My ancient Zeddy!

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Lardo Boffin
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Re: My ancient Zeddy!

Post by Lardo Boffin » Thu Apr 04, 2019 9:07 pm

Moggy wrote:
Wed Apr 03, 2019 4:52 pm
I too have a fan cooled zeddy which I put together after someone wondered (Lardo I think) if it was possible with standard cases. It's a 40mm 12v , tapped off the 9v input and sits in a square in the lower case, made by removing the vent slats. Fast enough to create air movement and whisper quiet with hardly any noticeable heating of the upper case at the regulator location or the ULA location.
Glad you managed to sort one. I couldn’t find a fan that did make the case vibrate. :?
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Moggy
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Re: My ancient Zeddy!

Post by Moggy » Thu Apr 04, 2019 10:47 pm

Enigmachine wrote:
Thu Apr 04, 2019 4:41 pm
Moggy, I might try to insert a tiny blower-style fan below or to the right of the CPU/PLA with an air tunnel blowing on PLA heat sink in a future project, like what you would find in portables. A blower might be thin enough to fit over the resistors in a standard case and even at slow speed should have enough cooling.

I have 3 TS1000's here so I have plenty of opportunity to experiment but I think I may have killed one of them running it without any cooling. We'll see when I'm done with this ZX-1881, I definitely want my next Zeddy to be a "Sleeper" upgrade and a fan on the bottom would give it away imho.
Also my guess is you could run the fan at much lower voltage (and more silently) if you can put the cool air precisely where it's needed.

Anyway, must add that to one of my to-do lists. :)
That's right I run a 12v fan off the 9v supply and it's whisper quiet, any lower voltage say 5v with the same fan and it won't spin up but if finger turned it will then continue running. the chips inside don't reach the furnace temperatures some may believe and as long as there is a throughput of air, no matter how slow, it does the job.

@Lardo.

The only reason the fan doesn't vibrate is because of the lower voltage slower speed setup. When I used a 12v supply for the fan the case resonated like hell! :lol:

Enigmachine
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Re: My ancient Zeddy!

Post by Enigmachine » Fri Apr 05, 2019 3:36 pm

@moggy I was wondering last night how your fan setup actually works, I think maybe what you're really doing is cooling the "legs" of the chips/the connectors, which are close to the internal temperature of the chip even under the board. Since cooling the legs is probably much more efficient than cooling the plastic chip casing (which isn't very thermally conductive), I had the crazy thought that maybe if we extend the legs below the board (or install new chip holders and don't trim the legs) they would make very decent and efficient heat sinks that might even be big enough for passive cooling. The only drawback is the likelihood of shorts. :twisted:

I don't have a vacuum desoldering tool or I would try replacing the chip holder, take the obsolete power converter aluminium heat sink and cover it with thermal tape and stick it on the pins. :) I'm curious to know how wacky my plan is. :)

Moggy
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Re: My ancient Zeddy!

Post by Moggy » Fri Apr 05, 2019 4:42 pm

In my set-up I removed the slats in the lower case and opened the aperture enough to house the 40mm fan.
At first I was going to fit a switching regulator to this board but decided against it as I wanted to see if it could sufficiently cool the standard regulator and its associated heat sink.

I then cut a small square hole in the top leading edge of both cases in front of where the ULA lies, the idea being air would enter here pass above and below the board then exit underneath which after testing with a smoke match I found it does it quite well.

I agree to a point about the thermal efficiency from the chip case hence my well known aversion to heat sinks in closed systems such as the 81 with no moving air to provide cooling, forty odd years of designing and fitting cooling solutions to my own self built stage gear has taught me that a surprisingly small air movement can achieve quite a lot cooling wise.

As said in my per my previous post these chips don't run at argon arc furnace temperatures and to be honest the breath of an angel would suffice. I have yet to find anyone who can honestly say conclusively that their ULA failed through heat damage, the usual culprit is plugging/unplugging interfaces whilst powered up or said interface blowing its stack causing a cascade failure in the ULA.

The panic over ULA failure is caused more by its rarity than any inherent design/usage flaw,place your finger over the die area of an older NMOS Z80 cpu and it gets reasonably hot too yet because they are readily available no such concern exists.

As for using the pins in the manner of a cooling radiator I would say knock yourself out experiment wise as I firmly believe the little wedge is there to be used/modified whatever and not polished and put in a case, but would think it lacks merit insofar as the legs on their own lack surface area compared to the chip case and joining them to a heat sink seems inefficient.

A small flow of air from rear to lower front I find works extremely well even with a fan running under spec.

