Focusrite Saffire Pro 40 re-cap

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

What exact chip might that be? I can make out the [BB] Burr-Brown logo, and "PCM", but no numbers.

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

Nevermind, a bit of squinting, and the flexible search engine from alldatasheet.com revealed that it's a PCM3168A.

https://cdn.badcaps-static.com/pdfs/...787658228e.pdf

Page 8 shows the pinout - those caps that are close to the chip itself seem to be only filtering the power supply rails and the various reference voltages that the chip generates / needs.

To get to the signal coupling caps, you'd have to trace the signal lines. The outputs seem to be quite clear (the pairs of traces leaving the chip, on the left side); the inputs might be a bit trickeir, they're on the opposite (right) edge. C20-23 (ceramics) seem to be, most likely, anti-RFI (ie. between the input lines and ground, or between the (balanced) input lines themselves).

[aaronrash]

Re: Focusrite Saffire Pro 40 re-cap

Awesome, so what would you replace those 10uF/16V caps with? I am guessing they are decoupling caps for the AD/DA chip?

I was thinking of changing to maybe 47uF/16V

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

That should be fine, extra filtering on those power rails definitely can't hurt. I'm just not sure if/how audible that might be

[aaronrash]

Re: Focusrite Saffire Pro 40 re-cap

Ok so my first attempt at replacing my op amps went horrid. The SMD station got the Op Amps out with no problem but the tip on my solder iron was way to big for the job and ruined all the pads on the first and second channel. The only way to recover at this point would be to trace where the damaged pads go and run wires to the op amps.

The elctrolytic recap process has gone fine so far with no problems but those op amps are so tough to replace!

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

Did you (even) try cleaning the old solder off the pads before installing (or attempting to install) the new opamps?

With the help of a bit of (good quality) flux, even a huge(-ish) tip shoulnd't be an issue.

Got any pics of the present state of affairs? And is your soldering iron temperature-controlled? Or is it just one of those mains-powered unregulated "firesticks"?

[surrealisticdukes]

Re: Focusrite Saffire Pro 40 re-cap

Hey there!

I also decided to recap parts of my Pro 40, especially the psu and some caps around the mainboard regulators. I noticed that it took more and more time after startup for the locked led to come up (always acompanied by the audible click of some relay). Also for quite some time i have occational problems with some kind of digital distortions where the drivers seems to get a hick-up, which i normaly solve by muting and changing the audio buffer to a different setting. Many different driver version updates and reinstalls didn't fix the problem, i could find the motivation to reinstall the operating system to see if it was the cause.

I thought maybe the startup-delay and occational gliches could have the same root in some power stability problem. Also the +48v test point only measured 43V and the 51V from the power supply took some time to come up and this seems to correlate to to the start-up delay, as you can hear it switch when a specific voltage is reached. When you switch it off and on again it will be faster in reaching this voltage and switching the relay.

The recap didn't bring any improvment in startup-time and unfortunally i can't look for the failure anymore. During some power up to test the voltages a dangling earth wire from the chassis managed to slide past the shield and supposedly touched the heatsink of regulator Q1.

So far it only seems to have blown out R37 which lies between the bridge rectifer and the heatsink. It was badly chared and clearly released the black magic smoke. I hope nothing else got fried and the resistor took all the damage. I tried to switch it on again before i knew i had lost a resistor and it took out the primary fuse. I didn't take any pictures of the underside of the psu, so now i have no idea about the value of the burnt transistor.

Would be very nice if somebody could look at their pcb for me and tell me the value? There is only marketing wank all over google and here seems to be the only place where people work on the pcb of the saffire range.

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

Sorry to hear about your loss

The heatsinked Q1 is in the power supply, i reckon, right?

Can you check the traces on the underside of the pcb, to see where the now-blown resistor is connected?

[surrealisticdukes]

Re: Focusrite Saffire Pro 40 re-cap

Hey, thanx for the quick reply!

