Hifonics BRZ 2100.1D

[jlind54]

I have a few LED's I could stick together in series, don't they work similar to a zener of sorts? Thats the closest I have to either of the items. Need to work on building up a better collection of useful parts.

 

[Perry Babin]

You can use any sort of diode. LEDs will work at about 2v each. Standard diodes, about 0.6v each.

Build a negative regulator as is shown in section 23 of the audio troubleshooting page. A 1k resistor should work to bias everything on. Check the voltage before connecting the output of the regulator to the circuit.

One note, the diodes and LEDs will be forward biased, not reverse biased like the Zener.

 

[jlind54]

Ok got it together and it is supply -5.1 volts to the driver board. With a 60hz signal on the RCA's ~1volt pp, I've got a square wave that corresponds on the output of TL072. If I reduce the volume it eventually turns into a somewhat normal looking wave but the lower the volume the more negative its pulled. Resting voltage of pin 1 is at -3.5 volts. With the source turned up there is a drive signal present on the outputs that appears to correspond with the input signal. It appears to be working more normal now than it has thus far. I wouldn't think that have a positive voltage on the negative supply of the opamp would have damaged it, but It also probably shouldn't be pulled negative with no signal. Should I replace it and recheck?

 

[Perry Babin]

Did you connect the 10k resistor from R201's pad to pin 1 of the TL072?

 

[jlind54]

I took that off, I'll put it back and check again.

 

[jlind54]

Ok, 10k jumper to r201 and there is clean output on the output of the tl072. Why does that clean up the output? Does it create some sort of feedback loop that's missing when the outputs are not in circuit?

 

[Perry Babin]

Yes. R201 provides feedback when the amp is working normally but with the outputs out of the circuit, the feedback is lost.

Do you have a drive signal of about 8v amplitude on the gate pads for all FETs?

 

[jlind54]

Rail is at 69.9 +\- and the drive pulses are pretty close to 8 over that. It appears to be functioning as it should.

 

[Perry Babin]

The drive signal should be from the rail towards ground, not above the rails.

 

[jlind54]

I'll double check, it's very possible I looked at it backwards.

 

[jlind54]

They are approximately 8 volts below rail, my mistake. I had set the volt per division so it was easier to tell the amplitude and mived its position down on the screen and didn't think to check what rail appeared as on the scope.

 

[Perry Babin]

High side is below the rail. Low side is above the rail.

If that's true, the amp may be OK. You can try installing the outputs. Install one side and check. Then the other side if everything seems OK.

Reinstall R201 if it's out and remove the 10k resistor.

 

[jlind54]

That is correct, do I need to install an entire bank or will one high and low side work?

 

[Perry Babin]

Either way will work. Be sure to install them with the correct height.

 

[jlind54]

Ok, one of each output installed, jumper removed from r201 to pin 1, the amp powers up produces drive pulses on all the gate pads, pin 1 of the tl072 now has a nice clean triangle wave and the speaker output has a clean signal. I drove the output into an 4 ohm speaker at very low power and it seems to be stable and alive.

For the LM211 and -5 volt regulator, just any of the parts I find on digikey will be OK replacments as long as the package size matches? Seems like there are a lot of different suffixes on them?

 

[Perry Babin]

The parts aren't critical. The datasheets will tell you what some of the suffixes are but others are for digikey (ct = cut tape, etc).

 

[jlind54]

Ok, thanks again for all the help! It looks like this amp will actually live again.

 

[jlind54]

One Last Question, It seems to work OK with the IRF640N parts I don't recall if it originally had the N suffix or if it was just the plain 640's. I think the gate capacitance and overall current capabilities are a little different between the part #'s Any input on which way to go with them?

 

[Perry Babin]

The photos I have show the 640N.

 

[jlind54]

Ok, Maybe I wasn't completely crazy when I ordered them then. I'll stick with the 640N's. And you have had OK results using Kapton tape as the Insulator between the Fets and Heatsink?