Tuesday, October 14, 2014

PC watercooling loop

Been putting this off for a very long time (taking photos requires partial computer disassembly), so I'll just post a few previews...
Leak test

Top left - heat exchanger (mostly called "radiator" even though the primary method of heat transfer is convection into flowing air, radiation is negligible at these temperatures), the Alphacool NexXxoS Xtreme II rev2. This is the single most expensive component of the build, closely followed by the pump. At 395 x 120 x 45 mm it fits 2 120mm fans (not pictured), in my case Arctic Cooling Arctic F12 CO PWM. Fairly cheap, yet they have 2 ball bearings, PWM and decent power (for the price). 6W at full power may not seem much, but a lot of the more expensive fans are even wimpier.
I have however found out that these fans seem to stall (increasing RPM doesn't increase airflow) when running over 40% PWM, they clearly were designed for free-flow operation, not to be mounted directly on the heat exchanger. One day I might get annoyed enough about this to go crazy and buy a pair of Deltas, since they have 120mm models with PWM and guide vanes (can create more pressure, downside is noise and manufacturing cost), but at the moment I can't justify spending over $80 on 2 fans, no matter how ridiculously overpowered they are...
Middle-ish left - the CPU block.
Middle-ish right - the reservoir/expansion tank. It's made from acrylic sheet (which is probably older then I am) bonded with CA glue. In/out ports are threaded brass, the input one is a flange nut that has been sanded flat, glued with CA to wall (which already had a hole in it) and after the glue set, I secured it with an acrylic plate that had a hexagon cut into it (prevents the nut from exerting shear forces onto the glued surfaces). The output is a threaded stub and a flange nut is holding it in place. So much CA glue was used to make sure it's not going anywhere. The output also has a...thing...on the inside to keep it from picking up air, it looks like a scoop.
The tank is has a baffle in the middle, it's intended purpose is to give bubbles more time to rise to the surface and not be sucked in by the pump. Secondary and unintended effects is a nice wave indicating flow.
Upper right - An Eheim 1048 bought waaaaay back (today I would have gone for a 12V powered pump) in ~2005. While it has nice ceramic bearings - picture a white smooth ceramic shaft that goes into a smooth ceramic tube of matching diameter, almost loose fit (slides freely but no perceptible play) - it's still a synchronous motor and as such, it can (and will!) spin in either way, depending on when (AC phase) you turn it on, which means the impeller has to have straight instead of nicely curved blades and can (deliberately) freely rotate some 60° in relation to the magnet. The end result of these features is not-so-unnoticeable AC hum from the coils and if air bubbles manage to get in the pump, you get horrible rattling and clackety noises, which subside only after the air is expelled out. The pump cannot to this on it's own, so it has to be re-started, usually a couple of times. Once this is done and it's snugly fit in it's foam vibration dampener, the fans (or magnetic HDDs) are louder then the pump.
As you can probably see, I tried my best to avoid galvanic corrosion as much as possible, the only critical place is the pump output fitting, as it's made out of steel, not nickel-plated brass like the nut on pipe is. In case you are wondering why, it's a fitting made for hydraulics, nobody seems to be making a G 1/4 male to G 3/8 male fittings out of brass in this country. I have coated the inside of the fitting with a resin-based lacquer, but I fear this may not be enough.
One other possible place might be the radiator, as it's not clear what it's actually made out of, flanges seem to be brass, but the tubes are supposed to be copper. Also, they are soldered/brazed (more different metals).
We will see how it held up as I will be doing scheduled maintenance in the near future, main reason being I need to add L-fittings to nearly everything in order for it to fit in the case the way I want, not the way the minimum bend radius of the pipes will allow me. Other items to be added is a drain and fill valve, because attempting to fill (or drain) the system without them is a pain in the butt I wish to never have to experience again.

Sunday, September 21, 2014

Converting a dual rail PSU into a single rail

Needed a 12V/2A peak power supply for a TV/monitor made out of junk (more on that some other day, if I ever get myself into finishing it), but didn't have one particularly like that, nor did I want to buy a new one. When I searched the junk pile, I found one of those IDE HDD to USB converters.
Like this one
The set has been long junked, but the PSU still worked. The problem however was, that it's designed to supply 12V/2A and 5V/2A at the same time. This means that the stabilization is referenced off of both rails, and generally will not be very happy if you try to fully load just one.
In my case, the load is a LVDS panel signal converter (and a TFT  LCD panel with it's backlight module). Once everything was stable and running, the PSU could crank enough juice and keep the voltage high enough that the converter logic didn't complain. But when starting, the current draw peaked at 2A and the logic kept shutting down, because the voltage dropped below 11,5V. (Not sure why that mattered, since all of it's internal power supplies need less then that)

So, surgery time...




