TSN 1-2450A instead of LM7905

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HigashiJun
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TSN 1-2450A instead of LM7905

Post by HigashiJun »

As you know, our Orics use a LM7905 as a voltage regulator, which can seem strange as there were simpler solutions even in the '80s...

Heat is of course an issue with this regulator which tends to get really hot, and adding a heatsink under the motherboard is a common way to prevent from overheating.

Time has passed since the first Orics were produced but even nowadays people seem to continue using this old LM7905 to replace a failed one, whereas a better solution exist.

This solution is the TSN 1-2450A from Traco Power:

https://www.tracopower.com/int/model/tsn-1-2450a

I do agree its price a slightly higher than the LM, but it's really worth it: our beloved Orics run very cool without a glitch and there's no need to think about a better cooling system.

I first thought I was the only guy using it (nobody on the forum except one member mentioned it) but then I discovered this very informative English website:

http://blog.tynemouthsoftware.co.uk/

where the webmaster also used the TSN to replace a defective LM.

I don't know if some of you guys have replaced your failing LM with this better part, but I can only recommend it warmly to everyone. :D

Cheers.
HigashiJun

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mikeb
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Re: TSN 1-2450A instead of LM7905

Post by mikeb »

These do seem like a good "modern replacement" for the 7905, and in fact not only will they run cooler as you observe, but the input current draw will also be lower (as instead of ditching the excess voltage as heat, a buck converter trades the excess voltage for greater output current).

Also, the input voltage range is quite wide, which means fewer accidents with "oops, wrong power supply voltage". Note C8 (100uf/10v) on Oric's board limits the input voltage here, so you'd need to uprate that if you were planning to go higher.

The only real reason for using a 7905 nowadays is -- if you already have them, or for authenticity!

You may want to warmly recommend the module, but you have to admit, a 7905 is a hot little number :)

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HigashiJun
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Re: TSN 1-2450A instead of LM7905

Post by HigashiJun »

:D

You greatly explained all the other benefits I have omitted, and it adds more "heat" to my warm recommendation...

Cheers !
HigashiJun

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tingo
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Re: TSN 1-2450A instead of LM7905

Post by tingo »

The VX7805-1000R might also be suitable if it can supply enough current in the negative configuration - it is so new that DigiKey doesn't have a datasheet yet. It is a bit cheaper than the other candidate.
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iss
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Re: TSN 1-2450A instead of LM7905

Post by iss »

tingo wrote:
Wed Jun 10, 2020 9:29 pm
... VX7805-1000R.
Datasheet here: VX7805-1000R.

This will NOT work :( because:
- only 500 mA output current:
Screenshot_20200611_003617.png
Screenshot_20200611_003617.png (63.83 KiB) Viewed 363 times
- and more important the negative regulator is common ground too and the equivalent connection inside Oric is as on picture bellow:
Screenshot_20200611_003750.png
Screenshot_20200611_003750.png (38.89 KiB) Viewed 363 times
i.e. without track cutting there will be definitely a short connection and lot of smoke :!:

EDIT: the same thing should be checked for TSN 1-2450A too.

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HigashiJun
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Re: TSN 1-2450A instead of LM7905

Post by HigashiJun »

I can confirm the TSN 1-2450A was a "plug'n'play" replacement for me.

No need to cut any tracks, just desolder your old LM7905 and replace it with the TSN and voilà...

:D

Cheers !
HigashiJun

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Vyper68
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Re: TSN 1-2450A instead of LM7905

Post by Vyper68 »

The Traco power VR mods are very popular in the Sinclair community and it is on my “to do” list for both my Atmos and also my Sinclair 128K “Toastrack”
Great thread :D
Bazinga!

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HigashiJun
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Re: TSN 1-2450A instead of LM7905

Post by HigashiJun »

It's really worth it... The Oric stays very cool. You should definitely give it a try.
HigashiJun

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