Author Topic: EEVblog #641 - Dumpster Cash Register Teardown  (Read 15897 times)

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Offline winfreak

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #1 on: July 15, 2014, 01:14:07 pm »
Great teardown, I have always wondered how they look from the inside...


BTW: How would you go about on displaying anything on that display you salvaged?
 

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #2 on: July 15, 2014, 01:32:48 pm »
BTW: How would you go about on displaying anything on that display you salvaged?

The LCD is easy of course. The fluoro one a bit harder. You'd capture the lines while it's working and decode the pinout and data required.
 

Offline winfreak

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #3 on: July 15, 2014, 01:38:11 pm »
BTW: How would you go about on displaying anything on that display you salvaged?

The LCD is easy of course. The fluoro one a bit harder. You'd capture the lines while it's working and decode the pinout and data required.

Sounds tricky but quite doable!
I'm looking forward to working with Arduino + such displays...
 

Offline dentaku

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #4 on: July 15, 2014, 02:12:10 pm »
It was even more interesting than I imagined.
I like those displays.

The big keypad could be used as a crude very low resolution push (as opposed to touch) sensor of sorts that knows where i's being pushed on.
 

Offline nomis

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #5 on: July 15, 2014, 02:16:29 pm »
Does it have any useful parts to salvage?

About the paper cutter: Note that there is a small rectangular notch in the center of the blade. By controlling how far the blade cuts down you can either cut the paper completely or leave a small connection between the receipts to avoid creating a mess of loose paper snippets.

I once had to deal with this kind of printers and it was quite fun to do not-really-complete-cuts in sub millimeter increments in the paper. Instant paper festoons!  :)

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Offline Hole

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #6 on: July 15, 2014, 03:31:13 pm »
Hmmm.

This German thing has a 16 bit RISC cpu with all the bells and whistles it can have. And an 8 bit cpu with not so much bells. And all that for adding some numbers every other second. And then do some odd multiplications or divisions?

Sure a big canon to shoot that small bird.
 

Offline homebrew

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #7 on: July 15, 2014, 03:51:58 pm »
Hi Dave,

nice teardown! But to my perception it is not engineered that well, when it comes to safety. In no way I can think of this device should be conform to any safety standard...

1) Obviously some parts of the case are grounded (like the drawer) and others should be as I don't see ANY form of double insulation from the mains. There isn't even the otherwise typically installed insulation foil between the PSU and the chassis.

2) Mains input wiring directly goes to the PSU, including the ground wire. From there the only connection to the rest of the system is through the wimpy metal bushing around the plastic PCB standoff. It looks like being made of copper and if it is pressing against the tinning of the PCB only (Video 14:40). Thus the whole ground system is held together by a PCB mounting screw that grabs into plastic...

Baaahhhh ...
 

Offline SeanB

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #8 on: July 15, 2014, 04:31:17 pm »
What Dave did not notice is that the power supply only delivers 24VDC. the individual boards have built in voltage regulators to generate the supplies they need from that. The VFD probably uses a serial data stream that generates the characters, i got 2 from Kolbep that use a single 64 output VFD driver that drives the various columns and rows of the VFD. That probably is the job of the one ASIC on the main board. You also will find around 64 or 128k of battery backed SRAM as well to store both the written description of the various items ( tea, coffee, tuna sandwich, BLT, Smoothie etc) as well as the assignations for the various keys on the keyboard, along with keeping a tally roll and day totals for the register.

The printer being a separate board is to enable the same main board to be used with the thermal printer, a dot matrix printer or even to drive a standard external parallel printer, you will probably have a centronics interface on the pins, along with the 24V supply. You would have a small board with a set of buffers and a 5V regulator if you had the external printer. The reason for the extra grounds is because they did not consider that those print heads draw a peak pulse current of around 200mA per pixel element, thus you see the multiple tabs on the head that are at the side that are the ground connections, you can have 5A or more flowing through those pins, and on the top side you will see a big ( though very low profile) decoupling capacitor on the 24V rail to the print head. You probably have 512 elements on that head, and they are driven at around 1MHz to clock the serial data into them along with the PWM value per element ( to give a gray scale of around 16 values from nothing to full black) and this has to be done for each line. The 2 motor drivers are for the stepper that does the paper feed and the cutter, and the cutter driver also drives the register open solenoid. You print an ASCII bel character ( ctrl G) and the drawer opens, typically for a POS printer.

Older POS printers used a single heater element running on a spiral track on a rod, that is driven by a DC motor and an optical encoder to scan along the paper, with the one end of the track having a ratchet that moves the paper up one pixel for each full stroke of the head. Slower and the head driver is then on the board with only a 4 connection flex to the head, 2 power and a pair to measure the head temperature for feedback to control the density. On the integrated heads the sensor is on the flex and feeds all the drivers to keep the print density constant ( same final instantaneous temperature ) as the head assembly heats up in use.
 

