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Need help troubleshooting Crown MA3600VZ please.


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#1 mikehende

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Posted 12 November 2013 - 08:04 AM

Hello guys, my cousin was rewiring his rig and he smelled something slightly burning and immediately turned off the power on his amp so he waited a while and he pressed the power button and now no power. He asked for my help, I am a pc tech but I've never tried to fix any amps before since I cannot read circuit boards, I told him I can open the amp to see what was burnt or try to troubleshoot but I would need some guidance from an experienced Electronics tech, can anyone here help in any way please?

I haven't opened it yet, I wanted to inquire here for troubleshooting help first to see if this is something I can handle. I can go to him on Saturday and can perform any testing then. He was using it Stereo with the switch in the middle. He did not notice any smoke, he only smelled something more "heating up" than burning. He also mentioned that he tried to open the outer cover but when trying to turn one of the screws on the outside cover the screw would not turn and he did not want to round out the head so that's our first issue. In my experience with computers, any time a screw appears problematic I usually tap the screw this a small hammer to loosen it then attempt to unscrew it, would this same process apply here or would there be a better strategy? I am assuming that the screws on the amp were screwed in by machines which is why he cannot remove it easily?

I found this from the manual on "No Power" "The amplifier's low-voltage power supply
fuse has blown. Return amp to Crown or an authorized Crown Service Center for servicing."
I am guessing once I can get the outer cover off I can see if the fuse has blown.

Also, this from the manual for the 2400:
All 120 VAC, 60 Hz units and all Macro-Tech 2400s have a separate fuse for the low-voltage power supply and cooling fan. All units have separate fuses or breakers
for the high-voltage power supplies

Does this apply to the 3600? If so, this suggests to me that for basically any problem it would be a matter of replacing a fuse? Help?

#2 joust

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Posted 12 November 2013 - 10:39 AM

Hello Mike and welcome!

As you mentionned the first thing is to remove the two covers (screws used are usually Torx; Probably the reason he was not capable of removing the screw. If Phillips screws are used, just turn!).
Verify the fuses, as you mention. The low voltage fuse covers the fan motor : the fanmotor is a two part device: fan motor and the low voltage supply. Though, in some newer models, you may find a stand alone transformer for the low voltage. The output of the fanmotor is 24VAC, and its load is on the main board. The output modules may use a relay instead of a fuse.
For each output board: Locate the (4) flyback diodes (diodes are reversed bias from pos rail to output rail, and another, from output rail to neg rail); Diode check the diodes : If the measurement is of the diode variety, then the output devices on that triple 'base' (base: 'B' from CBE) buss are fine; If you measure a shorted diode for instance, then you may have some leaky or defective output device(s) on that triple 'base' buss. Recommendation from Crown stipulates that 'all devices on the triple 'base' buss should be replaced with the same grade device'.

I would still advise that you contact your local authorized Crown service center.

Alain

#3 mikehende

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Posted 12 November 2013 - 11:01 AM

Hello Alain, your advice to take this to service center is duly noted but since I am a pc tech, I am sure you know that the challenge to fix this has already gripped me :) as would any tech whether electronic or pc. In the pc world the precoess is more or less simple, you isolate the problem then swap the faulty part with a known working one so I am hoping I can attempt this in the same way, if it should turn out to be a circuit board issue then I would need an experienced tech to repiar the board, if it's any other part then maybe I can swing this myself, I will certainly give it a try, will get back here with my findings on Sunday, appreciate the info and advice!

#4 joust

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Posted 13 November 2013 - 10:49 AM

If I can add to this troubleshooting technique: Once you have the amp covers removed, turn to the main board side. Each output module has two connecting grey ribbon, from the main board. Disconnect the four ribbon cables from the output modules and power up. In theory, the amp should power up in the low voltage state. This will permit you to verify if the low voltages are present. You should have the two red ODEP indicators as well as the green two IOC lit. (Note : In normal condition, the amp will power up with only the ODEP indicators lit. The <steady> ODEP indicators show you how much 'cooling' is availble to the output devices. When the outputs heat up too much and can't evacuate the thermal energy, ODEP kicks in and the red ODEP indicators start to flash and dim.)
Power down and discharge the power supply (the two same side heatsinks have the two rails (blue and red wires) connected to it. You just need to discharge via the heatsinks.). Connect one output module with two ribbon cables and power up: If all is well, the connected output side ODEP indicator should now have only the ODEP indicator lit. If not, then the connected output module has a problem. Verify voltages. Probably no rail voltages because of fault protection (psu channel relay not enabled). Power down, discharge both sides, remove the cables from the tested output module and connect the two other connectors onto the other module. Power up and verify indicators.
At least now, you may know what part of the amp is problematic.

