Digital Designs Z2HV

Replaced power supply fets outputs and rebuilt the audio driverboard .

This amp uses the driverboard with 4 ic’s (21844S)

I didn’t replace the KTD1304 muting transistors on the audio driverboard marked (MAX)

The amp powers up idles fine produces all of the regulated voltages and rail voltages . I replaced the D1302 muting transistor on the main board with a known working one .

The amp will not produce rail to rail oscillation .

Is there a way to tell if the MAX transistors are bad on the audio driverboard ?
They test fine but the amp will not oscillate
I replaced all of the ic’s 4x 21844s,TLO72,LM211,LM293
Also replaced all of the smd transistors only ones I didn’t replace was the muting transistors marked MAX

That’s why I was asking if there is a way to jump them or tell if they are bad from voltages since they check fine on ohms .

I replaced all of the 47mh inductors on main board and replaced the D1302

Which leads me to believe the problem is still on the audio driver board
If the previous failure was disastrous (output mosfets exploded) you have to check all gate resistors, even a small variation from the value in tolerance, it can mean a big difference during the operation of the amplifier (so it can cause big problems, too not immediately) also you have to check especially the "VS" resistors (which are the 4 resistors of 1 or 2.2 or 4.7ohm that reach the "VS" pins of each IRS21844, when the failure of the amplifier is catastrophic, these are the first resistors that open or modify their value / behavior, even in this case, reading values ​​after all "in the norm", does not necessarily mean that these resistors have perfectly survived the catastrophe (my advice is to replace them regardless, because they represent a point VERY IMPORTANT for your high side).
On the driverboard, there are some resistors that you can break or change their value when a catastrophic failure also leads to the failure of some smd transistors (even when nothing else fails) I for safety, I always replace everything, it costs you little money and little time and you avoid wasting more money and time later.

For the rest, if your amp really has everything else in place, then I could think of some "vias" that no longer work, otherwise nothing else.
Oh, I forgot, did you check the "VB" diodes on the driverboard?
I repaired this amp back in February of this year .

The amp worked perfect on the bench then it sat until today .

I powered the amp up in a vehicle and the first time it went into protection I turned off the head unit and turned it back on and all
Of the power supply fets blew .

Any idea what might cause this ?

It worked fine then the amp sat for around 7 months and blew all of the power supply fets .

I don’t believe any of the outputs blew just the power supply fets but I will have to double check this
What Output fets have you used ?
If i remember, HV version of this board, use 500v mosfet, so if you have used 400V (like irfp360lc or fda24n40f) you had not problem on the bench probably because on the bench you use 12 or closest volt power supply, so the amp PS don't reach a very high (and problematic) rail voltage, but in a car, with 14v (also with 13.7v) the amp ps section have produced a biiiig rail voltage that destroied your output fets and for the first time the protection circuit have saved you.

When you had turn on again the amp, the protection was not fast enough to protect you and the shorted output section have caused the catastrophic blown in ps section.