H8 Mishap and ATX Power Supply Conversion

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Les Bird

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Nov 15, 2022, 11:30:58 AM11/15/22
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Hi all, had a little mishap with one of my H8s. I inserted a card one pin off and smoked the backplane. It was a nice Trionyx backplane (sad face) so I took this opportunity to convert the board to use a PC ATX power supply. I found these really cool ATX power supply breakout boards on Amazon (didn't even know they existed).

Also after Terry Smedley's encounter with a blown capacitor I feel very uncomfortable with the classic H8 power system so another reason to do the conversion.

H8 is now up and running again :)

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glenn.f...@gmail.com

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Nov 15, 2022, 9:31:12 PM11/15/22
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Nice. Does the ATX supply sit outside of the H8 cabinet or inside somewhere?  What form factor power supply did you use? Pictures?

 

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Les Bird
Sent: Tuesday, November 15, 2022 11:31 AM
To: SEBHC <se...@googlegroups.com>
Subject: [sebhc] H8 Mishap and ATX Power Supply Conversion

 

Hi all, had a little mishap with one of my H8s. I inserted a card one pin off and smoked the backplane. It was a nice Trionyx backplane (sad face) so I took this opportunity to convert the board to use a PC ATX power supply. I found these really cool ATX power supply breakout boards on Amazon (didn't even know they existed).

 

Also after Terry Smedley's encounter with a blown capacitor I feel very uncomfortable with the classic H8 power system so another reason to do the conversion.

 

H8 is now up and running again :)

 

 

 

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Les Bird

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Nov 16, 2022, 5:06:27 PM11/16/22
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Glenn, pics attached. I'm using a 500w MicroATX power supply which fits snugly in the back of the H8.

Link to power supply is here: https://www.amazon.com/dp/B08R5NN4FJ

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Les


glenn.f...@gmail.com

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Nov 16, 2022, 5:37:16 PM11/16/22
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Great!  I used a similar approach in Big Blue. Nice use of the old transformer cutout for fan venting

https://photos.app.goo.gl/bPhV5MAZQRPMNkjs6

 

I wanted to retain the option to install the heat sink bar across the top (mostly for stabilization, not heat sink - my boards run cool as a cucumber on the ATX power) so I mounted the power supply using longer screws and spacers.  I think these were M3 screws… got them at my local Ace hardware store…

https://photos.app.goo.gl/e67bAKvVhRPGrSjd9

 

nice to see a few of the 2009 vintage “Les Bird” boards in your system!

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Les Bird
Sent: Wednesday, November 16, 2022 5:06 PM
To: SEBHC <se...@googlegroups.com>
Subject: Re: [sebhc] H8 Mishap and ATX Power Supply Conversion

 

Glenn, pics attached. I'm using a 500w MicroATX power supply which fits snugly in the back of the H8.

 

Link to power supply is here: https://www.amazon.com/dp/B08R5NN4FJ

 

 

 

 

 

Les

 

On Tuesday, November 15, 2022 at 7:31:12 PM UTC-7 Glenn Roberts wrote:

Nice. Does the ATX supply sit outside of the H8 cabinet or inside somewhere?  What form factor power supply did you use? Pictures?

 

 

 

From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Les Bird
Sent: Tuesday, November 15, 2022 11:31 AM
To: SEBHC <se...@googlegroups.com>
Subject: [sebhc] H8 Mishap and ATX Power Supply Conversion

 

Hi all, had a little mishap with one of my H8s. I inserted a card one pin off and smoked the backplane. It was a nice Trionyx backplane (sad face) so I took this opportunity to convert the board to use a PC ATX power supply. I found these really cool ATX power supply breakout boards on Amazon (didn't even know they existed).

 

Also after Terry Smedley's encounter with a blown capacitor I feel very uncomfortable with the classic H8 power system so another reason to do the conversion.

 

H8 is now up and running again :)

 

 

 

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Les Bird

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Nov 16, 2022, 5:52:16 PM11/16/22
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Funny that boards from 2009 are considered "vintage" now. Haha.

Yes, venting out the back through the transformer hole and I can still mount the heatsink bar by tilting the power supply forward a bit.

I have one other H8 (3 total, 2 converted so far) that still uses the old H8 power system. Will probably keep it that way for now. I don't really use it.

Nice work with your H8 and mounting the power supply.

Les

norberto.collado koyado.com

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Nov 17, 2022, 10:30:40 PM11/17/22
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My personal opinion is that the PC power supply is overkill. A short on the H8 backplane might burn out the system easily.

 

For +18V/-18V you can use this transformer from Jameco: https://www.jameco.com/z/PT-2866-R-Jameco-Reliapro-28VCT-Power-Transformer-2-Amp-115-230VAC-Primary_149797.html

 

For +8V, you can use this Power Supply: https://www.amazon.com/PowerNex-HRP-75-7-5-Single-Output-Function/dp/B01H334QV0/ref=sr_1_8?crid=WVA5OP67DHC8&keywords=mean+well+7.5v+power+supply&qid=1660324672&sprefix=mean+well+7.5v+power+supply%2Caps%2C129&sr=8-8

 

Then you can use the same AC On/Off switch that is on the H8 chassis to toggle them.