Red lettering notes what was added (it should be pretty obvious that a few parts have been removed prior to that).
A) is the new voltage divider, consisting of a 3k9 and 1k resistor.
B) is an additional low ESR capacitor, 1mF/25V (unncessarily too much, but it's what I had on in the junk pile)
C) is a 10µF tantalum cap, needed to keep the TL431 out of it's unstable region
D) TL431, scrapped from the same dead PSU as the cap in B)
E) a new 150Ω resistor (instead of 100Ω from previously) for the optotron (no idea what it, just assumed a 4N35 knock off, which it apparently isn't*)

*With a 3k9 and 1k resitor divider and a TL431 voltage reference (2,5V) the formula Vout=(R1/R2+1)*Vref yields should yield 12,25V.

A-PSU;B-current(x10 in mA);C-voltage;D-30A/300mV shunt;E-bigass rheostats as load (yes, a rheostat, you read that right)

Nope.
Seems that the mystery optocoupler is somewhat different from a 4N35 which I assumed it would be. But we are still within margin.
The powersupply is surprisingly well built (considering that the entire set of the converter cost the equivalent of $20, with import fees, taxes and all that crap),  the main transitor is a  STP4NC60FP (not sure if real or knockoff) and the primary and secondary sides are well separated. Eve the filtration caps don't seem like the cheapest crap that's out there.
The primary side of the power supply looks very similar to this one. The secondary side (now) looks like somewhat like this. The resitor divider is obviously different and there is a 10µF bipolar cap connected to the cathode and anode of the T431. If you leave this out, the TL431 will enter an unstable region (fig. 15 on page 7) and start to oscillate, since the LED in the optocoupler has capacitance.
In my case, that causes an audible whine of the power supply from no to full load, and quite notable voltage ripple (no footage, sry). With the cap it oscillates only when the load drops below approx. 120mA (even then the ripple is smaller and barely audible), which will not be a problem, since when on, the TV draws about 1A, and when on stand-by it will not mind the increased ripple.

video
Running with a 1A load
video
Relaxation oscillation with approx. 90mA load

Sorry for the crappiness of the footage (and lack of grid or frequency, the scope is from the 60s), but hopefully it's clear what goes on in the power supply.

Wednesday, June 25, 2014

DIY PC watercooling block done differently

This is one of those on-off projects that I am dragging maybe 6 years, because I don't have this, can't afford that, buy a "new" computer making the previous block incompatible, want to do it differently...

This time, I decided to try a rather novel approach to a low-cost DIY CPU block, where the most expensive tool being used was a drill press. (can be done even without it)
Most amateur blocks are the sandwitch type, 2 thick pieces of metal, one thick and one thin or a thick piece of metal and thick piece of plastic.
My construction is of the last type, using 10mm (10.2mm) aluminium, but the top where the hoses are connected to is made from 10mm LDPE. For some weird reason, a lot of people go for acrylic, which from my personal failures in attempts of this construction I can say is the worst possible choice one can make.
Here's why - 1) its brittle (tapping this is not for the fainthearted) 2) it's not particularly strong, this coupled with the brittleness means it's very easy chip/crack during drilling 3) it's fairly expensive 4) hard to come by in small, but thick pieces.

So why did I choose LDPE? 1) you can buy 10mm boards dirt cheap, search for "cutting boards". They can be had even thicker, but the price starts to take off quite rapidly after the 10mm mark. 2) availability. These cutting boards can be bought even in convenience stores, online stores have them in truckloads and keep trying to undercut each other on the price, bringing us back to n.1 3) while being quite tough, it's also soft. My construction doesn't use a seal, the screws squash it against the metal so well it doesn't leak. Also, machining it much easier, all you have to do is keep the tools sharp.

Metal time!

68x76mm aluminium block
(yup, it's AM2, 2+ and 3 compatible)

some more aluminium

As you can see, the block is mabe by drilling a bazilion holes (OK, more like 42 + 16 small ones for the fasteners) , first with an approx. 5mm drill, then the final 8mm. The remaining "islands" were twisted/torn off with pliers. So ghetto. Final cleanup is done by a "large" oblong mill for a Dremel-like tool.
If you don't have one, get one, you'll love it.

