My Toshiba HX-10 gets mighty hot!

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Van gdx

Enlighted (5714)

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10-12-2016, 13:52

The B435 can be replaced simply be a BD242. It support a very high temperature. The transition frequency is much less important but I do not think it is important for this use.

Van Colemu

Hero (539)

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10-12-2016, 15:01

gdx wrote:

The B435 can be replaced simply be a BD242. It support a very high temperature. The transition frequency is much less important but I do not think it is important for this use.

Sounds like a good idea if it's a simple 'drop in' replacement. But will it provide the same drop in heat generation that RetroTechie's solution would provide?

Van gdx

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10-12-2016, 15:33

I think it should heat a little less but I'm not sure. The main thing is that it supports the power to be supplied. Do you have a thermal probe? If it gets too hot, think about changing the nearby capacitors. If the temperature exceeds 80°, capacitors at 105° are required.

I ordered a z80 cmos at $1.16 to try. This solution is probably sufficient and it is the cheapest.

Van Colemu

Hero (539)

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10-12-2016, 16:11

My thermal probe is my finger Tongue

I'll hang fire for the time being, let me know how you get on gdx

P.S. I've ordered a couple of them Z80's too (one for my Grey Speccy) Cool

Thanks for your suggestions RetroTechie, as helpful as I remember!! Big smile

Van RetroTechie

Paragon (1563)

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10-12-2016, 21:09

gdx wrote:

I think it should heat a little less but I'm not sure.

A transistor just burns off the excess voltage, like a 78xx or any other linear regulator would. Efficiency depends on the ratio out:in voltage, which here is 5V/9V = ~56%. For example @ 1A that is 9W in, 5W out = 4W dumped in the transistor. Replacing transistor with another type changes nothing to that. Zero. Nada.

Max. junction temperature is rated as 150 oC for both 2SB435 and BD242, which is pretty much standard for transistors like this. Btw the BD242 has a much lower DC current gain, so isn't a good replacement anyway.

For a switching DC/DC converter: say it's ~85% efficient. Then at 1A it's 5.9W in, 5W out, 0.9W lost as heat in the DC/DC module. @9V in, that's 0.65A pulled from transformer vs 1A with transistor or 7805 regulator. Shocked! And 9W - 5.9W = 3.1W less heat released inside the machine.

Van Colemu

Hero (539)

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11-12-2016, 13:27

Very informative RetroTechie!

Will it provide enough power for additional hardware attached to the machine? (power hungry carts etc)

Am I on the right track with this one: http://www.ebay.co.uk/itm/HRD-DC-DC-Converter-DC-48V-36V-24V...

Or this one: http://www.ebay.co.uk/itm/Mini-DC-DC-12-24V-To-5V-3A-Adjusta...

Van gdx

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11-12-2016, 14:23

Thank you RetroTechie for clear advice.
I only said that the BD242 would heat a little less because as the diodes more the intensity exceeds the nominal value, more the heat increases. If the nominal value is never reached replace the transistor will indeed not change anything.

The z80 CMOS, the heat sink replacement and the addition of two heat sinks for SDRAM should suffice. We just have to find the right heat sink and an effective thermal paste.
About capacitors, I checked the two closest (2200μF 35V and 4700μF 16V). These support a temperature until 85°. We must check if the temperature exceeds 80° if so, replace them with new capacitors at 105°.

(PS: The ratio out:in voltage, which here is 5V/9V = 44.44%)

Van RetroTechie

Paragon (1563)

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12-12-2016, 01:36

gdx wrote:

(PS: The ratio out:in voltage, which here is 5V/9V = 44.44%)

Your calculator is broken... Wink LOL!

Van gdx

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12-12-2016, 08:07

You are sure that 9V - 44.44% is not 5V?! Shocked!

Van sd_snatcher

Prophet (3558)

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12-12-2016, 12:28

Quote:

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

To use up to the Z84C0010 is fine, but I would advise against the use of the Z84C0020. I've read in many places that this specific version has different buffers and require a specific motherboard design. Even to operate at lower clocks.

It may seem to work at first in your Toshiba, but then you might end up with a temperamental machine that will randomly refuse to accept certain cartridges or certain combinations of cartridges.

So, stick to any Z80 CMOS of 10MHz or less. The Z84C0006, Z84C0008 and Z84C0010 all cost nearly the same as a Z84C0020.

But be very careful about where you buy your CPU. There are a lot of fake Z80s out there,and even NMOS Z80s rebranded to look like a CMOS part. Be sure to check if the power consumption has gone down after the swap.

Another important tip is to do a Google search on the reputation of any eBay seller before buying tempting cheap parts from him.

I'm no expert, but IMHO that specific Z80 linked before look as phony as a $3 bill. :D

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