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Amcrons - Dilemma

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Category: General
Forum Name: Amp Forum
Forum Description: The 'Stopping Jake Fielder moaning constantly' forum description...
URL: https://forum.speakerplans.com/forum_posts.asp?TID=108174
Printed Date: 26 February 2024 at 8:59am
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Topic: Amcrons - Dilemma
Posted By: ChrisWard
Subject: Amcrons - Dilemma
Date 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...



Replies:
Posted By: kedwardsleisure
Date Posted: 08 November 2023 at 12:35pm
the caps will be fine

-------------
Kevin

North Staffordshire



Posted By: jbl_man
Date 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.


Posted By: ceharden
Date 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.


Posted By: shaun1264
Date 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.




Posted By: ChrisWard
Date 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...



Posted By: ChrisWard
Date 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.


Posted By: ChrisWard
Date 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...


Posted By: ChrisWard
Date 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



Posted By: ChrisWard
Date 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... 


Posted By: shaun1264
Date Posted: 22 November 2023 at 9:21am
If you going for replace the drivers and outputs.  They have to be matched VBE and Hfe 


Posted By: kedwardsleisure
Date 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



Posted By: ceharden
Date Posted: 22 November 2023 at 11:48pm
Can't offer any good advice I'm afraid, haven't worked on a Macrotech for a long time and always found them a bit of a tricky customer.  Mainly because the grounded bridge topology means that it's sometimes hard to know what to use as a reference because 'ground' moves in the opposite direction to the output.  When you're chasing offsets, it can be hard to know which side of the bridge the fault is on.

Have you got one good channel and one faulty one?  If so, have you tried swapping parts between the two to see if the fault follows rather than doing a blanket replacement?



Posted By: ChrisWard
Date Posted: 23 November 2023 at 8:36am
Originally posted by shaun1264 shaun1264 wrote:

If you going for replace the drivers and outputs.  They have to be matched VBE and Hfe 
Yes thank you, do you know the range or tolerance they should be Matched



Posted By: ChrisWard
Date Posted: 23 November 2023 at 8:40am
I think its the Output Board.....as I have checked and replaced obvious culprits on the main board...but when i pull the pre-drivers out I can validate 


Posted By: ChrisWard
Date Posted: 23 November 2023 at 8:48am
I have a good side, and I've been using that as a reference, I also have another 601 that has a bad channel, but I also have 3 others (601, 1201, 2401) so I don't mind having spares as some components seem to be going obsolete.

I pulled the Output Resistors off to allow the DC Fault protect to keep the power on for longer, before it was cycling on/off and it was hard to get any readings...it seems to be the high side that is causing the problem.

The 601's are used in the high to top range in a so they have only ever had >1khz loads at 16 ohms  for their entire life..


Posted By: ChrisWard
Date Posted: 29 November 2023 at 7:58am
Hi Guys.....so good news last night I found the main issue, it was a broken PCB track in the Voltage Translator section on the Main board...I was checking every component after reading some guy had wasted hours on a shorted cap....

I had also replaced 4 x 1N4148, the track was right next to a solder pad so even zooming in with a camera you can only just see it....I found it by tracking the Ch1 feedback route to the Voltage Translator with a DVM

It's producing a good output on the scope now, I still have a bright IOC led that needs resolving....

Good news is that I'm pretty clear on the function of most of this amp now, having studied the schematic for so long, also learnt some ways to isolate and bypass's functions, which is going to help me with amp no 2 another 601



Posted By: ChrisWard
Date Posted: 30 November 2023 at 7:22am
Sorted the IOC issue being on constantly....this was C501 on the display board small 0.47 cap in the comparator feedback loop, its strange as it measured fine but clearly defective


Posted By: ChrisWard
Date Posted: 21 December 2023 at 2:01pm
My 2nd MA601 had an issue with the Power Relay board next to the fan the Mains connector had a dry joint and the relay looked a bit tired to fixed and replaced the item


Posted By: EmPro
Date Posted: 25 December 2023 at 10:56pm
I have 12 Crown Macro/Micro Tech's starting with 600 and finishing with 2400,remember this,when you want to fix an amplifier (in this case MT's) first time you clean it,second time you check the expensive parts to be fine (mostly the output devices) and then you start to restore all the solderings from A to Z in both outputs boards (the driver board is double soldered so don't bother) after you restore all the soldering you move to connectors,check them,clean them,restore the solderings as well and apply glue betwin them and board (so the presure of the flex cable won't push anymore in the solderings) after that move to the +-15vcc supply for driver board,you have there two voltage regulators one for negative and one for positive also check and remake the solderings,after all this you power on the amp and check the suppy voltages and odep voltages as well according to heatsinks temperature,and only now you can start to troubleshot the fault,when you are sure that all the parts from the boards are in good contact.

-------------
EmPro Audio


Posted By: EmPro
Date Posted: 25 December 2023 at 11:07pm
I had faulty reservoir caps,blown odep led,open wide CMR resistor,open wide potts,and blown output (just one),but cold solderings??? thousands of them so far,so that is the nr1 reason why an amp like MT is falling,after fixing all the issues and restore all the solderings never had any sort of faults again :) people keep fail to understand that old amplifiers 10+ years old require a lot of attention to solderings...and MT's are 25+ years old...so.....not to mention the thermal compound that is turning into dust after those years and leaves the outputs floating on the heatsinks....

-------------
EmPro Audio


Posted By: EmPro
Date Posted: 25 December 2023 at 11:22pm
I found MacroTech's and MicroTech's the best amplifiers that Crown ever made,thanks to Gerald Stanley the designer of Ground Bridge topolgy,once you have fully and proper restored one of these amps will run 2R stereo mode all day and night with no signs of getting tired Clap or bridged in 4R,these tasks kills most of the amplifiers made nowdays...they don't stand a chance.
Btw,don't use any of these amplifiers for mid-high demands,you just loose your time and not performing,the best performance you get when are used to drive low's and mid-low's!


-------------
EmPro Audio


Posted By: Wikl109
Date Posted: 26 December 2023 at 12:29pm
Geralt?

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Cheers, Chris.


Posted By: EmPro
Date Posted: 26 December 2023 at 12:37pm
Originally posted by Wikl109 Wikl109 wrote:

Geralt?

Yep,saw it now LOL fix it


-------------
EmPro Audio


Posted By: Wikl109
Date Posted: 26 December 2023 at 12:44pm


-------------
Cheers, Chris.


Posted By: EmPro
Date Posted: 26 December 2023 at 1:01pm
Originally posted by Wikl109 Wikl109 wrote:

🤝


-------------
EmPro Audio


Posted By: ChrisWard
Date Posted: 15 January 2024 at 1:46pm
Originally posted by EmPro EmPro wrote:

I have 12 Crown Macro/Micro Tech's starting with 600 and finishing with 2400,remember this,when you want to fix an amplifier (in this case MT's) first time you clean it,second time you check the expensive parts to be fine (mostly the output devices) and then you start to restore all the solderings from A to Z in both outputs boards (the driver board is double soldered so don't bother) after you restore all the soldering you move to connectors,check them,clean them,restore the solderings as well and apply glue betwin them and board (so the presure of the flex cable won't push anymore in the solderings) after that move to the +-15vcc supply for driver board,you have there two voltage regulators one for negative and one for positive also check and remake the solderings,after all this you power on the amp and check the suppy voltages and odep voltages as well according to heatsinks temperature,and only now you can start to troubleshot the fault,when you are sure that all the parts from the boards are in good contact.
thanks for the advice



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