Crescendo 17k

[caraudioguy2100]

Removed the drivers now all of them read the same 0.478k ohms between Gate and source

 

[caraudioguy2100]

All drivers are removed from the power supply section and now I get all the same readings Gate to source 0.487K

What would cause the drivers to get very hot like they did

 

[Perry Babin]

Were the drivers shorted?

 

[caraudioguy2100]

Yes a few of the drivers were shorted

 

[Perry Babin]

Do the drivers get hot without the FETs?

Did you confirm that ALL FET locations had a good drive signal (with a loading capacitor) before installing the FETs?

 

[caraudioguy2100]

The drivers get hot without the fets installed .

I confirmed the drive signal before installing the fets with a loading cap 0.1uf

 

[Perry Babin]

Driving 500 ohms shouldn't cause the drivers to heat up. What drivers are you using?

 

[caraudioguy2100]

Bd139/140

 

[caraudioguy2100]

Since some of the drivers did not survive the first time around instead of ordering more wondering if I can get the following transistors

Originals are KSA1220/2690

Wondering if I can the following since I have them on hand

MJE172G,182G

 

[Perry Babin]

The 139/140 and the 172/182 are all perfectly good as PS drivers.

 

[caraudioguy2100]

Here is what I get on all banks of fets .

Scope set to 5us 5volts/div and trace centered

Do these look correct ?

 

[Perry Babin]

Yes. Are the drivers still heating up?

 

[caraudioguy2100]

With no power supply fets installed yet
The drivers remain cool

 

[Perry Babin]

Before reinstalling the FETs, confirm that all read OL/open (on ohms) when measuring from the gate leg to both other legs. Check every FET.

 

[caraudioguy2100]

I found 4 shorted fets

 

[Perry Babin]

Double-check all gate resistors.

 

[caraudioguy2100]

Reinstalled the fets double checked all connections and gate resistors .

The power supply board is powered up and idling fine let it sit 2 mins with no heating of parts

 

[caraudioguy2100]

Well that didn’t work . Let the power supply board sit and idle for 5 mins no heating of the parts .

Put the amp back together and powered it up it idled fine for 2 mins then shorted some fets

 

[Perry Babin]

If/when you repair it again, push/pull/twist the transformers, push on various parts of the board and various components to try to help rule out an intermittent short.

Did it blow the FETs for only one transformer of for multiple transformers?

 

[caraudioguy2100]

I found only 1 fet that shorted between all the legs all the other fets survived