Offline sergey

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #9 on: July 15, 2014, 04:57:55 pm »
Nice teardown indeed. Wouldn't really expect such a computation power in things like this. You can easily fly to the moon with those DSP :)

The good thing is even if you fail to decode the serial interface of the VFD you can always decode individual segments of VFD itself, so no worries at all and you definitely need to salvage parts like this!
 

Offline phenol

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #10 on: July 15, 2014, 07:26:45 pm »
The thermal head is made by Kyocera using thin film technology. The potted driver ics are basically shift registers with low side mosfet switches on every dot. The dot resistance is typically between 600 and 1500 ohms on those 24v heads. looks like a 200dpi head, each dot is 1/8mm big. The head can be clocked at speeds much higher than 1MHz, typically 5 up to 30 in faster models, and yes, it does draw a lot of current when a lot of dots are fired simultaneously. Today there are thermal printers that can operate at voltages as low as 2.7-3V.

the cutter can do partial or full cuts just by reversing the polarity on the dc motor inside.
 

Online dexters_lab

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #11 on: July 15, 2014, 07:29:13 pm »
never seen so many ferrite rings in one product!
"A common mistake people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools." - Douglas Adams
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Offline magiccow

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #12 on: July 15, 2014, 07:32:23 pm »
never seen so many ferrite rings in one product!
yeah nice collection of ferrites...
c:\> format c: /s
 

Offline Dave Turner

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #13 on: July 15, 2014, 07:37:51 pm »
I think I spotted another bodge on the main board - a flying resistor and capacitor at about 12:18.
 

Offline synapsis

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #14 on: July 16, 2014, 12:40:56 am »
I picked up two standalone IBM thermal receipt printers off eBay for dirt cheap. I used one to make an obnoxiously huge Welcome Home banner for a friend (200 feet long).

The cutter and printer would probably be good for making mailing labels or small instruction sheets for uCurrents.
 

Offline nitro2k01

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #15 on: July 16, 2014, 03:50:12 am »
never seen so many ferrite rings in one product!


This one beats it by a mile. 39:41 into that video. Granted, it's a one-off product, but look at those ferrites!
Whoa! How the hell did Dave know that Bob is my uncle? Amazing!
 

Offline David_AVD

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #16 on: July 16, 2014, 04:30:03 am »
The little release lever at the back of the cash drawer is common.  It's how you open the drawer in case of power failure.
 

Offline Rasz

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #17 on: July 16, 2014, 06:10:36 am »
awww
that board to board connector screamed 'get a hotair and demonstrate how to desolder me !!!!111!seven"


I cant picture in my head how a thermal head like that works. I mean I know how it works, it just doesnt compute, you would need a big thermal mass/heatsink to dissipate energy quickly between pixels, otherwise you wont get sharp edges ... but this thing has no problem with sharp edges, so wtf ?

btw thermal paper is great when you need to locate hot spots but have no access to thermal printer, just plaster your board in thermal paper, turn it on and wait for black to appear near hottest chips/shorts.
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Offline Paulusthewoodgnome

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #18 on: July 16, 2014, 07:03:34 am »
Make a nice microprocessor controlled toilet paper dispenser with the paper cutting module
 

Offline miguelvp

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #19 on: July 16, 2014, 07:28:11 am »
Make a nice microprocessor controlled toilet paper dispenser with the paper cutting module

I'm pretty sure there is no market for very narrow toilet paper.
 

Offline cengland0

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #20 on: July 16, 2014, 09:42:35 am »
Hey Dave, love your videos.  Just wanted to point out that you missed another bodge near the backup battery:
 

Offline German_EE

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #21 on: July 16, 2014, 10:39:40 am »
That VFD display is a thing of beauty, you could make a very nice frequency counter using that module.
Should you find yourself in a chronically leaking boat, energy devoted to changing vessels is likely to be more productive than energy devoted to patching leaks.

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Offline Niels

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #22 on: July 16, 2014, 11:05:14 am »
Why do they (RDC) denote the 80C186 clone as an RISC/DSP processor?

RISC architecture have more done in parallel to reduce execution time, this costs extra gates/silicon. In order to reduce the silicon the number of instructions is reduced.
The 80186 burns a lot of clock cycles to do noting..

And an DSP processor is expected to be able to perform Multiply-Accumulate on a vectors, the 80186 can't do this.

The 80186 has been used a lot in embedded applications, even if it have some drawbacks.
It does not have JTAG debug interface, it does not even have debug registers (Introduced on 80386)

Debugging was at best performed with a debug monitor in ROM, connected with a serial interface.
The debug monitor had to overwrite the code with INT3 instructions.
This required the code to be located in RAM, and often there was not enough RAM to support this feature.

