Troubleshooting & Repair of a Crown DCi 4|300N audio amplifier

[GBolamp]

Hi and thanks to all the good fellas who will try top give me a hand with this issue I have. To start, this is the unit we are talking about: https://www.crownaudio.com/en/products/dci-4-300n.

This audio amplifier is a 300W class D amplifier with blu link connection, I have this at my job's place, as we use them to power our audio circuits. Lately one of tese unit stopped to work and it went completely dead, from the backside the ethernet LEDs were OFF, no connection to the network, on the front side the POWER LED started blinking, in their manual they say this means the AC line voltage dropped or has risen 10%, but I don't think this tells you the real story, I replaced this unit with another one which is working on the same AC line with no issues so...

To get to the point I started to troubleshoot this unit, I remember 1 year ago another unit (same as this one) had the same symptoms and the amplifier board was replaced. I had a look inside and probed around with a DMM and an LCR meter, The power supply is a switching one, The voltage was present on the PSU board until the diode rectifiers (after the switching transformer), the switching frequency is in the order of 20KHz. After this part the is some smd components near a chip with 32 pins, I haven't done any research but my guess this is a sort of logic controller that can sense if there is a fault on the other boards (amplifier board/ethernet board), and stop the voltage to being sent to these boards, might be a correct guess?

If interested I can take some photos to give better ideas, in general what would you recommend to test? I wanted to the power transistor but the heatsink is soldered with pins and they are hard to be de-soldered (much pain), I don't get if the temperature of the iron is too low or I don't use enough flux..

one newbie question: is it possible that while using the DMM in continuity check mode(mine beeps for 30 ohms or lower) a capacitor tested in circuit would beep continuously when I probe across it with the DMM leads?

[jonpaul]

GBolamp, you cannot troubleshoot this unit with a VOM and cont tester.

Most likely a shorted FET or BJT in the SMPS bridge and perhaps blown driver ICs as well.

Suggest to get the complete schematic and service manual,

You need the proper tools for offline SMPS work, 1:1 safety isolation transformer, scope 2 chan 100 MHz, X10 probes, etc.

Beware that random probing of the amp while operating can cause damage and that SMPS offline has 360V DC LETHAL bus voltage.

Especially easy to mistake if probing SMD IC of fine pitch.

Judging from your note, I feel you may need to learn a lot more about SMPS to go further.

Best to send to Crown (warranty?) auth service.

Bon Chance,

Jon

[GBolamp]

well I would really like to get a schematic for the unit but it doesn't seem like a small task, do you think crown would send it if I ask?

Maybe you have recommended lectures on SMPS, to expand knowledge.

Thanks.

[jonpaul]

Rebonjour cher GBolamp

0/ Check serial number and original purchase it may still be in warranty.

1/ Crown may not give a schematic. Search for that model on any search engine and add   "schematic" or "service manual" you may find it.

2/ Learning how to design and repair SMPS takes a long time and lots of mistakes along the way. Besides the experience and theory you need the proper instruments and safety measures.

3/ I would suggest to scrap this amp and order a replacement (sell as parts only on ebay?) rather than attempt to repair with insufficient test equipment and experience.

4/ Finally search for a Crown amp/audio forum, others may assist with that specific model.

Bon Chance,

Jon

[GBolamp]

Ciao,

I understand, it is also true that if you never try you never learn.


Thanks, have a great day!