JL Audio 250/1 blown output transistors

[Brams96]

Hi all,

I definitely found 1, possibly 2, output transistors (IRFZ44R's at Q300-Q305) that are faulty. One was a bit discoloured & the other was completely burnt out. I was going to replace them with IRF3205's as they are 2X the current rating.
The problem I have is some of the SMD resistors in front of them are all burnt out too & I need to know what value they are.

Can anyone help with what value they are or know where I can download a schematic diagram??

Thanks in advance

 

[Leolabs]

You sure it's a output MOSFET instead of a DC-DC converter MOSFET??

 

[S Merlington]

The IRFZ44N's Q300-Q305 are the power supply transistors..

The resistors are 47 ohm..

Also check the drivers for thoose fets to make sure none are shorted And check the output transistors (irf540) to make sure none are shorted or leaking..

 

[Brams96]

Ahh, my bad I thought they were the output transistors. I'll get on & order some more resistors now, I might as well replace all 6 while I've got it in bits. I will use my multi meter tonight to determin if anything else has blown or is suspect. Thanks very much for the help, I'll let you know how I get on

 

[Brams96]

Well I tested all the z44r's & the other 4 still on the board are ok, as are the drivers for them all. All 6 SMD resistors will need replacing as 2 were missing/blown up & then the other 4 pretty much fell off when I touched them. The board around the blown z44 is a discoloured brown colour like the resin got quite hot & it even stained the aluminium heat sink too. The 540's are ok as well.
On a different note I managed to fix a Vibe A0 amp that wasn't working either. The cap for the power (1000uf 25V) had burst the top & leaked so I replaced it with a 35V spare I had & hey-presto! Fixed.

 

[Deadly Sones]

I would replace all of the ps transistors. Even the 4 that test good. Its the only way to make the repair reliable. Now if this amp is yours and you wanna go the cheapest route tis up to you, but if its going to someone else, I'd replace them all.

 

[Brams96]

I've just recieved the new resistors but they look a little small. I ordered the 805's but am now thinking they may have needed to be the 1206's. Can anyone confirm what size the should be?