help indetifing components

[scampo77]

how do i tell the difference between a output transistor and a power supply transistor? i am working on a smal MTX amp i have 4 small ones on one side of the amp and 2 large ones on the other side. the 4 on the one side are burnt and look failed. where do i buy them from?

the amp is MTX rtp251d and the numbers on the faild transistor are 18sf2f and 75339p

[Perry Babin]

One terminal of each of the output transistors will be connected to one of the speaker terminals.

One terminal of each of the power supply transistors will be connected to the power transformer.

The HUF75339P is used in the power supply. Mouser.com has them.
512-HUF75339P3

[scampo77]

i have 4 of these should i replace all 4 of them? one is a complete meltdown and one has no continuity between the outer legs

[Perry Babin]

There should be no continuity between the first leg and either of the other legs.

You should replace all 4.

[jol50]

Go to Perry's site and it shows a basic layout for most amps. Usually 12v comes in through fuses and 16v (or higher) cap(s) and to PS transistors*, they hook to round torrid transformer, then to rectifiers* (usually two), then to large rail caps, then to outputs*, outputs through large resistors in front of them to speakers. Usually PS transistors have torrid close by, and outputs have all the small input circuits next to them. A few amps twist it around, but most are PS/output/input from one end to other. If not then usually that in a circle. Sometimes rectifiers are across from PS transistors (smaller amps), sometimes next to them on both sides (large long amps). Can also look at the numbers on the board to ID them as transistor or diode.

* = on heatsink.

[scampo77]

here is a picture of them. what is that thing in the middle of the 4? does it need to be replaced alongside the resistors? should i look for anything else? or just change these 4 and go try it?

of the 4 there are 3 different manufacturers? is this important?

[Perry Babin]

The two on the left are the rectifiers. They're probably not defective and won't need to be replaced.

If there are only two of the 75339s in the amp, you only need to replace those two. Are there 2 more 75339s on the other side of the amp?

The device under the foam is a thermistor. It's unlikely to be defective.

[scampo77]

well there are 2 additional transistors on the opposite side but they are much larger. they are both the same and they have the number "IRFP240" on them

[Perry Babin]

Those are the audio output transistors. What model amp is this?

[scampo77]

MTX rtp251d