Kramer Electronics VM-24HC User Manual

KRAMER ELECTRONIC S LTD.

USER MANUAL

MODEL:

VM-2 4H C

2 Input 1:4 HDMI Distributor

P/N: 2900-000717 Rev 3

VM-24HC – Contents

i

Contents

1 Introduction 1
2 Getting Started 2

2.1 Achieving the Best Performance 2

2.2 Safety Instructions 3

2.3 Recycling Kramer Products 3

3 Overview 4

3.1 Defining the VM-24HC 2 Input 1:4 HDMI Distributor 5

4 Connecting the VM-24HC 6
5 Using the VM-24HC 2 Input 1:4 HDMI Distributor 8

5.1 Selecting an Active Input 8

5.2 Connecting a PC/Controller via RS-232 8

5.3 Acquiring the EDID 9

6 Technical Specifications 11
7 Default Communication Parameters 12
8 Default EDID 13
9 Protocol 2000 15

9.1 Syntax 15

9.2 Instruction Codes 16

Figures

Figure 1: VM-24HC 2 Input 1:4 HDMI Distributor 5
Figure 2: Connecting the VM-24HC 2 Input 1:4 HDMI Distributor 7

VM-24HC - Introduction

1

1 Introduction

Welcome to Kramer Electronics! Since 1981, Kramer Electronics has been
providing a world of unique, creative, and affordable solutions to the vast range of
problems that confront video, audio, presentation, and broadcasting professionals
on a daily basis. In recent years, we have redesigned and upgraded most of our
line, making the best even better!

Our 1,000-plus different models now appear in 11 groups that are clearly defined
by function: GROUP 1: Distribution Amplifiers; GROUP 2: Switchers and Routers;
GROUP 3: Control Systems; GROUP 4: Format/Standards Converters; GROUP 5:
Range Extenders and Repeaters; GROUP 6: Specialty AV Products; GROUP 7:
Scan Converters and Scalers; GROUP 8: Cables and Connectors; GROUP 9:
Room Connectivity; GROUP 10: Accessories and Rack Adapters and GROUP 11:
Sierra Products.

Congratulations on purchasing your Kramer VM-24HC 2 Input 1:4 HDMI
Distributor, which is ideal for the following typical applications:

 Home theater, presentation and multimedia applications
 Rental and staging

2

VM-24HC - Getting Started

Go to http://www.kramerelectronics.com/support/product_downloads.asp
to check for up-to-date user manuals, application programs, and to check if
firmware upgrades are available (where appropriate).

This equipment is to be used only inside a building. It may only be
connected to other equipment that is installed inside a building.

i

!

2 Getting Started

We recommend that you:

 Unpack the equipment carefully and save the original box and packaging

materials for possible future shipment

 Review the contents of this user manual

2.1 Achieving the Best Performance

To achieve the best performance:

 Use only good quality connection cables (we recommend Kramer high-

performance, high-resolution cables) to avoid interference, deterioration in
signal quality due to poor matching, and elevated noise levels (often
associated with low quality cables)

 Do not secure the cables in tight bundles or roll the slack into tight coils
 Avoid interference from neighboring electrical appliances that may adversely

influence signal quality

 Position your Kramer VM-24HC away from moisture, excessive sunlight and

dust

VM-24HC - Getting Started

3

Caution:

There are no operator serviceable parts inside the unit

Warning:

Use only the Kramer Electronics input power wall
adapter that is provided with the unit

Warning:

Disconnect the power and unplug the unit from the wall
before installing

!

2.2 Safety Instructions

2.3 Recycling Kramer Products

The Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC
aims to reduce the amount of WEEE sent for disposal to landfill or incineration by
requiring it to be collected and recycled. To comply with the WEEE Directive,
Kramer Electronics has made arrangements with the European Advanced
Recycling Network (EARN) and will cover any costs of treatment, recycling and
recovery of waste Kramer Electronics branded equipment on arrival at the EARN
facility. For details of Kramer’s recycling arrangements in your particular country
go to our recycling pages at http://www.kramerelectronics.com/support/recycling/.

4

VM-24HC - Overview

3 Overview

The VM−24HC is a high−performance switcher and distribution amplifier for HDMI
signals. The unit accepts one of two HDMI inputs and distributes the selected
signal to four HDMI outputs simultaneously.

