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Crown Macro-Tech 5000i Died On Me While DJing Tonight ! Help Required Please


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#1 JohnnySH

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Posted 05 October 2012 - 10:54 PM

Hello

Any help would be very much appreciated, and thank you in advance

My crown macro-tech 5000i amplifier developed a fault whilst I was DJing at a venue tonight, one channel totally died on me and both fans went in to ultra high speed mode. CH2 Ready LED no longer lights up!



I own Two Macro-Tech 5000i crown amplifiers, one of the amps has not been used because waiting to purchase JBL subs,

The other Macro-Tech 5000i is used every weekend when I DJ, I also own 4 JBL SRX 700 (1 by 15") cabinets

I sometimes run 2 SRX700 per channel (4 SRX 700 in total) and other times only run 1 SRX700 per channel (2 SRX 700 in total).

For the past 8 months the Macro-Tech 5000i amp has worked faultlessly with my JBL speakers, until tonight !!

I was always under the impression Crown was the best in amplifiers, but nerves have now been left in tatters after limping along whilst DJing on only one channel, after the fault occurred and I'm not even convinced CH1 sounded that great after CH2 died!

Here's the events of tonight

The venue I was DJing in tonight was larger than normal, so I decided to take all 4 speakers out,

The first two hours of the night everything worked fine, and the system was running fairly hard level wise, but no problems.

As the dance floor started to grow with people, I changed to music to a more dance style and pushed up the level, it's fair to say the system was now thumping.

after about 5 more songs I noticed my right hand JBL speaker stack (SRX700 x 2) was periodically cutting in and out about every 2 seconds, I went over to the macro-tech 5000i to turn down the levels and noticed both the fans on the amp were running at ultra high speed blowing very cold air out the back of the amp. I knew I had problems occurring as my amplifier had never done this before !

I turned down both channels to half way on the front controls,

I then noticed the right hand  speakers (CH2) went off totally, things were starting to go from bad to worse,

So I turned down CH2 control to off, and prayed that I would make it through the night with just CH1 and my left hand speaker stack.

I must also say even the left hand speakers (CH1) did not sound as crisp and clean as normal, could this fault on CH2 also affect the power/ quality of CH1 ?

One other thing I noticed whilst limping through the night on CH1 was... CH2 Ready LED was not lit, But the signal LED did flash for CH2.

At the end of the night I powered down the amplifier for 1 minute and powered it back up, both the fans stayed in ultra high speed mode, and CH2 Ready LED would not Light again, so the fault on CH2 is on now all the time.

The main reason I chose crown and these very high quality amplifiers is due to the great name crown has and the reliability of crown amps, after tonight my confidence has been shattered.

I am an electronics engineer by trade have repaired a few amplifiers in the past, normally output stage etc.


I was under the impression the macro-tech 5000i has protection in almost every area of the amplifier, so in theory what I am explaining should have never occurred ?

I'm still not sure what has gone wrong inside the amplifier and what caused it, other than driving the system hard.

I am based in the UK and plan to open up the amplifier tomorrow in my workshop and start to investigate.

I would love a circuit diagram of this amplifier, I have managed to track down the service manual for the macro-tech 2400i which I assume is similar, but it would be good to get the 5000i service manual.

Any help form the forum experts and professional guidance as to where to look first in trying to repair my very loved macro-tech 5000i amplifier will be very much appreciated.

My concern is, why did this major fault happen in the first place? and will it happen again?

Is this a known issue with this maco-tech 5000i amplifier range,  are they know to be unreliable ?

I have to have faith in the equipment I use / work with, and up until tonight I had total faith in these amplifiers.

Also I have never connected a cat 5 cable to the amplifier but I know there is software that can be installed on a pc to view running management of the amplifier, is there a fault logging system built in to the amp to give me any more clues as to what went wrong and why ??

I am in the UK and would really appreciate any help in this matter so I can repair this amp and get a better picture as to what went wrong and why.

