Crossfire C5-1700D

[RiLoWa]

I have one of these in that was serviced before and the outputs do not appear to be the original parts. Does anyone know what the correct parts are?

 

[RiLoWa]

For those that may encounter this amp, it uses FDA59N30 as outputs.

I replaced the IR21844S under the little heatsink, the TL072 & LM211 also.

I have clean audio signal reaching the driver board, but I do not have have clean signal on pins one, two or three of the TL072. The amp powers up and has a triangle wave (similar to what I see on pin 1 of the 072) riding on ~65VDC at the outputs and will protect when the signal level is increased. I have +/-5V, +12V, +/-15V and rail reaching the driver board and the appropriate legs on the ICs. I checked over the other components on the driver board before putting it back in but I must have missed something.

Once the IR21844S has failed, will it damage the MMBTA92 also? Or is it stressed like in the other driver boards and should have been replaced?

This board has the combination of transistors marked ZA and MAX connected to pin 7 of the LM211. I don't know what the ZA is (MMBT8050?), would the combination of MMBT3904 and MMBT3906 work here? Are they even prone to failure?

 

[Perry Babin]

Many times, troubleshooting is easier if you disable the 21844 by connecting a jumper between pins 2 and 5. I don't know if that's possible without removing the board in your amp.

Do you have rail-rail oscillation on the output transistors?

 

[RiLoWa]

I don't see rail to rail oscillation at the outputs.

I can bridge pins 2 & 3 without removing the board, 3 is connected to 5.

 

[Perry Babin]

If you drive a low frequency (50-100Hz) signal into the amp, what do you see at pin 1 of the 21844?

 

[RiLoWa]

~-61.5VDC, no square wave, this is without bridging the pins.

 

[RiLoWa]

This picture is from earlier when I had the board out.

 

[Perry Babin]

You need to bridge the pins to troubleshoot.

 

[RiLoWa]

Bridging the pins made no impact

 

[Perry Babin]

Increase the signal level, set the gain to max, set the crossover as high as it will go and the subsonic as low as it will go.

Do you see a square wave on the output of the TL072 and the output of the LM211?

 

[RiLoWa]

Yes on both.

 

[Perry Babin]

Do you have a square wave on pin 1 of the 21844 that swings from the negative rail up to about 10v above the negative rail?

 

[RiLoWa]

Yes

 

[Perry Babin]

Connect a resistor between pins 1 and 2 of the TL072. 10k preferable but anything between 1k and 10k will likely work.

Do you get clean audio out of the TL072?

Adjust the input signal so that the audio out of the TL072 isn't driven to clipping.

 

[RiLoWa]

Yes, dialing back the gain and input signal I can get a clean signal on pin 1 with a 10K resistor.

 

[Perry Babin]

That typically means that the TL072 is working properly. The square wave on the input of the 21844 typically means that the drive circuit beyond that point is OK.

You stated that you didn't have clean audio on the TL072. Pin 3 should be at ground. I wouldn't expect to see anything other than what you see on ground.

The signal on the other two pins depends on many things when the amp is in operation.

 

[RiLoWa]

The ER1D diode at D6 is bad on this board. I know I checked it and all the others when I had the board out so I don't know how I missed it. I have to order it. I read elsewhere to use the ES1G instead.

When those diodes go bad does it kill the 21844? The outputs still check fine, in circuit.

 

[Perry Babin]

The diodes are generally damaged when the outputs fail.

The ES1G is more likely to survive in amps with higher rail voltage when the outputs fail.

 

[RiLoWa]

Update:

I replaced the original ER1D diode with an ES1G and that has returned the amp to working order.

I'm sure I checked it when I had the driver board out, but I have noted to replace it when the IRS21844S is replaced from now on.

Thank you Perry for all your assistance.