 

For the H8 original transformer hole, I added a plate to take out some I/O cables as shown below:

 

 

Norberto

glenn.f...@gmail.com

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Nov 18, 2022, 7:00:14 AM11/18/22
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Power supplies always a topic that can generate discussion so I’ll pile on…

 

First a reminder that any of these power supplies will cause you grief if you mis-insert a card in the H8 buss. If you’re off by one pin, which is easy to do, you will short out the supply lines and have lots of trouble. On the traditional H8 power supply I’ve done this of course a few times and if you immediately notice that your system doesn’t come up you should hit the power switch and you may survive, otherwise you’ve likely burned out one or more of the rectifier diodes on the H8 system board.  The newer supplies may not be as forgiving and may burn out traces on the backplane or do other damage.  The lesson: be *sure* to install a blocking key in the gap between the two 25-pin edge connectors on all your boards. The original Heath boards had such a block but they were attached with double sided tape as I recall (?) and could easily fall off.  You can epoxy a shorting block there or even 3-D print blocking pieces similar to the ones originally used by Heath.

 

Second thought: If you’re running with an original power supply its worth thinking about replacing it with modern components.  Old capacitors eventually die with disappointing consequences… The supply options recommended by Norberto are pretty much drop-in replacements and will let you free up space and weight by removing the bulky original supply components.

 

The newer backplane allows you to choose between traditional Heath power supply and a modern ATX (PC) style power supply. 

https://koyado.com/heathkit/New-H8-Website/h8-backplane.html

 

and per Les Bird’s recent post there are even ATX power supply breakout boards that let you adapt them.  When you do this you’ll be applying 5V and +/-12V directly to the power lines on the backplane instead of the 8V and +/-18V that the Heath supply provided. This means that you no longer need regulators on the boards themselves and can short circuit the input/output on them, e.g. see some of the pictures Les posted when he first documented this approach:

https://sebhc.github.io/sebhc/pcbs/H8-2000_Construction.html

 

in fact, the 7805 and 7812 style regulators will not work properly if their input is 5 (or 12 respectively) volts so you do need to bypass them with this approach. 

 

some of the boards Norberto has built allow you to install a shorting block jumper to perform this purpose.

 

The danger of this approach comes if you mix boards between systems.  If you’ve jumpered out the regulators and then install that board in a traditional H8 system you’re now putting 8 V where the board expects a regulated 5 (and 18 on the 12V lines).  If you use the norberto style jumpers you need to remember to pull them out.

 

If you’re working in a mixed environment (some “original” H8 systems and some with ATX supplies) you could replace the 78xx regulators with Pololu step up/down regulators, which accept a wide variety of input voltages

https://www.pololu.com/category/133/step-up-step-down-voltage-regulators

you can then swap boards at will to any system.

 

so why even bother with an ATX supply?

 

  • Inexpensive simple one plug setup with the new backplane
  • Simple low cost supplies available
  • No need to put regulators on the boards
  • System runs extremely cool since there are no heat-generating regulators. No need for cooling fans, etc.
  • Auxiliary power from the supply lets you power floppy drives or Z67-IDE +.  You can create an “all in one” cabinet with the Z67 installed directly in the chassis and just plug it into the ATX supply line

https://photos.app.goo.gl/TvQdCqG1ppQpYrX4A

 

so pick what works best for you!

 

Enough rambling for one email.  Enjoy!

 

  • Glenn
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Les Bird

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Nov 18, 2022, 2:19:46 PM11/18/22
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Actually almost all modern ATX power supplies have short circuit protection built in. They will shut down immediately if a short is detected. I've seen this first hand when powering up an H8 with an ATX supply and a board inserted 1 pin off. In my opinion the ATX power supply is the best and safest way to go.

Les


Tom Wilson

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Nov 18, 2022, 2:23:45 PM11/18/22
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I have some H8 original power supply parts if anyone wants them
Tom

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glenn.f...@gmail.com

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Nov 18, 2022, 9:17:53 PM11/18/22
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Interesting.  Good to know. 

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norberto.collado koyado.com

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Nov 19, 2022, 4:14:36 PM11/19/22
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It all depends on how far away is the short and what resistance it sees. If it sees a load of 0.16 ohms, then it will deliver 32 amps.

norberto.collado koyado.com

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Nov 19, 2022, 5:45:50 PM11/19/22
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Also, on the new backplane I added the PTC to limited the current for the +5V, & +-18V rails.

Glenn Roberts

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Nov 20, 2022, 5:39:37 AM11/20/22
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I guess if people use the ATX power breakout board that Les uses they could add PTC devices to the lines as well.

I see the pros and cons of both approaches but have been happy for many years with my ATX-based system (“Rusty”) so wouldn’t hesitate to recommend that approach…

Sent from my iPad

On Nov 19, 2022, at 5:45 PM, norberto.collado koyado.com <norberto...@koyado.com> wrote:



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