The VM-24HC features:

 A maximum data rate of 6.75Gbps (2.25Gbps per graphics channel)
 HDTV compatibility
 HDCP compliance
 I-EDIDPro™ Kramer Intelligent EDID Processing™, an intelligent EDID

handling & processing algorithm ensures Plug and Play operation for HDMI
systems

 EDID handling that acquires the EDID from one output, from all connected

outputs (auto−mix) or uses a default EDID

 Kramer Equalization & re-Klocking™ Technology that rebuilds the digital

signal to travel longer distances

 HDMI support for Deep Color, x.v.Color™, up to 7.1 Uncompressed Audio

Channels

 3D Pass-Through
 Flexible control options via front panel, IR remote & RS−232
 Compact desktop size where two units can be rack mounted side−by−side in

a 1U rack space with the optional RK−1 adapter

VM-24HC - Overview

5

#

Feature

Function

1

IR Receiver

IR signal sensor for the IR remote control

2

IR LED

Lights yellow when the device receives an IR signal

3

POWER LED

Lights green when the device receives power

4

EDID READ Button

Press to acquire the EDID following selecting the EDID
source. Press again to indicate the EDID status

5

EDID SELECT Button

Press to select the EDID source (single output, Auto­Mix or default)

6

OUTPUT LEDs (1 to 4)

Lights green when an output is connected and active.
LED flashes to indicate the source of the EDID
acquired (see Section 5.3) or when connecting a
non-HDCP display while providing HDCP content to
the VM-24HC

7

INPUT SELECTOR Button

Press to select Input 1 or 2 (see Section 5.1)

8
IN 1 LED

Lights green when Input 1 is selected

IN 2 LED

Lights green when Input 2 is selected

9

INPUT 1 and INPUT 2 HDMI
Connectors

Connect to the HDMI sources 1 and 2

10

OUTPUT 1 to OUTPUT 4
HDMI Connectors

Connect to the HDMI acceptors 1 to 4
11

RS-232 9-pin D-sub Port

Connects to a PC/remote controller (see Section 5.1)

12

5V DC Power Connector

Connects to the power adapter, center pin positive

3.1 Defining the VM-24HC 2 Input 1:4 HDMI Distributor

This section defines the VM-24HC.

Figure 1: VM-24HC 2 Input 1:4 HDMI Distributor

6

VM-24HC - Connecting the VM-24HC

Always switch off the power to each device before connecting it to your
VM-24HC. After connecting your VM-24HC, connect its power and
then switch on the power to each device.

i

4 Connecting the VM-24HC

To connect the VM-24HC as illustrated in the example in Figure 2:

1. Connect the two HDMI sources, for example, a DVD player and a set top
box to the INPUT 1 and INPUT 2 connectors, respectively.

2. Connect the HDMI OUTPUT connectors to up to 4 HDMI acceptors. In this
example, connect:

Not all outputs need be connected.

 OUTPUT 1 to display device 1 (for example, an LCD TV)
 OUTPUT 2 to display device 2 (for example, an LCD TV)
 OUTPUT 3 to display device 3 (for example, an LCD TV)
 OUTPUT 4 to display device 4 (for example, a plasma display)

3. If required, connect a PC and/or controller to the RS-232 port (see

Section 5.1).

4. Connect the power adapter to the device and to the mains electricity (not
shown in Figure 2).

5. If required, acquire the EDID (see Section 5.3).

VM-24HC - Connecting the VM-24HC

7

Figure 2: Connecting the VM-24HC 2 Input 1:4 HDMI Distributor

8

VM-24HC - Using the VM-24HC 2 Input 1:4 HDMI Distributor

5 Using the VM-24HC 2 Input 1:4 HDMI

Distributor

The VM-24HC always displays the video output on all of the four outputs at the
same time (once they are ready to display the output) upon power up and when
switching an input (from IN 1 to IN 2 and vice versa).

This section describes:

 Selecting an Active Input (see Section 5.1)
 Connecting a PC/Controller via RS-232 (see Section 5.2)
 Acquiring the EDID (see Section 5.3)

5.1 Selecting an Active Input

but we need a note somewhere in there stating the video output will be displayed
simultaneously upon power up or introduction of new video once all output ports
are ready

To select an active input:

 Press the INPUT SELECTOR button to toggle between inputs 1 and 2

5.2 Connecting a PC/Controller via RS-232

You can connect a PC or serial controller to the VM-24HC using the RS-232
connection. Note that a null-modem adapter/connection is not required.

