Ashdown Mag300: In trouble

[MarkusBass]

The schematic posted by Zanzoon shows that C5 capacitor is 10 pF cap between V+ rail and the gate of TR5 MOSFET. So the "solution" does not seem to be correct. Maybe you ment C25 instead of C5? Or you are refering to a different schematic than you posted? This is very simple amp and I wouldn't apply any "solutions" like this. As far as I remember the power amp has a separate ground for the input stage and the first thing that I would check is whether this wire is correctly connected (or is broken). If you have regulated power supply with current limiter, you can check the voltages in the amp; what is the voltage on the bases of TR10 and TR11? The negative feedback should try to keep 0V on the output. If it's not doing this, I would check why. But first check missing ground wire on the input.

Mark

[paul_quan]

Hi, could anyone reupload schematic for ashdown mag 300 apc041 issue4 30/12/04?
I'm having similar problems with my combo. Fuses are blowing up every time I connect my amp. Even if speaker is disconnected.

Thanks!

[Jazz P Bass]

Ashdown Mag 300 Schematic

I am reposting the schematic.

[Zanzoon]

Hi all,
I got a notice from the forum robot this morning only.
So my mail is probably a bit late.

[Zanzoon]

Hm, I have trouble replying.
Ley's try again.
Got a message this morning of fresh replies...
Here are the requested schems.

[paul_quan]

Thanks!!!

[Zanzoon]

Hi Paul,

So how did it go?
I'm allways interested to find an easier way to face this problem.
The amps I changed according the info I gave are still running hard.
Since then I had a few more amps with the 041 pcb and none had that particular problem.
Very strange I would say...

[jbhwd]

Hello Zanzoon

Hello Zanzoon:
I do not normally post to forums, but, had the same unusual ACD041 problem.
I have spent days & days, and then weeks... trying to solve this.
I have attached a .pdf of my experience and the G5V-1 Relay.
Post back if this helped.
Jerry AC

ps: this is my first post and hope it goes through with attachments.01 AMP CRAZY Ashdown Mag 300 Repair Notes ReadMe .pdfG5V_1_0911-17099.pdf01 AMP CRAZY Ashdown Mag 300 Repair Notes ReadMe .pdfG5V_1_0911-17099.pdf

[jbhwd]

Hello Zanzoon 2

try loading attachments again.

[Zanzoon]

Hi Jerry,

Allthough I did some test where I controlled the relay manually.
I used a bench power supply (2x 0-65V, 4A) and the problem didn't go way.
That eliminates the relay circuit, the relay itself and the psu caps.

One pcb unit has been sent back to Ashdown and no fault could be found.
After arrival in the shop it worked flawlesly...

I had no such problems again and several Mag 300 passed my bench since then.
But the following that come's in with the same problem; I'll go your way and see if it is the solution to the problem.

btw; the relay I used to connect the output to the load is a heavy duty relay used in pa amps.
The relay in the mag had no problems and the contacts open and close at command.

Thanks Jerry for the hints.

Cheers,

ps: here are the attachments again
041 - MAG300 Change.pdf

[lolbou]

Thank you very much for all your schems and replies. Sorry to be so late thanking you, I have to admit that I left this amp out for a long time - and I'm more involved on some other forum - but I finally got a new transformer for it (the new one is definitely bigger and it's supposed to be wound without flaws).

The amp works again!

Again, with pure analog delay : THANK YOU!

[audiopete]

Hi everyone, I would like to add to this merry little thread.....unfortunately....

I have a Mag 300 that is doing the same thing. When I got it both T5A internal fuses were blown. I pulled the power amp board and there was a burn mark on the chassis underneath from the negative leg of C9 (I will have to look at the board and confirm that). The cap leg was getting close enough to the chassis to arc. I changed out all the electrolytics and fired it up on no load on the limiter and it scoped perfect with signal. I put it on 8 ohm load on the limiter and it immediately pulled limit with DC on the output. I cycled the power and it came up fine and showed nice AC on the load when I plucked a bass. I re-cycled and it would randomly come up good or limit out. That is where I left it yesterday. I'm going to pull and test TR1-4 and do some more investigating. I also want to look at the rectifier and C17-19.

I pulled each AC PT secondary from the power amp board and it limits out with either secondary attached. It also limits with the center tap pulled. Once I disconnect the power board, the preamp and fan come up fine.

[Eyefactor]

Ashdown Mag 300

[g1]

I think you meant this one:
http://music-electronics-forum.com/t40732/#post402245