Hifonics HFI 1000.1D

[S Merlington]

amp had a blown power supply ..

I replaced the drivers A1275 and C3228 with BD139 and BD140

I replaced all gate resistors 47 ohm

I also replaced all fets IRFZ44N'S

When i power it up the amp draws excessive current and 3 of the fets get red hot within 2 secs..

I swapped driverboards froma differnt amp and removed the rectifiers still same issue only 3 of the fets out of 6 get red hot within 2 secs..

Any ideas on what to check ??

 

[ultra]

do you have a clean square wave at the first leg of all fets without them on?

did you try to load the driver transistors by inserting a 10nf capacitor per bank between first and third pin ?
i am using 100Ω resistors with IRFZ44...

 

[Perry Babin]

Check the collector connection to ground for the BD140 that's driving those FETs. The vias commonly fail and since the ground is generally on the top of the board, the connection is broken.

 

[S Merlington]

checked the connection from the collector to ground for both BD140's and 00.2 ohms between collectors and ground..

With no fets in the amp i get a good square wave on the gate pads..

 

[Perry Babin]

Connect a 1000 ohm resistor across the gate and drain for one FET that's heating and one that's not heating up. Do you see the same waveform?

 

[S Merlington]

If i connect a 1K resistor Between Gate and drain i get identical sqaure waves for the ones heating up and not heaing up..

I also put a 10 nf cap betwen gate and drain after i removed the 1k resistors .. Still get identical square waves

 

[Perry Babin]

Reinstall the FETs and compare the waveforms on the gates and drains.

 

[S Merlington]

Reinstalled the fets even with a current limiter in line it blows the fets within 5 secs..

 

[brandes.cm]

Check the connection on the bottom of the board for all fet legs. These traces are extremely light and usually blow open on a supply failure.

 

[S Merlington]

Ok i found something wierd going on with this amp..

For the first 3 fets that burn up i checked the voltages on the pads of them..

For 2 of them everything is fine..

but there is 1 of them that measures off heres the voltages i get on the pads..

Gate pad:4.41
Source pad:13.89
Drain pad:11.61

the other 3 fets that dont burn up i get the folloing

Gate pad:4.41
Source pad:0.00
Drain pad:0.00

 

[seankane]

I think you should have battery voltage on the drains, gate drive signal and voltage on the gate leg, but you shouldn't have any voltage on the source leg.

Maybe I'm thinking of Rockford, should be similar.

 

[S Merlington]

Ok found the problems there had broken solder connections from the transformer to the board..

Ans also found the Vias bad in 2 of the pads..

 

[S Merlington]

Ok not that i get 13.89 volts on all 6 pads for the fets ..

Both banks now like to blow fets..

 

[seankane]

Is the transformer shorted together anywhere from vibration?

 

[S Merlington]

Thats what im guessing it is but its gonna be hard to find the short since theres a pound of silicone all over it

 

[Perry Babin]

You have the legs listed 1, 3, 2. Is that what you meant?

Pin 2 should directly connect to the transformer winding. Pin 3 should connect directly to ground.

Open traces are sometimes difficult to see (attached).

 

[S Merlington]

Now that i fixed the broken solder connction on the transformer and also fixed the vias issue Reconnected top of the board to the bottom of the board on pad 3 of 2 of the fets..

I get the following voltages on the pads for all 6 fets..

Leg 1:4.41
Leg 2:13.89
Leg 3:0.00

Since i fixed the broken connections i looked for solder bridges between the pads and found none but the amp likes to blow fets no matter what spot i put them in

 

[Perry Babin]

Reinstall the FETs, clamp them to the sink, power the amp up via a current limiter. If the amp draws excessive current, push/pull/twist the transformer to see if the current draw drops.

 

[S Merlington]

Yeah theres a short in the transformer somewhere..

If i find the short and fix it.. can i use the IF3205's in this amp with 47 ohm gate resistors and the BD139/140's?

Only reason i ask is because i dont have enough Z44's since i burnt alot of them up trouble shooting this amp

 

[Perry Babin]

That's what I use in all of the hifonics amps of this type.

With the limiter in series with the B+, you may be able to see an arc when the short is made/broken when twisted. They typically short either where the terminal windings first make contact with the body of the transformer or where the terminal windings make the first turn over the top of the transformer.