This 2200 has been quite problematic. I have done my usual upgrades (www.quirkaudio.com), and in this case I have been chasing a set of problems on the left channel.
The current state is that all electro caps have been replaced all the transistors from Q201to Q333, and Q327, Q325 and Q331 have been replaced as have a number of diodes, including D309/D311 and D301/D303, so now the unit comes out of protection, however Q305 gets very hot meaning their is excessive current draw.
Q305 is now a KSC3503D, which I have used mnay times here.
On measuring R307 there is 0.7v across this resistor, whereas on the right channel on R310 it is 0v, and across R303 there is 0.29v, whereas on R304 it is 0v. On R377 there is 0v the same as R378, so my assumption is that the problem is not on the output side. All the main outputs test fine, Q311 had a low Hfe and was replaced with a new 1302.
When I measure across R331 I have 1.5v, whereas on R332 it is 0v. The two reference points at D309 and D311 should be +1.77v and -1.77v respectively, whereas they are 2.2v and -1.5v. The base of Q211 is 8.7v and all the other voltages on the circuit are correct.
I have attached the circuit and any thoughts are appreciated- this has me quite puzzled.
Peter
The current state is that all electro caps have been replaced all the transistors from Q201to Q333, and Q327, Q325 and Q331 have been replaced as have a number of diodes, including D309/D311 and D301/D303, so now the unit comes out of protection, however Q305 gets very hot meaning their is excessive current draw.
Q305 is now a KSC3503D, which I have used mnay times here.
On measuring R307 there is 0.7v across this resistor, whereas on the right channel on R310 it is 0v, and across R303 there is 0.29v, whereas on R304 it is 0v. On R377 there is 0v the same as R378, so my assumption is that the problem is not on the output side. All the main outputs test fine, Q311 had a low Hfe and was replaced with a new 1302.
When I measure across R331 I have 1.5v, whereas on R332 it is 0v. The two reference points at D309 and D311 should be +1.77v and -1.77v respectively, whereas they are 2.2v and -1.5v. The base of Q211 is 8.7v and all the other voltages on the circuit are correct.
I have attached the circuit and any thoughts are appreciated- this has me quite puzzled.
Peter
So R331, which measured OK, when I pulled it measured low and replacing it seems to have addressed the overheating. I will measure the rest to be sure.