Awesomeness right here
The center is carefully cut down to just 2mm for optimal thermal conductivity/strength ratio(too thick doesn't cool that well, too thin could get warped by the clamping force). Somehow I also managed to tap all 16 of the M3 threads without stripping the thread or breaking the tap.

This is how the block sat for 2 years. Then I had a brainwave with the LDPE cutting boards and bought one as building material and one as an actual cutting board. And two G 3/8 set taps. And a 14,9mm drill bit, which turned out to be useless. (most drill chucks, including the one on my drill are smaller)
Along with the the LDPE idea, I also thought about the hoses. Turns out that you can buy a 50cm piece of 14x8mm steel braided rubber hose, with crimped-on G 3/8 male and female fittings on each side, all for the equiv. of $3.2 (exchange to $ on 25.6. 2014). 30 and 40 cm pieces cost a few cents less.

mmmm, braiding....

Yes, they are meant for water appliances, not PC cooling, but for the cost of  1 stainless steel fitting* that was made for PC cooling, you can get:
- a nice hose with all the fittings (crimped!), which are nickel-plated brass (more on that later*)
- a brass G 3/8 to 1/4 adapter (PC radiators seem to come only in G 1/4)
- a piece of teflon tape to make sure it doesn't leak.
Technically you can go nuts and have the hoses made with G 1/4, but the quote I was given (by a small company specialising in hydraulics, they have the crimp tool) was 3x as much, so I opted for pre-made with adapters.

Now, as for the * - if you google galvanic corrosion, you will quickly find that using stainless for water cooling is a dumb idea.
1st up, pretty much all types of stainless steels are quite far away (corrosion WILL** occur) from copper, 2nd stainless is the cathodic one, meaning copper (of which the expensive radiator thatIcan't(yet)fabricatemyselfsoIhavetobuyit is made of) is the one that is going to be eaten.
**For galvanic corrosion to occur, you need: 1) dissimilar metals (got that) 2) electrolyte (watercooling) 3) conductive contact. So, using stainless on your shiny new copper rad that costs as much as 4gb of RAM is a no-no.
As for bare or nickel-plated brass - they are practically next to each other in the relative electronegativity, so corrosion will be minimal.
But what about the aluminium block, whose electronegativity is on the other side of the chart (copper, brass and nickel are somewhat in the middle)? Well, for one aluminium is the anodic one (so IT gets eaten, not the expensive stuff), second - no contact. The LDPE block which holds the hoses is keeping them well away from ever touching the block, and if I ever get to actually mounting the system, the rad will not be directly touching the case.

So, enough bullshit, how does it look?

Not too bad given the cost is less then the cheapest of Chinese of waterblocks on ebay

Plenty of more room for even bigger ones :D

Crap picture n1
(camera seems to like the floor instead of my waterblock)

Crap picture n2
Last but not least, lapping the contact surface is usually a good idea, so here's the result of 2 hours of wet sanding, from 80 to 800 grit.

Shiny!

Performance data and more pictures will come if I ever kick myself into making a reservoir that doesn't suck or leak.

Butchering it apart

I've been putting it off forever, no more excuses.
So, let us begin:
Dissection in progress
Took a picture of both sides of the PCB, printed them out, stuck the paper onto a piece of cardboard and smeared the top with office glue-in-a-stick. I used this to practice hot air work, carefully removing each component at a time, "dipping" (more like touching) the leads in the glue stick and putting them onto their respective places. A rather time and patience consuming process.

Back side done
Then, after all the parts were removed the board was cleaned off, first nearly all the solder with a copper wick, then technical ethanol.

Barebones
(and yes, it's a bmp)

Backside of the FET preamp


Unfortunately, the free autotrace SW for Windows (haven't tried the Linux ones) failed miserably, the pictures just weren't good enough. So I converted the images to bmp and traced them "by hand".

Several hours later:

Front

Back
 The blue dots are vias. Without too much searching, you can find several that seem to go nowhere, meaning the board is more then 2-sided. Fuck.
While it is possible to carefully sand it down taking pictures every now and then, I am not that patient to do it.
Vectorized and superimposed
(back is blue, front is red)

The leads that go out of the picture are the flex cables that are...glued?..to the PCB directly, the ones on the left go to the LCD, the ones on the right come from the battery terminal.
If you feel you must have the infini-resolution vectorized version, email me. But before you do, be warned that some traces might be broken.

