TSN 1-2450A instead of LM7905
- HigashiJun
- Flying Officer
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- Location: Tokyo (Japan)
TSN 1-2450A instead of LM7905
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.
Cheers.
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.
Cheers.
HigashiJun
- mikeb
- Flight Lieutenant
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- Location: West Midlands, UK
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Re: TSN 1-2450A instead of LM7905
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
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
- HigashiJun
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- Joined: Tue Dec 10, 2019 9:29 am
- Location: Tokyo (Japan)
Re: TSN 1-2450A instead of LM7905
You greatly explained all the other benefits I have omitted, and it adds more "heat" to my warm recommendation...
Cheers !
HigashiJun
Re: TSN 1-2450A instead of LM7905
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.
Torfinn
Re: TSN 1-2450A instead of LM7905
Datasheet here: VX7805-1000R.
This will NOT work because:
- only 500 mA output current:
- and more important the negative regulator is common ground too and the equivalent connection inside Oric is as on picture bellow:
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.
- HigashiJun
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- Joined: Tue Dec 10, 2019 9:29 am
- Location: Tokyo (Japan)
Re: TSN 1-2450A instead of LM7905
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...
Cheers !
No need to cut any tracks, just desolder your old LM7905 and replace it with the TSN and voilà...
Cheers !
HigashiJun
Re: TSN 1-2450A instead of LM7905
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
Great thread
Oric Extended Basic V1.1
(C) 1983 Tangerine
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- HigashiJun
- Flying Officer
- Posts: 205
- Joined: Tue Dec 10, 2019 9:29 am
- Location: Tokyo (Japan)
Re: TSN 1-2450A instead of LM7905
It's really worth it... The Oric stays very cool. You should definitely give it a try.
HigashiJun
Re: TSN 1-2450A instead of LM7905
I finally bought one of these TRACO regulators and fitted to my Atmos but it wouldn’t boot. Just got the pre-boot screen. Checked the voltages and all good. So took it out and fitted another LM7905 and the Amos is back to normal and working happily. It was almost like when you turn the Oric on at the wall and it doesn’t start up correctly. I tried various combinations of power, direct, via RGB SCART, turned on from the wall. All provided the same screen, so my Atmos doesn’t play nice with this part. So others may have a similar experience.
I have an Oric-1 and I may try that next, but I don’t want to keep removing and fitting regulators on these PCB’s so I’m not sure if I will, I will have wasted £24 if I don’t use it
So if anyone has any insight as what may solve the issue I’m all ears, I replaced all the electrolytic capacitors last year so it’s not that.
Failing that If anyone wants it cheap pm me...
I have an Oric-1 and I may try that next, but I don’t want to keep removing and fitting regulators on these PCB’s so I’m not sure if I will, I will have wasted £24 if I don’t use it
So if anyone has any insight as what may solve the issue I’m all ears, I replaced all the electrolytic capacitors last year so it’s not that.
Failing that If anyone wants it cheap pm me...
Oric Extended Basic V1.1
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- HigashiJun
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- Joined: Tue Dec 10, 2019 9:29 am
- Location: Tokyo (Japan)
Re: TSN 1-2450A instead of LM7905
I'm sorry to hear that...
It's quite weird.
Did you receive the right part, ie. TSN 1-2450A and not another one (TSN 1-24150A) ?
It's quite weird.
Did you receive the right part, ie. TSN 1-2450A and not another one (TSN 1-24150A) ?
HigashiJun
- mikeb
- Flight Lieutenant
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Re: TSN 1-2450A instead of LM7905
Maybe the TSN module starts up a little slower than a 7905 and a snappy power supply, (either just how it is, or a deliberate soft-start feature).
Next time you come across this :-
1) Ensure that you are providing a good solid input supply, powered on smartly.
2) When Oric doesn't boot (as you found), with the power applied, short pin 1 and 40 of the CPU together (~RESET to ground) briefly with a wire and
release it.
3) If Oric now starts, it needs a longer reset pulse, because the +5v power supply is now too slow coming up. Replace C21 1uF/10v with something larger (4.7uF/10uF still at 10v) to get a x4 or x10 size reset pulse. And try again.
4) Do not get distracted and build a microcontroller based reset manager module, it's not needed!
Next time you come across this :-
1) Ensure that you are providing a good solid input supply, powered on smartly.
2) When Oric doesn't boot (as you found), with the power applied, short pin 1 and 40 of the CPU together (~RESET to ground) briefly with a wire and
release it.
3) If Oric now starts, it needs a longer reset pulse, because the +5v power supply is now too slow coming up. Replace C21 1uF/10v with something larger (4.7uF/10uF still at 10v) to get a x4 or x10 size reset pulse. And try again.
4) Do not get distracted and build a microcontroller based reset manager module, it's not needed!
Re: TSN 1-2450A instead of LM7905
Thanks Mike I will try that if I fit it again, I won’t probably do this for a while though.
Oric Extended Basic V1.1
(C) 1983 Tangerine
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(C) 1983 Tangerine
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Re: TSN 1-2450A instead of LM7905
It’s definitely the right part HigashiJun, I just have a very temperamental AtmosHigashiJun wrote: ↑Tue Sep 01, 2020 3:02 pm I'm sorry to hear that...
It's quite weird.
Did you receive the right part, ie. TSN 1-2450A and not another one (TSN 1-24150A) ?
Oric Extended Basic V1.1
(C) 1983 Tangerine
37631 Bytes Free
(C) 1983 Tangerine
37631 Bytes Free
Re: TSN 1-2450A instead of LM7905
I fitted the 2450A regulator again and the Atmos does boot if you short the Reset pin so I fitted a 4.7uf cap and had no joy but when I fitted a 10uf Capacitor the Atmos boots up so thanks to Mikeb for the tip on replacing the Cap with a higher value.
Oric Extended Basic V1.1
(C) 1983 Tangerine
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(C) 1983 Tangerine
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- HigashiJun
- Flying Officer
- Posts: 205
- Joined: Tue Dec 10, 2019 9:29 am
- Location: Tokyo (Japan)