Yamaha g100-112 guitar amp.power light comes on no sound.Transistor heat sink cold

There is either a shorted part in the power supply section or a shorted part (say a transistor if it uses them) in the main amp section. This will be located on the big heat sink. Power supply culprits are transformer, any semiconductor device, such as power regulator, rectifier etc.

I rather suspect IC1 TDA7293 is the cause of your problem. If this is the case you will need to check the speaker/s

Hi!
At this point, I would just take it to a tech rather than poke around in it. It sounds like the power section is the problem as you have guessed, but without the technical knowledge you'd be shooting in the dark. That particular amp is right on the line of being expensive enough that would be worth repairing, but you might do just as wel to check Ebay for another used one.
Good Luck!

This amp has a design defect in the TDA7290 power circuit board. The heat sink is too close to main board when installed (at 90 degree angle) and can TOUCH the power signal on the board shorting out the fuse and/or transistor. I bent back the heat sink bracket slightly and it powered on fine. Also, the cooling fan must be 100% flowing or the transistor will cook in a short time, replace it also with new transistors (its a 5v computer chip fan). Good luck from Arlington guitar shop dot com.

check fuse
and if fail, get a shop to fix it.
or buy the service manual

First check all speaker wiring to make certain there's no shorts.
Protection system come on if there's an overload. These are caused by shorts. If the speakers and wires are good then the only other cause is the main amp, possibly a transistor, has shorted.

You MAY be exceeding the capability of the unit causing the thermal protect of the PA chip to shutdown. A 15 Watt amp is NOT going to make a lot of noise unless you have super-efficient speakers that are say 15 inch ones in decent cabinets. You still will be limited in sound level. Just because the gain control goes to a paticular number doesn't mean the amp can take it !!! Mpost of these use 7 terminal amp chips about the size of a TO220 transistor. Heat sinks are OFTEN very inadequate.

Happy christmas

Problem solved.

Needed:
SCREW (those used to screw transistors to heat sink)
NTE5671 TRIAC TRANSISTOR
ELECTRONICS SOLDERING EQUIPMENT

Open the uc7058r inside the fan

look for the blue wire (lamp Wire), follow it inside the main board.

Keep following the wire to the internal trace conductor in the board wich connect to a transistor (triac) (located screwed to a heat sink)

Replace this transistor with NTE5671

you will need to replace the heat sink screw with a longer one

enjoy!

Hope it helps

Alexis J. Correa, PE

Hello nymnym999,

You did not specify which Fusion amp you have but if the insides looks like the Fusion PP-AM60020 image below, you'll have to "desolder" the transistor.


First remove the heat sink from the transistor case. You'll need a controlled heat soldering station, a desoldering vacuum tool commonly referred to as a "solder ******", and some desoldering braid. Be careful with the heat around other components.

After removing the transistor, use the desoldering braid to clean off any remaining solder from around and in the circuit board mounting holes. Position the new transistor and solder it to the board. Put a thin film of thermal compound on the heat sink and remount it to the new transistor. Use just enough of the compound to insure an air-free join between the transistor case and the heat sink. Reassemble the case and you're finished.

Hope this helps.

If you are lucky, it's only a blown fuse, but with a blinking light on the front, this is doubtful. I would pull the back cover anyway and check the fuse. If fuse is ok, then normally if you have no sound and no picture, you have a blown "horizontal output transistor". Look for the big wire (usually red) coming from the picture tube to the circuit board. The red wire goes to a large object on the circuit board called the "flyback" transformer". Usually very near this transformer you will find the h.o.t. (horizontal output transistor). It will normally be mounted on a silver piece of metal (a heat sink), about 2 or 3 inches square or possibly rectangular. The transistor has three pins coming out of it and is probably the largest transistor you will see that has only 3 pins. The upper portion of the transistor will be clamped (or screwed) into the metal heat sink. You have to desolder the h.o.t. and replace it with a new one. The h.o.t. usually costs only about $10.00. If the fuse and h.o.t. are good, then the "flyback" is probably bad and they run from $25 to $100. If the TV is worth only about $200, then replacing the flyback is not recommended, because there is no guarantee that this will solve the problem. Keever.