Following the progress of my YouTube channel DextersLab2013, this blog will detail some of my teardowns and other interesting things i find along the way.
My understanding of electronics is at a basic hobbyist level though i love reading and learning about things i dont know. I find it is not hard to work out the operation of things with theories and basic principals while looking at the insides of something.
As it was a hybrid i saved it to take a look at in the future and today i removed it's cover to see inside.
The IC has a standard 16 pin DIL pinout but is an oversized package. The package is ceramic with bonded gold plated pins. The top cover is also ceramic which is glued on top of the main body. The HVL100 is manufactured by LeCroy, famous for their high-end oscilloscopes and other test equipment. It is a discriminator and is a combination of the LeCroy MVL407 4 Channel Comparator and the Motorola MC10198 Monostable Multivibrator. The HVL100 here dates from 1996 and the following text is from it's datasheet:
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After some heating with a hot-air gun i was able to remove the top cover.
Inside is a ceramic substrate with the components bonded to it and usual gold bondwires connecting the silicon devices to the ceramic substrate.
There are a couple of ceramic capacitors and two main integrated circuits, i would hazard a guess the central one is the main LeCroy MVL407 comparator , you can easily see the 4 sections in the die. The smaller device to the right is the Motorola MC10198. Notice also the blue covering on some of the signal traces, generally this seems to be when a bond wire passes over the trace so maybe this is to reduce capacitance between the two traces?
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Click Image To Zoom Motorola MC10198. Note the copyright indication in the top right corner.
In this teardown i take a look at a vintage Solartron LM1619 Digital Volt Meter. This is a UK made product which dates from around the early 1970s.
Full Teardown Video:
The LM1619 is a 1999 count volt meter only with DC ranges of 200mV, 2V, 20V, 200V and 1kV. AC ranges are 2V, 20V, 200V and 750V.
The unit weighs about 5Kg and is housed in an extruded aluminium chassis with vinyl covered steel covers. The front panel is a thin layer of beige Formica with cutouts attached to the chassis. Has integral tilting bale.
Connections are provided on the front with three banana jacks, HI, LO & CHASSIS.
The display consists of three Mullard ZM1080 Nixie Tubes. Decimal places, polarity indication and the 1000 count indication are provided by discrete neon lamps.
Inside there are three main areas:
DVM Board
which contains most of the electronics for the voltage measurement. This includes two vacuum tubes, a Mullard CV4003 valve and a Mullard 83A1 which is the voltage reference.
Display Board
This contains the components to drive the three nixie tubes and consists mainly of descrete transistors on a hinged PCB for easy maintenance.
Front End
Located within a shielded can this houses the voltage dividers and trimmers along with a Weston cell and what appears to be a battery connection. Although the battery was missing from my unit i am insure what the battery was for.
This is a short teardown of an Avery Berkel D104 Post Office Scales, as used in post offices throughout the UK.
The case is constructed of cast aluminium with a large aluminium bed, large 2x20 high contrast LCD display. The unit is intended to be bolted to a work surface.
Three data connections are located on the base.
Inside the unit the is the load cell, small mains transformer, and three significant PCBs, one has a selection of voltage regulators and analog circuitry for the load cell, the other two are what appears to be the digital processing board and then the display board.
Inside the unit, with the LCD & Display board removed from the front. The dataports are located on the far right. The digital controller board at the front, load cell in the centre and finally the analog board at the back. As shown in the picture below.
Below is the reverse of the display controller, the LCD module is mounted on the other side, with a IDC cable connecting on the right. It contains 64kbytes EPROM, Intel 8032AH Microcontroller, SRAM, Intel n825306 Serial Communications Controller and two MAX232 RS232 drivers. There is a small power supply section at the top left as this board runs from a separate transformer tap so is isolated from the other boards.
Below is the analog board, power supply regulation on the left with discrete diode bridge rectifier and linear regulators for the voltages needed for the analog side. The analog front end for the load cell is located in the area to the right where i have removed the shielding can.
The digital board below takes a IDC cable from the analog board, located at that connector is a custom ASIC and an 32kbyte EPROM. Also on this board is another Intel 8032AH microcontroller, MAX232 RS232 driver and four opto isolators. I would guess these are for the three external ports and the internal display board which uses RS232 between the two boards.
