Same... What is the push-pull transistor?

Should be provided you only have a single transistor in the output power stage. If you have a pair of transistors in push pull arrangement, then those two units for that one individual channel will be different.

There are several reasons. If you find one shorted transistor in a push-pull stage you should always replace both. One might be faulty but not shorted, but when in operation it does the other one in. You might have also missed another shorted part such as a diode or voltage regulator. Hunt around looking at the circuit of the confirmed shorted parts and test or replace anything off that circuit.
Finally check your speakers and wiring to them. Shorted output transistors have generally two ways of going like that. Wires touching each other or bad speakers, or having it too loud!

If you have a volt meter you may try and repair it yourself. First however disconnect the speakers and see if the set still goes into protect. If so you may have shorted output and drive transistors. There will be open resistors near them as well. You can compare the bad channel with a nearby working channel since normally only channel shorts out at a time. Always replace outputs in pairs since they in push pull configuration .

It should be a push pull. The fact that you have negative voltage almost certainly means push pull. One side will be constructed using NPN transistors ran off the positive DC rail and the other side will be constructed using PNP transistors ran off the negative rail. I don't know the age of your amp but I know pioneer now uses integrated amp modules instead of discrete transistors.

http://pdf1.alldatasheet.com/datasheet-pdf/view/82968/SANYO/STK412-020.html

example of integrated amp module (sorry for the chinese)

Hi again! Been thinking about this and you might not need to wait for someone to answer. I assume the transistor in question has blown apart or burnt up so you can't read the number?
However does it come off the heatsink as part of the main amp? If it does then it might have a brother around it. For if it is say the left or right channel transistor, then the other channel will have the same type transistor. Remember the left and right channels are copies of one another. If you see 4 transistors on the heat sink then it's a push-pull amp. They work in pairs, one pair for each channel. By the way it's best to replace the pair, even if only one is blown.
If on the other hand the blown transistor is from the power supply section, then you will have to wait for someone to help, or get the service manual.

short answer yes... Long answer... Amp Failure: There are many different ways that an amp can fail but the two most common failures are shorted output transistors and blown power supply transistors (< those are not blown). There are several types of protection circuits in amplifiers. The most common are over-current and thermal. The over-current protection is supposed to protect the output transistors. Sometimes it doesn't work well enough to prevent the failure of the output transistors but it will work well enough to shut the supply down before the power supply FETs are destroyed. If the amp remains in protect mode, goes into protect mode or blows the fuse as soon as the remote voltage is applied, shorted output transistors are almost certainly the cause. If the fuse protecting the amp is too large, if the protection circuit doesn't respond quickly enough or if the power supply is poorly designed, the power supply transistors may fail. If you see a lot of black soot on the power supply transistors (near the power transformer), the power supply transistors have failed. Soot on the board doesn't necessarily mean the transistors have failed. Sometimes, technicians don't clean up the mess from a previous failure. Transistor Failure/Checking Transistors: In general, when a transistor fails, it will either short (common for output AND power supply transistors) or open (common for power supply transistors). Transistors act like valves. They control the current flowing through a circuit. A shorted transistor acts like a valve that's stuck open (passing too much current). In the case of an output transistor, the shorted transistors tries to deliver the full rail voltage to the speaker output terminal. If you've ever seen a damaged amp that pushed or pulled the speaker cone to its limits when the amp powered up (common on some Rockford amplifiers), that was almost certainly due to a shorted output transistor. When checking transistors, you most commonly look for shorted connections inside the transistor. You do this by using a multimeter to look for low resistance connections between the transistor's terminals. Note: I used the terms short and open on the previous paragraph. A short (short circuit) is a path through which current flows that should not be there. An open (open circuit) is a break in the circuit. It is most likely the power supply that has taken a ****.

Amp Failure:
There are many different ways that an amp can fail but the two most common failures are shorted output transistors and blown power supply transistors (< those are not blown). There are several types of protection circuits in amplifiers. The most common are over-current and thermal. The over-current protection is supposed to protect the output transistors. Sometimes it doesn't work well enough to prevent the failure of the output transistors but it will work well enough to shut the supply down before the power supply FETs are destroyed. If the amp remains in protect mode, goes into protect mode or blows the fuse as soon as the remote voltage is applied, shorted output transistors are almost certainly the cause. If the fuse protecting the amp is too large, if the protection circuit doesn't respond quickly enough or if the power supply is poorly designed, the power supply transistors may fail. If you see a lot of black soot on the power supply transistors (near the power transformer), the power supply transistors have failed. Soot on the board doesn't necessarily mean the transistors have failed. Sometimes, technicians don't clean up the mess from a previous failure. Transistor Failure/Checking Transistors:
In general, when a transistor fails, it will either short (common for output AND power supply transistors) or open (common for power supply transistors). Transistors act like valves. They control the current flowing through a circuit. A shorted transistor acts like a valve that's stuck open (passing too much current). In the case of an output transistor, the shorted transistors tries to deliver the full rail voltage to the speaker output terminal. If you've ever seen a damaged amp that pushed or pulled the speaker cone to its limits when the amp powered up (common on some Rockford amplifiers), that was almost certainly due to a shorted output transistor. When checking transistors, you most commonly look for shorted connections inside the transistor. You do this by using a multimeter to look for low resistance connections between the transistor's terminals.

