The Box MA1520Mk2 problem. Help to Fix

[nastorrent]

Hello
A good friend of mine is trying to fix a PA Active Monitor "The Box MA1520Mk2" that keeps blowing transistors. It's not an extraodinary equipment, but they have several of these on his small group and they fit exactly the space on the Van.

He can power it up again but after a short time it blows again.

We don't have any info about schematics, Thomann didn't help also.

My friend says he need further info about the circuit beacuse some component values are deleted and he needs them for further fixing (D6,D7,D5,C1,C2, for example).

Any help would be appreciated.
Thanks in advance

 

[nastorrent]

I would take in account any suggestion about a mono power amp that I could find on eBay or Aliexpress, that can work with the original transformer (50V-0-50V AC or its rectified DC)

Any suggestions?

 

[JonSnell Electronic]

Have you checked the quiescent current when powered up on a variac? Check driver transistors and bias components before anything else. It looks like there is only half a dozen or so to check.

 

[nastorrent]

Hi,
As a said, my friend is who is trying to fix that board (He has technical skills, so I guess Yes, he had checked out that.)

He fix some equipment for me (Guitar Tube Amps, Solid State PA Amps, Mixers,...) from time to time and I'm trying to give some help with this board as "favour return" because he doesn't speak English and he didn't found help on Spanish forums.

If anyone recognise the circuit it is based, or have a similar schematic lying around maybe it could help.

Any amplifier board suggestion for the mentioned transformer (50V-0-50V AC) would be appreciated.

Thanks in advance

 

[djk]

The 2SB817 is only rated at 12A, 140V, 100W.

Replace with the On Semiconductor 200W devices

http://www.onsemi.com/pub/Collateral/NJW3281-D.PDF

OR

http://www.onsemi.com/pub/Collateral/NJW21193-D.PDF