HMV Model 328A

Interface Electronics and Lighting

The interface electronics resides in a narrow area down the right hand side of the Main Chassis.  This must clear the right hand side of the Blu-ray/DVD drive.  Additional brackets support the circuit boards.


Tapping into the Power Good signal and +5VSB
 
 

Computer Power Sense Board

Computer Power Sense Board
Computer Power Sense Board
 

This small board has several purposes in life.  It controls the Power and LED indicators.  It also controls the Power Relay, located in The Dog Box.  An opto isolator ouptut is used to control amplifier muting.



HOW IT WORKS

The Power LED is fed from the Computer Power Supply +5V rail via R6, which was chosen to match the brightness of the Message and HDD LEDs.

The Computer Power Supply +5VSB rail is permanently active even when the system is shut down and is used to power U1 - a quad comparator IC with open collector outputs (LM339).

U1B detects when the system is shut down by comparing the Computer Power Supply +12V rail voltage with the +5VSB rail voltage.  The output of U1B acts as a switch to control the Standby LED.  The LED brightness is determined by R5.

U1D detects when the system is on by looking at the Computer Power Supply +5V rail.  U1A detects mains failure by looking at the Computer Power Supply Power Good signal.  The open collector outputs of these two comparators are connected together and pull to ground when the +5V rail and/or Power Good signal goes low.

When the system is first powered up, a timer consisting of R11, C3 and U1C delays the activation of the Power Relay for approximately 1 second.

When the system is powered down or the mains drops out, U1D and/or U1A reset the timer by rapidly discharging C3 and the Power Relay is turned off instantly.  Once this happens, the timing cycle must complete before the Power Relay can be turned back on again.

The Power Relay drive circuitry is powered by the Computer Power Supply +12V rail via R16.  When the Power Relay is off, C4 is charged to +12V.  When the relay is first activated, full power is applied to the relay coil, due to the charge stored in C4.  The current through the coil at this instant is approximately 35mA.  Relays only require about one third of the current to remain closed after they are activated.  Due to R16, the current drops to approximately 20mA to conserve power.  R17 reduces the maximum current through the opto-isolator.

 
 

10 Channel LED Driver Board

10 Channel LED Driver Board
10 Channel LED Driver Board

This board drives the chassis and cabinet lighting.

Each channel is a switchable current source, capable of delivering up to 100mA.  A channel is switched on by grounding its input.  A PWM signal can be used to control the brightness of each channel.

The 10 Channel LED Driver Board is controlled by the LED Controller Board, described later.



The maximum current (IMAX) for each channel is chosen to suit the type of LEDS used in that channel and is set by resistor Rn03 as follows:
 
Rn03 = 0.6 / IMAX
Since the LED drivers are powered from the +12V computer rail, the maximum number of LEDS that can be wired in series on the same channel depends on the type of LED.  Red, orange and yellow LEDs usually have a forward voltage drop (VF) of around 2.2 - 2.5V and there can be up to 4 on the same channel.  On the other hand, green, blue, aqua and white LED's have a VF of around 3.3 - 3.5V, limiting the maximum to number to 3.
Assuming either 4x LEDs @ 2.2V or 3x LEDs @3.5V, this represents a regulator efficiency of around 73% to 88%.
For higher current channels, the minimum number of LEDs should also be considered.  For example, for a 70mA channel there should be a minimum of 3 LEDS to limit the heat dissipated in the driver transistor (Qn02).
The RGB HMV Logo has 3 LEDs for each colour.  By adjusting the relative brightness of the red, green and blue channels, it is possible to obtain almost any colour.  There is plenty of light for the HMV Logo and a set of trimpots accessible through holes in the rear of the Main Chassis are used to set the correct white balance with all 3 circuits running at 100%.

Main Chassis Wiring

The chassis power wiring was covered in Section 6 - Power Distribution.  Other Chassis wiring includes LEDs, connectors, switches, the Computer Motherboard, Computer Sense Board and 10 Channel LED Driver board.





Chassis Lights

 
Testing the work lights
Testing the work lights
 
Illuminated chassis viewed through dial cutout
Illuminated chassis viewed through dial cutout
 

Channels 1 and 2 of the 10 Channel LED Driver Board are used for the work lights and chassis lighting.

