avt 100 problems , help needed

[geraint evans]

hello everybody,
help required ,the problem i have is diodes d217 and d218 burnt out. what causes these diodes to burn out ?.
thanks
Geraint

[Enzo]

Are you sure they are "burnt out?" Or do they just measure something like 10 ohms or less across themselves?

Look on the power supply page of the schematic. They are parallel, back to back with also C247 and R263 in parallel. The rsistor is only 10 ohms to begin with, but since the diodes and resistor and cap are strung between the circuit ground and chassis, they can show a dead short. it is normal for them to appear shorted while in the circuit.


What problem does the amp have that you want to solve?

If the amp blows its fuse, the most common reason is a blown TDA7293 power amp IC on the little module.

[geraint evans]

Thanks for the reply
The original problem was the power amp overheating and smoking , the fixing screw was loose , tightened screw, amp was working ok for a while although the tone of the amp was compromised
Then there was smoke coming from diodes d217 & d218 , turned amp off . turned amp back on again and fuse blew , and d217 & d218 where definitely burnt out , when removed they crumbled to bits , are these problems related, or are there two separate problems. by tightening the screw on the power amp(TDA7293) ,could this possibly
cause the ic to short out to the heatsink.( i should mention the circuit board was pretty dirty under the vent where d217 & d218 are located on the top of the amp and was cleaned up during the general maintenance i was caring out )

Geraint