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Behringer A500 as a DIY project
Behringer A500 as a DIY project
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Old 17th June 2015, 08:41 AM   #211
redgt3 is offline redgt3  United Kingdom
diyAudio Member
Join Date: Jun 2015
Hi All
new here so please be gentle !
I've been running 2 x A500's for a couple of years now
Active x-over (80Hz)
one running a pair of sound craft studio monitors, the other bridged running an 8ohm Sub.

I was running some LF tests yesterday (20-50Hz), at about 90% max power on the sub amp - at no stage did the front panel clip led light.
after a few mins of this test, the sub stops working.
My first thought was that the Sub speaker had given out.
immediately powered everything off, disconnected and checked the system bit by bit.
Turns out that one of the channels (channel B) on the A500 in bridge mode has died - no output at all - the other channel is still working fine.
I've popped the cover and initial observation is that the amp pcb LED on the amp that is non functional is not lit - ref des is LD2.
Cant find any reference in the manual to the purpose of this LED - any clues please?!

Looking to delve in deeper today with a view to fixing it - can't imagine it being too difficult - I have got around 20 years of electronic design experience behind me.. and a fair bit of test kit.
The amp design itself looks pretty conventional (from a PA POV)
However, any early heads up, gotchas etc would be much appreciated.
thanks in advance
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Old 4th July 2015, 08:03 AM   #212
James Freeman is offline James Freeman
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Join Date: Dec 2014
Have a Multimeter and schematics?

Check the VCC+-, 15V+- first.
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Old 8th December 2016, 03:35 PM   #213
redgt3 is offline redgt3  United Kingdom
diyAudio Member
Join Date: Jun 2015
holy thread resurrection !

After having some free time to look at the amp on the bench, I've found that a 15V Zener is SC.
(it's the one that provides the +15v for the op amp supply - D29)
The fact that R34 was trying to burn itself off of the PCB gave me a clue.
LD2 does come on for around half a second at power up;
BUT, and heres the strange thing - there is no -VCC rail;
Bridge diodes buzz out OK.
So, I think that there is another issue somewhere; but I'll replace the Zener first and go from there.
I've checked (power off) the -VCC rail for shorts, but non found.
ah well !
keeps me out of trouble
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Old 13th December 2016, 05:48 AM   #214
redgt3 is offline redgt3  United Kingdom
diyAudio Member
Join Date: Jun 2015
thought I'd update the thread with my findings.
Amp all fixed - it was just the Zener diode !
shocked that the diode was the only thing dead
19p from Maplin (quickest route to get one !)
all fixed & working well.
In fact rather too well... full power testing into my dummy load... it blew one of the power resistors up - proper good bang, smoke everywhere, end cap flew off it
ah well, obviously need to build a bigger one now !
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Old 21st April 2018, 11:09 AM   #215
kefeur is offline kefeur  Hungary
diyAudio Member
Join Date: Feb 2008
Hi all.
My amplifier was completely ruined.
Your circuit board was burnt to the hole.
Would you please give me a drawing of printed circuit board of the left circuit?
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