There are many different ways that an amp can fail but the two most common failures are shorted output transistors and blown power supply transistors (< those are not blown). There are several types of protection circuits in amplifiers. The most common are over-current and thermal. The over-current protection is supposed to protect the output transistors. Sometimes it doesn't work well enough to prevent the failure of the output transistors but it will work well enough to shut the supply down before the power supply FETs are destroyed. If the amp remains in protect mode, goes into protect mode or blows the fuse as soon as the remote voltage is applied, shorted output transistors are almost certainly the cause. If the fuse protecting the amp is too large, if the protection circuit doesn't respond quickly enough or if the power supply is poorly designed, the power supply transistors may fail. If you see a lot of black soot on the power supply transistors (near the power transformer), the power supply transistors have failed. Soot on the board doesn't necessarily mean the transistors have failed. Sometimes, technicians don't clean up the mess from a previous failure.
In general, when a transistor fails, it will either short (common for output AND power supply transistors) or open (common for power supply transistors). Transistors act like valves. They control the current flowing through a circuit. A shorted transistor acts like a valve that's stuck open (passing too much current). In the case of an output transistor, the shorted transistors tries to deliver the full rail voltage to the speaker output terminal. If you've ever seen a damaged amp that pushed or pulled the speaker cone to its limits when the amp powered up (common on some Rockford amplifiers), that was almost certainly due to a shorted output transistor. When checking transistors, you most commonly look for shorted connections inside the transistor. You do this by using a multimeter to look for low resistance connections between the transistor's terminals.
Note:
I used the terms short and open on the previous paragraph. A short (short circuit) is a path through which current flows that should not be there. An open (open circuit) is a break in the circuit.

There are many different ways that an amp can fail but the two most common failures are shorted output transistors and blown power supply transistors (< those are not blown). There are several types of protection circuits in amplifiers. The most common are over-current and thermal. The over-current protection is supposed to protect the output transistors. Sometimes it doesn't work well enough to prevent the failure of the output transistors but it will work well enough to shut the supply down before the power supply FETs are destroyed. If the amp remains in protect mode, goes into protect mode or blows the fuse as soon as the remote voltage is applied, shorted output transistors are almost certainly the cause. If the fuse protecting the amp is too large, if the protection circuit doesn't respond quickly enough or if the power supply is poorly designed, the power supply transistors may fail. If you see a lot of black soot on the power supply transistors (near the power transformer), the power supply transistors have failed. Soot on the board doesn't necessarily mean the transistors have failed. Sometimes, technicians don't clean up the mess from a previous failure.
In general, when a transistor fails, it will either short (common for output AND power supply transistors) or open (common for power supply transistors). Transistors act like valves. They control the current flowing through a circuit. A shorted transistor acts like a valve that's stuck open (passing too much current). In the case of an output transistor, the shorted transistors tries to deliver the full rail voltage to the speaker output terminal. If you've ever seen a damaged amp that pushed or pulled the speaker cone to its limits when the amp powered up (common on some Rockford amplifiers), that was almost certainly due to a shorted output transistor. When checking transistors, you most commonly look for shorted connections inside the transistor. You do this by using a multimeter to look for low resistance connections between the transistor's terminals.
Note:
I used the terms short and open on the previous paragraph. A short (short circuit) is a path through which current flows that should not be there. An open (open circuit) is a break in the circuit.

Amp Failure:
There are many different ways that an amp can fail but the two most common failures are shorted output transistors and blown power supply transistors (< those are not blown). There are several types of protection circuits in amplifiers. The most common are over-current and thermal. The over-current protection is supposed to protect the output transistors. Sometimes it doesn't work well enough to prevent the failure of the output transistors but it will work well enough to shut the supply down before the power supply FETs are destroyed. If the amp remains in protect mode, goes into protect mode or blows the fuse as soon as the remote voltage is applied, shorted output transistors are almost certainly the cause. If the fuse protecting the amp is too large, if the protection circuit doesn't respond quickly enough or if the power supply is poorly designed, the power supply transistors may fail. If you see a lot of black soot on the power supply transistors (near the power transformer), the power supply transistors have failed. Soot on the board doesn't necessarily mean the transistors have failed. Sometimes, technicians don't clean up the mess from a previous failure. Transistor Failure/Checking Transistors:
In general, when a transistor fails, it will either short (common for output AND power supply transistors) or open (common for power supply transistors). Transistors act like valves. They control the current flowing through a circuit. A shorted transistor acts like a valve that's stuck open (passing too much current). In the case of an output transistor, the shorted transistors tries to deliver the full rail voltage to the speaker output terminal. If you've ever seen a damaged amp that pushed or pulled the speaker cone to its limits when the amp powered up (common on some Rockford amplifiers), that was almost certainly due to a shorted output transistor. When checking transistors, you most commonly look for shorted connections inside the transistor. You do this by using a multimeter to look for low resistance connections between the transistor's terminals.

Seems as you have blown an output. Seek repairs.