I await your reply

and thank you in advance

john

#2 dakos

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Posted 05 October 2012 - 11:47 PM

Dear John,
Sorry to hear you had to go through such an unfortunate event. Crown Audios reputation is not there for no reason but those kind of failures happen even to the best of gear, as you can see, and for all sorts of reasons, driving a system hard is NOT one of them!!!

You can get the schematics for this amp by giving a call to the tech support team, they are a very helpful resource:
http://www.crownaudio.com/techsupp.htm
The phone call is still free if you use Skype...
The 2400 and the MA5000i are compleatly different.

For your own sake, when you drive a system hard, don't allow the clip light to be on, if you see it blink more then once every few minutes, turn down the volume and go get bigger/more amps/speakers.

Last thing, the issue you described is not a known issue. I'll let the more tech savvy forum members help you in solving the tech problems...

Good luck :)

#3 JohnnySH

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Posted 06 October 2012 - 09:58 AM

Thank you for your reply, appreciated...

#4 JohnnySH

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Posted 06 October 2012 - 05:59 PM

Well... what a complex amplifier!  A little more involved than previous amplifiers I have worked on.....

Working with no service manual is no fun but I have opened the amplifier up in my workshop and slowly started to strip out an array of circuit boards.

Heading towards testing the main output transistors for problems, thus working back from there.

I am pleased to say all output transistors read correctly using an analogue ohm meter, so it looks like the output stage of my maco-tech 5000i is still intact and no damage has been done there !

I next checked the supply voltage to both channels from the Power Supply and all readings read true, so no problems there

I then slowly reassembled, board after board, screw after screw and re tested the amplifier in my work shop.

from power off,

1) press the front panel power switch to on

2) The fans start slowly, no led's lit on front panel, (so far so good)

3) After about 5 seconds, CH1 Ready LED is on, thus working

4) At the same time CH2 Ready LED is OFF, and Fans run at crazy fast speed, as happened when fault first occurred whilst DJing the other night.


So my mind started to look slightly deeper in to the thermal sensing of each channel.

I stripped out the chokes for a 2nd time by the output stage to expose output transistor for each channel,

embedded in the heat sink of the bank of transistors for each channel is a thermal sensor, thus one for each channel

The amplifier and heat sink is stone cold,

When using a Digital Ohm Meter to take a reading across the CH1 thermal sensor, the reading is 6.18k

when doing the same for the thermal sensor on CH2 (faulty channel) the reading is 1.2k

Now I would expect these two thermal sensors to almost read the same value, after all they are on the same cold heat sink.

Now when using  a analogue ohm meter....

when using ohms x 10 range on the analogue meter CH1 thermal sensor reads 6.k

Yet Channel 2 thermal sensor is reading about 1.2K  !!!!

The same results also are displayed if I change the ohm meter range to x 100

so could this be my problem ?? i.e. a faulty thermal sensor on CH2 ?

Thus why my speaker bank was periodically muting about every 2 seconds when fault first showed, i.e. when the thermal sensor for channel 2 was breaking down ?

Thus why CH2 READY state is now NOT reached after power up

Thus why FANS run at ultra high speed, faster than you could imagine !

Could all this be down to one faulty thermal sensor on CH2 Output heatsink, I have to say I feel I am getting close even without a circuit diagram.

This sensor may have failed the other night while I was working and thus shut down CH2 !!!

I state the amplifier was working fairly hard so I would imagine the heat sinks may have been quite warm/hot ? just wondering if the sensor broke down with too much heat ?

is this a known problem of thermal sensors breaking down for output stage thermal sensing  ?


any help and feed back would be very much appreciated,

I would also like to say how amazed I am at how few output transistors there are in this amplifier and how small they are considering how powerful this amp is ??

