GAS PSP3500.1d going into protect

[Perry Babin]

The rectifiers are the FMG33... devices on the corner of the board. Output on the center terminal.

The 2010s won't generally get supply voltage while it's in protect.

 

[LatvianVideo]

Yep, checked the FMG33S and 33R, both have no voltage/pulses on any of the pins

 

[Perry Babin]

Do you read the same resistance from the gate to source for all of the PS FETs?

Desolder and lift the center terminals of the two rectifiers. Will that allow the amp to power up?

 

[LatvianVideo]

all of the IRFB7437s do have about 1000 ohm between gate and source. About 992-999ohm, mostly 994ohm. Now ill fire up the soldering iron and desolder it

 

[LatvianVideo]

disconnected the center pin, still the same behavior as before

 

[Perry Babin]

What are you using to power the amp?

 

[LatvianVideo]

currently a 12v 5a power adapter

 

[LatvianVideo]

hmm, the 27324 driver ICs Vdd has a 2ohm resistance to ground, could it just be internally dead?

 

[Perry Babin]

Slide the 4.7 ohm resistor off of the pads and recheck pin 3 to pin 6.

I don't know if the amp has low-voltage shutdown but the supply could be a problem.

 

[LatvianVideo]

the supply stays at a solid 12.5v. The 4.7ohm resistor was dead, like 35k ohm on it, happily i have 9 left as i needed some for the gate resistor

With it removed there still is 2.2ohm between ground and Vdd

 

[Perry Babin]

It appears to be bad. Generally, the outputs of the IC short. That's why I asked about the gate to source resistance but that indicated that they were OK.

Do you have a replacement? It's fairly generic so anything with the same pin configuration that's non-inverting will be OK, at least for testing.

 

[LatvianVideo]

I dont think i have anything, but ill check the other amplfiers i have, maybe they have a similar part

 

[LatvianVideo]

They do not have one, gotta hope stores over here will have one similar enough to this one (doesnt have this exact one)

 

[LatvianVideo]

There is a UCC27424D, to me seems like the same thing, but has enable pins (they are NC on this one). Reading the documentation, it says that the enable pins can be left open for normal operation, so should work.

Currently has the 27324

 

[Perry Babin]

Is that one readily available?

The 27524 is what they commonly use as a driver. It also has the enable pins (which can be left open).

 

[LatvianVideo]

Both are available, but the 27424 is 0.5eur cheaper (the 27424 costs 3eur)

 

[Perry Babin]

After removing it, did it still read low resistance 3-6?

 

[LatvianVideo]

After removing the 4.7ohm resistor yes. Havent tried removing the 27324, gonna do that now probably

 

[LatvianVideo]

Yep, the 27324 still has 2 ohm between ground and Vdd when not on the board. Would the 27524 be worth the little bit more than the 27424?

 

[Perry Babin]

I don't know if this was a random failure or due to the current rating of the IC. I've never seen the 424 being used. It's been either the 324 or the 524. I generally see the 524 being used as a PS driver.