Alpine MRV-F352 amp issues... some help would be appreciated!

[numeronada]

ok, so I just received this amp, a great 5 channel beast... and the 5th channel (subwoofer), is innactive.

I opened the amp up to find that two of the resistors are burnt, R513&R514.. so, my question is...where do I go from here??

I have already ordered some new resistors (hopefully they arrive soon)... but, should I go ahead and replace the FET output transistors for this circuit? (FET IRFZ44N) I am confused as to which ones would cause the resistors to pop? Q505/506 in the diagram?

Could the resistors being burnt be due to the output transistors shorting and allowing to much current draw for the resistors?

here is a diagram I found... http://www.bcae1.com/temp/mrvf352.jpg

I will try to get some pics soon, but all it is is two fried resistors and everything else looking good.

 

[Perry Babin]

Those (Z44s) are the power supply transistors, not the output transistors. The failure of the output transistors could have caused those resistors to have failed.

Did you check the output transistors (KTD718 and KTB688)?

 

[numeronada]

ktc718 and ktb688? The diagram I have has ktc3198's for the outputs, if I am reading the diagram right(seems I have already screwed up once).

I haven't pulled any of the transistors off of the board to check them yet, I might be getting to that today.

If I do need to get new outputs where would I be able to get them? And, should I just replace the power supply transistors while I am at it?

 

[numeronada]

oh ok, I see the outputs on the board now, both the ktc718 and ktb688. Is there any way to test them while they are still on the board?

 

[Hexhclass]

test them for short circuit and ktc3198 is a driver check it to

 

[Perry Babin]

You should not read anything near 0 ohms when measuring the resistance between the legs of any individual output transistor. Measure the resistance from leg 1 to leg 2, 1-3 and 2-3.

 

[numeronada]

You should not read anything near 0 ohms when measuring the resistance between the legs of any individual output transistor. Measure the resistance from leg 1 to leg 2, 1-3 and 2-3.

even if they are still connected to the board? Cause I get 0 readings on the z44 transistors, but they are still connected to the board.

The only ones that show a 0 reading are those z44's between what looks like pins 1&2... the q503/501's show no resistance for a very brief time then show resistance... all of the ktc718 and ktb688's seem to be fine, no 0 ohm readings.

 

[Perry Babin]

You can determine if any are shorted while they're in the board. Transistors connected in parallel with shorted ones can appear defective also, although it's not relevant here. All of the Z44s will have to be replaced.

 

[numeronada]

alrighty, I am ordering some irfz44n's right now. probably just replace the two for the 5th channel, or would I be better off just replacing all channels with the same FET's?

 

[Perry Babin]

I didn't realize it had 2 power supplies. If only Q505 and Q506 failed, you don't need to replace the other power supply FETs.

 

[numeronada]

that is what I was thinking. Thanks Perry, I will post up again when I get it all fixed!