To connect to the VM-24HC via RS-232:

 Connect the RS-232 9-pin D-sub rear panel port on the VM-24HC unit via a

9-wire straight cable (only pin 2 to pin 2, pin 3 to pin 3, and pin 5 to pin 5
need to be connected) to the RS-232 9-pin D-sub port on your PC/controller

VM-24HC - Using the VM-24HC 2 Input 1:4 HDMI Distributor

9

5.3 Acquiring the EDID

Initially the VM-24HC operates with the factory default EDID stored in the non­volatile memory. The source reads the EDID from the device when the device is
plugged in or powered on.

This is usually done only once when the unit is being set up in an installation. Once acquired,
the EDID is saved in non-volatile memory and further acquisition is not necessary.

The VM-24HC reads the EDID, which is stored in the non-volatile memory.

The EDID can be acquired from:

 One output
 The default EDID
 Up to four connected outputs using the Auto-mix Mode

The EDID acquired is a weighted average of all the connected outputs. For example, if
several displays with different resolutions are connected to the outputs, the acquired
EDID supports all the resolutions, as well as other parameters included in the EDID.

Repeatedly pressing the EDID SELECT button cycles through the EDID sources in
the following order:

If you attempt to acquire the EDID from an output that is not connected the default EDID is
acquired.

 Output 1 (Output 1 LED lights)
 Output 2 (Output 2 LED lights)
 Output 3 (Output 3 LED lights)
 Output 4 (Output 4 LED lights)
 Default EDID (all LEDs light)
 Auto-Mix EDID (the LEDs flash in a running sequence)

To store the selected EDID, press EDID READ as described in the following
example.

To cancel the EDID modification wait for a few seconds without touching any button.

To select the EDID from Output 3:

1. Press the EDID SELECT button repeatedly until OUTPUT 3 LED lights.

10

VM-24HC - Using the VM-24HC 2 Input 1:4 HDMI Distributor

2. Press the EDID READ button.
When the LED stops flashing the EDID from Output 3 is stored at the input.

Pressing the EDID SELECT button briefly once causes the relevant LEDs to
indicate which EDID is stored at the input as follows:

 OUTPUT 1 LED flashes—the EDID from OUTPUT 1 was the last acquired
 OUTPUT 2 LED flashes—the EDID from OUTPUT 2 was the last acquired,

and so on

 All OUTPUT LEDs light—the default EDID was the last acquired
 All OUTPUT LEDs flash sequentially—the Auto-Mix EDID was the last

acquired

VM-24HC - Technical Specifications

11

INPUTS:

2 HDMI connectors

OUTPUTS:

4 HDMI connectors

BANDWIDTH:

Supports up to 2.25Gbps bandwidth per graphic channel

COMPLIANCE WITH HDMI
STANDARD:

Supports HDMI and HDCP

CONTROLS:

EDID SELECT, EDID READ, IN 1, IN 2 buttons, RS-232,
IR

INDICATOR LEDs:

POWER, IR, OUTPUT

POWER CONSUMPTION:

5V DC, 1.1A

OPERATING TEMPERATURE:

0° to +40°C (32° to 104°F)

STORAGE TEMPERATURE:

-40° to +70°C (-40° to 158°F)

HUMIDITY:

10% to 90%, RHL non-condensing

DIMENSIONS:

21.5cm x 16.3cm x 4.4cm (8.5” x 6.4” x 1.7”) W, D, H

WEIGHT:

0.6kg (1.3lbs) approx.

