xx515-xx815 & xx517 Video Noise Elimination
Author: Craig Rounds
This modification deals with eliminating excessive video noise on v25 and v27 Mits CRT’s. The video noise is characterized by scrolling clusters of lines generally diagonal, but mostly scroll horizontally up and / or down the screen. Sometimes the noise takes on “diamond” like shapes and repeats its pattern in groups or clusters across the entire screen in vertical columns. The noise is not present on OSD’s (on screen displays) and is most prevalent at 1080i. The noise may be periodic appearing and disappearing at random or it may be constant.
All Mits models between xx515 through xx815, as well as xx517’s are built on the v25 chassis making them electronically equivalent (called v27 on the xx517 models). This modification does not apply to the xx315 models as they do not suffer from this issue because they are built on the more robust v22 chassis (called v24 on the xx315’s).
Problem Isolation Description
This white paper deals with one type (the most common type) of extremely excessive video noise that affects most v25/v27 units. If your v25/v27 Mits has video noise at 1080i on all inputs except for the HD tuner coax input, then this mod is for you. In other words, if you do not see noise on your coax DTV input when watching HD, but you do see noise on HDMI and component inputs, then this is the mod you need.
On severely affected units, you may also see this noise on both 480i and 480p as well as 1080i. However, the noise usually looks different on the 480’s then described as above. The key to determine if your set can benefit from this procedure is to check that there is no noise when using the internal antenna “A” in HD mode. You can not test for this with standard definition on antenna “A.” Nor can you test using any other input besides the internal HD tuner*. This is because only HD through antenna “A” is routed differently allowing the signal to bypass much of the video chain. All other sources Must pass through the terminal board, but ATSC is sent directly to the DM (see the block diagram below).
*FireWire may also not have the noise.
Note from the diagram that all sources (even SD on antenna A) are sent to the PCB-TERMINAL for switching. Also note that only HD on the ATSC HD tuner is demodulated and then sent directly to the ASIC on the PCB-DM; it is the only source that does not go through the PCB-TERMINAL. Since there is no noise on the HD antenna, this implies that the noise is being inserted somewhere up stream from the ASIC on the PCB-DM.
Also worth noting is that this noise is not present in on screen displays (OSD’s). When you bring up user menus you can not see the noise in any OSD. OSD’s are inserted on the DM, so this would imply that the DM its self is not the cause.
The following instructions are for informational purposes only. Doing the wrong thing could very easily render your TV unusable. I strongly recommend that you do not perform this modification procedure yourself. Do not play with anything inside your TV. Taking the front panel off your television will expose you to the potential of electrical shock, therefore use caution. This is for informational purposes only.
I must reiterate, the voltages found inside these TV sets are very high, up to 30,000 volts. Being hit with such a high voltage could be fatal or render very serious injury. Any steps taken by individuals are at their own risk. I am not advising that anyone attempt to do anything based on what they see here, I am only providing information about the function of the TV sets. Neither I nor The Home Theater SPoT can be held responsible for any damage or injury that may result from attempting this modification.
This modification may also affect your warrantee status. If components are damaged by following this procedure, Mitsubishi is not responsible. If damage or injury results from actions taken while applying this modification or as a result of this modification, no attempts should be made to hold Mitsubishi responsible.
Any actions taken by you or other individuals are at their own risk.
It turns out that the engineers at Mits created this chassis with a minor design flaw. They routed unshielded signal wires bundled along with power wires. All electric current broadcasts interference radially along the length of the wire. This interference is being picked up by the unshielded signal wires, thus appearing as noise on the screen.
Unplug the TV and let it to sit for several minutes to allow the 35,000 volt section to drain. Then remove the back panel from the TV.
You will observe a four wire bundle (three yellow and one brown) that runs between the right side of the PCB-SIGNAL, all the way to the left side of the PCB-DM (see diagram and photos below). These wires carry 12 volts, 6 volts, and ground to the PCB-DM.
The DM power supply wire bundle is literally clipped at two locations into harnesses along with two ribbon cables. These ribbon cables are what carry the video signal from the PCB-TERMINAL to the PCB-SIGNAL, and then along to the PCB-DM. The close proximity of the power and signal wires is what causes the noise to enter the video.
All one need do to eliminate the noise is up-clip the wire harnesses holding the ribbon and power cables. Remove the power cables from the harnesses, then re-clip the wire harnesses back together with only the ribbon cables remaining. The harnesses do a good job holding the ribbon cables in place, you just don’t want a power cable in there with them. Take a zip tie and secure the power cables to the ground clip next to the convergence IC heat sink. This places the power cables far enough from the video ribbon cables to negate the noise being broadcast by the power cables.
I only discovered this fix yesterday 12/17/07 and did not try this, but it would probably be a great idea to unclip the power wire harness from the PCB-SIGNAL board and twist the cable. This will further shield the interference being broadcast by the power cables because it will be picked up by the ground wires in the bundle.
Walla, no more noise. Plug in the set, let it boot, and you should be noise free 🙂
Many photos below to help illustrate the procedure.