Wednesday, January 16, 2013

Siemens EPD-1D dosimeter teardown

Ebay can get you a lot of really exotic items really cheap. Period. This was no difference. While browsing through looking for a cheap (and yet still functional) NaI(Tl) scintillator, I came across an offer that looked like this:

front
(please excuse the violet background, I'm not the author of the picture...)

back
(© goodgadgets2u)


If you are still clueless about WTF is that, you are looking at the business end of a Siemens EPD-1D gamma dosimeter. Three PIN photodiodes (no idea on actual part number), each with a different level of shielding. The opaque one has a thick lead alloy shield around it (pictured above it), the right one seems to have a thin lead disc on top and the middle one is covered by thin aluminium foil supported by a polymer substrate.
The blue thing are three separate very sensitive FET amplifiers.

Instead of the sawed off guts, I got an entire unit (non-functional though).

front
© me (you can shamelessly steal these)


The unit did do something after being connected to power and restarted, but after performing a self-test and a few beeps, it always stopped reacting, while displaying an error.
So, autopsy time:


front cover, backside view
(note the shields for the diodes)
back cover, backside view

back cover, front side view


PCB, front
note the second piezzo buzzer (no idea why)
PCB, back
PCB, back (again)
(slight corrections so that everything is readable)
For some (to me unknown) reason, they decided to use a 4-bit MCU(the biggest IC on the picture), made by NEC in Ireland (Damn this thing is old). The small one labeled "X24C16S" is a 16K (2048 x 8 bits) serial E2PROM, most likely to store the dose measurements. (I might attempt to read the contents some day)
I have no datasheets on the other ICs though.

I'm just speculating, but the IC closest to the blue amp board is probably an ADC, the logo is Texas Instruments, but the search on their website returns nothing.
(Feel free to contact me if you know anything about any of these ICs)

Other than that, there are two crystals, one is for the CPU (1 MHz), the other is a real time clock (32.768 kHz). Note that the 1 MHz crystal has a ceramic package with a transparent window, so you can actually see the crystal itself (the thin rod in the middle).
That about wraps up the summary of interesting stuff  I can tell about this board. (for now, at least)

I'm still in the process of reverse engineering the PCB, since actually I need to finish building a capacitance meter first (SMD capacitors do not have the value displayed on them and the coloring is not standardised). I'm really only interested in the analog part of the detector, so I can rebuild it with a different MCU.
All will be posted in due time, so until then...

Sunday, August 7, 2011

Grind & polish your scintillator part 2

Been lazy and didn't bother to take any pictures during the procedure...sorry. Wasn't that much to see anyway - wet sanding with 600, 800 and finally 1200 grit sandpaper. Then notebook polishing again. Turns out it's not communist since it was made by a shareholder company. Someday in the beginning of the 90s. Still worked though.

Still far from perfect, but it's nice & transparent.
Note the TIR.
Here you can better see the surface texture.
Again, note the TIR.

This side is not that good, I might have to do a bit of work on it later. 
One of these sides is going to face the photomultiplier.

Turns out that Mirelon is good safe-packaging material. Normally it's used under floating floors
I have quite a bit of leftover, which is why I use it for almost anything...

note: I've found out, that the paper I used for polishing quickly clogs up and instead of polishing starts to create sort-of clumps that stick onto the scintillator. You have to use just one paper per side, use a clean one for the next side. Sometimes even that is too much.
Also, the PVT significantly charges with static electricity when rubbed on the paper. Tends to attract dust and holds the charge quite well. Also, it tends to charge you. 

Well, that's the scintillator. Wasn't that hard now, was it? BC-408 is quite easy to machine, you just have to be careful with the heating, it doesn't seem to mind wet and dry sanding. You certainly couldn't do that with an NaI(Tl) crystal since it's hygroscopic.

To come: I've managed to score 2 FEU-36 photomultiplier tubes for a ridiculously low price. It's an old Russian-made cesium-antimony photomultiplier with 13 dynodes. Also quite big, since it runs on between 1,24 to 1,6 kilovolts. Did I mention it was made in 1963?
Quite nice it comes with it's own datasheet which has !hand! written measurements. Also, it's completely in Russian. Yay for me...

Sunday, June 5, 2011

Grind & polish your scintillator, part one...

