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Lm3916

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civvie

New Member
Hello,

I have just built a simple mono VU kit using this chip (velleman k4304) (first time I've used this chip, I have built tons of other stuff though)

It has an issue where ALL LEDs are on ALL of the time.
I have triple checked all components, polarity, short circuits..

Is it possibly a faulty chip or is there something I should be looking into?

Thank you kindly to any one who has advice on this matter.
 

fernando_g

New Member
That is the problem!
Pin 4 is almost always connected to ground or very close to it.

Pin 5 is the input. With no signal input it should be also 0 volts.

it appears that you could have a ground return path open somewhere.
 

civvie

New Member
Thank you for your insight,

how very strange!

It is the exact cuircuit posted by hotwaterwizard (thanks for that)

So I guess the voltage is leaking to pin 5 and driving the LEDs to full.
It has the same issue if I pull the amplifier IC out of it's socket, all leds still on. So I'm not sure how it's getting there...

I will check it all again tonight, it's such a dead simple circuit that maybe the problem is too obvious and I looked straight past it!

What is the best method for trouble shooting open ground return paths etc?
I don't usually have problems with the circuits I build, I guess I've been a bit lucky.
 

civvie

New Member
Testing the circuit:

If I isolate pin 3 of the LM3916, I stop getting voltage readings on pins 4 and 5. This to me indicates that the voltage is arriving at pins 4 & 5 through the LM3916. Does this mean it is faulty?

One other experiment had interesting results. With the circuit wired normally, If I run pin 4 straight to ground, the level meter works, sort of... the 10th Led never shines and the first 3 are always on. (I think this is because there is still voltage arriving at pin 5 through the LM3916, but most of it is being drained to ground through R4.)

My understanding of circuits is very basic. I would love to know if this LM3916 is faulty so I can order a replacement. What do you guys think?

[/IMG]
 

hotwaterwizard

Active Member
What position is J1 in?

Oh here is the Datasheet,
 

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civvie

New Member
I have tried both positions with J1.
Both have same issue: all LED's on.

When I grounded pin 4 and got the meter to half work, as mentioned above, J1 would switch the mode from bar to dot as it should.

Maybe I could try testing the LM3916 in isolation from the circuit. I could hook up a 9v battery to pins 2 & 3 and see what I read on pins 4 & 5, would this be useful information?

Thanks for all the help, very much appreciated, I am learning.
 

ecerfoglio

New Member
Hello, thanks for your reply.


From a 9v PSU. (8.8 to be precise)

4 - 8v
5 - 8v
6 - 7.1v
Pin 4 is at 8 V, and you have a 6V1 zenner between it and ground - Check that zenner, if it has 8V across it you should change it, if it has zero volt then there is an open circuit in the pin 4 - zenner - ground path.

You have pin 6 (Rhi) at 7.1 V and pin 4 (Rlo) at 8v - if pin 4 is at a higher voltage than pin 6 it may cause some strange behaviour like the one you are having

The diagram you posted asks for a 10 to 15 V supply, and you used less than 9V. Try it with a higher supply voltage.
 

audioguru

Well-Known Member
Most Helpful Member
Now that the schematic is posted:
1) Pin 4 and pin 5 should be 6.2V (the zener diode's voltage).
2) Without an input signal then pin 5 should also be 6.2V and the LEDs should be off.
3) Pin 6 and pin 7 should be about 6.93V.
4) The minimum supply voltage is 6.93v + 0.7V + 1.5V= 9.16V.

The LEDs have a current of only 6mA each so they will not be very bright.
 

civvie

New Member
Thank you all for your help and suggestions, it is very much appreciated.

Unfortunately after pulling the LM3916 out of the IC socket many times during testing, one of the pins broke off! :( so the project is on hold for now.
It still baffles me though and I would have liked to get to the bottom of it. I racked my brains trying to find a fault with the circuit but I couldn't. I am convinced that a component is at fault.

Anyway, I have discovered a good and knowledgeable community here, very encouraging. Good work and thanks again.
 

fernando_g

New Member
You can sill purchase a new LM3916 from any of the electronics stores...and while you are a it, get an IC socket......a good quality one is advised.
 
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