protect tripped after running awhile...
OK, there are several possibilities, starting with a weak protection relay driver transistor (heat related?), through having the dreaded 2sc1451 (and 2sa726) transistor(s) in your amplifier.
I didn't want to confuse the situation earlier. I now regret not telling you to get them too, at the same time, for future need.
The bright side is, that as far as problematic transistors go, with the addition of a pair of 2sa725's in the control amp (like in the phono amp) that's all the transistors that get dicey over time. Toss in (out really) the few sky blue Sanyo caps and only age related effects of things drying out (small or cooked electrolytic caps - transistor thermal paste etc) are working against you.
2sa725,2sa726 are replaced by the ksa992's
the Q7 relay driver transistor 2sc1384:
512-KSC2690AYS to-126 ecb 120/a160 1.2a 20w 155mhz 35-320hfe $0.40
(q6 a 2sc945 could be replaced by:
512-KSD1616AGBU to-92 ecb 60v 1a 0.75w 160mhz 135-400hfe $0.09
while you're in there and get a 1n4004 diode
512-1n4004 to add on across the relay coil to protect Q7 in the future)
the 2sc1451's:
512-KSC3503estu to-126 ecb 300v .1a 1.2/7w 150mhz 40-320hfe $0.28 ea
for now, just see if heating / cooling the relay driver transistor Q7 on the awm-062 board cures the protection trip if the offset voltage is ok, which it probably is, it takes quite a bit of offset to trip...
I'm a little confused with this last post from you above...
Those trouble transistors have already been replaced (except for pair on the control board)
This is my progress of components changed so far...(as of 2/10/11)
amp board (awh-030)
Q1, Q2, Q3, Q4, Q5, Q6, Q7, Q8, Q9, Q10, Q11, Q12
C1, C2, C3, C4, C5, C6, C11, C12
protection board (awm-062)
Q6, Q7
C1, C2, C3, C4, C5, C6
1n4004 diode across pins 9 and 10
control amp bd (awg-027)
Q1, Q2 (I put back the orig. 2SA725's because I only had enough
left to replace the ones in the EQ board at the time.)
EQ - Phono board (AWF-013)
Q1, Q2, Q3, Q4
Q5, Q6, Q7, Q8
and all the Electrolytic caps
---------------------------------------------------
NOTE: the only two remaining 2sa725/726 are Q1 & Q2 on the ctrl board.
I am not completely sure my offset voltage/idle current is ok, I will check carefully again tonight.
Are you saying in the last sentence of your post to simply run the unit for awhile (heating up) and then turn off, let rest (cooling down) and see if it stops going into protect ? like a break-in period ?