AQ -1200

[mike49504]

I recieved this Audio Q amp in for repair. The power supply fets are missing but i believe the orginals were DFP50N06's with 47 ohm gate resistors .

Is there a good sub to The DFP50N06's??

Second question is The rectifiers are missing out of the amp beside 1 which is a FMG22U will the FMG22R and FMG22S be good replacements??

 

[Perry Babin]

I didn't find a datasheet for that FET but from the part number, I'd think a Z44 would be a good sub.

Does the rectifier have any diode symbols on its face? If so, which way are they facing?

 

[mike49504]

The fmg22u arrows are pointing like this: -->+-->+

Also i may have another problem It appears that parts may be missing off the power supply driver board. Do you have any pics of the board by chance?

 

[Perry Babin]

That's a doubler. The FEP16DTD should be a good sub.

I'm not familiar with the amp. Post a photo of the driver board. I'll see if I have anything on it.

 

[mike49504]

I found a Brand new board in my collection of stuff Only difference between them is the board out of the amp has a 393 on it and the new board i found has a 293 on it Will that work or do i need to change the ic?

 

[Perry Babin]

The 293 and the 393 are essentially the same.

 

[mike49504]

2 other things real quick.

All of the rectifiers are suppose to be the FMG22U's correct?

Can i switch the 3228's (drivers ) to 2383's? Since the drivers in this amp are missing legs

 

[Perry Babin]

In amps that use doublers, all rectifiers are generally the same.

If these are the transistors you asked about previously, they should be good subs.

 

[mike49504]

How do i figure out what order the drivers go in.

C3228 ad thw A1275

 

[Perry Babin]

The PNP drivers will have their collectors connected to ground.

 

[mike49504]

Ok I put the new power supply driverboard in the amp. Pulled all of the outputs out of the amp and have 1 power supply fet per bank in the amp right now.

I power it up through a current limiter amp idles around 6 amp of current and the fets heat up in about 30 to 40 secs.

Any idea on what to look for next?

 

[Perry Babin]

Are the gate drive signals OK?

 

[mike49504]

10 us .5 Div ?

 

[Perry Babin]

That would be a good starting point if your scope is marked for a 10x probe and you're using a 1x probe.

 

[mike49504]

Can i check the gate drive signal with the fets removed? Cause even with a current limiter it blows the fets within 20 secs

 

[Perry Babin]

It's more difficult to determine if the gate drive signal is OK without a load (gate capacitance load). If possible, leave the gate and source in the circuit but desolder the drain legs.

 

[mike49504]

So leave leg 3 unsoldered? IRFZ44's

 

[mike49504]

Sorry on the Z44's middle leg would be the drain leg. With the drain leg disconneted this is what i came up with on the gate legs of the fets.

 

[Perry Babin]

Neither of those look good. Can you post a photo of the driver transistors?

 

[mike49504]

Ok the surface mount drivers on the board go to the gate leg of the fet the 3228 and 1275's go to the 3rd leg of the fet