Monster ClarityHD model 1 ... active speaker system ISSUE ...

Hi All ...
I'M BaaacK !!!

Got a new conundrum for Y'all to twist yer brains around here today ... as usual ... NO schematics or service manual available ... Luke Skywalker troubleshooting scenario ... AGAIN ... use the FORCE Luke !
A client brought me this set of studio monitors made by Monster with a major problem ... no power up.
After a bit of poking around with a DMM, I found the woofers amplifier chip to have multiple shorts where there should be none. So my 1st action was to replace the STA516B amp chip and after installed and powered up ... still no power up and blew ( as far as I can tell ) again ... the woofer amp chip.
After this happened, I took a closer look and saw that on the original (blown chip) I removed there were some missing pins. When removing it I did not notice or see any broken pins floating around the work area. Inspecting the original chip under high mag ... it looks like they were left OFF the chip at manufacture of the chip ... NOT just cut off before placement & reflow.

SO back to the troubleshoot mode ... I found the 3.3V regulator had a short between output and GND. After using the FORCE, I decided to remove the STA309A multi-channel digital audio processor and found this was the OFFENDING component that had the short ... lucky guess ? ... NO I used the FORCE Luke !!!

SO ... I ordered another amp chip and the new STA309A ... after I placed the new STA309, I decided to see if it would power up BEFORE I placed the 2nd new amp chip and lo & behold ... we had power up and sound from the tweeter ... YAHOO !

After this, I placed the 2nd new STA516 with the missing pins on the original ... LIFTED so as not to be connected as per the original missing those pins. And those pins were the 4 Vcc pins that you can see in the datasheet block diagram here ... Vcc-1A, Vcc1B, Vcc2A, Vcc2B ...


So as I can see from this block diagram ... IF all the Vcc pins are NOT connected ... this thing SHOULD NOT function ... The tweeter side that WORKS ... have all these pins intact and connected to the voltage source that feeds the tweeter Vcc pins, and are connected to the main power supply that outputs 34VDC as seen in the partial schematic I drew up here ... keep in mind this is the woofer side which I am trying to troubleshoot ...



So as one can see there are some notes about some findings ... the one that is of import was the C4 cap that had a 1K short to GND and so was replaced. I'm hoping/thinking that this cap possibly could have been the reason for blowing the amp chip ... who knows ...that cap is from Vss-SIGN to GND on the input side which would be the left side on the diagram ... pin 36 thru cap to gnd.

So ... after I blew the 2nd amp AGAIN ...I decided to draw up a schematic and just get a better idea of how the output was configed and that's when I found the defective cap.
So my BIG question is ... why would those missing pins for Vcc be missing on the original chip ?
And why when I installed new chip number 2 blow up if those pins were supposed to be OMITTED ... and lifted after I installed it that way and it blew up ?
I just can't see how this amp could work missing the Vcc connects ???
It doesn't make sense without a positive Vcc supply for the internal FET's ...
There are 2 configs that this chip can work in via the CONFIG pin either being grounded or tied high ? In one config it uses more current for more power OR in other config less current HALF power.
As far as I can tell ... CONFIG pin IS at gnd and is working in full power mode.
Refer to full datasheet here ... and see schematic as I ringed it out with the DMM.
https://www.st.com/resource/en/datasheet/sta516b.pdf

So far at this point ... I am waiting to place another NEW amp chip until I find whatever it is that is blowing this chip ... so far that one cap I found that had a 1K ohm short to ground is the only glitch I have found so far.
It seems that there may be something on the output AFTER the coils (22uH) that may be causing a problem but I haven't found anything at this point ... I'm still leaning towards that bad cap on a power rail that may have been the problem.
There is no dead short or small or large resistance across the output terms .... at this point I'm stumped for now ...any ideas would be appreciated ...

As far as the filters go ... the cap values are irrelevant except for one cap that got lost in the carpet.
But I'm sure that because both sides are mirrored ... I can find the right value to replace ... I think it's just a bypass or part of the crossover filter(s).
They are all caps from signal to ground so shouldn't be an issue ...

