resistor burnt out

[ben craig]

Hi,

I have now removed and tested all larger transistors, you were right, no presuming!- one of the 2SC5200's is broken.

Also both of the smaller transistors (A1306 8F and C3298B 8A)  and a tiny one (2n 5551 y114)  that were soldered to the board and on the heat sink have gone too.

Am i right in thinking i will need to replace these smaller components before putting in one pair of the larger ones and starting to test as shown below?

while im ordering components is there anything else i should look at testing based on what has blown?

[Roly]

Good result.

Yes the damaged drivers etc have to be replaced, then try a pair of known good output transistors with the limiting lamp in series with the mains feed, and with the loudspeaker disconnected.

Lacking a circuit it's pretty well impossible to predict what else, if anything, may still be damaged.  That is why the limiting lamp and the need to establish that the mid-rail, the output line, is correctly balancing to the midpoint of the +ve and -ve supply rails.

Given the three pairs of output transistors, we need to repeat this test after fitting each pair to ensure that this condition is being maintained.

BTW, the latter parts of the numbers you posted are actually batch numbers (and more likely to confuse a supplier than help), so the devices are;

A1306  aka  2SA1306
C3298B  aka  2SC3298B
2n 5551  =  2N5551