vortex amp problem

[ampjunkielikeme]

i have a vortex amp that powers up and has sound, but there are 2 big white resistors that get very hot. so hot you can smell them burning after a couple minutes after it powers up...one is right between the torrid and the big capacitor. the other one is right beside the other big capacitor to the left. at the end of the row of white output resistors...you can see burnt spot on the glue...

when i probe these resistors for dc , i get a reading of -46.30v on one side, and 2.5 volts on the other...but the other one has a reading of 42.21volts and 2.5 volts on the other leg...
i took a dc reading off the middle legs of the output transistors, one side reads -46.23, the other side reads 42.15

494
Pin 1: 2.566
Pin 2: 4.816
Pin 3: .074
Pin 4: .016
Pin 5: 1.526
Pin 6: 3.708
Pin 7: .002
Pin 8: 10.80
Pin 9: 4.314
Pin 10: 4.306
Pin 11: 10.80
Pin 12: 10.85
Pin 13: 5.031
Pin 14: 5.030
Pin 15: 5.64
Pin 16: 5.27

[Veronica]

While I am not all that familiar with the Vortex Amp, I understand some basic electronic concepts. First one is the function of resistors (to restrict, regulate or oppose current). When the current flow is greater than the resistor can handle, they are prone to overheat and can reach a failure threshold and fail. The danger is that as they heat, other nearby parts which have less heat dissipation capability can catch fire. So this is a very dangerous situation.

How to solve this:

Look for shorted components that can be causing excess current draw.
These are often easiest to find by using an Ohmmeter. Advantage of this method is that it can be done with the power off, preferably disconnected. Please be certain to properly discharge the power caps before beginning this procedure to avoid injury and or damage to the components.

Find the current draw using an Ammeter. Of course this requires removing one of the pins and connecting an ammeter in series with the resistor. This must be tested with power on, but safety dictates powering off, removing power source, properly discharging power caps and then un-soldering one end, attaching Ammeter, testing and then powering off, removing power source and discharging caps again.

Find the voltage drop across the resistors by using a voltmeter to probe the voltage on either side of the resistor.

This may seem basic, but I am a basic minded person. I tend to keep things simple. One nagging though is that since it all works, it is possible that these resistors do not have a high enough wattage (heat dissipation) rating. Which is why knowing the voltage drop and current are so important. However it could be a short somewhere or a part that is passing too much current that is causing this.

Where the problem exists with this can be determined by asking:
Has this problem always existed within this amp since it was new? If so, perhaps a part was installed incorrectly (such as a reversed cap or diode, incorrect resistor, cap or diode etc). If this developed over time and use, perhaps someone overloaded the amplifier output by putting too many speakers (too low impedance) on the output side causing damage to something, or perhaps the amp was a victim of a power issue. (Brown out or spike).

A third option is that this could be a bad design with a value that pushes some components too hard. such as a Zener diode with a knee voltage value too high to protect a component, (but not so high as to cause total failure), or too small of a resistor to restrict current in one area, causing overheating in another.

[Perry Babin]

What are the numbers (value/wattage) on the resistors?

What was the reference (black meter probe) when you measured the voltage across the resistors? If it was not one of the non-bridging speaker terminals, measure the voltage again (on both sides of each resistor).

[ampjunkielikeme]

they are 5watt 560ohm resistors

i grounded the black probe to the negative of the battery powering the amp, used the red to probe around..
do i need to use the ground off of a speaker terminal ?

[Perry Babin]

For this, it would be better to use a 'non-bridging' speaker terminal.

[ampjunkielikeme]

edit.....lol

[Perry Babin]

No. I wanted the voltage on the resistors. It's probably not important. If one terminal is directly connected to the output of the rectifiers and the other terminal is directly connected to the non-bridging speaker terminal, the resistors are used to quickly drain the rail caps when the amp is switched off.

They're only dissipating ~3.5 watts so they're operating at less than they're power rating. 3.5 watts will produce significant heat but it shouldn't cause any problems (unless the heat is damaging the circuit board).

The fixative often becomes conductive when it turns brown. You should remove all of it that has become discolored.

[ampjunkielikeme]

on one side of the 560ohm resistor it reads 44.56volts . the other side is -0.001
the other one reads the same , except it reads -44.56 volts / -0.001

so this one is kinda like the mtx 500d. ? it has parts that are made to run hot on the board?

[Perry Babin]

Large resistors are used when power dissipation is high. High power dissipation (with insufficient heatsinking) will produce high temps (which isn't necessarily a problem). From the information you provided, I'd say that this is perfectly normal for this amp.

[ampjunkielikeme]

cool....that makes me happy....lol.