MSX PSU help

Enlighted (5918)

22-06-2015, 09:20

Hi,

If i plan to run "normal" MSX2 with slot expander, Music Module, FM-PAC, SD-card interface, Network card and memory mapper, what kind of values I should have in my PSU?

I have understood that -12V is there more for decoration, so probably something like 150mA is fine for it (???) but what about +5V and +12V lines? I can see that 3A DC-DC converters are practically free, but I'm pretty sure they are not strong enough... 5A, 8A, 10A? Any better ideas? How much amperes original PSU's usually give out?

Unfortunately it seems that more amperes very fast tend to increase both size and price... I try to find a reasonable priced solution that would fit in to the original Yamaha case.

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Par RetroTechie

Paragon (1563)

23-06-2015, 04:11

About 2A @5V will power practically all MSX1's and quite a few MSX2's.

If you don't believe me, just check continuous output rating for the 5V regulators in some machines. For example SI-3052 (used in Sony HB-F700 and a few others) is rated for 2.0A continuous. Same goes for STR2005 (used in NMS8245 and some VG8020), and STK770 (used in some other Philips machines).

Philips NMS8250/55/80 machines have a beefier 5V regulator (STR9005) which is rated for 4.0A continuous. Which isn't surprising given the large mobo, number of discrete 74LS... IC's, and 1 or 2 floppy drives. But I doubt these machines draw 4A all the time, more likely somewhere ~3A continuous.

Of course current peaks may be a bit higher. As for floppy drives: older ones use 12V (100~200 mA per drive?) and possibly less on the 5V line. Newer floppy drives typically have a 5V/400 mA (2W) current draw per drive (and zero on the 12V line). So 12V requirements might be tricky to estimate.

It would be good to have some actual measured figures for power draw from different MSX machines. Too bad I don't have those...

NYYRIKKI wrote:

If i plan to run "normal" MSX2 with slot expander, Music Module, FM-PAC, SD-card interface, Network card and memory mapper, (..)

Slot expander has its own power supply (for the cartridges in, that is), right? If not, it should. Bad practice (and against MSX standard) to power that # of cartridges from the MSX machine itself.

Quote:

I have understood that -12V is there more for decoration,

True. Some audio cartridges may use it though (Philips Music Module comes to mind).

Quote:

I try to find a reasonable priced solution that would fit in to the original Yamaha case.

Which Yamaha?

Par NYYRIKKI

Enlighted (5918)

23-06-2015, 09:52

Thank you RetroTechie... This does not sound too bad...

RetroTechie wrote:

Slot expander has its own power supply (for the cartridges in, that is), right? If not, it should. Bad practice (and against MSX standard) to power that # of cartridges from the MSX machine itself.

I know... One of my slot expanders have option to use external PSU and other one does not... Anyway I thought that if I put strong enough PSU to the MSX it self, I don't need to have a mess of wires (or worst case PC internal PSU) hanging on the table.

Quote:

Which Yamaha?

IIRC it was beaten up YIS503II that I have as parts at the moment... Unfortunately someone has stolen the PSU, but I like the hardware... At the moment it has a Russian network card, but actually I'm planning to replace it as I have few extra SFG-05 cards lying around that have the same connector...

Now one option that I found is to use some old laptop PSU together with this one... Earlier I looked for these, but they were all powered by 12V and I don't have such beefy transformers lying around either...

Another option was to build the voltages with individual DC-DC converters, but after I found the previous option I don't think that it is worth it... I also don't feel sure if I can do -12V by just connecting one regulators "+" to ground (?)

Tiny packet with all in one would be best, but laptop PSUs I can get for free, so this sounds like a way to go as I'm not planning to invest huge amount of money to this project anyway... It just makes no sense when you are not planning to restore it to original condition anyway and you can get already working MSX2 for ~50€ + shipping.

Par RetroTechie

Paragon (1563)

24-06-2015, 01:20

NYYRIKKI wrote:

Now one option that I found is to use some old laptop PSU together with this one...

Agreed... laptop brick + PicoPSU would be a nice option. Although you would have the external brick then.

Had a look around recently for MSX psu replacement options. For example check this page:
http://www.meanwell.com/webnet/search/seriessearch.html
Especially models under "Enclosed Switching Power Supply" and "Open Frame Switching Power Supply" in 25-45W range and marked with "Dual" or "Triple". Under 25W quickly gets too weak, over 45W quickly gets too big.

The NET-35B would fit most MSX2's like a glove, if space for it allows. And not too expensive either.