The load cell below is a 6kg rated device, no manufacturers name can be found on it, given Avery Berkel's size this could be of their own design.
So it's taken a couple of months to figure this Magstim 200 out and i have finally made it charge, trigger and discharge the capacitor.
After my last blog entry where i had disabled the 'Replace Coil' error / interlock by brute-forcing the PAL (Programmable Array LogicIC that seems to control the final safety interlocks to find the correct combinations that would disable the lock, this worked but left me with the device unable to trigger.
The PAL IC on the breadboard along with a binary counter IC (Motorola MC14060B) to run through all the 512 combinations of logic inputs to find the state that would disable the 'Replace Coil' error.
You can see on the scope picture above the top trace is the 4th stage counter output to the PAL, the other stages connect to each of the other PAL input pins so it will cycle through every combination as the counter (a Motorola MC14060B) counts upwards. The 2nd lower trace is the output pin that controls the replace coil error, so this is showing there are only two input states that bring the coil error output low indicating a fault.
Note there is a total of 512 output states from this PAL IC but not all the input pins will be applicable to this output condition. Clearly you can see there is only a few input states that control the output which is why there is only 9 clock cycles before the pattern repeats.
I simply clocked the counter first at high speed (a 100khz or so) watching the output on my oscilloscope in roll mode to first check the coil error state does change, then slow down the clock (to just a few hz) so i can stop it when it's in the output condition i want. I can then read off the state of the inputs. This can then be compared to the states seen when the IC is in the actual magstim board when the error is showing. In my case pin 5 was low and should be high. Disconnecting the input pin from it's source and bringing it high removes this lock.
Bodge wire from VCC to pin 5, this should be pulled high to disable the interlock. The bodged on resistor is from the factory!
I also look at the charge voltage of the capacitor, i see a maximum reading of around 1700v, this is less than i expected. In the documentation i have seen from Magstim it indicated it would be around 2800v as seen in this excerpt from "Guide to Magnetic Stimulation" by Reza Jalinous:-
Full video after removing the interlock:
I spent much time tracing the trigger circuit, and found the front panel board supplies 5v to the trigger input of the potted trigger block. This is pulled low by the front panel trigger button only when pin 'K' on the front panel connector is also pulled low to ground.
This pin would be for the interlock switch located on the Magstim coil itself, intended to be held in by the operator when they are ready to trigger the device. So typically they would place the coil where they wanted, hold in the coil interlock and then either press the front panel 'Trigger' or depress a pneumatic foot switch to actually trigger the unit.
So a simple fix, once this was discovered i could remove the multi-way connector from the front panel and solder a bridge wire across those pins on the front panel board.
Bodge wire to remove the coil switch interlock.
In the future i will make some binding posts for the front panel to allow easy connection and disconnection of things i want to blow up or experiment with.
So currently the unit will charge the capacitor to about 1700v in 1% steps. I have done some measurements of this and found the accuracy of this is very approximate and certainly at the higher charges the charge leaks away requiring the unit to keep topping up the capacitor. At the higher voltages the hysteresis of this can be as much as 40v or so. At the moment i am not sure if this self discharge is natural leakage in the capacitor or other parts of the circuit.
At 100% the capacitor is charged to about 1680v so has about 268 Joules of energy stored. The lowest power (1%) will charge the capacitor to about 40v which is 0.15 Joules. The scaling of the % power value to the actual voltage is non-linear, certainly at power levels below 30%. Upto 30% it is much better, at 30% the charge will be about 525v which is actually closer to 10% of full power. Above the 30% the power does rise in more linear fashion to 100%. The capacitor seems to measure 190uF and is oil filled. Magstim rated the capacitor to a minimum 200,000 full charge cycles. Quite impressive for what it does. I would expect the capacitor was a significant part of the BOM for this device along with the Thyristor. The capacitor i believe is a General Atomics DP Series 39504 which are general purpose pulse capacitors capable of upto 25kA. The 39504 is rated at 185uF at 3000v. I have also noticed that the mechanical counter only counts when its triggered at over 80% power.
