TC Electronic Studio Konnekt 48 revival

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

Well, all of these readings were supposed to be taken while OFF...

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

Sorry for that, i'm not so good with this but always wanted to learn more about it..
Without 220v cable connected, there are 45mV on both spots, so I suppose that's good..

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

That's a bit TOO low, actually... I would've expected at least something like 300mV (a Schottky diode forward-voltage drop), or closer to 5-600mV (a standard silicon diode/junction drop).

It might be worth removing L68, for starters, and see if the 3.3v rail is still low.

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

I've removed L68 and voltage jump to 1.42V..., one interesting thing while measuring voltage with digital multimeter was that first it shows 3.3V for half of second than steady 1.42V... Don't know why is acting like that.

Dice II chip and two Schottky diode are still going extremely hot after switch ON...

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

I've removed and tested this smd element tagged in attach, which is directly connected to C489. It's marked with code RL A, but I didn't found anything abot it on google.. I suppose it's voltage regulator or something similar.

Diode test; in one direction 0.64v and 0.61v, and in other OL and 0.8v, so that's not good... am I right?

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

That's connected to the GROUND leg of C489 (since the + of the cap is definitely connected to the band-end of that rectifier diode ). And with all those resistors and caps next to it, it's a safe bet it's actually the TL431 (or variant) that's part of the feedback - D74 on the schematic.

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

Ok, I'm still trying to find culprit for dropped voltage, so I removed R486, R504 and raised up two first legs of IC46 to disconnect this 3V3 part of the board... but to no avail..

L68 is still outside of the board, so what's left to test now... I've already tested two schootky diodes and they are ok (forward voltage 0.147v, reverse was OL), C489 and C488 were changed with Rubycons, so I suppose we can trust them. Only thing left is L64 but what can be bad about it... Or TR5, but how to test it, I think I will need oscilloscope to see what's happening there.

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

Removing R486 (and thus disconnecting the feedback) most definitely could NOT have helped. Although, to be perfectly honest, i'm not 100% sure if the feedback-less voltage would've (normally) went up, or down...

What you could do, in this case, is reconnect all the components you've removed. Before soldering back L64, measure its DC resistance (expect a few milliohms). Or actually, if you have something like a 1 ohm resistor to solder in series with L64, that would be great - then, you can use that as a current shunt. The voltage across that series 1 ohm will be directly proportional with the current going through that (1V/A).

On the other hand, i guess we (still) can't be sure what would be a normal current draw to expect...

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

When I had removed L64, and turn power ON, after few seconds C489 has bulged and trow out liquid, huh..no more YXF Rubycons to swap... I suppose that's happened because of high voltage on it...
I think it was around 20v.. but I'm not really sure cause I've quickly turned device OFF when I've noticed something's burning on other side..

I've changed bulged cap with MBZ one, and reconnected all the components, so everything's in its place now, but we have same situation like before (1.4v instead 3.3v)...

When C489 is not connected to the board, there is not voltage there... two schootky diodes SS24 and Dice II chip are not heating only in that case.
It seems like C489 cap is really important element in 3v3 rail..

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

Well, there you go - did you really expect anything good to happen, with the feedback disconnected?

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

It was happened after I've reconnected back all the feedback components on the board, except D74 and L68... my mistake... I don't have 1 ohm resistor to test current, it would be interesting to see what's happening there..

But I don't understand why there is no voltage on 3.3 rail when C489 is out of the board? And is it safe to take out L64, when all components were connected..?

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

*sigh* D74 is a crucial part of the feedback circuit, which limits the duty-cycle of the switching transistor, which in turn keeps the voltage from going too high. With that missing, your YXF cap blew up.

You can see the schematic, right? What do you think might happen with L64 missing? See where R486 is connected?

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

Yes, I understand now, sorry for the dumb questions, but like I said I'm not so good at reading schematics...
I've believed that something in that circuit was wrong so I've tried to randomly pull components in hope of finding root of the problem.. obviously in wrong way..

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

Weeeeeell, the "randomly" part is where you went the wrong way, unfortunately

But in this case, you can only hope you didn't toast the Dice chip (or anything else), when the feedbackless 3.3v went as high as to blow that cap...

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

I think I got lucky When that have happened, L68 was also out of the board so high voltage didn't go further...
Any idea what else might be smart to do test on?

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

It would be pretty great if you had two adjustable / lab power supplies, to "replace" what comes out of TR5. 3.3v for the whole digital side, and a 5v to supply the buck converter that supplies the firewire chip (which provides the main clock to the Dice).

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

Can I use PC power supply for this purpose..? It has all the combinations of voltages I need for this test.

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

I suppose you could, although i'm not sure how important the isolation of the firewire chip's supply is. And "of course", unless you use some ammeters, you can't really monitor the current consumption on each rail

[solozabal]

Re: TC Electronic Studio Konnekt 48 revival

Ok, thanks. I would try to do a 3.3v rail test first, because I think that is a root of the trouble..
I already have 1.3/1.4V there, so I will need to take off TR5 before applying 3.3V from power supply..

But with C489 disconnected, I have clear situation because there is no voltage there. So I just need to connect external 3.3v between TP672 and DGND... and hope for the best

[Khron]

Re: TC Electronic Studio Konnekt 48 revival

I'd rather suggest you remove L65 (on the primary of TR5) as well as L64 (or D103) and D81.