Focusrite Liquid 4 pre

[spoontex]

Hi,

anybody have schematics or service manual for this unit?

Thanks.

 

[Khron]

How about you try describing whatever issues you're encountering, and possibly adding some photos of the (potentially) affected area, hmm?

 

[pucho812]

Hi,

anybody have schematics or service manual for this unit?

Thanks.

Focusrite. They are impossible to get any service docs out of as of late. I had an 8 channel focustiee pre on the bench, a focus rite 828. Luckily for me, it was full of dead capacitors which went out from heat.  But  anyway I tried to get a schematic from them and they refused. 

 

[spoontex]

I bought an used Focusrite Liquid 4 Pre, very cheap ( 100€ ). Because the old owner tell me that the only issue was a little hum on the four channels. Si, I though that was an easy fix. WRONG. Somebody tried to fix.

The unit didn't work, a hear a relay open and closes continuously. And when I open I found some surprises.

https://ibb.co/RYtH8F0
https://ibb.co/4p2gVXH
https://ibb.co/YTkjQsd
https://ibb.co/yXy8twZ
https://ibb.co/KbL0XCh
https://ibb.co/CJbNnYw
https://ibb.co/GspTdj1

The voltage reulators section es very strange:

7812
7805
7905
Lm317 ?!?!

So, I need some photos of other unit, schematics... something...

Thanks.

 

[Brian Roth]

Those are VERY standard/generic voltage regulators, especially the LM317:

https://www.ti.com/product/LM317

The 78/79 regulators are also "jelly bean" parts.

Bri

 

[spoontex]

Yes, I know.

But it seems that if it's a symmetric power supply... It's more common a 7912 in place of a lm317...

 

[Khron]

I'd guess the LM317 regulates the 48v phantom power. Because mic preamp :

 

[spoontex]

Yes, I thought but there is another lm317... This is the reason that I think that this LM317 near 7805 is not correct...

 

[Khron]

There is also a 7912, SEC-branded, just not on that same heatsink. That and the 7812 will likely be supplying the analog circuitry.

So the regulator in between the 7812 and the 7805 is a(nother) LM317? That's certainly not right, there's no voltage-setting resistor pair that I can see, unlike for the one at the right-most end of the heatsink.

Those added diodes on the back of the 7805 make no sense, though. Unless the axial one is a zener? Because the first and the last are pointing the opposite directions.

You could try probing the input and output voltages for each of the regulators (being careful not to slip and bridge adjacent pins, of course), as a starting point...

 

[spoontex]

There is also a 7912, SEC-branded, just not on that same heatsink. That and the 7812 will likely be supplying the analog circuitry.

So the regulator in between the 7812 and the 7805 is a(nother) LM317? That's certainly not right, there's no voltage-setting resistor pair that I can see, unlike for the one at the right-most end of the heatsink.

Those added diodes on the back of the 7805 make no sense, though. Unless the axial one is a zener? Because the first and the last are pointing the opposite directions.

You could try probing the input and output voltages for each of the regulators (being careful not to slip and bridge adjacent pins, of course), as a starting point...

I agree with you, these diodes on the back side... I see very strange things... But without another unit, or some schematic... I think this will be very difficult to repair...

 

[Khron]

It may, or it may not. Are there no test-pads with some potentially-revealing markings anywhere, at least for the supply voltages?

Although my indication of probing the existing parts still stands.

On another note... You might want to look through something like my teardown of a Scarlett 18i20 over on my blog, and look for structural similarities. I'd do it myself, but I'm not home right now, and it's a PITA on a phone...

 

[spoontex]

Okey,

today I desoldered the voltage regulators, and only one of them work. And I discovered the reason of that diodes under the board. The board have a short somewhere...

 

[Khron]

A short between what and what?

 

[spoontex]

GND and input on every regulator.

 

[Khron]

Ouch... And that's with all the regulators removed? And also, I assume, with the transformer disconnected?

Might be time to look at the bridge rectifiers. Although, how long did you measure that short for? Do keep in mind, there's "some" hefty(ish) amount of capacitance on the regulator inputs, to smoothe out the rectified AC, and until those get charged up from the tiny current the multimeter provides on the resistance test setting, they will appear as shorts.

 

[spoontex]

Yes... with the voltage regulators removed. So, I will wait a response from Focusrite... If I have luck and they can send some type of info.

 

[abbey road d enfer]

So, I need some photos of other unit, schematics... something...

PSU seems to be a weak point with Focusrite. I recently serviced a Voicemaster that had significant hum. Turned out one diode of the bridge was open. It was an SMD, that I replaced with a good old 1N4002.

 

[Khron]

Fat chance of getting schematics or repair info from them.

That being said though, their spares department has been nothing short of stellar, amazingly so. Must be at least on four occasions that I needed some knobs or screws or buttons, even a rear panel for a Scarlett 18i8, and they graciously mailed me the parts, for free(!!!).

A few years ago, I too bought a dead Octopre Platinum, that melted the connector coming from the transformer (and maybe the bridge rectifier?) due to bloated/blown electrolytics.

 

[spoontex]

Some progress...

I de-soldered all the filter caps ( the big ones ) and short is gone. I think that the guy that tried to repair put under voltage caps  ( 25V ).

How I want a photo... only a photo...

 

[Khron]

Well, if the short's gone, you're golden. What do you need photos for?

Since the regulators are removed, you should be able to measure whatever AC voltages the transformer puts out. Then choose the biggest capacitors of the appropriate voltage that fit in there (mind the pin pitch), and job done.

Or are problems even "after" the regulators?