But I have no idea how these psu's are quality-wise. Although Mean Well is a well known brand for psu's like this. Note there's quite a few cheap knock-offs out there! Often same or similar type designations, no-name brands, and cheapest-of-the-cheap components. Which might not even be a problem if used only now & then.

Quote:

I also don't feel sure if I can do -12V by just connecting one regulators "+" to ground (?)

If only it were that simple... but especially those cheap DC-DC converters will be non-isolated type, meaning there's restrictions on how you can tie inputs or outputs together.

If you start with +5 and +12V, then you have much more psu models to choose from. And if you start from a single voltage, there's like 1001 choices. -12V could be made using an MC34063 for example, which is tiny & costs peanuts. Problem is not so much component cost, but the construction work needed / wiring mess you may get. That might work for me, but not for most people. So 1st choice would be an all-in-one replacement like that NET-35B. 2nd option would be a single output psu (say 5V @4~5A or so) with an add-on board that contains AC filter / fuse(s), and DC-DC converters for the other voltages. But there's no ready-made solution for this... (although some DC voltage -> +12 and -12V modules are out there too, like what's used in the 1chipMSX).

Par NYYRIKKI

Enlighted (5918)

24-06-2015, 11:47

Indeed I think that NET-35B would fit nicely although it might not power the cartridges anymore... I need to think about this... There are pros and cons on both solutions. The nice thing in PicoPSU is that I don't need to have 240V anywhere near my hands or other electronics inside the project computer and it gives me more than enough power for all my needs... On the other hand NET-35B makes the device more portable when extensions are not needed and more close to original solution. In price there seems to be no major differences.

Also if 65W laptop brick would be enough then the "external brick" could be maybe mounted inside together with PicoPSU... but that would not solve my power need problems anyway... *just speculating out loud* ... let's see... Too bad transformers have not got smaller and more powerful in same rate as other electronics

Par NYYRIKKI

Enlighted (5918)

25-06-2015, 08:56

After measurements I ended up ordering NET-50B that seems to be a tight, but perfect fit replacement. I think it should be enough for any normal use. Thanks, RetroTechie!

Par djh1697

Paragon (1635)

26-06-2015, 21:38

NYYRIKKI wrote:

If i plan to run "normal" MSX2 with slot expander, Music Module, FM-PAC, SD-card interface, Network card and memory mapper, what kind of values I should have in my PSU?

The "MegaFlashROM SCC+ SD" will only work in a primary slot, since it is a slot expander in its self? I am sure you know that though?

Par sirnak

Supporter (2)

14-07-2015, 23:48

If you need a compact supply that will give 12V and 5V I think there are laptop PSUs that could give you what you need. And when one laptop PSU is not enough, just stock in another to supply all your modules. The problem now is that, if two will fit in your case. You could also use a laptop adapter to supply the rest of the modules.

Regards,
Sirma
http://blog.7pcb.com

Par S0urceror

Master (204)

05-09-2021, 12:45

I bought a non-working Sony HB-F1XD on eBay. After fixing the HIC issues it is now almost working like new. Now I want to focus on the PSU.

Ideally I want to fit a PSU that is universal and takes everything above 100v to 240v both 50hz and 60hz. This way it works in it's mother country Japan and also in the US and Europe.

I found out that the current transformer dimensions are 75x50x40 mm's (WxDxH). A bit too small to fit a Meanwell RT-50B which is 100mms square.

Do you know about other options? Alternatively I have to use an external brick with a picoPSU to create the voltages. Or a tiny 5v Meanwell but loose the 5v/12v options.

What do you recommend?

Par djh1697

Paragon (1635)

05-09-2021, 19:13

The 5v output power from the MSX cartridge port 5v pin is 300mA, in the past I have had a MRRSCC (first version), Sunrise CF, and FM PAC all running from a slot expander without issues.

Par Grauw

Ascended (10581)

05-09-2021, 20:26

Hey Sourceror, I also got an HB-F1XD on the bench right now . Gave it a deep clean to get rid of the dust nests, new HIC capacitors are ordered, and also a conductive paint pen to fix a trace on the keyboard. Still have to test the FDD.

It is a beautiful machine! On the outside, but also on the inside, I think the board looks amazing, the surface mounted ICs embedded in the board looks very cool. And all the sections of functionality so clearly indicated, arrows for the screws, etc. looks very repair-friendly. Although I understand the second layer’s carbon traces are quite fragile for rework, so have to be careful with those.