Microamplifier Series Power Supply and Power Amp
Assembly Line Start-Up Procedure
GK# 420-0071 Power Supply Board #206-0071-C
Power Amp Boards 206-0064-D, and 206-0074-D, -75-D, and –76-D
6/7/90 Rev. 9/10/99-SW
Scope
This procedure is for bringing up Rev. C power supplies and Rev. D power amps for the assembly line. ( It can also be used for
troubleshooting and technical purposes.) This procedure is written with the board oriented in such a way so that the heat sink is on the bench
and the rear panel is facing from the technician, so that the channel on the technician’s left is labeled the Right Channel. There are various
combinations of units (heads and combos) that will be turned on with this procedure.
Preparation
Equipment. The equipment list includes a 35MHz oscilloscope connected to the output through the load box, a 100MHz scope and probe for
looking at the supply, a variac w/ current meter, a VOM, a Panasonic VP-7201A oscillator, a load box with toggle switches and monitoring
features for 2 each 4 ohm and 8 ohm loads, and an 8.2 ohm load on a ¼” jack.
Line Jumper. For 117V and 100V operation, the jumper on JU528 should be towards the rear panel. For 230V operation, this jumper should
be away from the rear panel.
Transformer Jumpers. For 117V and 230V operation, JU524 and JU527 should be towards the right side of the board. For 100V operation,
they should be towards the left side as noted on the silkscreen.
Power Amp Output Jumpers. The power amp is provided with jumpers that disconnect the output transistor emitters. Move them when
there is a power amp problem- there will be no output current. The unit should then have the emitters connected unless there is a problem. To
disconnect them, move P612A, P655A, and P683A away from the rear panel and P602A towards the center of the board.
Floating Instruments. All instruments, including the oscilloscope, must float with respect to the chassis. Use a three-pronged adapter for this
purpose, and also float the loads.
NOTE: The voltages listed in this procedure are for a 117V ac line.
CAUTION
Primary common (transformer T523/7) floats at –160Vdc with respect to the chassis and must be distinguished from
the secondary common, which is referenced to the chassis. Never look at primary and secondary voltages
simultaneously on the same scope or a scope that is referenced to earth, but always check that loads are floating when
looking at the primary. The following procedures do not require monitoring primary voltages. If it is necessary to do
so, the scope must be floating and referenced to primary common. Do NOT touch the primary, which is 640V square
wave at 100KHz, and readily burns flesh.
Power Supply Start Up
Visual Check
Position the unit with the heat sink on the bench and the rear panel away from you. Check that all the jumpers are in the proper positions, as
described above. Visually check the solder connections near the center of the board. The components to check are (parentheses denote parts
not applicable for mono): Q823, 824, 827, 808, 783, (Q782 and 758), Q759, VR601 and VR602. Also check Q742 for a build-up of solder
flux. Inspect the board edges for holes not filled with solder.
Scope Setup
Connect the 100MHz scope probe to the cathode of D537, which is the secondary for the main negative supply. Hook onto the left leg
between the body of the part and the board. Secondary common is available on the bottom of the rightmost of the two power supply 2200uF
filter caps on the power amp board, or on the topmost pin of the connector between the two boards. Also, the power supply shield and rear
panel may be used for common when the rear panel is assembled. Set the 100MHz scope to 20V/div and 2 usec/div, with zero at the
centerline.
