Film-Tech Forum ARCHIVE: MS-100 Booth Monitor Schematic?

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Posted by Jim Cassedy (Member # 4115) on 01-17-2010, 09:25 AM:

One of my Componant Engineering MS-100 booth monitors
has gone dead. The power supply appears to be working,
but nothing else. The PDF in the "Manuals" section only
has a functional block diagram.

>Does anyone have or know where I can find a schematic?<

For now, I've jumpered a pair of self-amped computer
speakers off the mono output that feeds the assisted
listening device system. So at least I know I have sound!

Posted by Mark Gulbrandsen (Member # 72) on 01-17-2010, 10:05 AM:

Those monitors are easy to repair. They use a single chip audio amp. There is one other problem... they also use a cheapo socket to connect the amp chip to the board. Those little socket many times is the culprit. The chip amp is also inexpensive and I replace the chip amp and solder it directly to the PCB. If you have DC at the correct pin of the chip amp all else is probably just fine... in fact there isn't very much else that can go wrong in them.

Mark

Posted by Jim Cassedy (Member # 4115) on 01-17-2010, 01:17 PM:

Thanks for the info Mark.
I haven't had time to pull the whole unit out of
the rack & do some real troubleshooting yet, but
I'll take a crack at it this week.

Posted by Steve Guttag (Member # 268) on 01-17-2010, 04:14 PM:

When you DO pull it out of the rack...note that the connection panel is held in by screws...unscrew the few screws that hold it on rather than undoing all of the connections to your amps and processor. There are pull off connectors inside...this will save you time on unwiring/wiring.

Steve

Posted by Jim Cassedy (Member # 4115) on 01-29-2010, 08:27 AM:

FOLLOW UP:
Thanks for all the suggestions.

Some quick basic signal tracing revealed that the
big amp chip was "dead".

I bought one on e-bay from a supplier in Hong Kong
and installed it earlier this week and the monitor
is working normally once again, and I can now put
my computer speakers back on my computer.

But Wait- - there's more:
The amp chip failure led me to discover and avert
a possibly even bigger problem.

The the chip may have failed due to over-heating.
The booth monitor was directly above a QSC amp in
which the fan had failed. Both were getting rather
warm! Fortunately there was an old QSC backstage I
was able to pull a replacement fan off of. I also
re-arranged the equipment in the rack to put a space
between the amp and booth monitor.

So, in an ironic way, I'm rather fortunate the amp
chip in the booth monitor failed. It may have saved
me from cooking one of the power amps.

Posted by Mark Gulbrandsen (Member # 72) on 01-29-2010, 06:48 PM:

The QSC fans are also NLA because QSC claims the company went out of buisness. Of course they COULD have them made in China or Taiwan if they wanted to. So if you loose any more fans you need to remove the old one and insttall a 4" muffin fan on the back of the amp. Get the mating cord for the new fan and wire it to the two terminals on the PCB just as the internal fan was wired. Then you still have the two speed cooling plus a little more air flow to boot.

Mark