Ok, i have a Powerbass Xa3000D here, which i'm repairing for a friend.
All 20 power mosfets blew.
I replaced all 20, powered it up (before resinking it) and it worked (turned on and played tones, gains worked etc....).
So i re-sinked it up, then powered it up again, and bang, a fet went pop, so i de-sunk it again, and changed the fet (hoping it was a poor solder joint or the like).
When i powered it up the second time it worked fine again, great.
But when i put it back into the heatsink again it blew the fet once more....
All 20 fets are 2 sets of 10 parralleled, which are joined to the SMPS control board by a set of 8 transistors.
What would cause the fet to only blow when they are back on the sink? I assume another component blew when the fets went, any ideas???
All 20 power mosfets blew.
I replaced all 20, powered it up (before resinking it) and it worked (turned on and played tones, gains worked etc....).
So i re-sinked it up, then powered it up again, and bang, a fet went pop, so i de-sunk it again, and changed the fet (hoping it was a poor solder joint or the like).
When i powered it up the second time it worked fine again, great.
But when i put it back into the heatsink again it blew the fet once more....
All 20 fets are 2 sets of 10 parralleled, which are joined to the SMPS control board by a set of 8 transistors.
What would cause the fet to only blow when they are back on the sink? I assume another component blew when the fets went, any ideas???
the gate resistors provide best damping when they are attached directly to the gate leg with a VERY short lead.agithegreat said:
They are there to create resistance between the inductance of traces and leads from the capacitance seen at the gate. If this RL circuit is not damped the FET may oscillate.
Each FET needs it's own gate resistor.
If you are measuring continuity (near zero ohms) gate to gate then the designer has forgotten to place the gate resistors.
Car audio quality - what quality?
Ok, well i will remove the broken fet once more, and re-test the resistors.
Will the fact that the resistors are still in the circuit affect the resistances at all? Obviously i just popped the DMM across either 'leg' of the resistor.
Sorry when you mean the only good one, do you mean the only good connection with the rest of the cirucit. i.e, it's blowing as all the others don't have that 100ohm resistance?
For £1.50, ($2.50 ish) i'm going to definatly change the resistors, but how can i be sure that they wont blow again when i power it up, as something else is blown???
Also if i have a tighter tolerence 1-2% instead of 5% will that matter. I undertsand you can't put a 5% tolerence in a 1% place. But does the other way matter?
As my current ones are 5% tolerence, but the ones i'm looking at are 1%.
Sorry for all the typical noob questions
Will the fact that the resistors are still in the circuit affect the resistances at all? Obviously i just popped the DMM across either 'leg' of the resistor.
Sorry when you mean the only good one, do you mean the only good connection with the rest of the cirucit. i.e, it's blowing as all the others don't have that 100ohm resistance?
For £1.50, ($2.50 ish) i'm going to definatly change the resistors, but how can i be sure that they wont blow again when i power it up, as something else is blown???
Also if i have a tighter tolerence 1-2% instead of 5% will that matter. I undertsand you can't put a 5% tolerence in a 1% place. But does the other way matter?
As my current ones are 5% tolerence, but the ones i'm looking at are 1%.
Sorry for all the typical noob questions
Blown transistors can change the value read inline. Check the transistors for shorts, see Perry's site if you need to see an example of testing them.
Put a 10A fuse on your 12v power, I think that amp will power up on it but I don't see large amps much.
What I would do (cause I'm scared, lol) is put one or two good mosfets in each bank, check everything and make sure the resistors are all good for them, and try to fire it up that way. If you get it running you can check voltage on all the resistors and all that, see if anything gets hot, etc. And I put them in the sink that might save a part...might not.
Put a 10A fuse on your 12v power, I think that amp will power up on it but I don't see large amps much.
What I would do (cause I'm scared, lol) is put one or two good mosfets in each bank, check everything and make sure the resistors are all good for them, and try to fire it up that way. If you get it running you can check voltage on all the resistors and all that, see if anything gets hot, etc. And I put them in the sink that might save a part...might not.
Thanks andrew, i've used rapid before.
Do i need to get 5% resistors, or will a better tolerence be ok (1%?) As i think the resitors in currently are 5% aren't they???
The only thing i dislike about rapid is the mental postage cost. I was looking at these off the flea bay.
http://cgi.ebay.co.uk/100-x-100-Ohm...66:2|39:1|72:1688|240:1318|301:1|293:1|294:50
I'm going to remove all the resistors later and measure exactly what they are, then check over all the fets, put a new set of resistors in, then 'add pairs' of fets, hopefully with them working.
Jol50, i have a limiting power supply (4a RMS).
It will allow the amplifier to function as when i fixed my previous one i tested it on this supply.
Then worked my way up fusing my cars supply, 40a, 80a, then 200a.
Do i need to get 5% resistors, or will a better tolerence be ok (1%?) As i think the resitors in currently are 5% aren't they???
The only thing i dislike about rapid is the mental postage cost. I was looking at these off the flea bay.
http://cgi.ebay.co.uk/100-x-100-Ohm...66:2|39:1|72:1688|240:1318|301:1|293:1|294:50
I'm going to remove all the resistors later and measure exactly what they are, then check over all the fets, put a new set of resistors in, then 'add pairs' of fets, hopefully with them working.
Jol50, i have a limiting power supply (4a RMS).
It will allow the amplifier to function as when i fixed my previous one i tested it on this supply.
Then worked my way up fusing my cars supply, 40a, 80a, then 200a.
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