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MA12000i


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#1 kevvywevvywoo

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Posted 10 September 2011 - 03:38 PM

Hello, we have here an MA12000i which has only worked a few hours.

Two weeks ago the main (large) cooling fan started making groaning noises when the amp was warm . We fitted a new fan, the correct one. The old one tested ok.

Last weekend the amp was in use and the new fan started making the same noise, so we switched the power off.

Now, back in the shop, the amp powers up but the main fan immediately runs absolutely flat out: it is almost like a vacuum cleaner. Sometimes the amp will work but most of the time the two 'ready' lights stay dark.

Any ideas, good people?

youtube clip of fault

Maybe the guy who designed the amp would be interested in the video.


#2 Kevin Heber

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Posted 13 September 2011 - 10:55 AM

Per Kip Whitehead: You may have a thermal sensor out of tolerance in the power supply or on the output FETís. These four sensors drive the fans and if one is out of tolerance it will make the fans run full speed.

Age of the amp may be another thing. Early amps were mounted with plastic rivets and when the fans ran that rattled and where loud. They changed the rivets to a rubber type and placed a foam pad on the fan hub to keep it from rattling so much. Newer units have a rubber boot around the fans and then the fans fit inside pins designed into the chassis.

You may have two issues;

1) Thermal sensors for the fans running.
2) If older amps, a foam pad on the fan hub for the BCA side fan and rubber rivets vs. the plastic style will improve the fan rattling noise.

Of course updating the firmware changed fan operations would always help.


#3 kevvywevvywoo

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Posted 13 September 2011 - 12:07 PM

Is there a way to interrogate the sensors via System Architect?

Yes this is an early unit with plastic rivets.

I noticed when taking another look that the amp is taking over 2 amps in idle  from the mains when the fan is running fast, then if and when the fan goes down low, the mains current drops to around the 1A area.



#4 Kevin Heber

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Posted 14 September 2011 - 04:01 PM

Yes, you can make a custom control panel to monitor channel temperature.  Easiest way to start is to right click on any control window and say "Convert to Custom".  The parameter you want to monitor is listed under "CH1 Amp Output" for channel 1.

#5 kevvywevvywoo

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Posted 14 October 2011 - 03:50 PM

Ok, got the amp back from ST.

The fault report said 'new fan fitted'  (I had already fitted a new fan the week before, sent by them).

and 'Firmware updated' (I had plugged the amp into System Architect and when the amp was doing the whole fan-out-of-control thing the PC kept saying 'a device on the network has malfunctioned' and I couldnt interrogate it without powering down and back again.

Time will tell!!!
dry.gif



#6 kevvywevvywoo

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Posted 16 October 2011 - 03:07 PM

Ok..first night out last night since being 'repaired' (Saturday).

Lasted 10 minutes and failed again, same way, shut itself down, fan screaming.

mad.gif



#7 kevvywevvywoo

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Posted 19 November 2011 - 06:00 PM

OK The MA12000i has gone back to Sound Technology for another go at repair.