Good luck with your experimentation which to my mind shows that the spirit of electronic endeavour is alive and well and should be applauded. :D

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msch
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Re: My ancient Zeddy!

Post by msch » Fri Apr 05, 2019 5:24 pm

Enigmachine wrote:
Wed Mar 13, 2019 10:18 pm
Hope you like it! Oh btw don't freak out vintage lovers, the original case & keyboards are totally unharmed. :)
Great composition! Do You have more pics?
Mathias

ZX-Team, classic computer collector

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1024MAK
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Re: My ancient Zeddy!

Post by 1024MAK » Fri Apr 05, 2019 11:00 pm

The legs thing (down tiger! :lol: )... Keep in mind that the chip itself is connected to the legs via thin bond wires, so although some heat will flow via this route, not that much really. The (plastic) resin encapsulation is not a good thermal conductor, but it does have the advantage of having a good contact with the chip die. So you will find that there is a hot spot in the very middle where the chip die actually is, while being only warm at the ends.

Silicon semiconductors can happily operate at surprising high temperatures (internal temperatures of up to 100 to 125 degrees C). But for some reason lay people get concerned if they find that the chip is too hot to touch.

Any system to aid in cooling a semiconductor has to increase the heat flow from the semiconductor. Either passive (metal heatsink on it’s own, if, and only if cool air can circulate freely around the heatsink) or forced airflow.

A semiconductor that runs warm/hot is a hot body. So just like if you hold your hand out of a car window when driving at speed, the air will cool your skin, even if the air is warm, the same applies to semiconductors. The aim is to remove the (waste) heat generated by the semiconductor faster than, or at the same rate that it is created. This limits the temperature rise of the encapsulation and in turn, the temperature of the chip die.

So for a ZX81 ULA, a small fan running at 9V or so is more than enough if the airflow is right.

Myself, I am happy by just replacing the 7805 voltage regulator with a DC/DC switching regulator. This substantially reduces the temperature inside the case. But I have only done this on the Zeddies I use the most. Most of the other err, numerous Zeddies are unmodified and they all work fine. No ULAs have died on me yet (I do have a couple where the ULA was dead when I got them, and which now have ULA replacements courtesy of Andy).

Mark

Moggy
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Re: My ancient Zeddy!

Post by Moggy » Sat Apr 06, 2019 12:27 pm

Ditto the switching reg for me too. The fan mod I did was for proof of concept only and my other zeddies trundle along quite happily with changed regs only.

An excellent and well worded post,absolutely spot on Mark. :D

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1024MAK
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Re: My ancient Zeddy!

Post by 1024MAK » Sat Apr 06, 2019 4:12 pm

Thanks :D

Mark

Enigmachine
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Re: My ancient Zeddy!

Post by Enigmachine » Sat Apr 06, 2019 4:31 pm

Thanks for the great comments guys, I feel like some good idea will come out of it. :)

I just got into the habit of cooling everything from being in crypto mining for years. The reality is that some GPUs are stable at 85 c for long periods, all of my properly-designed 5 year old GPUs are still running fine. I'm guessing that's much higher than what the PLA ever reaches under normal conditions, but I should find a way to measure that. :)

I'm absolutely certain my Zx-1881 does NOT need a fan at all but I added one because going overboard was part of the design idea. :lol: Not only is the case really big (It was meant to fit a Zeddynet with the akward-pointing cable and a cherry-keys keyboard) but I designed it to have a chimney effect for passive cooling.
(warning: unflattering pics as requested, you can see what I mean when I say it's not finished :) )
Front slot, cold air goes in:
Frontslots.jpg
Rear slot, hot air & cables go out:
rearslots.jpg
I tested with incense sticks and get nice airflow passively when the PLA/CPU heat up. When I turn the fan on my own lap gets cooled, so it's really overkill.

But for my next Zeddy, I definitely want to treat the case with more reverence (it reminds me too much of the Monolith bringing the spark of intelligence :) ). Replacing the 7805 is mandatory but the heat sink could be reused to shape a passive cooling air path with almost-invisible external changes and ensure the machine works for another 40 years. :mrgreen: Well, without actual numbers I'm just shooting the breeze (eheh).

Moggy
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Re: My ancient Zeddy!

Post by Moggy » Sat Apr 06, 2019 7:55 pm

Incense sticks to test the air flow!!! :lol:

That one sentence has just made my day.
No dreary smoke match or taper but a bloody joss stick. :shock: A nice aroma as well as a flow test.

Something tells me Mr Machine that you will fit in right well here. :D

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