If you have no idea what a scintillator is, in short it produces short pulses of light when ionizing radiation passes through. That being said, it's quite obvious, that it's a key part in a scintillation counter/detector. (Note - it's NOT A GEIGER counter if it has no GM tube...)
Since I've always wanted to build my own radiation detector, I've been collecting information on them wherever I could. To build your own, you have several choices - 1) a GM tube, 2) an ionization chamber, 3) a scintillator.
GM tubes come in different shapes, sizes, materials, capabilities and prices. Old surplus soviet made tubes are dirt cheap, however they ignore most of the radiation passing through them, but have a sturdy construction. Unless it's a "pancake" probe, it's unlikely that it will have an end window, so it won't detect alpha radiation & will ignore low energy beta. Western made end window tubes do detect alphas, but are quite expensive and hard to find. Pancake probes go from $50 up on e-bay. Also, they are incredibly fragile, they need to have a mesh at the end window to protect it, even so it's still very easy to destroy it. They also do not like rapid pressure changes.

Ionization chambers differ in construction, I will not describe them here. hint - fluorescent tubes for lighting can be used in this way as well...

Now for scintillators - unlike the previous two, the detection medium can be both solid or liquid, meaning they have greater density, so they capture(and detect) more radiation. I may play with liquid scintillators in the forseable future, but not now. As for solid scintillators, they can be inorganic or organic. Since growing large inorganic crystals is expensive, so are the scintillators. As for gamma detection, they are far superior to organic ones, but in cost and versatility the organic ones win.
When searching, I found that a user Geoelectronics sells small quantities of plastic scintillators on e-bay at a very reasonable price. The one available was RP-408 made by Rexon. Aparently (judging from the emision spectrums), it is identical to BC-408 made by Bicron. It was for $8 a 1x1x1'' piece, so I ordered a 1x1x2'' piece. The picture (yes, I know...) showed neat looking, straight and polished pieces of it.

This is what I recived.

Not that I want to bad mouth someone, but if I can't cut straight with a hacksaw, I would at least clean it from metal shavings(not shown).

See the cuts?
(And yes, none of the sides is straight.)

So I looked for the most leveled side (took a while), and then just stuck a piece of 80 grit sandpaper onto a slab of glass (it's the most straight thing normal people can get their hands on) with sticky tape... (hey, it was at hand and did it's job)

After approx. 15 minutes of sanding. 

It's straight!!!

Now, how the hell do I level off the other side?! Sanding?

F-no!

Yup, that is a normal drill press, with a slab of glass taped to it... No, you should definitely not do this with a normal drill press. The bearings are not built for being loaded on the other 2 axis. But this thing is just flimsy polyvinyltoluene with some anthracene in it, it should't hurt the poor CCD (Cheap Chinese Drill). At least not too much...

more machine abuse...

Now, one more thing CCDs do not like is prolonged run. Like more then 20 minutes... The motor gets too hot to touch, if I continue, the elamel on the wires starts to smell...

Where there's a will there's a way...

"That" is a universal grinder/sander/table reciprocating saw/fan... Made in Czech Republic some while ago, it doesn't seem to be around for sale anymore. Too bad. Wasn't even expensive back then.

Being a bit too hasty...

Since I'm using my own hands, it pays to be patient. Oh well, just turn the drill on and clean it off with a random piece of wood.

Some more machine abuse...

Note the paper, without it, the half an hour of sanding would be lost. Also, PVT is rather easily damaged*.

"machining" done!

* - See the beveled corner? I've managed to drop the damn thing when I was laping it oustide onto a terrazzo surface from approx. 20cm. Instantly, two corners were chiped.

Lapping done!

I've used 80 grit dry paper to level the sides, then 220 grit wet and last 600 grit wet.

 
Clear side - this is how it will look finished.
( I hope )   

 
After some polishing...

Not perfect, but it's a start...

 Because I'm a cheapskate, I didn't buy sanding paper with more grit and a real polishing solution. What did I polish it with then?

Comunist made school notebook!

Thats right, the coarse paper this notebook is made out of is perfect for the job. The bad thing is that 600 grit is apparently not enough to properly prepare the surface for polishing. Oh well, that's what part 2 will be for...

From left to right - 80, 220 and 600 grit paper.

I forgot to take a picture before I started, so these are after I was done with them. Note the darker stripes on the 80 grit paper - that is it's original colour. It's impossible to get the fine dust out of the paper, doing this outside or wearing a respirator is probably a good idea...