Replacing 7805 voltage reg on 48k Speccy and ZX81

manic23

Only Amiga Makes it Happen
Joined
Apr 25, 2013
Posts
3,105
Country
United Kingdon
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Bromley, Kent
I heard a lot recently about the advantages of replacing the old and inefficient 7805 voltage regulator on old Sinclair computers to a newer Traco Power TRSN 1-2450 so I thought id give it a go on my 48k Speccy and ZX81.

This is a great MOD to do as the Traco Power TRSN 1-2450 is about 90% efficient (7808 is about 40%), does not get hot and uses much less power. You don't even need to put the heat-sink back you can leave that out. It produces much less heat in the case as well, the ULA's get ho enough as it is without adding more from the 7805.

I am rather pleased with this MOD, I found the soldering easier than I thought, the trick is to use flux, not much but it really goes give a nice join. Anyway here are some pics!

Speccy, Before
2017-06-24 12.20.33.jpg

Speccy, During
2017-06-24 12.54.00-1.jpg

Rather proud of my soldering joins, this on the ZX81!
2017-06-24 14.42.45.jpg


Speccy, After
2017-06-24 13.01.18.jpg

And success!
2017-06-24 13.17.11.jpg
 
Hi Manic,
i see that You have recapped Your unit - it's a great idea. Also prom was swapped to Eprom, You have used 27C256 but propably burnt Your ROM twice as i can't see the switch..
do You actually know how much power Your Spectra Interface needs?
the qustion behind it:
It is good enough for bare computer, as Your Speccy consumpts about 600-650mA, so You have approx. 350mA left (these TRSN 1-2450 are 1 000mA) but in case You attatch too many interfaces - Your traco will run unstable or burn out.
Just try to find more powerfull DC - DC converters. For example:
http://www.ebay.de/itm/DC-DC-Wandle...1-5-A-7-5-W-Anzahl-Ausgange-1-x-/222446760819
regards,
Viktor

 
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You got me worried now!

Can someone confirm if DjCook is right? should I not have done this MOD? I'm seeing loads of other people doing this.
 
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You don't have to worry if Your setup works without any issues.
I just saw the Spectra interface and divMMC on Your pics and i wanted to warn You, if something goes wrong - You will know where to start.

Some years ago i was building custom psu for C64 and used a traco power.. it was a bad decision, didn't use them since then. Another problem - there are a lot of chinese fakes on the market, sometimes you can't even see the difference so it is better to buy these converters from realible suppliers like mouser, digi-key, and farnell..
 
OK thanks, it all seems to be working at the moment and yes I bought from RS a respected supplier here in the UK. Thanks for your advice :mad:)
 
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