My Toshiba HX-10 gets mighty hot!

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By tvalenca

Paladin (728)

tvalenca's picture

09-12-2016, 02:25

gdx wrote:

There is no reason to change the transformer except when the varnish gets too old.
The European HX-10 are already 220-240V. If you use a Japanese HX-10, You must use an AC adapter to 100V with a power more than 30W.

Changing the regulator that heats up the most is a good idea. It is necessary to know the reference of the component and to take another one of higher intensity. I do not know if the service manual is available.

I recommend taking like me waiting for something better. I think both regulators without radiator are for the +12V and -12V because my memory expansion is the MMM, the version that use these tensions. FM-PAC and some other cartridges also use these tensions.

You can change the regulator, but (at least on Japanese machines) the transformer is pretty much at its current supplying limit. Forced ventilation may achieve a compromise between cost and benefit.

By Colemu

Hero (531)

Colemu's picture

09-12-2016, 14:32

RetroTechie wrote:

Can you see how the part is "named" according to silkscreen marking on the board?

Also: do you have a voltmeter? If so: find a 0V (Ground) point, and measure voltage on each of the pins of that part. Results may give us some clues what we're looking at, for example whether it's a plain 78xx 7805 regulator, or a power transistor.

No problem, will do that this weekend. Smile

By sd_snatcher

Prophet (3092)

sd_snatcher's picture

09-12-2016, 23:35

@tvalenca

Let me just add more details here and correct some info, because otherwise people might damage their machines.

- Toshiba's MSX models have some of the worst power supplies I have yet seen on MSX computers.
- Toshiba's Japanese models can only be run at 100V and that's it. Do not try to run them at 110V, and even less at 127V. It can both melt the transformer or literally toast the power supply PCB.
- The heatsinks are way too small, or even missing.
- Because of that the power supply heats up a lot. It's even worse when you plug extensions. And even worser when you plug modern FPGA/CPLD based cartridges.
- For those who want to preserve their beloved machines better and minimize the chance of damage, I published some tips on the Brazilian mailing list that I'll prescribe here too

So, here are my tips to preserve your Toshiba MSX machine and avoid to damage it. But I don't take any responsibilities for such changes. Try them at your own risk:

1) For those who want to keep the machine original, without any mods

- Only use it at the native specified voltage. That is: 100V for Japanese models, and 220V for European models. Do not go over that, or it can melt the transformer and toast the power supply PCB. The MSX2 models have the power supply circuit integrated to the main PCB, so this mean that the machine will be kaput.
- Do not use slot-expanders that don't have their own power supply
- Do not use combo cartridges with an internal slot expander
- Do not use cartridges that have a too high power consumption, like OPL4, V9990, Franky, Playsonic etc

IOW, if you want to keep the machine all original, maybe it's better to just place it in a glass box. Smile

2) For those who want to fix the problem and be able to use the machine without so many restrictions

- Add heatsinks to all regulators that don't have them
- Screw a 4x4cm 12V fan over the biggest original heatsink of the power supply. This will be the +5V regulator. Try to position the fan in a way that the air flow also goes to the other regulators around. There are easy points in the PCB where you can solder the wires for the fan.
(I.e.: In the Japanese HX-22, I had to fix it with only one screw, rotated in 45 degrees in the Z axis. In the HX-23F I had to fix the fan with 2 screws, leaving the "south" part of the fan suspended over the other heatsinks)
- Swap the old Z80A NMOS for a Z80A CMOS, like the Zilog Z84C0004 or the Toshiba TMPZ84C00AP

With these mods you'll be able to use modern cartridges and even slot expanders without restrictions, but will still be restricted to the specified voltage for what it was built, namely 100V or 220V. *Do not use them over these original voltages*. I can't stress this enough.

For 220V machines, the mods explained until this point are sufficient.

3) for those who want to be able to use a Toshiba 100V MSX machine on 110V or 127V

- The transformer *must* to be rewinded. Find a good professional/company who's specialized in such work, and give them the voltage specs you want them to adjust the transformer too. Maybe it's better to ask them to rewind the transformer to 127V, so it'll have a bit of margin in case of any unexpected oscillations in the mains.
- AFAIK, it's not possible to replace the transformer with a new one, because the original transformer is slim and it's absolutely not easy to find one that fits on its place. This is why you have to rewind the original.

4) For those who don't care to completely change the design and have much more power, then for the MSX1 models there's always the possibility to:

- Remove the slim transformer and the power supply PCB
- Insert a new switched power supply, preferably one that can take 100V to 240V and output at least 2A

With this mod you won't need to replace the Z80 NMOS with the Z80 CMOS

But for the all-in-one MSX2 models such mod isn't that easy, because the power supply circuit is integrated in the motherboard.