The main purpose for the work lights is to assist in connecting things to the computer and the rear chassis connectors.  In my long-term plan, the chassis illumination will only be seen from the back of the unit.  In the short term, until I find a suitable touch screen it will also be seen from the front through the cabinet cutout for the old tuning dial.

Both of these sets of lights also throw light onto the wall behind the unit and can be part of the overall lighting effect.

In addition, the Power LED (driven by the Computer Power Sense Board), the Message and HDD LEDs (driven directly by the computer motherboard) are mounted on the chassis but shine into the speaker enclosure area.

 
TESTING THE LED CIRCUITS
Dial Lamp Switch
In addition to being controlled by the LED Controller Board, the Work Lights and Chassis Illumination circuits (channels 1 & 2 of the 10 Channel LED Driver Board) can be turned on manually by the Dial Lamp Switch.
 
Circuit Test Jig
Temporary test jig for controlling the last 8 channels of the 10 Channel LED Driver Board manually without the LED Controller Board.  This can only switch individual channels on and off.
 
Gramophone in blue
Gramophone in blue

Cabinet Wiring Harness

 
 

All of the low voltage cabinet wiring is in one loom, connecting via a single DB25 connector (P3) to the Main Chassis.  I pre-made this loom, cut and shaped to fit the cabinet.  When the speaker enclosure area is sealed, it will not be removeable!  This includes wiring to:

  • Power Switch
  • Standby LED
  • Power Relay
  • Chassis Ground
  • HMV Logo board
  • Four connectors for the speaker enclosure area LEDs
  • Spare circuit



Cabinet Lights

The Standby LED (driven by the Computer Power Sense Board) is mounted directly on the cabinet in the chassis area but shines into the speaker enclosure area.

Ch 3-5 of the 10 Channel LED Driver Board are wired to a socket which connects to the HMV Logo Board inside the speaker enclosure area.

Ch 6-10 of the 10 Channel LED Driver Board are wired to 10-way 0.1" (2.54mm) receptacles, mounted in the 4 front corners of the speaker enclosure area and hidden from view.  These sockets are wired in series and up to 5 LEDs can be inserted into each of these sockets.  There can be up to 4 LEDs per channel only if they are red, orange or yellow.  For other colours where there can only be 3 LEDs per channel, the 4th position must be by-passed with a link.  Using this socket system allows LEDs to be easily changed and allows versatility in the final lighting setup.  If necessary, an individual LED could be relocated by plugging in a 2-pin header and extension cable.


Constructing the Cabinet Wiring Harness
Constructing the Cabinet Wiring Harness
HMV Logo Board
HMV Logo Board
Testing the speaker enclosure area circuits
Testing the speaker enclosure area circuits
 
HMV Logo in blue Testing the HMV Logo LEDs
Testing the HMV Logo LEDs with a paper printout to check light dispersion angles
 
Corner LED assembly
Corner
LED assembly
 

LED Designations

All LED's except the ones mounted on the HMV Logo Board are on sockets.  There are 36 high efficiency, high power (and high priced!) 5mm LEDs used in this project.

This is the current lineup:


Cct Description IMAX Rn03 LEDs
 1 Work Lights 27mA 22R
3x ZD-0280
 2 Chassis Illumination 27mA 22R
1x ZD-0284
1x ZD-0285
1x ZD-0178
 3 HMV Logo - R 5mA-50mA 112R -> 12R
3x ZD-0283
 4 HMV Logo - G 5mA-50mA 112R -> 12R
3x ZD-0282
 5 HMV Logo - B 5mA-50mA 112R -> 12R
3x ZD-0281
 6 Speaker Rear - R 67mA 09R
4x ZD-0283
 7 Speaker Rear - G 50mA 12R
3x ZD-0282
 8 Speaker Rear - B (Cree) 27mA 22R
3x ZD-0291
 9 Speaker Rear - W + B 50mA 12R
2x ZD-0280
1x ZD-0281
10 Speaker Front 67mA 9R
4x ZD-0284
- Standby Indicator 1.5mA -
1x ZD-0285
- Power Indicator 10mA -
1x ZD-0282
- Message Indicator - -
1x ZD-0284
- HDD Indicator - -
1x ZD-0283