Yeah, its on the psu. Actually Q1 is the switching Mos-FET, i mistook it for a regulator and R37 is on the underside of the PCB next to a big solder-blop which holds the heatsink. There should be a Silkscreen Label next to it. The blown Resistor is connected to the Output of the Diode-Bridge-Rectifier and via another Resistor (if i remember correctly 10K) to the Gate of the FET.

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

is it connected also to the source pi of the FET? The source pin is the first from the right, when you look at the FET from the front ( standard pinout is gate-drain-source, as viewed from the front, starting from the left).

if that's it, that's the current sense resistor (under 1 ohm in value), and if that's blown, there's a good chance the FET itself is blown as well...

[kod2nd]

Re: Focusrite Saffire Pro 40 re-cap

This thread is awesome, im gonna take a shot at modding the pro40s caps.

[surrealisticdukes]

Re: Focusrite Saffire Pro 40 re-cap

No, the blown one is not the sense resistor. In this power supply it consists of 4 Resistors in parallel (2x 1R0 2x 3R3).

I think R37 is part of 2 pull-down resistor in series on the Gate of the FET. R11 is 10k and connects the heatsink to the gate of the FET, R37 connects the heatsink to ground of the Diode-Bridge Rectifier.

No idea why the heat sink is connected in circuit like this anyway?

[surrealisticdukes]

Re: Focusrite Saffire Pro 40 re-cap

I unsoldered the FET and checked it using my multimeter. It should be OK.

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

Any chance you could post a (half-decent) photo of the power supply, top and bottom? Maybe with indications with which component is which...

[danmol14]

Re: Focusrite Saffire Pro 40 re-cap

Hello Khron666.
I decided to recap my Pro 40, and follow your steps. I`m trying to buy the caps, but I don`t find an online store to buy them all together. I live in spain. Do you recommend any store?
Thanks

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

I can't say / guarantee it's the cheapest choice, but there's a guy on ebay selling a wide array of japanese caps (among others). You can search for his id, egekecu, or "PC Motherboard Capacitors Store".

I've seen him recommended by a few guys around here, and i myself bought some Sanyo lowESR caps a while ago, for some ATX PSU recaps, and all went fine.

[surrealisticdukes]

Re: Focusrite Saffire Pro 40 re-cap

So.. here are the pictures of the failed Saffire Pro 40 SMPS PCB.

The heatshink for Q1 is where the mains earth wire touched and on the underside you can see the missing R37.
I already cleaned up all the mess, there has been quite some soot after R37 burned out.

If somebody could tell me the value of R37 it would help quite a lot to repair the bugger.

Note that the input protection devices (NTC Thermistor & Varistor) are missing because i unsoldered them for testing.
I found the Thermistor shorted out (maybe during the failure, or even before?). Another thing i have to fix.

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

Hmmm... From what i can tell, there's a reasonable chance that R37 was just a "0" jumper.

The FET is in an isolated TO220 package, and that solder-tickened trace is going to the negative leg of the bulk filter cap, right? The trace going to the FET gate goes under R37, and those 3R3 and 1R0 form the current-sense resistor (from the FET source to the negative leg of the bulk filter cap). So it wouldn't make much sense if R37 had some (greater) value. Most likely it's just employing the heatsink as a small EMI-shield of some sort, i'd reckon.

Although i AM open to corrections from more knowledgeable types

[surrealisticdukes]

Re: Focusrite Saffire Pro 40 re-cap

Yeah the solder tickenend trace goes to the filter cap. If it was just a "0" jumper for layout reasons, it would actually connect the heatsink to ground, which makes sense. I also was thinking it might have been some sort of fusible smd.

But i'm anxious to solder some jumper wire instead, maybe it still was some Resistor, probably fine tuned to prevent some stability problems or something.

I hope somebody can check the value for me when they recap their SMPS. Would be very much appreciated.

[Khron]

Re: Focusrite Saffire Pro 40 re-cap

The heatsink's not connected to anything (else), so there's not much to tune with it. If anything needed adjustment, that would be done in the passive components surrounding the PWM controller chip

Actually, i'm reasonably sure the power supply works fine even as it is, with the heatsink "in the air". But, as before, i stand to be corrected