Saturday, 25 July 2015

Teardown: Magstim 200 TMS Transcranial Magnetic Stimulator Base Unit

In this video i disassemble a Magstim 200, this is a TMS device manufactured in the late 1980s. Production began in the mid 1980s and ran through until at least 1999.

TMS is a medical technique to stimulate the brain and nerves throughout the body using a closely coupled induction coil placed on the head that is energized with a short duration high voltage/high current pulse. The magnetic field from the coil induces small currents into the brain or nerves through the skull and skin.

The Magstim Company was founded from research performed at Sheffield University during the early and middle 1980s.

I recently purchased two used Magstim 200 base units for teardown. One appears to be working and dates from the late 1990s, the other is broken and dates from the late 1980s. It's the broken one i teardown in this video.

Saturday, 11 July 2015

Repairing An M5 Thread On A Capacitor

I salvaged four capacitors from the Red Light Camera i did a teardown on a while ago. I found when i removed them that one capacitor had one thread completely gone. It looks like it might have just been over tightened at the factory.

The damaged thread.

I opted to try and Helicoil it, i have used them before to repair larger threads like M12, the capacitor uses two M5 which are much smaller but i thought i would give it a try.

The procedure involves buying a kit which contains the coils, drill, tap and a couple of insertion tools.

The first step is to drill out the old thread with the included drill bit then you tap and then insert the coil. The coil becomes the new thread at the original size.

In this instance there is a small issue in that these are not really designed to be inserted into shallow blind holes, you need enough depth to get the drill in and the tap has to work to a minimum depth to cut the thread.

So first off i ground the tip off the drill and the tap so i can work with a shallow hole.

Drill and Tap with ground ends.

After drilling out the old thread.

Cutting the new thread with the supplied tap.

The new intermediate thread for the coil.

The coil on the insertion tool. The coil will become the new M5 thread.

Inserting the coil. It simply screws in.

The end result, a new M5 thread that will actually be stronger than it was originally.

Saturday, 4 July 2015

Midland G9 PMR446 5 Watt Full Power Export Modification

In this article i will detail how to convert a normal Midland G9 Plus or G9E Plus 2-way radio to the export version that has enhanced 5 watt output. It also allows the two PTT buttons to be used to operate the radio in standard 500mW and in 5000mW.

The modification is quite simple on this 2015 version Midland G9E Plus.

Take your Midland G9 and remove the belt clip and batteries. You will find four screws located in the battery area and one next to the belt clip. Carefully remove these with Philips screwdriver.

Open the cover carefully, note the wires to the vibration motor, these can easily be broken if they are pulled hard.

At the top of the PCB next to the On/Off/Volume control you will find three jumper links labelled J-1, J-2 & J-3.

To make the modification, simply cut links J-2 & J-3. 

The radio can be re-assembled. When you next turn on the power the settings will reset to factory default.

The radio will operate as it did before but with the exception that the PTT & PTT Boost will work differently. In the menu if you change PRL setting to be 'L'. This will make the PTT button transmit at 500mW and the PTT Boost button will transmit at 5000mW.

Other Notes:

The radio seems to be operated by a Beken BK4811 transceiver IC.

Power consumption measurements at 5.00v
Idle: 78mA
Idle + Backlight: 95mA
TX 100mW: 170mA
TX 500mW: 470mA
TX 5000mW: 980mA

I also made some measurements of the battery level indicator:
Full battery indication at 4.77v+
2 bar battery indication at 4.72v
1 bar battery indication at 4.5v
Bat Lo warning at 4.3v