Haunz

iTrader: (3)

Check across their legs with an ohm meter for dead shorts..... this will reaveal most blown outputs...

Sometimes its necassary to remove them and test individually with a scope (which I dont have experience with)

Its generally good practice to replace them all (on that channel) if you find one blown....

Good luck... and remember, many shops wont fix what someone else has already fiddled with !
(so if you doubt your ability and its a nice amp you might want to take it to a professional)

Edit: Also be sure to check the transistors & diodes used in the powersupply/check supply voltage.... as seahag pointed out these can go as well.... [img]graemlins/banghead.gif[/img]

[ January 23, 2005, 01:36 AM: Message edited by: Haunz ]

Seahag

yep.
Was inside making coffee.
? ? Coincidence ? ?

Fabe

Hey guys, I was scrutinizing the amp again and saw remnants of magic smoke - although after the deed is done they it is invisible, they still leave evidence (see pic). So one of the transistors is cracked. I looked at a few sites posted here on CCA and two of them have the part, or a replacement. I guess there's only one thing to do now...

Haunz

iTrader: (3)

^ make sure you check every single one esspecially on that channel man ! Usually only the one that fails will let out the smoke, crack, explode... but they will often take other transistors with them... !

You dont want to order parts only to find out you need more later.... [img]graemlins/laugh.gif[/img]

Also make sure it was not a short after the amp that caused this to happen.... you dont want to fix the amp, then have it happen again !

[ January 23, 2005, 04:01 PM: Message edited by: Haunz ]

Fabe

See, I'm having some conceptual problems with these transistors here: As seen in the pic above the legs on the transistor from left to right are base, drain and source. This is a Class D amp so they're MOSFETs but should I then be reading a resistance between source and drain without a field applied to the base, or not? [img]graemlins/cry.gif[/img]

Haunz

iTrader: (3)

If you want you can do that if you take them out of circuit... but I think most of the time looking for dead shorts when everything is open is enough...

Like I said it might not be a bad idea to replace them all on that channel anyway....

Fabe

Haunz, when I took out the blown transistor, the rest of them still read no resistance across their source and drain...which must mean that one or all of the rest are messed up inside right? Tabarnaque it's about $3-$4 each and there's ten of those transistors on the board. How would I know it's only them that's the problem and not some other shortcake?

[ January 23, 2005, 08:35 PM: Message edited by: Fabe ]

Haunz

iTrader: (3)

Welcome to trouble shooting lol..

You should not get a reading between any of the legs that lasts for more then 1/2 a second... ie, put the ohm meter leads across the various legs and it might flash a couple numbers (or may not) then it should read "1 ." (or infinate resistance)

Once you get the bad fets off the amp should power up and give you rail voltage and the other channel should work... if it dosent you know something else is d!cked up... trouble shoot from there...

Remember to do all initial testing on a small 12V supply !

Seahag

There is a procedure.

YOu must touch 2 leads to 'charge' the device in order for the transistor to turn on.

you touch the left one and the middle one for
1-2sec. and then read the resistance on the outter pins.. maybe not in that order.
Search around for the procedure.

Like Haunz said.. you mostly looking for dead shorts. 0 resistance. If its ****ed it
WILL read 0 resistance.

Fabe

Well, I thought I'd update you guys on my success or failure: I pulled off all but one MOSFET of the ten on the output and now the amp doesn't suck crazy amounts of current and actually turns on! Sadly, it means I should change all 10 though. However, with only one in there I'm not getting any sound to a speaker. The journey continues...