Hi,

Before you look for the poor solder connection that Mark referred to, make sure your install doesn't have problems.

1) Make sure you have a good connection from the Amplifier to the frame of your vehicle. This includes a large diameter wire (4 AWG or larger) to the vehicle frame local to the amplifier. This connection can become corroded with environmental conditions over time. It's best to clean both the lug and the chassis frame connection area initially to provide a good bond, then seal the connection to prevent corrosion. Check your positive and negative connections to your Amplifier and or Bulk Capacitor (sometimes referred to as a power stifferer capacitor).

2) Make sure your RCA connectors are not corroded. Amplifiers often have gold plating on their RCA connectors. It's best to use gold plated RCA connectors on your cables. It makes a long term gas-tight connection. If you have not used gold on gold, you may have galvanic corrosion from dis-similar metal migration. This is often seen as a black dot of oxide where the surfaces meet. You can clean the connection and it will work for a while, but the problem will return later. Just use gold-on-gold to eliminate the problem.

Inside the amplifier, look at the following...

1) Look for an open ground on the input. This may be a poor solder connection at the connectors where they are stressed by cable/connector movement, or a burned open trace on the circuit board.

2) Clean the input level controls (if you can get to them) with De-oxit D5 to clean them, then Pro-Gold to maintain them.

3) Look for burned resistors in the front end low level stages of the amplifier.

4) Look for radial capacitors (tall cans) that are bulged (the top is not level or puffed up from outgassing), overheated capacitors (the plastic wrapper around it has shrunk and doesn't partially cover the top of the can), or have leaked electrolyte onto the circuit card. The ones usually suspect are located near heat producing components like power resistors, power transistors on small heatsinks, or capacitors that have to handle high ripple currents in the power supply. The same thing happens in TVs too. Always look for capacitors around heat producing devices like the flyback transformer, power resistors, vertical amplifier, audio amplifier, pincussion circuitry, power supply, etc. Sometimes they take out small fusible resistors less that a few ohms too.

If this is the problem, it would most likely be a smaller capacitor <100 uF in the signal path somewhere. They can be used to AC couple signals between stages or can be used to set the gain of circuits when they bypass an emitter resistor too.

5) It could be a bad op-amp in the front end too. Always check the voltages on the op-amp before declaring it deceased (common pins are pin 7 (+V) and pin 4 (-V) for 8 pin op-amps like the 4558) to ground. The voltage could be +/- 6 to 15V, but should be equal on both pins to ground (like +6V and -6V to ground). If the voltages are not equal, check for 2 small regulators that may or may not be on the main heatsink. They will supply the low level supply voltages. If one of them are bad, look for other problems too.

6) Check that you have proper voltage to the output devices. The outputs are rows of black devices mounted on the main heatsink assembly. They will likely have 2SAxxxx, 2SBxxxx, 2SCxxxx, or 2SDxxxx, labled on them. If it is a FET output stage (digital amplifier), they will be 2SJxxx, 2SKxxx, IRFxxx, or BUxxx. Don't confuse these with the power supply MOSFETs in the power supply. They will be locaed away from the power supply section. These are easy to measure as the devices are likely TO-220 or TO-247 packages. The center pin will be the supply voltage. They will be arranged as paralleled sets of 2SA/2SC or 2SB/2SD for the positive and negative rails. The amplifier will be split this way and if you measure from the center pin of a 2SA and a 2SC device to ground, you should see a similar voltage + to ground and - to ground within a volt or so. Be careful measuring this and don't short anything out. The voltage will probably exceed 30 volts for each of these voltages. If this is there, the problem is likely back in the input stage again.

This should get you started.

Ross