Apple I work in progress

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Sid6.7's picture
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Joined: Jan 20 2019 - 15:51
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Apple I work in progress

Hi everyone.
I have a question about the power transient heatsink.

I installed it using a thermoconductive paste that I placed between the sink and the PCB. Today I was advised to remove the thermoconductive paste from where I put it and to buy mica instead. Precisely this product:

https://www.ebay.it/sch/i.html?_odkw=lm323&_osacat=0&_from=R40&_trksid=m570.l1313&_nkw=mica+to-3&_sacat=0

I have also been advised to interpose the thermo-conductive paste between the heat sink and the mica itself, in addition to using also those rubber protections for the screws.

I used a multimeter to check that the LM323A transistor pins are not shorted and are not.

I like the idea of protecting the screws so that they do not make contact and I thought to put the thermoconductive paste under the mica exactly as I was advised. But I would like to keep the thermoconductive paste even between the sink and the PCB.

The motivation of the board to remove the thermoconductive paste between the PCB and the sink is the fact that according to those who advised me it is not correct to ensure that both the PCB to dissipate the heat itself, but only the sink.

What do you think?

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The board was designed with a lot of Copper

The board was designed with a lot of Copper around the TO3 regulator, likely to help with heat sinking, but my way of thinking would be to depend LESS upon the board and more upon the heat sink itself.  Over time, with the heat generated from that 5V regulator, I would expect board discoloration.  Lower temps will minimize that.  (my opinion) 

I put a small 5V fan atop the heat sink to cool the regulator.  It's small and fits perfectly in the corners of the heat sink.

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It's been a while since I

It's been a while since I built one of these,  but I used to add thermal grease between the regulator and the heat sink, but that was all.  I never had excessive temperature problems, and I've run these all day at shows, quite a number of times.  Make sure your enclosure has plenty of ventilation, a fan would be a good idea if there is no way for air to circulate freely.

 

regards,

Mike Willegal

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I agree with Mike.  However I

I agree with Mike.  However I should mention that depending on the RAM you use, the other regulators could also get very hot so whenever possible use a fan blowing across the entire power supply area.    I have run original Apple-1 and Mimeos with the Mostek RAM without an issue for hours without a fan,  however I have run replicas with non-Mostek RAM that have become way too hot after 10 minutes.    

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