Replacement power supply for the Toshiba T1200 laptop computer | Hacker News Reader

Replacement power supply for the Toshiba T1200 laptop computer

github.com

82 pointselvis7033 comments

It's amazingly smaller than the original. Author says he's removed quite a few non essential features ; but I wonder how much of the difference in footprint is due to technological advances in PSU components. (I am assuming here that the original PSU was a switchmode design as well?)

Whoa, the T1200 was my first computer as a child and I found one a while ago without a power supply.

This could be extremely useful for me, so thank you very much for posting this! :)

As we are here, let me ask you what is the most vintage computer, or computer of historical interest, you still enjoy tinkering on nowadays?

My Sharp MZ-80K[1] and BBC Micro Model B[2] are still in working order and I tinker with them from time to time. Recently I've spent a lot of time messing around with 1980s/1990s French Minitel terminals:

https://blog.jgc.org/2022/03/using-minitel-1b-as-serial-term...

https://blog.jgc.org/2022/03/voiding-warranty-on-1993-minite...

https://blog.jgc.org/2022/04/setting-up-and-running-mame-emu...

[1] https://blog.jgc.org/2011/11/back-from-dead-with-power-suppl...

[2] https://blog.jgc.org/2009/08/in-which-i-switch-on-30-year-ol...

Nice! And congrats on the care you put forward to keep those machines in good working order. In Italy we had a very similar videotex network called Videotel, whose terminals are still being resold on eBay. I was considering using one of those as a distraction-free terminal. However I still have with me a few Olivetti VT100 and VT220 terminals from the 1980s that would serve the same purpose very well, and have not enough space for everything. Thanks for your answer, and happy hacking!

The keyboards on the Minitel/Videotel terminals are nasty. As much as it's fun to use one for a short while for retrocomputing karma purposes, they are no fun for real work.

The mechanical keyboards on actual VT100/220 terminals tend to be much, much nicer and more robust.

Well noted, thank you for letting me know!

Got my hands on a 80286 the other week, and have been tinkering and having lots of fun, but forgot how painful and cumbersome things used to be; BIOS doesn't have a built-in menu but has to have setup run from disk, the 5 1/2 inch floppy drive doesn't read disks anymore because it's been bumped or something, thank god there's a 3 1/2 drive that works, but hold on it's not 1.44mb but 1.2mb so that causes its own issues trying to transfer things from PC, the hard drive is so small (20mb) that it can barely hold anything and so you have to make a decision if you want to sacrifice performance and install DoubleSpace/Stacker to compress the whole drive to gain more space etc etc :) another fun thing I learned is that you can use Hydrogen Peroxide, UV lights (and/or sunlight) and cling wrap and restore old discoloured computer plastic parts (keyboards, cases, drives etc) to new looking!

Aha, I know how does it feel! I have my first programs lost on a bunch 5 1/2 inch floppies, which, I know, will require some serious tinkering. I hope one day I will feel the urge to go after all of this.

I also have a collection of 8 inches floppies that belonged to my father. However in that case accessing them again would require some sort of "computational archeology". To begin with I don't even have any longer 8 inches drives... :-)

If you can find a group that does computer archiving they may be able to assist - especially if local.

Commodore 128. To the point that I've made a replacement PCB for it and have started reverse engineering the system specific ICs. It was my first computer and I really like how much of a frankensteins monster it is (6502 and Z80 on the same bus, two video chips, etc)

https://github.com/jgrip/open128

Kudos! It is wonderful to see how the computers from Commodore's age invite us to explore them in full.

One thing I'd love to see is a replacement PSU for the 128DCR. The flat 128 seems to have modern replacements, but I could not find one for the DCR.

I got a 128DCR as a thrift-shop find like 5 years ago, but it had an iffy PSU. I was lucky to find a surplus vendor with a cache of NOS units a few years ago. (If they had mentioned the word 'Commodore' on their product description, they would have likely long ago sold through, but it was mentioned on some old Amiga forum in passing) I'm sure you could bolt together two of those metal-cage SMPS units to provide the right voltages, but even a simple guide like "Buy models X and Y, and here's how you wire it to a harness" would be a useful resource.

It can be done for sure I've seen some designs for it. The 128DCR generates +5, +12 and 9V AC so pretty straight forward.

Small meanwell unit and a transformer should do the trick.

https://www.youtube.com/watch?v=TCQE-rmo8XM for example.

My 1st computer was a TRS-80 Model 1 and I recently acquired one which I will likely start restoring after the summer when I need some inside activities for my free time.

I have a Zenith Z-160 PC compatible luggable from 1984 which I restored and use frequently. I love that the floppy drives pop up from the top of the machine and that the machine is based on an ISA slot backplane rather than a traditional motherboard. I mostly use it to play old CGA games. It has a CGA composite output which I connect an external monitor to in order to enjoy the glory that is CGA color.

https://www.old-computers.com/museum/computer.asp?st=1&c=465

Cool! While I never had the chance to work with Zenith Z-160 or a TRS-80 Model 1, I can relate! My first PC was an Olivetti M19 (1986), which featured, like the Zenith, an ISA slot backplane and CGA graphics. No hard drive but a couple of 5 1/2 inch drives. It was powered by 4.77Mhz 8088. [0] I never had more fun than with that tiny box. It was my first machine I used to connect in dial-up to BBSs too.

