Audiobahn A16000V amp in Protection

[adelphia83]

Perry, thanks for that helpful advise. After all this work, there will be a fair bit of testing before I completely put things back together, and I will add that to the list.

If I'm understanding correctly, I should read voltage across the emitter resistor as the amp heats up to see any changes? Is there an acceptable increase? Some elaboration would prove most helpful when I finally get to doing this.

As a preparation for the new parts arriving, I removed all output transistors from the board. The amp now powers on completely with no protection light. I must say how happy I am to see a blue LED finally instead of red! Kudos to the protection circuit for not blowing up my 200$ subwoofer, or my nice new power supply components.

I suppose there's a lot of current going through those things when they're shorted. When I removed them, I just cut the leads and left them where they were. When I fired the amp up, two of them arced across the gap in the leads and fused themselves back together! Wasn't expecting that.

Though you guys might enjoy some pics of the repair. I must warn you, I'm well short of an expert at soldering, and next time I do this I'm investing in a much smaller tip or lower power iron. I suppose my saving grace was that I noticed one leg of the resistors going to a common, and that it was possible to solder the other leg straight to the leg of the transistor.

One leg of three power FETs go through the resistor to one common, the other three go to a different common. It's like this for both power supplies. Does this mean that each power supply puts out + and - rails?









I apologize for the myriad of questions, just trying to learn as much as I can about these. But what are the two (on each side) [transistors?] in the middle of the power FETs and output transistors? They are inscribed with something that looks like this -> <- and FR1003C. A google search turned up nothing. Many thanks again for all the help and patience to us newbies.

[Perry Babin]

This amp should read 0.00v DC across the emitter resistors (at idle, no load). If the bias current holds, there will be no increase as the amp heats up. You will run the amp into some sort of load (speakers or a high power handling resistor) and every few minutes, you'll remove the signal and measure the voltage.

You'll have to run it hard enough to heat it up. If you don't have a large power supply, you may have to reinstall it in the vehicle. You can do the tests with only ~30-40 amps of fuses (all combined). You don't have to run it up to full power to heat it up. 1/2-3/4 power will be enough. The smaller fuses will help protect the amp if something fails again.

If you're in the market for a good iron, the WES51 is a very good choice. Order the ETA, ETB and ETC tips but make sure you get genuine Weller tips.

The rectifiers are the components between the outputs and the power supply transistors. Generally, you'll find two different part numbers. Are all 4 in this amp identical?

[adelphia83]

You're right, the rectifiers have two part numbers, only difference being the suffix. Two end in C, other two end in A.

I have a 40A 15V DC rectifier I can use for testing, or I can bring home a 100A 15V DC switching power supply from work if need be. The higher voltage won't harm anything, correct?

For now I'm waiting patiently for the new parts to arrive. My other Audiobahn amp (approx half the power of this one) has been running solid for several years now. It's now driving the same subwoofer this broken one was, and keeps on trucking. I guess I should knock on wood...

One last question-- Is there anyway to accurately determine output power simply by looking at the internal components and output transistors used?

[Perry Babin]

If you have one C and one A on each side, both supplies produce both positive and negative voltage.

A 40 amp supply (assuming you meant supply) would be sufficient.

The only way to accurately determine the power output would be to measure it.

[adelphia83]

Actually there's two A's on one side of the board and two C's on the other side. So each power supply seems responsible for providing + and - respectively. I'll post back when I receive the new transistors and what the result is after testing.

[adelphia83]

Originally posted by Perry Babin
You will run the amp into some sort of load (speakers or a high power handling resistor) and every few minutes, you'll remove the signal and measure the voltage.

Perry, can you recommend a resistor for this purpose? I live in a townhouse with a neighbor to the side, and since this is a garage project, I'm certain she's not going to be happy with 20 minutes of pounding bass next door.

I've got several 10W resistors here, or do I need something larger? If I wire resistors in parallel, will this increase the power handling? I'm assuming the resistance needs to be 2 ohm, the same as a speaker load would be.

[Perry Babin]

Four of the following in series/parallel. They can take a lot of abuse (well over their rated power with music peaks) especially with fan cooling (from the end, blowing air through them.

Mouser:
588-L100J2R0E

If you don't want to spend the money and you have two woofers in an enclosure that's divided, run the woofers out of phase. They won't produce much bass.

The parallel 10 watt resistors will handle 10w times the number of resistors. If you have at least 300 watts worth of resistors (30 resistors), it may work with fan cooling.

If you intend to do more repairs, invest in the resistors listed above.

[adelphia83]

Replaced all output transistors.

Tested the amp on 10A battery charger, powered up just fine. Replaced 10A fuse in amp with standard 80A set.

Installed amp in vehicle and like a moron I wired it reverse polarity. It blew the 80A fuse closest to the battery.

Now when the amp is connected to any source of power, it immediately tries to draw up all available power, whether the remote is connected or not. Did it fry the power FETs again? Is there any way to test each individual one?

How likely is it that it just burned up a couple? I have a few spares from the same batch.

[adelphia83]

I should note that I put a meter on all the power FETs.

All showed normal readings, with little to no resistance across middle and outside of ONE leg, and not measurable on the two outside, and middle to other outside leg. This is exactly how it was when everything was working, nothing is shorted.

Any other possibilities? I guess I don't know where to begin after reversing polarity.

[Perry Babin]

The FETs with relatively high resistance (100 ohms) from leg 1 to 2 may be OK. Pull the ones with something near 0 ohms between leg 1 and 2 to see if the short from leg 2-3 goes away for the rest of the FETs.