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Amcron DC300a overhaul.

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djeddie View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djeddie Quote  Post ReplyReply Direct Link To This Post Posted: 13 July 2020 at 5:00pm
 Bravo Sir!
Chas n Dave : it's like Drum and Bass but with beards.             E=mc² ±3dB
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Post Options Post Options   Thanks (0) Thanks(0)   Quote APW Quote  Post ReplyReply Direct Link To This Post Posted: 13 July 2020 at 5:09pm
Originally posted by madboffin madboffin wrote:

.....
For future information, I'll be very surprised if all those brown capacitors really needed replacing. They are silver-micas and are usually very reliable. And they often have a "burnt" look about them, it's just the brown encapsulation.
......


As Kevin pointed out on the first page of this thread old silver mica caps can suffer from "silver mica disease". I doubt it was the issue in this case but in something this old I'd change them as a precaution.



Edited by APW - 13 July 2020 at 5:15pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 13 July 2020 at 10:55pm
great result. Always a relief when you fix that elusive fault and hopefully a satisfying sense of acheivement
Kevin

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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 14 July 2020 at 8:41am
More than likely! Or the schematic that made it into the net archives was just one of many in the original library given out at one point.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 14 July 2020 at 8:51am
Thank you gents. I will not be beaten by a 47 year old amplifier! Of course,it doesn't help that the official schematic is wrong....the voltages they give,and some of the components dont match at all,including at least half a dozen resistors,transistors and capacitors that simple dont exist on my board. I guess they modified these on a yearly basis,and no-one bothered to update the schematics.
Confused

I even emailed Crown direct,and asked if they had the correct schematic for my amp, the reply, "Thank you for your enquiry, we do not release schematics,these are only available to our official service centres" suggesting i take the amp there!

As if anyone is going to do that with something this old.

They even had the cheek to send me one of those customer satisfaction surveys afterwards.....so that will be Zero, zero,zero,zero,zero and zero then.

LOL

In the slim chance of anyone from Crown ever reading this,dont be so bloody stupid,it's not as if anyone is going to steal the design of this thing after all this time.
Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 14 July 2020 at 8:53am
Originally posted by odc04r odc04r wrote:

More than likely! Or the schematic that made it into the net archives was just one of many in the original library given out at one point.


Yes,this exactly. There appears to be three version out there,unfortuantly none relate precisely to my amp here,so was a lot of guesswork involved filling in the blanks.
Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 14 July 2020 at 9:23am
Possibly the result of a long production run. Components become obsolete or expensive, better parts become available, feedback from the customer, new design staff, all conspires to change the design over the years. It's the same with the macrotechs. There are many circuit revisions and one bears little resemblance to another.

Kevin

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Post Options Post Options   Thanks (0) Thanks(0)   Quote boominbob Quote  Post ReplyReply Direct Link To This Post Posted: 26 April 2022 at 9:38pm
Hi guys. 

There are 7 different main pcbs on dc300a / dc300a mk2

With overlap between mk1 and mk2

5 different versions on mk1

3 different versions on mk2

Early mk2 had mk1 pcb. Essentially early mk2 was a mk1 turned upside down with different mains switch and relocated level pots. 

Apparently mainboard was redesigned due to the main 739 ic going out of production. 

Mk2 had drain resistor across one smoothing cap. Drain resistors across pre drivers and a solid state switch across main ic supply. All these mods were to stop farting and whistling at switch off. 

Always follow number on underside of pcb

Spent a lot of my life working on them.

Good luck. 


Edited by boominbob - 26 April 2022 at 9:46pm
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