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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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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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
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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?
https://photos.app.goo.gl/TvQdCqG1ppQpYrX4A
so pick what works best for you!
Enough rambling for one email. Enjoy!
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Interesting. Good to know.
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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.
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Also, on the new backplane I added the PTC to limited the current for the +5V, & +-18V rails.
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On Nov 19, 2022, at 5:45 PM, norberto.collado koyado.com <norberto...@koyado.com> wrote:
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