Modifying a Pioneer SP-99D AC-3 processor with TOSLINK digital out

During the later years of Laserdisc in 1995, Pioneer started releasing Laserdiscs with AC-3 sound capability.  This meant you could get 5.1 surround sound on newer movies, as long as your player supported it and you could feed the audio signal into a demodulator or processor.

The big difference between processors and demodulators are the capabilities and how they output their signal to a receiver.  Demodulators normally have an input for AC-3 via a coax connection and sometimes will have an input for TOSLINK(SPDIF) optical.  From there, the demodulator processes the signals and outputs them via a single cable to a receiver whether that be coax or optical.

 

Example of a demodulator - Pioneer RFD-1

Processors, however, would normally output their sound via 6 discrete cables.  On receivers, these are sometimes referred to as Multi Channel In.  The 6 channels are Front Left, Center, Front Right, Subwoofer, Surround Left and Surround Right.  This is all well and good if you have an older receiver capable of accepting 5.1 multi channel in, but modern receivers no longer come equipped with this input.

 

Example of 5.1 Output on Pioneer SP-99D

From my own experience, the Multi Channel Input on receivers is not adjustable to add or remove a delay on the signal.  This can cause audio and video sync issues with your television.    The solution I have found is to install a TOSLINK or SPDIF output on processors that only output via 6-channel analog.

In this post, I will detail how I went about the modification including where I sourced my parts and where to make your connections.  Keep in mind, this is only for the SP-99D, but other processors can have this mod performed as well.  However, the connections will be different and the boards are different.

Tools Needed

-    Soldering Iron

-    Phillips #2 Screwdriver

-    Small File and/or dremel

-    (1) SPDIF/TOSLINK plug - Link

-    22 gauge wire (preferrably different colors)

-    Wire Strippers

-    Drill (for screw hole to secure TOSLINK to chassis) 

-    Optional, heat shrink tubing to go over the connections at the terminals on the TOSLINK jack since       they are close together.

First, you need to remove the rosewood side panels.  This involves 2 screws on each side.  Once these are off, there are 4 screws on the back, then the top can be pulled off.

Once inside, you can see a black shroud.  There are 3 screws to remove, then this can be pulled out.  The shroud serves to funnel air from the front fan, through the heatsink and out the back.

Next, there is a metal plate with an X on it.  This plate needs to be removed to access the audio board below.  Remove the screws highlighted in yellow on the photo below.

After the metal plate is removed, the audio board is visible.  Luckily, it does not need to be removed to solder in the new wires.  The image below shows an overview of the board.  Following that are zoomed in photos to show where to connect wires to.

To begin soldering new wires, cut to length your leads that will go between the tap points and the TOSLINK adapter.  You will have to determine where you want the TOSLINK to go on the back of the chassis to help with wire length.

First, connect your Digital Out wire to Toshiba Chip TC9245F

 

 

Next, you need to connect the +5V and Ground wires.  These are on the other side of the chassis close to the power supply.  

In case the diagram on the TOSLINK/SPDIF adapter is confusing, here is a photo explaining where each of the 3 connections go.

When you are preparing the spot on the back of the chassis, aim for the area with the vents.  These are easier to cut into and are one of the few open spots on the back.  You can use a dremel or a small file to cut into the air vent space.  Once the hole is cut and the TOSLINK is fitted, you will need to make a small hole above the jack for a screw.  The screw is necessary to secure the jack to the chassis.  The screw I used was a spare from another Pioneer machine and it was a match for the other screws.

That's it!  Close up the unit, plug the TOSLINK cable into the SP-99D and into your receiver to receive sound through Optical.  There is nothing further needed on the SP-99D, the digital audio will automatically output through the new jack.