Blown Alpine MRD-M605 amp

[paulieb81]

I have an Alpine MRD-M605 amp that was wired up and working just fine for a few days. Today it worked up until the time I turned my truck off and when I turned it back on no more thump. The blue LCD display on top just blinks on and off, and does not display any messages at all.

I checked all connections, all are good, tested voltage with the multimeter, all is well up to the amp. So I took it apart. There does not appear to be any burnt smell, or bulging or leaking capacitors. I did notice that one of the MOSFETS on the side had a leg that was broken, I am not sure if I broke it while taking it apart or if it damaged earlier today, however I soldiered it back together and retested the amp with no success.

Please let me know what would be the next step to check out on this amp.

[mike49504]

I would start by testing all of the power supply fets and all of the output transistors you should reading nothing near 0 ohms between any of the legs if you do its likely blown

[paulieb81]

On the MOSFETS which are on the sides of the amp where the power leads hook up part number IRF3205, my multimeter reads 0 ohms between legs 1 + 2, and 2 + 3, but reads high numbers on 1 + 3, on all of them.

On the MOSFETS which are on the side of the amp where the speaker output terminals are part number IRF540N, my multimeter reads various numbers on all leg combinations on all of them.

On the output transistors on what would be the front side of the amp, I have 5 transistors, 4 different ones and 1 duplicate one. The tests as follows:

FRH20A15:
Leg 1 + 3 = .1 ohm
Leg 1 + 2 = 1.5 ohm
Leg 2 + 3 = Various numbers all over 1 ohm

RF2001:
Leg 1 + 3 = .1 ohm
Leg 1 + 2 = 4 ohm
Leg 2 + 3 = 4 ohm

C3421:
Leg 1 + 3 = Various numbers all over 1 ohm
Leg 1 + 2 = Various numbers all over 1 ohm
Leg 2 + 3 = Various numbers all over 1 ohm

A1358:
Leg 1 + 3 = Various numbers all over 1 ohm
Leg 1 + 2 = Various numbers all over 1 ohm
Leg 2 + 3 = Various numbers all over 1 ohm

C3421:
Leg 1 + 3 = Various numbers all over 1 ohm
Leg 1 + 2 = Various numbers all over 1 ohm
Leg 2 + 3 = Various numbers all over 1 ohm

[mike49504]

sounds like that 3205 has failed also check the gate resistor for that 3205 the resistor is connected to 1 of the legs what reading do you get ?

[paulieb81]

Mike i just want to make sure i understand you. The 3205 is bad, but all four of them are reading the same, so that I am taking means all 4 are probably bad. Where would I be able to find replacement transistors locally, what type of store has these things?

[mike49504]

Ok unsolder them from the circuit board all 4 of the 3205's then test each one and see what reading you come up with

[paulieb81]

I have a standard soldering iron, do I need to hit up radio shack to pick up anything special to remove them from the board so I don't damage it? Also would they carry replacement 3205's?

[mike49504]

you also need to check the drivers for theese irf3205's Im sure Perry could tell you what drivers they are using in this amp.

If you find any blown fets (irf3205's) when you check them. I would replace them all. You can get the parts from the link below





Search results for "irf3205" - Allied Electronics

[mike49504]

i dont think they sell the replacements for the 3205's

Also u need a desoldering gun u can pick up a bulb type one at radio shack not very expensive. But be careful with applying heat to the board dont keep the soldering or desoldering gun on the parts for very long just enought time to heat the soldered up and suck it off the board. Ive seem alot of the amps that come to me for repair with missing pads and missing traces due to heat so be careful but if u apply heat just long enough to suck the solder off the board u should be fine I suggest applying some new solder to the legs of the fets just need a dab before u try to unsolder them Ive been doing it that way for years and have had no problems

[I Am An Idiot]

If the 3205s read 0 ohms from 1 to 2 and from 2 to 3, there is no way you will get a high reading from 1 to 3. I would not pull them out of the board untill you do some more testing.