TSN 1-2450A instead of LM7905

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Vyper68
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Re: TSN 1-2450A instead of LM7905

Post by Vyper68 »

I am pleased I got to the bottom of it with Mikeb’s help. Sorry to hear about your Cumana Reborn issues HigashiJun, hope it works okay from now on.
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Re: TSN 1-2450A instead of LM7905

Post by mikeb »

Vyper68 wrote: Mon Sep 07, 2020 12:12 pm 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.
OK, so that shows you how slow the module is at achieving full voltage compared to a 7905 and a decent switch-on :)

It's probably buried in a datasheet for the module, somewhere, in the diagrams at the back!
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Re: TSN 1-2450A instead of LM7905

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mikeb wrote: Mon Sep 07, 2020 4:44 pm
Vyper68 wrote: Mon Sep 07, 2020 12:12 pm 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.
OK, so that shows you how slow the module is at achieving full voltage compared to a 7905 and a decent switch-on :)

It's probably buried in a datasheet for the module, somewhere, in the diagrams at the back!
It says startup time is 15ms at nominal vIn with constant resistive load and time for 10% to 90% of vOut is 10ms, how’s that compare to a normal 7905?
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Re: TSN 1-2450A instead of LM7905

Post by HigashiJun »

Vyper68 wrote: Mon Sep 07, 2020 3:43 pm I am pleased I got to the bottom of it with Mikeb’s help. Sorry to hear about your Cumana Reborn issues HigashiJun, hope it works okay from now on.
Thank you. No worries, it works fine now.
HigashiJun
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Re: TSN 1-2450A instead of LM7905

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Vyper68 wrote: Mon Sep 07, 2020 5:55 pm It says startup time is 15ms at nominal vIn with constant resistive load and time for 10% to 90% of vOut is 10ms, how’s that compare to a normal 7905?
10ms of ramping up. OK. Well, I just checked an SGS-Thompson 7905 datasheet, there is no mention of time at all because it's going to be almost instant, it's just a pass-transistor and some feedback/monitoring circuit. Not a multiple-cycle charge-chucking design with inductors which take a few cycles to get going :)

For 1uF/2k2 original Oric reset circuit, it's about a 2.2ms time constant. So the processor is being released while things are struggling to start. 4.7uF is about 10ms -- as you found, marginal/not working. 10uF more like 22ms, and that works for you!
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Re: TSN 1-2450A instead of LM7905

Post by iss »

Correct! :)
Just to clarify mikeb's magic numbers: the time depends on the RC group charging/discharging constant i.e.
T=R*C, or in the 'standard' case T = 2200[ohms] * 0.000001[farads] = 0.0022[seconds] or 2.2ms ;).
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Re: TSN 1-2450A instead of LM7905

Post by Dbug »

Is that the proper part:
https://no.rs-online.com/web/p/switchin ... rs/7880604

They only seem to have the model without the bent legs on this norwegian shop, would that work on the Oric, or would that be too tall and definitely require the one on the right on https://www.tracopower.com/int/model/tsn-1-2450a ?

EDIT: If I'm going to order, I can also probably get the capacitor at the same time:
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.
There are thousands of these, what should I go for in term of voltage rating?
https://no.rs-online.com/web/c/passive- ... hTerm=10uf
That goes from quite small to quite high :D

And yes, I'm a super n00b in electronics, but since my Atmos is getting harder and harder to startup, and apparently bad reset need to be fixed, I though it would make sense to do that and be done with it, am I missing anything? (I also wanted to test a 65c02, 65c802 and 65c816 adapter board)
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Re: TSN 1-2450A instead of LM7905

Post by mikeb »

As for the capacitor, any 10uF small electrolytic, rated at 10v to 16v should fit in there. Modern electrolytics tend to be slightly smaller, value/voltage being the same, than older ones.