ACCESSORIES:

Power supply

OPTIONS:

RK-1 19” rack adapter

Specifications are subject to change without notice at http://www.kramerelectronics.com

6 Technical Specifications

12

VM-24HC - Default Communication Parameters

EDID

EDID data is passed between Output 1 and Input 1

RS-232

Protocol 2000

Baud Rate

9600

Data Bits

8

Stop Bits

1

Parity

None

Command Format

HEX

Example (Output 1 to Input 1)

0x01, 0x81, 0x81, 0x81

7 Default Communication Parameters

VM-24HC - Default EDID

13

8 Default EDID

Monitor

Model name............... VM24HC

Manufacturer............. KRM

Plug and Play ID......... KRM0023

Serial number............ 505-707455010

Manufacture date......... 2009, ISO week 10

Filter driver............ None

-------------------------

EDID revision............ 1.3

Input signal type........ Digital

Color bit depth.......... Undefined

Display type............. RGB color

Screen size.............. 520 x 320 mm (24.0 in)

Power management......... Standby, Suspend, Active off/sleep

Extension blocs.......... 1 (CEA-EXT)

-------------------------

DDC/CI................... n/a

Color characteristics

Default color space...... Non-sRGB

Display gamma............ 2.20

Red chromaticity......... Rx 0.674 - Ry 0.319

Green chromaticity....... Gx 0.188 - Gy 0.706

Blue chromaticity........ Bx 0.148 - By 0.064

White point (default).... Wx 0.313 - Wy 0.329

Additional descriptors... None
Timing characteristics

Horizontal scan range.... 30-83kHz

Vertical scan range...... 56-76Hz

Video bandwidth.......... 170MHz

CVT standard............. Not supported

GTF standard............. Not supported

Additional descriptors... None

Preferred timing......... Yes

Native/preferred timing.. 1280x720p at 60Hz (16:10)

Modeline............... "1280x720" 74.250 1280 1390 1430 1650 720 725 730 750 +hsync +vsync

Standard timings supported
720 x 400p at 70Hz - IBM VGA
640 x 480p at 60Hz - IBM VGA
640 x 480p at 75Hz - VESA
800 x 600p at 60Hz - VESA
800 x 600p at 75Hz - VESA
1024 x 768p at 60Hz - VESA
1024 x 768p at 75Hz - VESA
1280 x 1024p at 75Hz - VESA
1280 x 1024p at 60Hz - VESA STD
1600 x 1200p at 60Hz - VESA STD
1152 x 864p at 75Hz - VESA STD

EIA/CEA-861 Information

Revision number.......... 3

IT underscan............. Supported

Basic audio.............. Supported

YCbCr 4:4:4.............. Supported

YCbCr 4:2:2.............. Supported

Native formats........... 1

Detailed timing #1....... 1920x1080p at 60Hz (16:10)

Modeline............... "1920x1080" 148.500 1920 2008 2052 2200 1080 1084 1089 1125 +hsync +vsync

Detailed timing #2....... 1920x1080i at 60Hz (16:10)

Modeline............... "1920x1080" 74.250 1920 2008 2052 2200 1080 1084 1094 1124 interlace +hsync

+vsync

Detailed timing #3....... 1280x720p at 60Hz (16:10)

Modeline............... "1280x720" 74.250 1280 1390 1430 1650 720 725 730 750 +hsync +vsync

Detailed timing #4....... 720x480p at 60Hz (16:10)

Modeline............... "720x480" 27.000 720 736 798 858 480 489 495 525 -hsync -vsync

14

VM-24HC - Default EDID

CE video identifiers (VICs) - timing/formats supported
1920 x 1080p at 60Hz - HDTV (16:9, 1:1)
1920 x 1080i at 60Hz - HDTV (16:9, 1:1)
1280 x 720p at 60Hz - HDTV (16:9, 1:1) [Native]
720 x 480p at 60Hz - EDTV (16:9, 32:27)
720 x 480p at 60Hz - EDTV (4:3, 8:9)
720 x 480i at 60Hz - Doublescan (16:9, 32:27)
720 x 576i at 50Hz - Doublescan (16:9, 64:45)
640 x 480p at 60Hz - Default (4:3, 1:1)
NB: NTSC refresh rate = (Hz*1000)/1001

CE audio data (formats supported)
LPCM 2-channel, 16/20/24 bit depths at 32/44/48 kHz

