The Philips VP415 Domesday LaserDisc player (as well as the VP410) uses a small module with in-built switches to control the loading and unloading of the disc tray. The original Philips design uses two small plastic switches that are custom designed for the board. The original design is a weak-point of the player and is prone to damage (especially if the player is transported). As the original switches are custom Philips parts, it’s not possible to simply repair or replace the switches when they get damaged.
This project provides a complete replacement for the front-loader module using industrial Omron micro-switches which provide a superior solution to the original in terms of robustness. The module is a drop-in replacement for the original and requires no alteration to the player.
The schematic for the front-loader replacement module is shown in the following diagram:
The design consists of 2 switches that detect when the tray is ready to be loaded and when the tray is loaded. In addition, a simple H-bridge provides power to the loader motor based on the LMOT-L (load direction) and LMOT-R (eject direction) signals. Additionally the H-bridge has a motor jam protection circuit that prevents damage to the H-bridge in the case where the tray becomes stuck. The replacement design also includes a 600mA PTC (self resetting fuse) to protect the module – this replaces the NFR protection resistor present on the original design.
The following picture show the overview of the PCB design:
The PCB is designed to be professionally produced as a two-layer board. The following specifications are recommended:
- Layers: 2
- PCB Thickness: 1.6mm
- PCB Colour: Green
- Surface Finish: HASL
- Copper Weight: 1oz
- Material Details: FR4-Standard Tg 140C
Bill of Materials
The required materials are shown in the following table:
|D101, D102||2||SS16||Diodes_SMD:D_SMA||Schottky diode|
|D103, D104, D105||3||1N4148W||Diodes_SMD:D_SOD-123||Diode|
|F101||1||600mA Polyfuse||Fuse_Holders_and_Fuses:Fuse_SMD2920||resettable fuse, polymeric positive temperature coefficient (PPTC)|
|J101||1||Drive Processor||Lumberg-25-MSF:Lumberg-25-MSF-08||Generic connector, single row, 01×08|
|J102||1||Loader Motor||Lumberg-25-MSF:Lumberg-25-MSF-03||Generic connector, single row, 01×03|
|Q101, Q102, Q103||3||BC848C||TO_SOT_Packages_SMD:SOT-23||45V Vce, 0.8A Ic, NPN, SOT-23|
|Q104, Q106||2||BC327-25||TO_SOT_Packages_THT:TO-92_Molded_Narrow||45V Vce, 0.1A Ic, PNP Small Signal Transistor, TO-92|
|Q107, Q105||2||BC337-25||TO_SOT_Packages_THT:TO-92_Molded_Narrow||45V Vce, 0.1A Ic, NPN, Small Signal Transistor, TO-92|
|R102, R104, R105||3||10K||Resistors_SMD:R_1206||Resistor|
|R107, R109, R108, R110||4||750R||Resistors_SMD:R_1206||Resistor|
|SW101, SW102||2||Omron D2HW-BR221DR||D2HW-BR221DR:D2HW-8BR221DR||Switch, single pole double throw|
The board is fitted to the player using the two original screws and washers located at the back-right of the upper-deck. The two mounting holes are elongated to allow the board to be moved; this causes the switches to activate sooner if required (by moving the board right) or later (by moving the board left). If the loader motor continues to rotate once the tray is ejected, move the board to the left slightly.
Before powering up the player to test, move the tray in and out manually and ensure that the board (and components) are clear of any moving parts of the loader mechanism.
Files for download
The KiCAD files for the replacement board can be found in the Github repository along with the Gerber files required for PCB manufacture: