8?

 

let me check....what about the resistor in between D7 and D8?

I missed it in the zoom, rewrote post.

Now looking for voltage across that resistor, which should be about 9V, to get an idea of current.

If you do a quick temporary short of CE on the 2N2219, does the output pulse once?

 

Now looking for voltage across that resistor, which should be about 9V, to get an idea of current.

yes, 9.30V

The 3V on D8 is a problem, as Zeners aren't made that small.

yeah, i think there is a problem around that area, but i get stuck there drawing, there is a op amp that i cant find the datasheet

If you do a quick temporary short of CE on the 2N2219, does the output pulse once?

when i did that, the speaker beeped, like adding and "extra pulse" but i couldnt check for pulses on the pads. let me check that

 

If you do a quick temporary short of CE on the 2N2219, does the output pulse once?

nothing happens, just an extra beep, but no pulse

 

Does voltage appear across the secondary of the transformer when you short C-E for a very short time?

 

Does voltage appear across the secondary of the transformer when you short C-E for a very short time?

i would need a couple of hands more to test that let me try

 

nothing happens

 

That simply checks to ensure the transformer functions, it will be a short output pulse, so put the meter in peak (min/max) mode if it has one.

Hopefully the meter is fast enough to catch it.

If there an output, the pulse transformer is good, and the problem lies upstream of it, if there is no output, then the transformer isn't working, but that doesn't mean something else isn't wrong, since the transistor isn't getting turned on.

 

If there an output, the pulse transformer is good, and the problem lies upstream of it, if there is no output, then the transformer isn't working, but that doesn't mean something else isn't wrong, since the transistor isn't getting turned on.

i dont understand why is not working shorting E-C, even if the meter is not fast enough to catch the pulse, at least the Red Led should turn on with that pulse

 

i dont understand why is not working shorting E-C, even if the meter is not fast enough to catch the pulse, at least the Red Led should turn on with that pulse

Which one is the red one? LED1 should be on all the time when power is applied.

LED2 also relies on some other components being good, transformer, SCR, inductors, etc.

 

Which one is the red one? LED1 should be on all the time when power is applied.

LED2 also relies on some other components being good, transformer, SCR, inductors, etc.

LED2 is the one that pulses with the pads, if the pads get signal, that led should blink, it shares output

 

Then the pulse transformer or something after that point isn't functioning.

That's why I asked to see if there was any output on the secondary, it's simply following the signal to the output and seeing where it stops.

 

Then the pulse transformer or something after that point isn't functioning.

That's why I asked to see if there was any output on the secondary, it's simply following the signal to the output and seeing where it stops.

but the readings on that pulse transformer looks good...should i go ahead and replace that transformer? if i can find it a replacement...

 

Is there a pulse on the secondary when a voltage is applied on the primary?

I don't suppose you have a signal generator?

Circuits like this tend to require a signal generator and scope to get to the problem quickly, e.g. to test the output stage, remove transistor, add signal generator, see if output is good. If it isn't, most of the circuit is eliminated as a major fault. If it is, then a scope is used to follow the signal.

Trying to do this with somebody else with only a multimeter is... difficult, but possible. I don't know how it functions or why, but I can show you basic troubleshooting skills.

 

Is there a pulse on the secondary when a voltage is applied on the primary?

I don't suppose you have a signal generator?

unfortunately i dont

what do you think i should do at this point?? try to get a scope??

 

I was stating what would happen in ideal circumstances.

Right now, it's just a matter of finding out if the transformer shows a pulse on the secondary or not, if not, ensure there is a voltage across the primary when C-E is shorted if there isn't one there, it's backing up a bit.

 

Right now, it's just a matter of finding out if the transformer shows a pulse on the secondary or not, if not, ensure there is a voltage across the primary when C-E is shorted if there isn't one there, it's backing up a bit.

i dont understand exactly how that pulse transformer works. pin1 has 16V and is also connected to colector, pin2 also 16V, pin3 is ground and pin4 is output??

 

The pulse transformer works the same way a regular transformer works.

The difference is pulse transformers are designed to be 50% or less duty cycle, and more friendly to square wave input. Standard transformers "prefer" sine wave input due to the function of inductors. Pulse transformers are constructed the same way, but with intent to lower effects of inductance so a square wave pulse (on/off) can pass mostly undistorted.

A pulse on the primary results in a pulse on the secondary of a different magnitude (depending on the turns ratio).