The reason for using the 80186 is its days, was the possibility to run DOS, and/or use DOS development tools and library’s.

Paradigm (The site you were linking to) makes tools to locate, and debug 80186 a target without DOS.
 

Offline phenol

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #23 on: July 16, 2014, 12:31:43 pm »
The company i work for makes all sorts of thermal printers, the lightest one being 27 grams or so.
We also have a big variety of printers with built-in driver boards the same size as that printer in the video. all you need to start printing is power and paper. it can work as a windows printer or independently printing ascii chars rx'd over serial or usb.

The print head itself does not necessarily need large thermal mass to dissipate heat between lines; the dots are designed to cool down sufficiently between print cycles. If they fail to do so, the image bleeds. Even then there are software tricks to mitigate bleeding, ie historic control.

As for the VFD, i recently made a freq counter with 8 7-segment ussr-made VFD tubes...all in all, filament voltage, grid voltage and whatnot, it draws a lot less current from the 5-v rail than 8 7-segment led displays
 

Offline nixfu

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #24 on: July 16, 2014, 02:59:41 pm »
I was wondering what he was going to do with that big thing that had been sitting up on top of the shelf, I noticed they had to move it when they were making the new bench the other day.  I am guessing the removal of that shelving unit is where the idea for this teardown came from.  Either tear it down or throw it out.

>Why do they (RDC) denote the 80C186 clone as an RISC/DSP processor?

I will tell you why.  RISC was a major buzzword in the 80s and they were simply trying to jump on the bandwagon.

« Last Edit: July 16, 2014, 03:02:23 pm by nixfu »
 

Offline Niels

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #25 on: July 16, 2014, 03:43:37 pm »
>Why do they (RDC) denote the 80C186 clone as an RISC/DSP processor?

I will tell you why.  RISC was a major buzzword in the 80s and they were simply trying to jump on the bandwagon.

1980's ? The 80186 was common in industrial automation into the mid 90's.
http://www.cpushack.com/2013/01/12/the-intel-80186-gets-turbocharged-vautomation-turbo186/

The 186 is still available:
http://www.innovasic.com/Products/ia186es-ia188es

The company that I work for replaced the 186 with StrongArm, this turned out to be a bad idea.
Intel stopped production 3 years after introduction despite promises of extended support.

This is a major headache when you need 1-2 years for development, a product life of 8 years, and to support with spare parts for 25 years.

 

Offline Stonent

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #26 on: July 16, 2014, 06:47:44 pm »
The thermal head is made by Kyocera using thin film technology. The potted driver ics are basically shift registers with low side mosfet switches on every dot. The dot resistance is typically between 600 and 1500 ohms on those 24v heads. looks like a 200dpi head, each dot is 1/8mm big. The head can be clocked at speeds much higher than 1MHz, typically 5 up to 30 in faster models, and yes, it does draw a lot of current when a lot of dots are fired simultaneously. Today there are thermal printers that can operate at voltages as low as 2.7-3V.

the cutter can do partial or full cuts just by reversing the polarity on the dc motor inside.

Also on the outside of the printer is an SII logo with a circle after it.  That would indicate the full part was made by Seiko Instruments.  They make the "Smart Label" series of thermal printers that are sold at office supply stores.

A bit of trivia on cash drawers, the old parallel port ones in the 80s and 90s could be triggered to open by sending an ASCII CTRL-G (ASCII Beep Code) to the printer port.

I used that trick once to open a drawer when the key was misplaced.

The old DOS command to do it was :

ECHO ^G > LPT1:

The raised caret is put there by pressing CTRL-G not by typing the caret and G.

From windows you can type ECHO ^G and it will make your computer make either a beep or windows alert sound out your speakers if they are turned on.

So, knowing that, if you can figure out the interface for the cash drawer, sending ASCII code 7 might trigger it to open.
The larger the government, the smaller the citizen.
 

Offline misterm

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #27 on: July 16, 2014, 07:45:26 pm »
I've used several tills like this when younger

As mentioned the latch at the back is to open the drawer without power, this doesn't work if drawer is locked though

the key on the side is to select modes, there are normally keys which restrict which modes you can select to allow say x read but not z reads or programming

L is locked - no transactions
H - I presume this is for normal use
X - X read - a sub totalled list of all sales, typically used during day to monitor sales
Z - Z read - as a bove but zeros the totals, typically used at the end of the day
M - not sure, but probably to program prices for some buttons
P - programming mode

Martin
 

Offline David_AVD

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #28 on: July 16, 2014, 09:04:41 pm »
As mentioned the latch at the back is to open the drawer without power, this doesn't work if drawer is locked though

Yeah, it's only an override for the solenoid.  The lock on the front is for when the till is unattended for some time and more secure than putting it into lock mode.

