Carver M1.5 Service Manual

Page 1

CARVER

M-1.5
MAGNETIC FIELD POWER AMPLIFIER

SERVICE MANUAL
INCLUDING SCHEMATICS
FOR THE M-1.5t

Page 2

M~1.5 SERVICE GUIDE

Table of Contents

Page
Introduction ............ . ............ . ................ . ..... 1
Amplifier Card Circuit Description ,,,,,,,,_,_,__,,,,,..,,,,. 2
Power Supply Circuit Description Introduction .,,, . ...... , 5
Primary Regulator Card .................. ....... . ........ 5
Main Supply Board ............. ..... .......... ..... ...... 6
Display Board Operation ................... ...... ....... ..... 9
Table l . ......... . ..... . ............... .. ............. .. 10
Test Procedure Equipment List ................... ....... ..... 11
Test Procedure Presets ..... ..... ....... ........... .......... 12
Test Procedure .......................... .... ........... 13
Troubleshooting Guide
Introduction ....... ... .............. ........ .......... 17
I. No Power (all LEDs fail to light) ...... . ...... ..... 17
II. Fault LED lights when power is applied ............. 18
III. DC-Offset ............ ..... . ...... . ........ .. ..... .. 19
IV. Over-current, high frequency shutdown
is activated .... ..... ...... ..... ................... 20
V. Over-voltage sensor is activated ...... ............. 20

VI. Excessive current draw before triac fires .......... 21
VII. Excessive current draw after triac fires ...... ..... 21
VIII. Early clipping on one side of waveform . ..... ....... 22
IX. Clips early, both channels ......................... 23
X. Clipping eliminator not working .................... 24
XI. Excessive noise ..... ............. .... .............. 24
XII. Excessive turn-off thumps ..... ..... ..... ...... ..... 24

XIII. Figure Index ..... .... .......... ....... ...... ....... 25

Page 10

M-l.5 CIRCUIT DESCRIPTION Page 8

Q2. This biases Q2 on and turns the amplifier off. Over-voltage
shutdown should occur between +130 and +140V.

Over-current and high-frequency shutdown signals from the amplifier
cards are sensed by Q1. when Ql is biased on, the base of Q2 will
exceed 1.3V and the amplifier will shut down.

An integrator shutdown" circuit is provided for additional
speaker protection. The output of the right and left channels is
rectified and summed by D2 and D3. This voltage is averaged over
approximately 3 minutes by the integrator network of R8 and C4.
If the output exceeds 35V rms for too long a period, the amplifier
is either clipping,or extremely-low dynamic material is being
played at too high a level. Both of these conditions will damage
speakers and need to be avoided. The rate of charge on C4 is
determined by the output level of the right and left channels.
When C4 is sufficiently charged to raise the base of Q2 above
1.3V, the amplifier will shut down. This circuit allows full

dynamic range, yet limits long-term average output.

DC offset and excessive low-frequency differences are sensed by

a low-pass differential amplifier (ICl Pins 1, 2, and 3). C6

and C7 roll off the output in the audio spectrum while dc offset
and single-channel, low-frequency signals (below 5 Hz) will be
amplified. If Pin 3 goes positive, Q2 will be biased on when its
base reaches 1.3V, turning the amplifier off. If Pin 3 goes
negative, the base of Q3 will be pulled down. If pulled down to
less than 0V, Q2 will turn on shutting the amplifier off.

The positive and negative 12V supplies are summed by R57 and R56,
and compared by 02 and Q3. If the negative 12V supply fails, the
cathode of D6 will go positive, raising the voltage on the base

of 02 above 1.3V which will turn the amplifier off. If the positive