Hifonics BRZ2400.1D No Output...Used to be in Protect

[Perry Babin]

The regulators and rectifiers rarely fail. The output and power supply transistors are more likely to fail if there is a mistake when hooking it up.

All components on the board are soldered in place.

[danterakin]

I quickly checked the transistors along the side of the board. I did not pull any off, I just measured the resistance between the outer legs and this is what I got:

Left side of board:
5 FQP12P20 = 19.88 kohm
5 FQP19N20 = 19.80 kohm
6 IRFPO64N = 0.8 ohm

Right Side of board:
5 FQP12P20 = 12.5 ohm
5 FQP19N20 = 32.1 ohm
6 IRFPO64N = 0.8 ohm

Is this method okay to use? I know I really should pull the transistors off the board but I am on a crunch for time. The IRFP064N's catches my eye along with the right side of the board. I have not checked the driver board yet because I don't want to start unsoldiering. Let me know if I should perform other procedures.

[Perry Babin]

The output transistors on the right side appear to have failed. You need to replace those and all of the power supply FETs.

When checking semiconductors, you should not read anything near 0 ohms between any of the legs, no matter the orientation of the probes. Generally, the only exception is the rectifiers. The outer legs of the rectifiers in most amps will appear to be shorted because they are connected across the secondary windings of the power transformer.

[danterakin]

For thermal paste I know you recommend Dow Corning 340 but the tubes I find (5oz) is more than I need. Is there an alternative that will work just as good for much cheaper price?

[Perry Babin]

Radio shack has small tubes of heatsink compound. Sometimes it's dried out (or just too thick to be displaced properly) but if you get a good tube, it's usable.

There are also smaller tubes of compound available from Digikey. Search for Wakefield. The 345-1006 or 345-1007 may be what you're looking for.

[danterakin]

I went and pulled out some of the output fets and they checked out to be good (diode check) but with the fets not in the board I went and checked the outer pin holes resistance and it read same value even if the fets were still soldered in. I then checked the resistors right next to each fet and one resistor value matched the color band but the other resistor was way off. Here is what I got:

Right Side

Resistor Yellow, Purple, Brown, Gold = 8.5 ohm Resitors along Power Fets
Should be = 47ohm
Brown Black Yellow Gold = 19.88kohm *Resistors along output fets*
Should be = 100kohm
Brown Black Black Gold = 10 ohms*Resistors along output fets*

Left side

Yellow, Purple, Brown, Gold = 8.5 ohm *Resitors along Power Fets
Should be = 47ohm
Brown Black Yellow Gold = 5-33 ohms * Resistors along output fets*
Should be =100kohm
Brown Black Black Gold = 10 ohms * *Resistors along output fets*

The thing that bugs me is that each resistor has the same wrong value. For example, the brown black yellow gold should be 100kohm but all 5 of them on one side read 19.88kohm and I was taking the readings directly between the resistor. Is that normal? Also can my amp be going into protect if the resistance values aren't true?

[Perry Babin]

For the 100k resistors, they may essentially be in parallel which would make five 100k resistors read 20k.

If you're concerned about the others, desolder one leg and re-check them.

[danterakin]

I realized that I was measuring parallel resistance and removed all fets and got the right value once the bad fets were out. I have replaced the rows that had bad fets and replaced the blown cap.

The amp works but there is now a noticeable high pitch noise coming out of the speaker. The noise stays the same sound level ands the sound regardless if the signal RCAs are in or not. Basically if I turn on the amp and just connect the speaker wire only, it makes the high pitch sound.

What can it be? I'm thinking it might be because the different capacitor I put in but not really sure. Anyway I can go about trouble shooting? Can I clip off a lead on the cap and see if it still happens?

[Perry Babin]

Does it sound like someone tuning a shortwave radio?

How loud is the sound?

What sort of speaker are you using for testing?

[danterakin]

I am using a 8inch Midbass driver. The sound being produced is not really high pitched but it is in the region of 1500 Hz to 3000 Hz comparing it to my freq generator on my computer. The sound is not too loud, it almost the similar tone you'd hear when you have a bad ground causing engine noise but this one doesn't change tone or volume, its the same tone and volume regardless if you turn the gains, crossovers, boost, or signal input volume. The sound is faint but you can defiantly hear it if your driving with no music and windows up.