For all of the people wondering about this 8 usec mod, this is something that can be done only to one of the first 200 TDI's built. The TDI 8 usec mod can't be done on any of the newer TDI's. These early units are called the through the hole units, which refers to the components and how they are mounted. Later TDI's use surface mounted parts plus the adjustments are now done in software rather than by using regular components. Thus, only the original units have the internal controls that can be adjusted to reduce the minimum delay.
The way to tell as to which unit you have is to look at the conductivity switch. If the words GB on Required are directly above the Conductivity switch then it is one of the newer units. The original TDI's simply have the words High, All, and Low around the Conductivity switch and no other wording except the wording Target Conductivity below the switch.
Now, with that said, there is no other internal control that can be adjusted by the user. All other adjustments are extremely critical and any adjustment can and will screw things up, with some easily rendering the detector with severe problems.
Several of the internal controls require special special test equipment and detailed procedures to properly adjust the controls, so anyone who thinks they are going to tweak their unit will only degrade the performance if they touch any of the other internal controls. This is why there is little written about this mod. In fact, one of the controls require that control be set to one millivolt. That is one thousandth of a volt. This is something that can't be done with most test equipment. Other nearby controls are just as critical and require the settings be even less to assure proper adjustment.
At one time I considered providing the service to make this 8 usec adjustment for a fee, but decided against it. Also, once the adjustment is made people need to realize the detector will not act the same at the minimum delay. Because of badmouthing by a few "know it all" people I have elected to minimize any technical information I will divulge.
All internal controls are generally glued in position once they are adjusted and the factory can tell if someone screws with them. Now, with that said, one can't simply put any control back to the factory setting by trying to line up the glue pieces because of just how critical adjustments are. Without special equipment and knowing the procedures this is an impossible task to get things back to factory speck. Anyone who tries may think things are back to normal, but there will be some depth loss or some other issue to deal with once internal controls are adjusted. The worst case is the detector may not work or work so poorly it is rendered useless.
Personally, I if I were to decide to work on such units messed with by the owners, I would charge double to recalibrate a detector. This would amount to about $200 plus shipping if I were to decide to recalibrate one of the units. Because of the time and techniques required, presently I won't touch anyone else's unit at this time because of the time and effort needed to put things back to the correct settings, so please don't ask.
Reg