A common practice used to be to leave the drawer ajar overnight if there was no money in there.  This was in case of a break-in so (dumb) thieves didn't destroy the till trying to open the drawer with a lever.

I remember years ago my parents ran a clothing store.  One day there was a power outage for half the day so my dad hooked a piece of fishing line to the override lever and draped it over the top of the till.

That way he could pop the drawer open each time he made a sale.  That was better than leaving the drawer ajar as it still made the "bing!" sound (mechanical bell & striker) when opened via the override so less likely to have a casual theft occur.
 

Offline Monkeh

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #29 on: July 16, 2014, 09:15:48 pm »
Make a nice microprocessor controlled toilet paper dispenser with the paper cutting module

I'm pretty sure there is no market for very narrow toilet paper.

Hamsters.
 

Offline The Adjuster

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #30 on: July 17, 2014, 04:59:30 am »

I cant picture in my head how a thermal head like that works. I mean I know how it works, it just doesnt compute, you would need a big thermal mass/heatsink to dissipate energy quickly between pixels, otherwise you wont get sharp edges ... but this thing has no problem with sharp edges, so wtf ?

There are actually two sets of heaters on the head.  One large heater to hold the head just below printing temperature, and all of the individual print elements which can quickly raise (and lower) their temperature to darken the paper.

When I got trained (more then a couple of years ago), the trainer referred to the individual print elements as 'nibs'.
 

Offline mxmarek

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #31 on: July 17, 2014, 11:55:05 pm »
cool oscilloscope in top-right corner at 20:30
 

Offline f4eru

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #32 on: July 18, 2014, 06:05:58 pm »
maybe you want to unsolder the flat flex connectors, to keep together with the keyboard film.
 

Offline f4eru

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #33 on: July 18, 2014, 06:18:49 pm »
Notice how the resistors in the printer are all in series, probably there is a muxing scheme going on, and a residual current into the off ones.

A creative use for the paper cutter ? a confetti machine for Sagan ?
Notice the notch at the center of the blade for keeping a small link so the paper does not fall off.
 

Offline phenol

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #34 on: July 18, 2014, 06:29:27 pm »
The resistors are not in series; their hot end is commoned to a single track connected directly to 24v. Also, the off current is the leakage current of mosfet switches, a microamp or less. There are no other heaters and stuff to keep the head warm. A thing like that would waste energy for nothing and this is not a good thing in devices like eft pos terminals where power is on a budget.
 

Offline david77

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #35 on: July 18, 2014, 09:37:48 pm »
In my last job we had a nice old cash register made in 1986. One morning I came in and heard a very sickly sounding beeper. As I came closer to the cash desk the smell of cooking electronics became stronger until I could eventually see a constant stream of smoke rising from the cash register.
The poor thing was dying and crying for help.
I pulled the plug and after some head scratching decided to open it up. It used a 6502 processor and a 7 pin matrix printer. The noises this thing made when operating were brilliant. Turned out some caps on the PSU PCB had given up after >25 years. Problem was I really needed the register for daily business and so decided to try and fix it - after all this was an electronics shop I was working in.
This actually worked and the thing booted up after this but as it turned out it had forgotten its configuration. The user manual was of no use to me, I couldn't figure out how to program this old beast so had to call the service tech to re-programm it.
He did it from memory, took him about an hour of keying in arcane codes and the cash register worked again. He told me we were the last ones using this ancient model and he hadn't seen another in service for at least five years. I was impressed that he remembered how to set it up - he's probably one of the better service techs.

All cash registers I've seen so far have that release catch for the drawer on the bottom. You have to be able to get at the money even without power and keys.

The key switch is the mode selector, P is Program mode, X is used for things like cashing up at the end of the day, Z is normal register mode. Have forgotten what the others do but they're usually the same on all cash registers. The keys used for these locks are quite nifty, there are usually at least three different keys, each key performs another function. So there's the P key to get into P mode, then there usually are user keys for the people operating the machine and superuser keys for the boss, for things like cancellations and sub-totals.
« Last Edit: July 18, 2014, 09:44:58 pm by david77 »
 

Offline misterm

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #36 on: July 19, 2014, 09:08:09 pm »
On every till (probably 5 or 6 models) I've ever used Z mode is for zeroing, it allows the user to print a summary of whats been sold and then reset that (normally everyday)  so you get a record of daily takings

Martin
 

Offline david77

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Re: EEVblog #641 - Dumpster Cash Register Teardown
« Reply #37 on: July 20, 2014, 01:21:38 am »
Yeah, you are probably right, I mixed that up. Funny how fast you can forget things you used to do every day for years  :palm:.
 


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