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Crown I-tech repair advice
Crown I-tech repair advice
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Old 14th March 2019, 06:31 PM   #1
Bogdantogo is offline Bogdantogo  Romania
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Default Crown I-tech repair advice

Hi guys,

I'm writing here hoping that someone found the same behavior or can give me any advice to repair a Crown I-tech 6000 amplifier.

The amplifier came to me not turning on at all. Power diode D1005 from BCA output stage was shorted. I replaced the bad one and the one that is in parallel. After some preliminary tests everything looked OK with one exception. The repaired channel (CH1) is overheating and in ~ 2 minutes it reach over-temperature and is shut down. I must stress out that it passes clean audio until it is cut down by overtemp protection. Cooling system is ok and is throttled progressively to max speed.

First thing to do was to adjust overlap/underlap according to service manual. No improvement. After that I swapped the front-end PCBs between channels and the problem moved on CH2. I made a lot of measurements with oscilloscope and compared with the working channel but nothing came out. Feedback, differential drive to gate drive boards, VP/VN voltage was measured and everything looks ok. Also each component ohmic resistance from bad front-end was compared to the same component on working front-end and nothing. I have no idea what can cause excessive heat dissipation in this BCA topology.

Now I'm out of ideas and ask for diyaudio community help.

If someone needs the full service manual please write me a private message.
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Old 14th March 2019, 07:45 PM   #2
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by Bogdantogo View Post
Hi guys,

I'm writing here hoping that someone found the same behavior or can give me any advice to repair a Crown I-tech 6000 amplifier.

The amplifier came to me not turning on at all. Power diode D1005 from BCA output stage was shorted. I replaced the bad one and the one that is in parallel. After some preliminary tests everything looked OK with one exception. The repaired channel (CH1) is overheating and in ~ 2 minutes it reach over-temperature and is shut down. I must stress out that it passes clean audio until it is cut down by overtemp protection. Cooling system is ok and is throttled progressively to max speed.

First thing to do was to adjust overlap/underlap according to service manual. No improvement. After that I swapped the front-end PCBs between channels and the problem moved on CH2. I made a lot of measurements with oscilloscope and compared with the working channel but nothing came out. Feedback, differential drive to gate drive boards, VP/VN voltage was measured and everything looks ok. Also each component ohmic resistance from bad front-end was compared to the same component on working front-end and nothing. I have no idea what can cause excessive heat dissipation in this BCA topology.

Now I'm out of ideas and ask for diyaudio community help.

If someone needs the full service manual please write me a private message.

It can be driver ICs could have problem,

measurements can look perfect good luck
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Old 14th March 2019, 09:02 PM   #3
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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I have had an output choke with a shorted turn or more. Ensure, as per the service manual just after the over/underlap adjustment, the capacitors shown in the photos are red.
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Old 15th March 2019, 04:49 PM   #4
Bogdantogo is offline Bogdantogo  Romania
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Thank you for responses guys,

@NMOS by drivers you mean the LM361 ICs? As last solution I'll try to replace blindly some components with new ones but I'm trying to find a clear defect before doing that.

@JonSnellElectronic good idea. I'll measure the inductance of the output coils to see if something is not OK. But that doesn't explain why if I swap the front-ends the problem moves to the other channel.
The gate drive is the old one with ceramics. I attached a picture bellow. You think I should try to update it and replace the ceramics with some good polypropylene?

Also as a note i replaced capacitor C629 as sugested on service manual on both front-ends.
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File Type: jpg IMG_0750.jpg (719.7 KB, 97 views)
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Old 15th March 2019, 06:21 PM   #5
NMOS is offline NMOS  Germany
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Quote:
Originally Posted by Bogdantogo View Post
Thank you for responses guys,

@NMOS by drivers you mean the LM361 ICs? As last solution I'll try to replace blindly some components with new ones but I'm trying to find a clear defect before doing that.

@JonSnellElectronic good idea. I'll measure the inductance of the output coils to see if something is not OK. But that doesn't explain why if I swap the front-ends the problem moves to the other channel.
The gate drive is the old one with ceramics. I attached a picture bellow. You think I should try to update it and replace the ceramics with some good polypropylene?

Also as a note i replaced capacitor C629 as sugested on service manual on both front-ends.

only certified Crown Service Tech can help you he know secrets and known problems @ this circuit and how to fix

Class D circuits like this same todays car


If you certified fpr BMW,

you cant fiX special problems for Mercedes BENZ / Audi / Volkswagen...


Better you not waste lifetime, take your girlfiend and have nice weekend

circuits like this not worth to waste lifetime, if you not get full technical support training

Last edited by NMOS; 15th March 2019 at 06:26 PM.
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Old 15th March 2019, 07:02 PM   #6
Cresnet is offline Cresnet  Jordan
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Crown I-tech repair advice
The I-Tech amplifiers are one of the most complicated amplifiers to repair, there is a line where you can test, replace, afterwards you need to start replacing those small cards.


But this is not going to be an easy repair.
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Old 15th March 2019, 07:12 PM   #7
chris661 is offline chris661  United Kingdom
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Seems to me there's a problem with the input board.
My bet is some VHF signal is getting through to the power amp section, causing it to overheat.

Chris
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Old 17th March 2019, 08:06 PM   #8
ViennaTom is online now ViennaTom
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I have some idea about the schematic and how it (Class I) works.
first, make sure all power diodes are good. then check all the gate-source signals using an oscilloscope with insulated channels (those exist!), otherwise the high side gate would be difficult to measure (or maybe use differential probe).
If you swap the "front-ends", the problem moves. But what do you mean? What exact components are included in the "front-end"?
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Old 18th March 2019, 06:03 PM   #9
Bogdantogo is offline Bogdantogo  Romania
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Thank you all for your suggestions. I really appreciate your help.

First advice I took was NMOSs and this weekend didn't touch the mighty Itech.

But today I took some time to make some tests.
Measured all output inductors with LCR bridge and they seem OK. Also no visible visual damage.

After that according to Chris advice I soldered out R741 from the bad front-end board. This way I disconnected the input board and signal. Same problem, no improvement. This make me think that input board is good and not in HF oscillation.

Checked all power diodes and are good. Measured the output of front-end modulators and to me looks ok. (attached pic bellow. oscilloscope channel order is the following: CH1 - VP + DRV | | CH2 - VP - DRV | | CH3 - VN + DRV | | CH4 - VN - DRV)
@Tom the front-end is the PCB in photo bellow. It handles modulation, feedback, DC detect, I monitor, IOC, temp monitoring

P.S. I already contacted Harman and they told me that this amplifier reached end of service state and they don't have parts for it any more.
Attached Images
File Type: jpg IMG_0756.jpg (970.9 KB, 59 views)
File Type: jpg vnvp - bad.jpg (103.9 KB, 61 views)
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Old 20th March 2019, 07:37 PM   #10
ViennaTom is online now ViennaTom
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Did you check the quiescent current through the coils using a current probe (no signal)? Is it any different than on the good channel?
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