Audio Output, Troubleshooting Stability Feedback
HIGH FREQUENCY OSCILLATIONS
SEVERE-DRAWS CURRENT-GROSS DISTORTION
C27 (62) missing or wrong, or series R367 (368)
C 25, 26 (60, 61) missing
Secondary filter capacitors missing or open (unlikely that ALL are defective).
SEVERE, BUT DOES NOT DRAW LARGE CURRENT
R22 (146) open.
MARGINAL -- MAY APPEAR ONLY AS EXCESS DISTORTION
Cl4 (49) missing
Cl 6 (50) missing or too large
C28 (63) missing
C 25 or 26 (60 or 61) missing or too large
Cl95 or 196 missing (input board).
EXCESSIVE OSCILLATION JUST BELOW CLIPPING, 2-4 ohms
Cl 7 (52) missing
NOTE: about 0.1% oscillation right below clipping at 2 ohms is normal.
EXCESSIVE SWITCHING INTERFERENCE.
Switching interference may LOOK like an instability, however it is at a much lower frequency
(1lOkH.z)
than
most instabilities. It will be more visible at low frequencies
(2OOHz)
and at lower impedances.
Missing jumper at
R224.
Missing
Cl29,
134 on output board.
Grounds not connected to chassis at output board and front chassis mounting screw.
FEEDBACK PROBLEMS: GAIN INCORRECT
Gain of output stage set by
R23,
31 (147, 153)
Gain of Ch 1 volume control buffer stage set by RI
1,
16.
Gain of Ch 2 volume control buffer stage set by
Rl37,
139. Make sure
Q48
is turned on
-
grounding
RI37
at Q48 should not affect gain. Check RI 32 (drives Q48).
Gain of balanced input is set by 4 matched resistors
R9,
8, 12, 13 (129, 130, 135, 136). Confirm both sides
of balanced input are working. Check
R5,
6 (123, 124).
Audio Output, Troubleshooting Clipping, Limiting
EXCESS STICKING (TOO MUCH DISTORTION DURING CLIP LIMITING)
Cl4 (49) much too large (also causes increased high frequency distortion).
R38 (161) missing.
R38-39
(161-162) have wrong values.
Q9,
10 (54, 55) missing
R34 (157) or
R35
(158) missing
Q8
(53) missing
18
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