Focusrite Liquid 4 pre

[spoontex]

well...

I've changed al regulators and all filter caps, and when I turn on... R364 resistor get very hot ( smoke included ) and burn the 78/79 05 regulators again...


It will be very difficult to repair...

 

[Khron]

Well, you know... you COULD have measured some things "after" the regulators, before soldering in the new ones (resistance measurements, with the power off).

What's that resistor connected to? And i'm assuming the photo is from BEFORE the re-cap? Because those look dirty enough to be the original Jamicons...

 

[spoontex]

This resistor is connected to the input of 7805, the other side of resistor is connected to V+.

I'm a bit lost...

 

[Khron]

V+ being the same voltage that feeds the input of the 7812?

What value is that resistor, by the way? From the previous photo, it might be 220 ohm, if that third band is brown(?), not black.

What are the 7805 / 7905 regulators supplying?

 

[abbey road d enfer]

I've changed al regulators and all filter caps, and when I turn on... R364 resistor get very hot ( smoke included ) and burn the 78/79 05 regulators again...

That means you have a short downstream. You must trace it before attempting anything. It's a PITN, because you have to unsolder several IC's, but it's the only (right) way.
When I had to troubleshoot gear that had that kind of problem, I used a high-power PSU and quite often the culprit would end up in smoke. Sometimes the PCB tracks gave up before... 

 

[spoontex]

Okey...

I do some brute force. I injected 5V 2A directly to the 7805 output regulator, and two 74HC40660 of the preamp section start to evaporate the isotropic alcohol and get very hot. I de soldered, and now I didn't have any short betwen the GND and de +5 rail. what do you think?

 

[Khron]

Congrats then, you just might've found the culprits then!

Those will rather be 74HC4066D - D being the designator for the SOIC package (as opposed to the through-hole DIP).
Should be easy enough to find from any reputable suppliers, and dirt cheap to boot.

 

[spoontex]

https://www.arrow.com/en/products/74hc4066d652/nexperia

this one?

I have a question about thermal pad's.

When I disassembled the old ones has thermal grease over thermal pad. It's normal? I always thinking that when use a thermal pad isn't necessary the use of thermal grease.

 

[Khron]

That looks about right, sure.

Well, that depends on the pad. If it's the silicone-y kind, that shouldn't need any grease, but having the grease there can't really hurt either, I don't think.

 

[spoontex]

https://www.arrow.com/en/products/aos220/fischer-elektronik

I think that I will buy this one, it's 1.5mm height. And I don't put any grease paste.

 

[Khron]

I think those aluminium oxide ones NEED thermal grease.

They're nowhere near flat / smooth, in fact they're quite porous, and very much non-compliant (they don't bend or squish down), so you need the grease to fill in all the pores and transfer the heat away much better than the air that would otherwise be there.

 

[spoontex]

I think those aluminium oxide ones NEED thermal grease.

They're nowhere near flat / smooth, in fact they're quite porous, and very much non-compliant (they don't bend or squish down), so you need the grease to fill in all the pores and transfer the heat away much better than the air that would otherwise be there.

Thanks!!

 

[Khron]

Also, they're considerably thicker than your usual "thermal pads", so test-fit the regulators before soldering them in, just to make sure the legs are long enough, and bent the right way.

 

[spoontex]

While I wait for replacement parts. What to do with this?

I see some jumpers, U12 was de soldered, track cut... disaster!!


https://ibb.co/1M3zZBV
https://ibb.co/jr5y7Rp
https://ibb.co/Xj6rxd5
https://ibb.co/fnVDJ49
https://ibb.co/dm5fPD1

 

[Khron]

Well, considering these were probably not manufactured in the millions, and that's at least a 4-layer board (considering the BGA chips there), i'd say there's a chance that those bodge-wires could be straight from the factory. It must've been cheaper to correct a couple issues with some wires, than re-spin entire batches of boards...

And anyway, who else would know what signal comes out at the STP-N5(?) test-pad, for example?

Just wait for the new muxes, install those, and then see if the thing comes back to life. If it does, great. In case it doesn't, THEN it might be worth questioning those bodge-wires.

 

[spoontex]

Well...

I've replaced the two burned muxes. I've mounted new voltage regulators, and new thermal pads. I've changed the Zener. I've mounted two new voltage drop resistors ( 5 watts instead of 3 watts ).

And... works!

The Ethernet connection works as well. I connected to my computer and updated the firmware.

Only a few issues.

Channel 2 and 4 are louder than 1 and 3. When I move the gain potentiometer there are a noise, I attach a video.

I need to check the digital inputs and outputs, but I need an interface with ADAT.

Some ideas for the gain scratch and the difference of volume?

https://ibb.co/G9FDDG3
https://ibb.co/Fsqp1g2
https://ibb.co/hWf6vsM

https://vimeo.com/user48828015/review/459024161/22b3ebf8e0