CE vendor specific data (VSDB)
IEEE registration number. 0x000C03

CEC physical address..... 1.0.0.0

Maximum TMDS clock....... 165MHz

CE speaker allocation data

Channel configuration.... 2.0

Front left/right......... Yes

Front LFE................ No

Front center............. No

Rear left/right.......... No

Rear center.............. No

Front left/right center.. No
Rear left/right center... No

Rear LFE................. No

Report information

Date generated........... 08-Dec-11

Software revision........ 2.60.0.972

Data source.............. File

Operating system......... 5.1.2600.2.Service Pack 3

Raw data
00,FF,FF,FF,FF,FF,FF,00,2E,4D,23,00,01,01,01,01,0A,13,01,03,80,34,20,78,EA,B3,25,AC,51,30,B4,26,
10,50,54,A5,4B,00,81,80,A9,40,71,4F,01,01,01,01,01,01,01,01,01,01,01,1D,00,72,51,D0,1E,20,6E,28,
55,00,07,44,21,00,00,1E,00,00,00,FF,00,35,30,35,2D,37,30,37,34,35,35,30,31,30,00,00,00,FC,00,56,
4D,32,34,48,43,20,20,20,20,20,20,0A,00,00,00,FD,00,38,4C,1E,53,11,00,0A,20,20,20,20,20,20,01,B7,
02,03,1B,F1,48,10,05,84,03,02,07,16,01,23,09,07,07,65,03,0C,00,10,00,83,01,00,00,02,3A,80,18,71,
38,2D,40,58,2C,45,00,07,44,21,00,00,1E,01,1D,80,18,71,1C,16,20,58,2C,25,00,07,44,21,00,00,9E,01,
1D,00,72,51,D0,1E,20,6E,28,55,00,07,44,21,00,00,1E,8C,0A,D0,8A,20,E0,2D,10,10,3E,96,00,07,44,21,
00,00,18,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,00,47

VM-24HC - Protocol 2000

15

MSB

LSB

1st Byte

DESTINATION

INSTRUCTION

0 D N5

N4

N3

N2

N1

N0 7 6 5 4 3 2 1 0

2nd Byte

INPUT

1

I6

I5

I4

I3

I2

I1

I0 7 6 5 4 3 2 1 0

3rd Byte

OUTPUT

1

O6

O5

O4

O3

O2

O1

O0 7 6 5 4 3 2 1 0

4th Byte

MACHINE NUMBER

1

OVR X M4

M3

M2

M1

M0 7 6 5 4 3 2 1 0

9 Protocol 2000

This RS-232/RS-485 communication protocol uses four bytes of information as
defined below.

For RS-232, a null-modem connection between the machine and controller is
used. The default data rate is 9600 baud, with no parity, 8 data bits and 1 stop bit.

Note: Compatibility with Kramer’s Protocol 2000 does not mean that a machine
uses all of the commands below. Each machine uses a sub-set of Protocol 2000,
according to its needs.

9.1 Syntax

1st Byte: Bit 7 – Defined as 0

The 6-bit INSTRUCTION defines the function performed by the switcher(s). If a function is performed using the

machine’s keyboard, these bits are set with the INSTRUCTION NO. performed. The instruction codes are defined
according to the table below (INSTRUCTION NO. is the value set in N5…N0).

2nd Byte: Bit 7 – Defined as 1
I6…I0 – INPUT
When switching (i.e. instruction codes 1 and 2), the 7-bit INPUT is set as the input number to be switched. If switching is

done using the machine’s front panel, these bits are set with the INPUT NUMBER switched. For other operations, these

bits are defined according to the table.
3rd Byte: Bit 7 – Defined as 1

O6…O0 – OUTPUT
When switching (i.e. instruction codes 1 and 2), the 7-bit OUTPUT is set as the output number to be switched. If

switching is done using the machine’s front panel, these bits are set with the OUTPUT NUMBER switched. For other

operations, these bits are defined according to the table.
4th Byte: Bit 7 – Defined as 1

Bit 5 – Don’t care
OVR – Machine number override
M4…M0 – MACHINE NUMBER
This byte is used to address machines in a system by their machine numbers. When several machines are controlled
from a single serial port, they are usually configured together and each machine has an individual machine number. If
the OVR bit is set, then all machine numbers accept (implement) the command and the addressed machine replies.
When a single machine is controlled over the serial port, always set M4…M0 to 1, and make sure that the machine itself
is configured as MACHINE NUMBER = 1.