By rderooy

Hero (583)

rderooy's picture

10-12-2016, 00:47

FYI

Back in January 2003 in Europe, voltage was harmonised to 230V. Meaning there is no 220V any longer. Before that, most countries had 220V, but the UK had 240V. So if the system was designed to handle both mainland European 220V and UK 240V, it should have no issues with 230V.

By tvalenca

Paladin (728)

tvalenca's picture

10-12-2016, 05:17

rderooy wrote:

FYI

Back in January 2003 in Europe, voltage was harmonised to 230V. Meaning there is no 220V any longer. Before that, most countries had 220V, but the UK had 240V. So if the system was designed to handle both mainland European 220V and UK 240V, it should have no issues with 230V.

if those machines have this info (240v) printed on bottom label, I can't see any problem. but if it shows 220V, that's an issue.

By RetroTechie

Paragon (1563)

RetroTechie's picture

10-12-2016, 06:05

sd_snatcher wrote:

Swap the old Z80A NMOS for a Z80A CMOS, like the Zilog Z84C0004 or the Toshiba TMPZ84C00AP

Second that.. can take almost 1W + associated losses in power supply off the table. NMOS Z80: max. 200 mA (=1W at 5V, a lot of heat for a 40-pin plastic DIP). CMOS Z80: max. 5 mA (=25 mW at 5V) per MHz, so 0.1W at 4 MHz.

Quote:

4) For those who don't care to completely change the design and have much more power, then for the MSX1 models there's always the possibility to:

- Remove the slim transformer and the power supply PCB
- Insert a new switched power supply, preferably one that can take 100V to 240V and output at least 2A

Would be a good option in this case. But requires changes to the mainboard, probably removing some components, cutting/re-routing some pcb tracks etc. Kinda difficult to figure out what needs doing, when schematic is missing. Sad

I dislike machines with power circuit integrated on mainboard, for this very reason. Evil Makes it unnecessarily difficult to cut out the power supply as a whole & replace with something else.

By gdx

Prophet (3090)

gdx's picture

10-12-2016, 10:38

A CMOS Z80 as solution is interesting. The CPU is on socket, it's easy to replace.
This with a newer more powerful regulator should be the best choice. For both regulators without sink seat, add heat sinks for SDRAM seem suffice. There is no question of putting a fan in one of my MSX.

The LH0080A (used in the HX-10) consumes 200mA and the Z84C0020PEC consumes 20mA.

The Z84C0020PEC can be found on ebay.
www.ebay.com/itm/1PCS-Z80-CPU-Microprocessor-IC-ZILOG-DIP-40...

The Z84C0004PEC is more expensive:
http://www.ebay.com/itm/ZILOG-Z84C0004PEC-DIP-40-Z80-Microco...

By Colemu

Hero (531)

Colemu's picture

10-12-2016, 10:44

Measured the voltages and they are as follows (from front - left to right):
B=8.3V ; C=5V ; E=9V

The silkscreen marking on the board is TR8

It's this part: http://www.semicon-data.com/transistor/tc/b0/B435.html

The other 2 transistors (not heatsinked) are: D880 & A473

By gdx

Prophet (3090)

gdx's picture

10-12-2016, 12:18

Colemu wrote:

The other 2 transistors (not heatsinked) are: D880 & A473

I had noted D880 & A478 but you are right. A473 is more coherent. I do not think we need to replace them. 3A is more than enough.

sd_snatcher wrote:

- Do not use slot-expanders that don't have their own power supply

This is a rule to follow on all MSX if the expander has more than 2x slots.

By RetroTechie

Paragon (1563)

RetroTechie's picture

10-12-2016, 13:40

Colemu wrote:

Measured the voltages and they are as follows (from front - left to right):
B=8.3V ; C=5V ; E=9V

Well if -as it seems- that transistor is sitting directly between unregulated DC voltage (9V here) and 5V out, then you could easily replace with a 78xx style DC/DC converter module. But you'd have to use one rated for at least 1.5A, a 1A one either won't do or leaves too little margin to plug in cartridges. Typical example: Aimtec AMSR2-7805-NZ
Many more of such 78xx drop-ins can be found. Biggest disadvantage is their price, and cheap equivalents from eBay... well, you never know what you'll get.

Left pin of such a 78xx drop-in would go to the point carrying 9V now, right pin would go to the point carrying 5V now, and centre pin would be connected to Ground elsewhere on the mainboard.

Or you could try your luck with a cheap DC/DC board from eBay. Suggested search term: "XL4005 module" (without quotes)

EDIT: both DC/DC converter modules would drop the overall heat produced inside the computer, no matter what's on the mainboard or inserted as cartridge. Current on the 5V would be the same, but current drawn from unregulated DC would be lower. Seeing that input DC is ~9V now, you could expect roughly 1/3 less heat inside the machine. More gain if eg. Z80 is also replaced.

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