Hifonics BRZ 2100.1D

[Perry Babin]

The transistors along the top commonly fail because the operate at very high temps. The 470 ohm resistors fail somewhat commonly. The ICs sometimes randomly fail. The rest of the components generally only fail when there is a catastrophic failure.

 

[jlind54]

Should this amp power up and not go into protect when the audio driver board is removed? I was hoping to verify audio to the driver board and the voltages before putting it back in.

 

[Perry Babin]

It shouldn't go into protect. Is yours going into protect mode without the driver board installed?

If it is, check for solder bridges on both sides of the board.

 

[jlind54]

Ok, Cleared up some solder and I've no longer got the issue of going into protect with the audio driver board out.

Replaced Q11, Q7, Q19 and Q22. 2 of them had failed so I replaced them all.

Checked the rest of the transistors on the board and they all appeared to Check OK once removed from the board.

Prior to removing the driver board the amp would not go into protect but there was also no rail to rail oscillation either, the 9640's would just heat rapidly on both banks. Since replacing the small 1D transistors the amp goes straight into protect when the driver board is installed.

Any advice on what to check next?

 

[Perry Babin]

Are all of the 470 ohm resistors near the transistors you replaced within tolerance?

Have you cleaned up all of your solder connections so that you could confirm that you had no bridges and no bad connections?

Did you possibly pull any vias when you removed the driver board?

 

[jlind54]

All of the 470ohm resistors are within tolerance most being right around 469Ohms. I went back and verified all of my solder using a 10x eye loupe and there are no visible bridges. There were no traces of via on the pins when I removed the driver board I'll meter the connections to make sure everything is as it should be. I guess there is a chance that whoever was in this amp prior could have damaged them but the solder appeared factory at this location.

Q5, Q6, Q9, Q12 and Q16, Q20, Q21, Q23 warm up quickly right before the amp goes into protect.

Update- all thru holes meter ok

 

[Perry Babin]

Check every FET in the output stage by measuring the resistance from base to collector and base to emitter. Do all of the same part number components read the same? Use the same probe to leg configuration for both sides of the amp.

 

[jlind54]

Do I need to remove them from the board for this measurement? If so when I put them back will the amp run with only one installed in each bank?

Also you are referring to the 640's and 9640's in the output correct? Id be measuring gate, source and drain?

 

[Perry Babin]

Yes, the 640s and 9640s. Try it with them in the circuit.

 

[jlind54]

Ok, I pulled them all out of the board and checked them per the tutorial they all seem fine. I did however just noticed that I managed to purchase 640N's instead of 640's. And I have discovered the speaker out put jumps up to the positive rail voltage just prior to the amp going into protect.

 

[Perry Babin]

I wanted you to check them in the board because that could have helped to determine if there were differences in the drive circuits between the two halves of the amp. You can still do it by checking the empty pads.

 

[jlind54]

Ok I put them back in and measured from gate to source, all measure between 19.87-19.9k ohms and from drain to source all between 136k - 139k ohms on the 9640's. The 640s are the same with the exception of drain to source was lower 129k-131k.

 

[Perry Babin]

If all of the supply voltages are present, you may have a bad IC on the board.

 

[jlind54]

Pin one of U2 has a small square wave present until the amp hits protect but it's going from approximately 3 to 5 volts. Which chip is which on the driver board, is U2 the TL072?

 

[Perry Babin]

It could be either one. The TL072 is the one responsible for minimizing the DC offset but if the LM211 is defective, the signal from the TL072 can't make it to the drive IC.

The square wave should probably have an amplitude of 6v p-p. Not sure, never measured it at that point.

 

[Perry Babin]

I have a similar amp in the shop today. If you want something checked, let me know.

The output of the LM211 should swing to each 5v rail.

 

[jlind54]

I think the lm211 in this amp is dead. I'm hope to have time tonight to sit down and compare the pin wave forms to know good ones and go from there.

 

[Perry Babin]

Were you seeing a signal out of the TL072 but nothing from the LM211?

 

[jlind54]

ok, driving a 60hz signal into the amp pin 12 on the driver board which I'm guessing to be the audio pin is only showing the top half of the audio signal coming in, I'm checking for voltages on the opamps at the input of the amplifier now. I don't recall this being an issue when I first looked at the voltages present on pins 1-22. Also, No dc pulses on any of the transistors on the drive board.

 

[jlind54]

ok R131 has an amplified signal of the 60hz being feed in on the side nearest the rca's the other side that is going to the driver board has only the tops of the wave present. I'm not sure that is correct.