It's not under any particular stress (temperature, heavy currents) like those used in switch mode power supplies. The only problem seems to be after 37-odd years, the 1uF isn't 1uF any more, so doesn't provide a lone enough pulse.
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Re: TSN 1-2450A instead of LM7905

Post by iss »

I will second @mikeb, from practical side any small 10uF electrolytic capacitor will do the job. About the voltage even 25V is OK.
This are good quality ECA1EAK100X, but if you decide to use the expensive TSN 1-2450A then to complete your "boutique" Oric I'll recommend to use a polymer capacitor like 25SEP10M - this should guarantee stable work for a century ...at-least. :)
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Re: TSN 1-2450A instead of LM7905

Post by iss »

Maybe this deserves own topic, but posting here because it's related to the reset capacitor you want to change.
While working on one project I found something curious and annoying in the Oric RESET signal:
orics-reset.png
Here is the quick sketch of the schematics:
orics-reset-sch.png
orics-reset-sch.png (10.94 KiB) Viewed 5376 times
As you can see both signals RESET-04 and ROMDIS-05 are driven from the same source.
The ROMDIS-05 signal repeats the input pulse exactly.
The RESET-04 signal is delayed because the R+C inside Oric (i.e. RP1=2,2k and C21=1uF) - this OK, the falling edge is OK (the capacitor is discharged trough the external 7407 buffer on the sketch), but what the heck are this spikes while expecting delayed but clean rising edge?
In fact this is a quickly repeating reset and maybe this can be the reason for not always booting Orics. What do you think? :)
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Re: TSN 1-2450A instead of LM7905

Post by mikeb »

I've no idea what the Arduino circuit is doing (or trying to do), so won't comment on that too much -- I can't think of a good reason to drive the ROMDIS low at the same time as reset, while RESET is low the 6502 is dead anyway, so won't see the ROM whether it's there or not.

I think the mess you see is a signal that is transitioning from low to high, via the "undefined" stage of TTL chips. It's noise.

Nobody told the capacitor to charge digitally ;)

The correct way to fix that is the R/C goes into a Schmitt Trigger, not a plain old inverter/buffer. This means it will neatly snap from one state to another.

In practice I don't suppose it matters that the processor gets reset, reset, re re reset, reset .... as long as the LAST reset comes AFTER sufficient time for the power supply to be stable, and for the ULA to have un-knotted itself at startup (takes a few cycles at 12MHz to properly get the clock division running, and then a short time where the row/column counters could be rubbish -- they right themselves eventually).
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Re: TSN 1-2450A instead of LM7905

Post by iss »

mikeb wrote: Sat Feb 06, 2021 7:04 pm...
Sure. Everything is clear for me - I wanted only to show one more strange thing in our Orics - full of bad engineering practices...
but 'it lives' and this makes Oric attractive in a weird way.

Else, I'll reveal the purpose of the Arduino very soon, my project works now and I'm very happy. Here its goal is just to assure "clean" pulse and to prove that source of the spikes is not an "undebounced" button :).
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Re: TSN 1-2450A instead of LM7905

Post by HigashiJun »

Dbug wrote: Fri Feb 05, 2021 8:47 am Is that the proper part:
https://no.rs-online.com/web/p/switchin ... rs/7880604

They only seem to have the model without the bent legs on this norwegian shop, would that work on the Oric, or would that be too tall and definitely require the one on the right on https://www.tracopower.com/int/model/tsn-1-2450a ?

EDIT: If I'm going to order, I can also probably get the capacitor at the same time:
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.
There are thousands of these, what should I go for in term of voltage rating?
https://no.rs-online.com/web/c/passive- ... hTerm=10uf
That goes from quite small to quite high :D

And yes, I'm a super n00b in electronics, but since my Atmos is getting harder and harder to startup, and apparently bad reset need to be fixed, I though it would make sense to do that and be done with it, am I missing anything? (I also wanted to test a 65c02, 65c802 and 65c816 adapter board)
The angular pinned one is the TSN 1-2450A. You can find it on Digikey.

Your Oric will not boot if you do not change the capacitor.

Cheers.
HigashiJun
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