D – DESTINATION:

N5…N0 – INSTRUCTION

0 – Sends information to the switchers (from the PC)
1 – Sends information to the PC (from the switcher)

16

VM-24HC - Protocol 2000

Instruction Codes for Protocol 2000

Instruction

Definition for Specific Instruction

Notes # Description

Input

Output

1

SWITCH VIDEO

Set equal to video input that
is switched
(0 = disconnect)

Set equal to video output that is
switched
(0 = to all the outputs)

2, 15
31

REQUEST WHETHER
PANEL IS LOCKED

0 0 16

61

IDENTIFY MACHINE

1 – Video machine name
2 – Audio machine name
3 – Video software version
4 – Audio software version
5 – RS-422 controller name
6 – RS-422 controller version
7 – Remote control name
8 – Remote software version
9 – Protocol 2000 revision
10 – Control data machine
name
11 – Control data software
version

For names:
0 – Request first 4 digits
1 – Request first suffix
2 – Request second suffix
3 – Request third suffix
10 – Request first prefix
11 – Request second prefix
12 – Request third prefix

For versions:
0 – main board
or the number of external board

13

62

DEFINE MACHINE

1 – Number of inputs
2 – Number of outputs
3 – Number of setups

1 – For video
2 – For audio
3 – For SDI
4 – For remote panel
5 – For RS-422 controller
6 – For control data

14

9.2 Instruction Codes

All the values in the table are decimal, unless otherwise stated

NOTES on the above table:
NOTE 2 – These are bi-directional definitions. If the switcher receives the code, it performs the instruction. If the

instruction is performed (due to a keystroke operation on the front panel), then these codes are sent.
For example, if the PC sends HEX code:
01 85 88 83
then the switcher (machine 3) switches input 5 to output 8.
If the user switches input 1 to output 7 using the front panel buttons, the switcher sends HEX code:
41 81 87 83
to the PC.
When the PC sends one of the commands in this group to the switcher, if the instruction is valid, the switcher replies by
sending the same four bytes to the PC that it received (except for the first byte, where the DESTINATION bit is set high).

NOTE 13 – This is a request to identify the switcher/s in the system. If the OUTPUT is set as 0, and the INPUT is set as
1, 2, 5 or 7, the machine sends its name. The reply is the decimal value of the INPUT and OUTPUT.
For example, for a 2216, the reply to the request to send the audio machine name is HEX code:
7D 96 90 81 (i.e. 128

If the request for identification is sent with the INPUT set as 3 or 4, the appropriate machine sends its software version
number. Again, the reply would be the decimal value of the INPUT and OUTPUT - the INPUT representing the number
in front of the decimal point, and the OUTPUT representing the number after it.
For example, for version 3.5, the reply to the request to send the version number would be HEX code:
7D 83 85 81 (i.e. 128

If the OUTPUT is set as 1, then the ASCII coding of the lettering following the machine’s name is sent.
For example, for the VS-7588YC, the reply to the request to send the first suffix would be HEX code:
7D D9 C3 81 (i.e. 128

NOTE 14 – The number of inputs and outputs refers to the specific machine being addressed, not to the system.
For example, if six 16x16 matrices are configured to make a 48x32 system (48 inputs, 32 outputs), the reply to the HEX
code:
3E 82 81 82 (i.e. request the number of outputs)
would be HEX code:
7E 82 90 82 (i.e. 16 outputs).

NOTE 15 – When the OVR bit (4th byte) is set, then the video commands have universal meaning.
For example, instruction 1 (SWITCH VIDEO) causes all units (including audio, data, etc.) to switch. Similarly, if a
machine is in FOLLOW mode, it performs any video instruction.

NOTE 16 – The reply to the REQUEST WHETHER PANEL IS LOCKED is the same as in NOTE 4 above, except that
OUTPUT is assigned with the value 0 if the panel is unlocked, or 1 if it is locked.

+ 22

for 2nd byte, and 128

dec

dec

+ 3

for 2nd byte, 128

dec

dec

+ ASCII for “Y”; 128

dec

+ 5

dec

+ ASCII for “C”).

dec

+ 16

dec

dec

for 3rd byte).

dec

for 3rd byte).

For the latest information on our products and a list of Kramer distributors,
visit our Web site where updates to this user manual may be found.

We welcome your questions, comments, and feedback.

Web site: www.kramerelectronics.com
E-mail: [e-mail]

P/N:

2900-000717

Rev:

3

!

SAFETY WARNIN G
Disconnect the unit from the power
supply before opening and servicing