Alain

#5 mikehende

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Posted 13 November 2013 - 01:23 PM

Hello, I am attaching a pic here of a 3600vz I found on the net, can you pinpoint exactly what are the "output modules" please?

http://img600.images...0/6067/gb5o.jpg

#6 joust

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Posted 14 November 2013 - 10:34 AM

In reference to the image above :
What you see in the picture is the power supply section of the amp : We can see two power transformers, one for each side; The output modules are located on the other side of the transformers, where the air vents are located. On top of each output module, we have the 'bi-level switches' and capacitor banks for each channel. There are (4) screws that hold the bi-level modules; Remove the screws and you now have access to the heatsink section and power devices xcof the power modules. Each channel has the red wire attached to the positive rail while the blue wire is attached to the negative rail. There are two massive heatsinks per channel: The side with the red wire rail has the positive output devices while the side with the blue wire rail has the negative output devices. On each heatsink, the six devices are seperated into two banks of three devices that I will call HS (high side) and LS (low side). All three devices are linked to the base junction of the output devices. The six devices are 'interleaved' : Trio devices 1, 3, 5 are tied together and trio 2, 4, 6 are tied together. It is highly recommended by Crown to replace all three devices or trio if one of the devices is discoverd shorted C-B : the device has been probably stressed by the high voltage if the device had not succumbed to the short.

#7 mikehende

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Posted 14 November 2013 - 11:40 AM

Ok, taking into consideration that I have not seen the amp yet and I am only making preparations to have a plan for when I visit the cuz on Saturday, please see this link here? http://img198.images...8/1871/fqbs.png

Trying to understand what you've written, please clarify, the no.1 are the 2 power transformers and the no.2 are the ouput modules so there are 4 pairs of them, 2 pairs on the left and 2 pairs on the right? Somehow I don't think I am correct so if those 4 pairs of black cyclindrical things are NOT the output modules but those are "capacitor banks"? If yes, then the output modules should be the flat rectangular long items which stratch from the top to bottom of the amp as shown in this image on top right and bottom left?
http://img716.images...16/927/i18z.png

#8 joust

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Posted 14 November 2013 - 01:07 PM

You have it right for the transformers (#1). What is #2 are the 'bi-level switches' and capacitor banks, 1 module per side; This is not an output module.  
If you remove the 'bi-level switch' module, you will discover the  (#1) output devices (transistors, output) on a thick metal plate (heatsink). This is the heat exchanger side of the output module. The 'module' per se, is the printed circuit board with components on the other side (bottom) of the amp.

Alain

#9 mikehende

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Posted 14 November 2013 - 03:50 PM

ok, can you confirm whether or not the output modules are what the arrows are pointing to in my 2nd image?

http://img716.images...16/927/i18z.png

They are like long rectangular boards stretching from top to bottom of the amp with heat sinks attached to them, one on the left side and the other on the right?

#10 joust

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Posted 15 November 2013 - 11:51 AM

The long rectangular boards are called the 'bi-level switch' modules (has the capacitor banks), not the output modules. Underneath the 'bi-level switch' module is the output device section and heatsink, still not the output modules but part of the output module.
In the image, you're still not showing the correct side of the amplifier! The #1 arrow shows only the output transistors installed on heatsinks; This side of the amp is called the power supply section. Turn the amp upside down and remove the bottom cover to access the main and output modules! (If you went back to my first post : I did write down that you should remove the (2) covers! :))

#11 mikehende

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Posted 17 November 2013 - 11:19 AM

I looked at the amp yesterday, all fuses are ok and nothing looks or smells burnt but I don't think for safety reasons I should attempt to fix this as this involves a lot of stuff I have never encountered in all of my years as a pc tech so I think your original advice will be best here that my cousin take to a service center since we are dealing with a very high powered amp here. I am just very sorry you spent all that time giving me so much detailed instructions and explanation, please accept my apologies?

#12 joust

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Posted 18 November 2013 - 04:49 PM

Well, did you try to power up the unit? :) I would at least try to see its behavior. Just have your hands ready to remove the plug! :)

Note : All of these instructions and explanations can be used by other techs for their own repairs. This is not lost!
Apologies accepted; You couldn't know ahead of time that it could be complicated!

Have a great evening!

Alain

#13 mikehende

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Posted 19 November 2013 - 07:05 AM

Problem was that I still could not see the 2 'grey ribbons' in the way you had mentioned to disconnect them so I could not carry out your instructions but thanks for understanding.