DS18 Amp

[caraudioguy2100]

Amp came in with blown power supply fets .

I replaced the fets and driver ic’s (IR4427)

Amp will not power up I get no voltage or drive signals on the gate legs .

Any ideas ?

 

[caraudioguy2100]

The smd transistors are marked FR and BR for the power supply I’m assuming these are drivers since they
Connect to the gate legs of the fets .


Wondering if there is a good replacement I can use in this amp ?

If not does anyone know the part numbers for these ?

 

[Perry Babin]

Transistor marked BR - 2SC2412K

Transistor marked FR - 2sa1037ak

The following site gives the part number from markings:
Marking smd

I use the MMBTA06 and MMBTA56 for PS drivers.

 

[caraudioguy2100]

I have 2 of these amps in with 2 different problems I will start a new thread for the other amp .

 

[caraudioguy2100]

Working on this amp .

The original problem with the amp is it had blown power supply fets .

I switched the fets and driver ic’s .

Also replaced Q226

Amp is still in protection pin 1 of the 494 is at 6.52 volts .

Any ideas on what to check ?

 

[caraudioguy2100]

Pin 1 is high on the 494 at 6.52 volts .

Is there a way to disable the protection in the is amp ?

Or any pointers on what to check

 

[Crazylogix]

I use MMBT3904 and MMBT3906 for the drivers. This looks like a S&I type design. If pin 1 is higher than pin 2 on the 494, then you need to check the LM293, pin 7 and pin 1, one of those will be high going through diodes to pin 1. If its pin 1on the LM293, that come in from the pin 11 of the power supply board header, to pin 3 of the LM293, its part of the output protection. If its from pin 7, that is from pin 10 of the header, and is thermal protection to pin 6 of the LM293.


Fair warning, I am no expert, just a goober.
Damon

 

[caraudioguy2100]

Anyone have any idea what else I could check I still can’t get this amp to power up . It acts like I’m not adding remote voltage but have battery and remote voltage at the driverboard

 

[Perry Babin]

Do you have the PS board out in wire jumpers so you can access the components when it's powered up?

 

[caraudioguy2100]

Yes

 

[Perry Babin]

If pin 1 of the LM293 is high, lift/remove the diode that connects pin 1 of the LM293 to pin1 of the 494.

 

[caraudioguy2100]

Pin 1 was at 7.42 volts .

It lifted the diode amp still doesn’t power up

 

[Perry Babin]

Did pin 1 of the 494 drop to below the voltage on pin 2?

 

[caraudioguy2100]

Pin 1:0.00
Pin 2:2.42

 

[caraudioguy2100]

Ok I think I see the problem .

I’m gonna resolder the diode back onto the driverboard .

When the power supply fets blew originally it damaged the traces that supply 12 volts to the drain legs for the fets

 

[Perry Babin]

Didn't the IC start producing output when the voltage on pin 1 dropped to 0v?

 

[caraudioguy2100]

Yes the ic started producing output but amp still won’t power up .

I fixed the connections on the drain legs for the fets .

I’m gonna replace the driver ic’s again .

Since the diode is still lifted and the amp will draw excessive current when trying to power up

 

[Perry Babin]

Which FETs heat up when you power it up?

 

[caraudioguy2100]

Q16,16A ,19,19A

 

[caraudioguy2100]

Pin 7 of the driver ic go’s through a 4.7 ohm resistor then to the fets .

The 4.7 ohm resistor is measuring 7.9 ohms

Would this cause an issue with current draw ?