CROWN CE2000 POWER AMP.

[geobee]

Hi all, hoping someone has had the pleasure of working on one of these monsters. Customer said it was working ok, then it just started to ''buz'' from both outputs, so he shut it down. On the bench, I confirmed what he said, and proceeded to do some tests. On powering up, the buzz is there straight away, but no audio with it, just the 50/60 cycle buzz. After around 10 seconds, the protection cuts in, and shuts the outputs down. On removing the main board, which is a pain, as it is a very tight fit in the chassis, and must be removed to gain access to the solder side of board, then it is very difficult, almost impossible to run any powered up tests, due to the earthing points, other cable length etc. Customers wonder why labor on these things has to be so expensive. I replace the main diode block in the supply, but still the same. I would have thought, if it was blown output devices, it would not be allowed to come out of standby, by the protection circuitry, and it has no DC present on the outputs whilst it is emitting the buzzing sound. If anyone has tackled one of these and had any sort of luck, it would be a great help. Cheers. Geoff

[Runco990]

Did you check the main filter capacitors?  The newer stuff has been known to not be as robust as the legendary Crown.  And yeah, it's a BEAST!.

Check power rails that are common to both channels/input stage.

[geobee]

Thanks for that, yes, took them out and metered them. you know what though, I might just change them, I have a good stock of 15,000uf, 50 volt, so I could make up a cap bank at no cost really. Will give it a go and advise.

[shakalnokturn]

I'd start by looking for a broken ground or defective power supply regulation on the low power (preamp) side of things.

I've only ever had a couple of Crown amps to repair, the one I do remember had been sucking in dust and fog machine smoke until the heaps of muck on the power stage got corrosive and conductive enough to bridge adjacent tracks and cut resistor legs.

[coromonadalix]

service manual  581 pages around 15 megs

https://elektrotanya.com/crown_ce1000_ce2000_ce_series.pdf/download.html



Hum not sure      but in the ac main filter, i think they used the earth ground as a neutral in the psu section  ... a friend had a strange problem, and he had to redo his main ac socket ...

[geobee]

Hi, thanks for that, yes, I tried redoing the grounding etc, replaced all the anodized grounding screws with plain metal ones, tried adding better chassis grounding, to no avail. I am leaning towards the earlier post regarding filtering around the pre stages of the main board. I might just replace all the small caps in that dept. See how we go with that.

[Runco990]

Why not just look at it with a scope OR measure AC ripple with a meter across the caps before you "just" replace them?  Verify the problem...  I don't argue with cap replacement, but I want to be sure that's the problem first.  And it's a quick check.

[geobee]

Yes I will do that, but I dont like the fact that it trips into protection after a few seconds, just dont wish for it to do any further damage.

[andy3055]

I cannot get an idea as to what the "buzz" sound is. Usually is is a hum and the speaker cone gets drawn in or pushed out and stays there if there is DC on the speaker terminals. Make sure you do not get DC on the output terminals.

If you do, then it is time to check the output and the driver transistors.

[geobee]

It isn't the usual DC hum that causes a cone to burn very quickly if it is a large amp. This is more like a square wave signal, and there is no DC at the speaker outputs. Maybe there could be when the square wave gets louder, I did hear it become a hum, but that is where I switched it off. I may be able to remove the main DC supply and work on the pre stages which are powered from a lower current supply from the tranny. I will work through the schematics and go from there.