ZX81 cooling fan

Discussions about Sinclair ZX80 and ZX81 Hardware
Lardo Boffin
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ZX81 cooling fan

Post by Lardo Boffin » Fri Nov 10, 2017 11:41 pm

Out of curiosity I bought a very small cooling fan off eBay. I was wondering if it was possible to use it to draw warm air out of the case by placing it on the vents where the heat sink used to be. This way heat sinking the ULA might actually be of some benefit and not get me in trouble with a certain someone... :?

The image below shows it more or less where I would like to place it and the case still closes!

999FC139-4080-4D54-84A9-E9A5308D7982.jpeg
999FC139-4080-4D54-84A9-E9A5308D7982.jpeg (775.21 KiB) Viewed 218 times
But being new to all this where would I best connect it to the motherboard? I would like to solder in a couple of pins so that it can be unplugged easily enough so a couple of holes would be ideal rather than just soldering wires to the surface of something.

The three solder fillled vias to the immediate left of the traco regulator look ideal position wise but do they have the necessary feeds? I can find a 5v feed pretty easily using my multimeter (I assume) but what about ground? Would I just check continuity with something like the modulator case?

Many thanks for any advice so I don’t fry my zeddy...

I guess another question is as to whether this is actually a good idea in the first place?...

Lardo
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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Paul
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Re: ZX81 cooling fan

Post by Paul » Sat Nov 11, 2017 6:24 am

Your idea finding ground is correct.
But I suggest doing the easiest thing in the world.
Just solder the jumper to the pins of the traco.
If someone (you) looks at this year's after everything was forgotten it would be immediately clear what the pins are meant to be used for.
Any other positions would start a search which signals could be at the jumper.
One could be tempted to short this jumper just to see what happens. Invert the screen, m1not, hrg...

But nobody would try to short a jumper at the traco.

Kind regards Paul
In theory, there is no difference between theory and practice. But, in practice, there is.

Lardo Boffin
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Re: ZX81 cooling fan

Post by Lardo Boffin » Sat Nov 11, 2017 8:28 am

Very good points thanks Paul. I will attach the pins to the traco.

Looking at the 7805 pinouts:-
75B3109D-3EBC-43B8-91D8-B996890CB65B.jpeg
75B3109D-3EBC-43B8-91D8-B996890CB65B.jpeg (71.92 KiB) Viewed 191 times
It would be black cable to the middle pin and given the orientation of the zeddy the red cable to the bottom pin nearest the fan.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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Paul
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Re: ZX81 cooling fan

Post by Paul » Sat Nov 11, 2017 9:02 am

Correct :D
In theory, there is no difference between theory and practice. But, in practice, there is.

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1024MAK
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Re: ZX81 cooling fan

Post by 1024MAK » Sat Nov 11, 2017 9:50 am

A 12V fan may have been an easier install, as you could then have run it off the nominal '9V' DC input. Just connect to the DC in socket pins.

For a 5V fan, connect to the output and 0V pins of the 5V regulator. It is also possible to power it from the 9V rail via a suitable value resistor, but I need to know the fan's normal current in order to guesstimate the value of the resistor...

Mark

Lardo Boffin
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Re: ZX81 cooling fan

Post by Lardo Boffin » Sat Nov 11, 2017 10:35 am

It’s rated at 0.12A but I’m happy to fit it to the regulator pins. Or at least have a go!
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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siggi
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Re: ZX81 cooling fan

Post by siggi » Sat Nov 11, 2017 11:27 am

Lardo Boffin wrote:
Fri Nov 10, 2017 11:41 pm
I was wondering if it was possible to use it to draw warm air out of the case by placing it on the vents where the heat sink used to be.
Hi Lardo
cold air is heavier than warm air. Thus the warm air will leave the case at the highest possible hole in the case (MIC, EAR sockets?). Since the fan is located at the lowest (coldest!) position, it should support/enhance the natural thermal flow within the case. Thus is should suck cold air from outside into the case (from beneaht the case). Is that given?

Regards
Siggi
My ZX81 web-server: online since 2007
http://zx81-siggi.endoftheinternet.org/index.html

Lardo Boffin
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Re: ZX81 cooling fan

Post by Lardo Boffin » Sat Nov 11, 2017 11:33 am

siggi wrote:
Sat Nov 11, 2017 11:27 am
Lardo Boffin wrote:
Fri Nov 10, 2017 11:41 pm
I was wondering if it was possible to use it to draw warm air out of the case by placing it on the vents where the heat sink used to be.
Hi Lardo
cold air is heavier than warm air. Thus the warm air will leave the case at the highest possible hole in the case (MIC, EAR sockets?). Since the fan is located at the lowest (coldest!) position, it should support/enhance the natural thermal flow within the case. Thus is should suck cold air from outside into the case (from beneaht the case). Is that given?

Regards
Siggi
Thanks siggi

I was wondering whether to have it:-

1) suck air through the case by having it blow through the vents

2) blow air through the case by having it suck through the vents

I wasn’t really sure if it would be more effective one way or the other to be honest.

Regardless I will put a card blanking plate round it so that the air only moves through the fan and not through the vents to either side of it. Hopefully this should maximise air flow through the case and not just recirculate it around the vents.

We have a thermal camera at work - I may try and see if it can borrow it...
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Moggy
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Re: ZX81 cooling fan

Post by Moggy » Sat Nov 11, 2017 12:18 pm

Leaving aside witty comments about my aversion to heat sinks in confined/closed spaces I can honestly say this idea has merit.

Having spent 40 odd years building stage amplification and more in respect to this thread the cooling solutions required for said beasties may I offer the following....

1) Suck the warm air out rather than cold air in as atmospheric pressure will give you a gentle nudge in this respect and regardless of which ever hole the the cold air comes in from the vacuum effect will make sure any static air over the ULA is drawn out, also I wouldn't get too hung up on thermal flows in some thing this small with no natural thermal flow, rather than spend a month theorising just do it. ;)

2) You would be amazed at how small the amount of air that has to be moved to provide an effective solution is, so a 12v fan tapped off the 9v input (one of the three blank holes you mention is 9v) will not only provide cooling but will be quieter too.

You might be surprised to learn that the three test rig zeddies which I use that are mounted on open chassis each one has sinks and a 12v PC case fan tapped off 9v enabling long running with no associated heat problems, but I still maintain,silly comments notwithstanding,that in a closed zeddy the sinks are redundant without some form of forced air cooling which this small fan idea should provide.

All in all an excellent idea worth pursuing although having thought about it a bit more I feel the opening on the case underside may be a bit restrictive causing some back-pressure, in which case removal of the "slats" would provide an unobstructed airflow at this point but I do understand any reluctance to butcher the case in this fashion.

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1024MAK
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Re: ZX81 cooling fan

Post by 1024MAK » Sat Nov 11, 2017 2:08 pm

Lardo Boffin wrote:
Sat Nov 11, 2017 10:35 am
It’s rated at 0.12A but I’m happy to fit it to the regulator pins. Or at least have a go!
Back of an (insert comedy comment) calculation gives the trial result of a 47 ohm, 1W resistor.

Mark

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