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Amcron DC300a overhaul.

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Robbo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robbo Quote  Post ReplyReply Direct Link To This Post Posted: 26 April 2020 at 2:04pm
Could that one possibly going into use on your Hi-Fi Ian
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robbo Quote  Post ReplyReply Direct Link To This Post Posted: 26 April 2020 at 6:19pm
Certainly takes me back a bit seeing one in pieces again Ian---I had 28 of the buggers when Slade packed in touring and sold off all the PA gear and they were all in double racks with 4 way fan cooling.
We had to repair a few and I think most of them had seen a soldering iron at least once in their lives---Charlie, Slades FOH engineer used to buy them cheaply in the States and smuggle them back to the UK bolted inside the bands backline cabinets in order to avoid paying duty--Nod was very careful with money back in the day
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djeddie Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2020 at 9:01am
C'mon John, when's the book coming out?
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 concept-10 Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2020 at 10:11am
Originally posted by djeddie djeddie wrote:

C'mon John, when's the book coming out?

Agreed, John you are a gold mine of cool stories, a book is essential :)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robbo Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2020 at 10:17am
Its quite funny you mentioning that Eddie as I have started a few topics and got the format sorted while we have been on lockdown---even got the book title sorted now as well(don't ask).
Its going to have to go on the back burner for a while now though as I have just started work on my Mini Cooper S getting it up to 225bhp as I am hoping to be able to use it back on the road later in the summer---Cheers--John.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2020 at 1:14pm
Dont worry about the the Mini Cooper, it's the book we need, you can spill the beans on all the showbiz prima donnas John!  Edited to 'Mr.X' in case they sue of course! 
Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djeddie Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2020 at 4:40pm
Originally posted by Robbo Robbo wrote:

Its quite funny you mentioning that Eddie as I have started a few topics and got the format sorted while we have been on lockdown---even got the book title sorted now as well(don't ask).
Its going to have to go on the back burner for a while now though as I have just started work on my Mini Cooper S getting it up to 225bhp as I am hoping to be able to use it back on the road later in the summer---Cheers--John.


Is that a proper Mini or a BMW John? If it's the former then that's OK, if it's a Beemer then you know the book is the way to go!!

Sorry for hijacking your thread Ian! But, I do refer to these older amps as Helen Mirren's and Joanna Lumley's... maybe old but I'd still have a go and you know they're still gonna work!!!
Chas n Dave : it's like Drum and Bass but with beards.             E=mc² ±3dB
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Robbo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robbo Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2020 at 7:31pm
I would prefer Helen Mirren as the only blow job that you will get from a Crown DC300A is when it goes DC
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djeddie Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2020 at 9:08pm
Ah, a Beemer then!!!LOL
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 Robbo Quote  Post ReplyReply Direct Link To This Post Posted: 27 April 2020 at 10:04pm
Yeah--As far as I know you cannot get a classic Mini up to 225bhp without putting a Honda engine in it.
Don't knock the Beemers until you have tried one Eddie as they are surprisingly good--Mine is one of the very first ones with the supercharger and drives amazing when it was a standard car but with the mods I am doing, it will be even better.
BMW certainly did a good job on these early Cooper S models--they even managed to get them leaking oil and water just like the originals used to
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Post Options Post Options   Thanks (0) Thanks(0)   Quote jbl_man Quote  Post ReplyReply Direct Link To This Post Posted: 30 April 2020 at 1:41pm
Originally posted by APW APW wrote:

Check C4 and C5 (the two caps closest to the Red Switch) as they are part of a diode pump (in conjunction with D1,D2, R1,R2 and D3) that generates about 70volts that feeds both channels driver circuit. Check you have about 100volts with respect to ground on one end of the 2k2 resistor R2…. R2 should have about 30Volts across it.




Ok...just to give you an update....changed the 2 capcitors around the diode pump, C4 and C5,and also changed 2 out-of-value resistors on the input offset pots. Result is exactly as before,very low,distorted output. 

Now measuring each side of the resistor (R2) to ground on the diode pump you mentioned,i get 61v one side,81v the other.

Have also changed the ua739 ic, incase that was faulty.same result.

But output DC is perfect, 0.00v left. 0.01v right.

Any ideas from here?


Be seeing you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robbo Quote  Post ReplyReply Direct Link To This Post Posted: 30 April 2020 at 3:50pm
We had a bad batch of DC300As once with very weak and tarnished jack input sockets---I presume you have checked them Ian as it could be a real daft problem.
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