[0] https://en.wikipedia.org/wiki/Olivetti_M19

You inspired me to download KiCad, modify a shared board on OSH Park, and place my first order for 3 custom PCBs for $1.95 total with free shipping. Thanks for your inspiration!

Switched power supplies are notorious for causing EMI; why didn't he test for it? Frankly, it sounds like he just copied the circuit from a datasheet and called it a day.

How would you suppose he tests for EMI? He says he is using mostly power supply modules which will have some thought already put into EMI suppression. Beyond that, if the system works why should he worry about EMI? To take any quantitative measurements would require a chamber and calibrated instruments. This is akin to asking why a hobby software project doesn't have full coverage unit testing.

Also if their layout wasn’t a total mess I don’t imagine it’ll be too bad.

If a software engineer said: this Rust code leaks a bit, but it shouldn't be too bad, you only have to restart it once a day, then what would you think of it?

so glad to hear none of the code you’re working on has ever leaked, even while it’s in development and being worked on. what the hell is wrong with you?

The point is not whether my code has leaked or not, but whether I was even aware that leakages are a possibility. I'd be happy if someone pointed it out, even if not entirely in the correct tone.

You’re pointing out an extremely common issue with switch mode power supplies. It’s so common that it comes off like you’re calling the author an idiot. It’s not helpful —- you’re 100% not at all being helpful.

The way to be helpful would be to LOOK at the layout, component choices, and design, and suggest changes, but you’ve done nothing of the sort.

>He says he is using mostly power supply modules which will have some thought already put into EMI suppression.

He is not. MAX776 are controllers, and older ones at that. These require some skill to apply effectively. I wouldn't do it this way, I'd look at the LMR36xxx series (and friends, you'd want the 60V switches here) sync bucks for this. Hot loop on die = goodbye EMI!

So what? Seems to work fine. It’s not a commercial product.

It might be used in the vicinity of commercial products.

E.g. medical products.

Some useful notes...

Designing switched mode supplies is hard. I've just barely started playing with them, but it's really tough choosing component values that don't ring like a bell, a loud bell, at pretty high frequencies. I've found these two series of web pages [0] [1] to be very useful, even for an electronics neophyte such as myself. Also, for simulations Xyce [2] handles the large current transients much better than Ngspice [3] (the default simulator for KiCad), and the Xyce docs gave me some really good guidance on how to tweak the settings.

One trick I stumbled on was to run the input voltage as high as feasable; for the part I'm trying to use the source/drain effective source/drain capacitance drops dramatically as the voltage goes up. It's the MOSFET capacitances that are causing me the most grief.

And testing for EMI seems to be a black art. Hack-a-Day has listed some do-it-yourself projects for probes and testing ([4] [5] ...), but haven't gotten that far yet.

[edit.. toned down a little]

[0] https://www.powerelectronicsnews.com/the-dc-dc-boost-convert...

[1] http://tuks.nl/Mirror/SwitchModePowerSupply_smpstech_com/map...

[2] https://xyce.sandia.gov/

[3] http://ngspice.sourceforge.net/

[4] https://hackaday.com/2014/03/18/listening-to-electromagnetic...

[5] https://hackaday.com/2021/05/21/simple-probe-sniffs-out-emi/

>it's really tough choosing component values that don't ring like a bell, a loud bell, at pretty high frequencies

That doesn't sound right to me. It's not really about the component values. It's about the parasitics and the edge rates that can ring those parasitics. The main LC elements are not usually the problem (especially at high frequencies).

> for simulations

You cannot simulate any SMPS for EMC reasons without including the layout. Full stop, do not pass Go, etc. You can simulate for functionality and you can avoid some well-known traps, but you'll never be able to be confident without the layout included. Never.

> run the input voltage as high as feasable

Usually you want your duty cycle around 50%. Higher input voltages will push that down, which is usually a bad thing and requires special measures to compensate. And switch capacitances are rarely a major problem below line voltages, so you don't get much return on it either.

What, exactly, are you trying to do?

(Disclaimer: professional EE but not a power guy. I do little SMPS stuff up to 24V all the time though, especially low-noise analog supplies.)

I'm just getting into analog electronics. Nominally, I'm trying to synthesize 90VAC @ 30mA (telephone ring signal) using buck/boost from a "reasonable" input voltage with reasonable efficiency. Not anywhere close to worrying about interference, but seeing simulated 3A swings at 1MHz is not encouraging... A big chunk of that is due to gate/src & src/drain capacitance. I'm finding that jacking up the inductance leads to really high average currents, cutting the inductance means really small damping resistors and high current again, shrinking the output capacitance helps the ringing and quickly gets the voltage where I need it, but now the ripple is horrible... fun times!

> Switched power supplies are notorious for causing EMI; why didn't he test for it?

The necessary equipment - anechoic chamber, proper antenna and scope - goes into the six figures. Way out of reach for hobbyists and most if not all maker associations.

It appears the author agrees with you

> This is the initial commit, revision 1, and has a few issues, but it works and the computer boots! It will no doubt be obvious that I am not an engineer, and I certainly don't specialise in SMPS circuit design. I have used modular power options where possible and have tried to follow the recommended design for the -22V SMPS circuit as closely as possible. Please feel free to improve on this design. [emphasis mine]

More critical than EMI, methinks, is something he takes pains to point out:

> There is NO output protection (I'm not sure if there ever will be), so if you build one of these then make sure to check the voltage rails before using it.

Sounds like a nice, humble attitude. Despite the humility, the end result is a project that meets his needs and provides useful details for others to use or build upon.

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