i have a blow up time and still diagnosing where the problem is, it will be slow as i have to retest all the related components for damage to narrow down where the problem source is... in the mean time i would like to ask... refer to diagram below, adapted from
http://cds.linear.com/docs/en/application-note/an18f.pdf (page 7). i havent put any load yet, just a 1Kohm R278. its functional correctly before as a 4.8X volt gain amplifier for few minutes until the power source Vr+ and Vr- (±50V)which are BJT (not shown in another sheet) in linear mode blew up. after 2nd replacement and retest, the power source blew up almost instantly. Q45 and Q56 are also taking some heat as solder paste i put on the metal tab melted a little bit during operation, Q44 and Q57 are not installed yet as this is only a test, i will desolder and check Q45 and Q56 after this for functional integrity...
in this query i would like to take attention to 4 diodes stack D46-D49,
is it possible due to higher volt differential to bias the push pull bjt, both Q45 and Q56 is shorting each other? the usual setup is 2 diodes stack to bias, but i use 4 diodes due to Q45,Q56 are darlington bjt. i measured using DMM diode mode, the volt drop Vbe of both darlington is about 0.79V each making both drop is about 1.58V, and Vdrop on all 4 diodes stack is about 1.3V, this should be safe ie no shorting of push pull, but during operation,
is it possible that Vbe drop on both NPN-PNP darlington reduced during temp rise and in effect shorting each other and worsen the situation? the questions are in bold, hope someone help, thanks.
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