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Amcrons - Dilemma

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ChrisWard View Drop Down
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    Posted: 08 November 2023 at 12:21pm
Hi Guys,

Nice forum this, great people and content...

I have quite a bit of old kit that i bought new back in the day, it earnt its money many times over, so now I don't really tour anymore, so i incorporated the kit in my house....

3 x MA601 (1 spare)
1 x MA1201
1 x MA2401
running 4 way active into some JBL's
4756 (three way 2x12 + CD + Tweeters)
4785 TCB bass bins running 2 x 15

Now I know this is over kill for a house but it makes for a great front speakers in my home theatre setup...

My dilemma is that a couple of the amps have issues with crackly signal or dropped channels, I've tried to find someone that would repair them but no luck, now i have repaired amps myself back in the day, and have one MA601 in bits at the moment, but they are pretty complicated amps, and I'm struggling...do I ditch them for a replacement like Crown XTIs but these are not class AB...my heart is telling me crack on and try and fix them as they are great amps...if I can get some good quality caps then we should be in a good starting place...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2023 at 12:35pm
the caps will be fine
Kevin

North Staffordshire

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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2023 at 5:13pm
I see you are in France, maybe try one of the french pro-audio forums, there must be someone over there who can service them for you?

Ma601 is a quality amp, so doubt if it's anything too seriously wrong.
Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ceharden Quote  Post ReplyReply Direct Link To This Post Posted: 08 November 2023 at 5:55pm
You may find that after being dismantled, cleaned, detaching and reconnecting all the ribbon cables that some of the faults may go away. The gain selection and stereo/parallel/bridge switches may also benefit from being cleaned.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shaun1264 Quote  Post ReplyReply Direct Link To This Post Posted: 11 November 2023 at 10:32am
Cleaning of all switches including sensitivity switch, pots and remove all dust in the chassis.  Clean front foam filter, clean input jacks.  Check for any broken solder joints in the pots.  

Makes sure ODEP lights do not dim when amplifier under a bit of load.  ODEP activation can cause distortion if it's on quite hard.  

Shorted output power transistors would be more obvious though!  The outputs are very reliable though. Gerald Stanley of Crown invented their own SOA analyser to stress test the output devices before installing them in the amps.  They are also graded by VBE and HFE.  Analysis were incorporated into a third-generation nondestructive power transistor SOA analyzer, which upon command will produce the needed power stimulus and cool-down temperature data which helped Crown design ODEP. 

These grounded bridge amps are actually quite reliable.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 12 November 2023 at 2:05pm
Thanks for all your replies guys, I'm on the case with cleaning and replacing a few suspect caps, it might be the Pre driver on one side that is causing my issue, I've ordered more they arrive tues....Just had massive floods here in northern france so my time has been diverted...

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 15 November 2023 at 8:37am
Still struggling with this amp...1 channel seems to go into a DC protect cycle which i.e. it turns off the relay for the mains transformer, every 3 sec when there is a rise of DC (15v) on the output...Output Transistors are all ok, I've disabled lots of areas on the main board to identify the fault...bit of a head scratcher, cleaned all the switches and ribbon cables.

Trouble is it's not on long enough to take good readings, I don't want it cycling on off,  but maybe i have to...will update on progress, I'm only doing and hour a day on this due to other work.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 16 November 2023 at 2:54pm
So I read another thread on here for the MA2400, which is similar, I changed all the 1N4004 diodes on the output board still no different. Mostly I've been looking around the High Side / ODEP / Voltage Translator areas, what I have not looked at much is the Low side Pre-driver area....this is my quest tonight...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2023 at 10:18am
I'm continuing to update this thread, mainly because there is little MacroTech repair content on the web...I know this is only of interest to peeps with Amrcons / Crowns

I pulled all the Output devices and all are ok, I've order more as I have a few of these amps and they might come in handy...

Over the weekend I did a bit of a deep drive on each section of the amp and also did it powered (all be it cycling in and out of DC protect)

ODEP seems fine and I've set the Trims to the manual settings...

Input section seems ok and switches (Bridge / earth Lift) seem fine

Voltage Translator is getting a lot of input from the fault circuit, which is guess is normal in this scenario, tonight will see more work on the output Bias sections...Low and High side

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Post Options Post Options   Thanks (0) Thanks(0)   Quote ChrisWard Quote  Post ReplyReply Direct Link To This Post Posted: 22 November 2023 at 8:28am
It seems like the central Bias section of the output module is being flooded with +VCC, so i've pulled the power transistors out again and them seem to check out, the drivers for these I've checked in situ, I've ordered new ones so will just replace and report back... 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote shaun1264 Quote  Post ReplyReply Direct Link To This Post Posted: 22 November 2023 at 9:21am
If you going for replace the drivers and outputs.  They have to be matched VBE and Hfe 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 22 November 2023 at 12:30pm
sounds like an expensive way to go about it. A dc fault could be any single component inside any of the closed loops, and they are pretty big loops on a macrotech. Is the fault caused by the output board or is it on the control board? Do you know?
Kevin

North Staffordshire

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