Majestic Quantum 1000watts

[brandes.cm]

Is there a schematic reasonably close to this amp. It is in protect mode and finding it tough to figure out.

TL494
1) 4.172
2) 2.317
3) .535
4) 2.363
5) .792
6) .989
7) 0
8) 1.224
9) 0
10) 0
11) 1.224
12) 1.224
13) 2.4
14) 2.4
15) 1.715
16) 2.399

 

[ultra]

You need to find out why pin 4 has 2.36V

This is the reason that the pwm goes to protect.

 

[Perry Babin]

This supply has multiple problems. The 5v supply (pin 14) isn't at 5v. It could be that pin 14 is being dragged down or the 5v regulator in the IC has failed.

If you pull pin 14 from the circuit to check voltage on it, you have to also pull pin 13 and connect them together before you apply power.

 

[brandes.cm]

With 13 and 14 pulled and shorted together I get .3V on them.

VCC on pin 12 is low as well, that could be the reason for the +5 reading.

 

[Perry Babin]

If the IC has 12v on pin 12, the IC is defective.

 

[brandes.cm]

Pin 12 is the VCC pin, does that not supply power for the ref?

 

[Perry Babin]

Pin 12 is the power supply input pin for the logic circuits inside the IC (including the 5v reg).

 

[brandes.cm]

Is there a circuit like this in the DVD you sell. All the schematics I have use the LM339 for the power supply shutdown circuitry. I just ordered the DVD this morning.

 

[Perry Babin]

Check your email.

 

[brandes.cm]

Got it, I will compare the two later today.

I was thinking of using my smaller bench supply to source power to pin 12 and see if the 494 starts running. This would possibly show me if the 5V ref is functional.

 

[Perry Babin]

Looking back at the voltages on the IC, I see that you don't have 12v on it. I should have noticed that earlier. Have you followed the circuit back from pin 12 to see why there is no voltage?

 

[brandes.cm]

I goes to a transistor. Most of the transistors don't measure correctly in circuit or out. I thought the datasheet says something about a biasing resistor built in, not sure if that is causing the messed up readings.

I will look into that part of it right away. I was just going to bypass the circuit and apply +12 to pin 12.

 

[Perry Babin]

There won't likely be any of the digital type transistors in the power supply line to pin 12. Those are typically only used where a few milliamps need to be switched.

 

[brandes.cm]

So I have been trying to draw a diagram of the majestic 494 circuit and the transistor "Q1" makes no sense to me. It says A1266 pnp but a npn would make more sense to me in the circuit.

Any thoughts

 

[brandes.cm]

the pics I am working off, inverted the bottom image to match the top parts.

 

[Perry Babin]

It looks like a protection circuit driver. The base gets pulled down by something in the protection circuit and that drive 5v into pin 4 shutting it down.

 

[brandes.cm]

Is the pinout for the a1266 ECB? Looking at the flat side left to right.


Sent from my DROID using Tapatalk

 

[Perry Babin]

Yes. That's the pin configuration for most all small transistors that use the 2S type part numbers.