Look forward to hearing from you

Regards John

#5 dakos

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Posted 07 October 2012 - 12:32 AM

Dear John,
The thermal sensor going bad was an issue on the older itechs, not the itech HD nor the MAi series, it has to do with the Teflon coating getting cracked and changing the reading of the thermistors. The onboard reading of those thermistors when cold should be around 7K ohm and the outboard resistance should be around 20K ohm. I'm wondering if connecting a plain 20K resistor instead of the faulty thermistor, for testing purposes only, would fix the problem. If it does then all you need is to replace both thermistors even if the other thermistor looks OK, those cost $90 or $30 for the pair the last time I checked, not sure which are cheaper, the SMPS thermistors or the output module thermistors you checked.

Since you already took the amp apart, I would check the SMPS thermistors as well.

Isn't the amp still under warranty?

Let me know how it goes?

#6 JohnnySH

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Posted 07 October 2012 - 08:43 AM

Dear Dakos

Thank you for you informative reply,

I'm still waiting to speak with Crown on Monday,

1) to try to get a circuit diagram and

2) to find out a little more about the thermal sensors and thus what values they should be?

When you say the outboard thermal sensors, do you mean the ones on the heatsink ? if so, the values you suggest are different to mine ?

The working CH1 from cold is about 6.2k and the bad CH2 is around 1k thus seems to have gone low in value ?

Please forgive my ignorance but what are the SMPS thermistors, and where can they be located.

I am also a little amazed that such an expensive, high quality well built and constructed amplifier can fail over one poorly designed thermal sensor ?

The amplifier was built in 2009, so not very old and it may still be warranted.

I appreciate your feedback

Thanks again

#7 dakos

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Posted 07 October 2012 - 09:22 AM

 JohnnySH, on 07 October 2012 - 08:43 AM, said:

Dear Dakos

Thank you for you informative reply,

I'm still waiting to speak with Crown on Monday,

1) to try to get a circuit diagram and

2) to find out a little more about the thermal sensors and thus what values they should be?

When you say the outboard thermal sensors, do you mean the ones on the heatsink ? if so, the values you suggest are different to mine ?
When I say outboard I mean out of the board, that means to actually get soldering and pull the thermistor out of the board and measure its resistance.

 JohnnySH, on 07 October 2012 - 08:43 AM, said:

The working CH1 from cold is about 6.2k and the bad CH2 is around 1k thus seems to have gone low in value ?

Please forgive my ignorance but what are the SMPS thermistors, and where can they be located.

I am also a little amazed that such an expensive, high quality well built and constructed amplifier can fail over one poorly designed thermal sensor ?
It really bothers me as well so I have to agree with you, something should have been done to resolve this issue better in this model.

 JohnnySH, on 07 October 2012 - 08:43 AM, said:

The amplifier was built in 2009, so not very old and it may still be warranted.
If it were me I'd check for the warranty status before trying to fix this type of gear unless the Crown repair shop wasn't that reachable or out of pure interest :)

 JohnnySH, on 07 October 2012 - 08:43 AM, said:

I appreciate your feedback

Thanks again
Look at this link for additional info, I had similar issue on an older itech about two months ago.
http://www.crownaudi...?showtopic=4309

#8 JohnnySH

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Posted 13 October 2012 - 09:42 PM

Please to say I have repaired my much love amplifier,

My diagnoses was spot on, it was the 20k thermister, on the output heatsink, ch2 thermister had gone low to about 1k!

Crown UK distributor want to charge me about £16 and I would have to wait for 3 weeks to get the parts from the usa to the uk.

I did some research and managed to get the exact same part from a uk electronics supplier for £2 each

I have ordered 4 so I can change all thermisters in my 2 crown macro-tech 5000i amplifiers.

I am truly amazed that this grade of amplifier uses such a cheap thermister that can fail as has in my case and cause such problems,

Even though I have replaced all thermisters with brand new items, I now have little faith in them, I know the could fail again,

Crown really does over inflate the replacement cost of there parts,

anyway any one else with this problem, you now know how to resolve.

regards john

#9 dakos

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Posted 13 October 2012 - 11:27 PM

How did varify that it is indeed fixed? Did you put a 20K resistor instead of the thermistor?

