Yamaha DSP-A780 Service Manual?
- Thread starter sWiZzLe
- Start date
OK. I have the service manual, but printed not PDF.
The protection circuit monitors abnormal current or DC at the output stages, and the ±5v ±15v and ±B voltage rails. You need to check which one is causing the problem.
You have a few seconds to check before the protection kicks in. You can check the output stages at the 0.1R resistors near the output transistor pairs. They are 3W resistors for the front and center channels and 2W for the rears.
The protection circuit monitors abnormal current or DC at the output stages, and the ±5v ±15v and ±B voltage rails. You need to check which one is causing the problem.
You have a few seconds to check before the protection kicks in. You can check the output stages at the 0.1R resistors near the output transistor pairs. They are 3W resistors for the front and center channels and 2W for the rears.
Whoa, i forgot i posted this on here. I just googled the Service Manual again as i was considering buying one, and this thread came out top lol
Hi Sinopa, thanks for replying
I don't suppose you could take a picture of the circuit diagram and mail it to me could you?
I gave your instructions to my electrician friend, im sure that it will make more sense to him. Are the output transistors on the bottom of the 2 large heatsinks?
I think he showed me which ones he thought they could be, but i dont think he took a picture.
Hi Sinopa, thanks for replying
I don't suppose you could take a picture of the circuit diagram and mail it to me could you?I gave your instructions to my electrician friend, im sure that it will make more sense to him. Are the output transistors on the bottom of the 2 large heatsinks?
I think he showed me which ones he thought they could be, but i dont think he took a picture.
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Yes, all the output transistors are bolted to the heatsinks.
There are 3 pairs of larger transitors for Main L+R & Centre and 2 smaller pairs for Rear L+R.
In your picture, at the top on the left heaksink is the Main Right pair. Opposite at the top of the right heatsink is the Main Left pair. Bottom of the left heatsink is the Centre pair.
The Rear output transistor are at the bottom of the right heatsink. There are 6 devices in this area, the two nearest the rear of the amp are positive and negative regulators. You could check the 15V supplies here. Each regulator has 3 pins. The pin nearest the front of the amp is the output. One should be +15V and the other -15V.
The + and - 5V regulators are on a U shaped heatsink just below (in your picture) the main heatsink on the left. The output pins are the ones nearest the centre of the board.
The resistors I mentioned are the green ones located between each output transistor pair. You can check for over-current (voltage across the resistor) and DC offset (voltage between one end of the resistor and ground) at these resistors.
I don't have a photocopier and the print looks a bit small to photograph but I could get out my macro lens and give it a go if needed.
Good luck.
There are 3 pairs of larger transitors for Main L+R & Centre and 2 smaller pairs for Rear L+R.
In your picture, at the top on the left heaksink is the Main Right pair. Opposite at the top of the right heatsink is the Main Left pair. Bottom of the left heatsink is the Centre pair.
The Rear output transistor are at the bottom of the right heatsink. There are 6 devices in this area, the two nearest the rear of the amp are positive and negative regulators. You could check the 15V supplies here. Each regulator has 3 pins. The pin nearest the front of the amp is the output. One should be +15V and the other -15V.
The + and - 5V regulators are on a U shaped heatsink just below (in your picture) the main heatsink on the left. The output pins are the ones nearest the centre of the board.
The resistors I mentioned are the green ones located between each output transistor pair. You can check for over-current (voltage across the resistor) and DC offset (voltage between one end of the resistor and ground) at these resistors.
I don't have a photocopier and the print looks a bit small to photograph but I could get out my macro lens and give it a go if needed.
Good luck.
I'll pass that on to my mate, see if he can get it working again.
Another friend has just given me a pair of very nice looking Wharfedale 507.2's
He's says they're about 20 years old, but recently re-coned. The cheap amp im currently using with them just doesn't do them justice!
Cheers Sinopa
Another friend has just given me a pair of very nice looking Wharfedale 507.2's
He's says they're about 20 years old, but recently re-coned. The cheap amp im currently using with them just doesn't do them justice!Cheers Sinopa