Journey

 

Hi MicroMe ...
Thanks for chiming in.
If the pins vaporized, I would imagine there would be some carbon traces left behind and there was no sign off a massive flare up ... no carbon left behind. There even may have been some remaining bits but there were none.
Also since the problem still persists, why didn't the 2 new amp chips I put on blow their pins to kingdom come ? Not only that ... in order to completely vaporize them, it would require and enormous amount of heat which would surely have damaged neighboring pins, burned the board and there's no sign of this. This amp can operate in 2 different modes and as far as I can see it's configged to run in full half bridge mode which would require those missing Vcc pins to be connected in order to operate.
At this point ... I did remove all the inductors and 2 caps and all the silicone that was blocking most of the view of the pcb traces. Which was the only way I could have drawn up the schematic.
As I mentioned in my initial post, I did end up finding a bad cap while taking measurements to draw the schematic.
It was C4 in the diagram which connects Vcc-SIGN across ground ... This cap had about 1k ohm leak thru to ground.
This may or may not have been enough to burn the chip ...
At any rate, I set it aside for a while to work on other items ... will be getting back to it soon.
I'll see if I can get a nice super zoomed pic of the missing pins. Being that I am very familiar with manufacture processes, I am quite confident they weren't just snipped off prior to placement and reflow.
This chip missing those pins just CANNOT function in this way ...

 

Forgot to mention about the speaker ... It's a healthy 6 ohms and jim dandy ...

 

Here's some pix ...

 

Hi All and thanks once again for your interest ...

As far as someone else working on this unit ... nope ... this is the only time it has been reworked/repaired.
As far as it was me who damaged the IC when removing it ... not very likely as I am very good at SMT rework. It was mostly all I did for the 5 years I worked at an electronics manufacturer and another 20 years after that intermittently working on my own.

As far as what Whonoes brought up ... I looked into how the chip is configured since it can be run in 2 different modes ... and per the datasheet ... grounding the config pin, which it is ... it runs in full half bridge mode.
Now when you say running bridged ... I'm assuming you mean this tweeter amp is somehow bridged with the woofer amp ?
If so, I'm wondering how they might be doing this as far as connections between the two in order to accomplish this.
I think I remember doing some poking with the DMM to see if those 2 amps were some how linked and as far as memory serves ... I didn't find anything but I am going to look again now that I have a schematic for the tweeter section.
If you look at the pic of the actual pcb ... one can see and probably assume safely that the two sections are mirrored ... being that they are both the same except for the output filtering ... which would lead me to think that they are not linked in any way but I could be wrong.
One thing that also occurred to me is that the 2 replacement IC's I installed may not be blown but after taking DMM measurements after power up and no tweeter output ... it SEEMED as if they had blown due to many pins seemly shorted to ground that weren't before and also compared to the good amp looking for the same results.

 

Hi Again,
Back with a quick update ...
Well Baa Lo me down !!! It appears that there is connections between the woofer O/P section and the tweeters O/P.
I will draw up another schematic showing how it connects ... I will use the existing schematic for the tweeter section for the woofer section as I believe they are a mirror copy of each other ... just ignore the output filters for the woofer section as I'm pretty sure the values would be different.

 

Another Update ...
Well ... I was right the 1st time ... no output connections between the 2 amps.
I wasn't paying enough attention and was measuring the ground connections which are common to both chips.
Sorry guys my bad !
So it's back to head scratching as to why all the Vcc pins were either purposely left out or just how in hell some malfunction vaporized them leaving ZERO signs of such a catastrophic failure !

 

A CORRECTION ...
I seem to have gotten mixed up as to which amp is which ... in my initial post I had it right I think ... the tweeter is working ... it's the woofer side that is the issue ... my bad again ... sorry if I made it even more confusing ...

 

Ah gotcha ... I see what yer sayin. I'm a hardcore old schooler ... still trying get class D amps wrapped around my head.
YA as for the filters ... I hear ya on that but I might have a problem.
I'm 99% sure I got the schematic drawn out correctly ... I did a lot of checking and rechecking ... spent a lot of time on it. In my adventure to draw it up, I had to cut and scrape out a bunch of silicone and unfortunately two chip caps got broken off and one of them got lost in the carpet. Since both left and right channels are identical mirrors of each other I can more than likely figure out what the value of the lost cap is ... I HOPE ! The cap that went missing is either C34 or C35 in my schematic. I'm gonna take an educated guess and say that they are both the same value in parallel maybe ? I thought I had it figured out and put a replacement in and the capacitance across that output and ground still doesn't quite match the the other side. I'll keep at er tho !
I don't have a decent Capacitance meter and my DMM's cap measurement doesn't work at all anymore so I'm looking at getting a dedicated LCR meter any suggestions for a reasonably good one that isn't super expensive ?Found this one on Amazon here ...
https://www.amazon.com/5000-Handhel...coding=UTF8&psc=1&refRID=YWESKAK20KGV1079628K