Just becase a part is cheap doesn't automatically make it unreliable. If I'm not mistaken this problem was addressed by changing the manufacturer of the thermistor to a more reliable one but I guess this issue should have been delt on the design level.

Can you post a link to the replacement thermistor or the vendor you purchased it from?

#10 JohnnySH

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Posted 14 October 2012 - 09:47 AM

Hi

No I did not try a 20k resistor,

I first cut the two old thermistors legs from the circuit board and did a resistance check with a analogue ohm meter

I always prefer using this type of meter on the lowest possible reading because in draws more current through the part when taking a measurement, thus if part if faulty, it's more likely to show, instead of using a DVM.

The good thermister read about 22k and bad thermister read about 1k,

with the parts connected to the circuit board I was getting lower reading, so I knew to get true readings I had to isolate the two thermisters from the circuit board.

From my two reading 20k and 1k i knew there was problems

I then started to investigate thermisters and managed to find a similar device and check the spec of the device and viewed a chart of temperature vs resistance for this part.

At 1k on the chart the temperature would have been very high can't quite remember exactly, so I knew this part had failed and was fooling the amplifier in to thinking the heatsink was very very hot. I also knew that both thermisters should have been 20k in value and thus were not.

the 4 new parts I ordered were from RS components, RS Number 697-4581, Part Number NJ28PA0203F Made In France By AVX

http://uk.rs-online....7633D4E4F4E4526

I did have to sleeve the two legs as the original parts had sleeve coated legs and these new parts did not. apart from that they look identical in every way.

A little bit cheaper than what UK Crown distributor wanted to charge me ! and I got the parts next day ! not in 3-4 weeks time.

Now when I turn on my amplifier CH1, CH2, Ready Light turn on, NO fans spin until you start working the amplifier

One Fixed amplifier, not bad for under a week from failure and at a cost of £2

Hope this helps others,

Regards

John


PS also I was a little shocked that there was so little help, support and input from the tech guys on this forum, though I would like to say thank you to dakos. I'm only too pleased to be a professional electronics engineer and able to repair this type of equipment myself, 1) I know the job has been carried out correctly, 2) It saves me a small fortune.

#11 joust

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Posted 18 October 2012 - 01:29 PM

Hello John!

Dakos had such a great lever on the problem that I didn't find that my intervention would have brought new water to the mill! :)
Yes, your problem was the thermistor. Usually, the supplied thermistor is quite relaible, even in the older amps (rarely found any bad ones).
The newer generation of BCA modules use a better thermistor (cylindrical instead of eye drop) than the older generation. It should be more reliable.
It is also easier to set up! No more paste on the fet tab and hands are clean!

Regards,

Alain

#12 JohnnySH

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Posted 19 October 2012 - 07:29 PM

Hi Alain

Thank you for your reply,

I have really ended up replacing the same part, only not from crown but a UK supplier

Are you saying the new upgraded design uses a different type of body thermister,

If so, can this type of thermister be used on my macro-tech 5000i ?

and would it be beneficial to change to this type ?

also how does it mount to the heatsink

do you have a part number or supplier ?

does the new thermister have the same characteristics as the old part

anymore info would be very much appreciated as I would like to make my two amplifiers as reliable as possible

Thank you for your feed back

Kind Regards

John

#13 joust

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Posted 23 October 2012 - 10:06 AM

The newer part number is: 142142-1. I haven't tried the newer sensor in place of the old but it should be OK. In the past, you had to lay some thermal paste on the fet tab, then lay the sensor on the tab (Note: I would set it with a lot of paste in the fet tab's hole) and add a foam to hold the sensor in place. Quite messy. You don't need any paste with the newer sensor. Just place it on the tab and secure the sensor with the foam.
If I were to change a sensor I would replace both at the same time. Caracteristics appear to be the same, 20K at room temp.

Good luck!