I decided to power up the new H8 backplane to test voltages on the H8 bus. On power-on the power supply turns on and then it shutdown. It seems that I do not have minimum load on the ATX PSU to keep it on. The only voltage I get is the Standby voltage along with it’s LED. I do have the “blue” jumper installed to keep it “on” all the time.
Do anyone knows the minimum A load to keep it running? Not sure if minimum load is on the +5 or +3.3 voltage rails. I hope I do not have a bad PDU as it was expensive to buy.
Thanks,
Norberto ☹
Sent from my iPhone
Thanks for the link, very detailed information. Let me also check the PSU specs as well.
Norberto
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Thanks for the link, very detailed information. Let me also check the PSU specs as well.
Norberto
From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of Steven Feinsmith
Sent: Friday, July 9, 2021 10:32 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Initial H8 Backplane test!
From: se...@googlegroups.com <se...@googlegroups.com> on behalf of norberto...@koyado.com <norberto...@koyado.com>
Sent: Saturday, July 10, 2021 1:22:15 AM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: [sebhc] Initial H8 Backplane test!
I decided to power up the new H8 backplane to test voltages on the H8 bus. On power-on the power supply turns on and then it shutdown. It seems that I do not have minimum load on the ATX PSU to keep it on. The only voltage I get is the Standby voltage along with it’s LED. I do have the “blue” jumper installed to keep it “on” all the time.
Do anyone knows the minimum A load to keep it running? Not sure if minimum load is on the +5 or +3.3 voltage rails. I hope I do not have a bad PDU as it was expensive to buy.
Thanks,
Norberto ☹
<image001.jpg>
Sent from my iPhone
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Thanks! The original Heathkit backplane as a 150 ohm 2W resistor to discharged the big blue capacitor. Let me buy a 100 ohm 2W instead to get the 50ma range.
Norberto
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Got it working now and feel much better now that is not broken. 😊
All voltages checked out (+5V, +3.3V, +5V Standby, +12V, and -12V). Today I will test the 555 timer circuitry that controls the PSU momentary pushbutton latch.
Two minor issues.
I added two 3mm LEDS to the backplane as shown on the picture. One on the front next to the Front Panel to indicate +5V is on. A second one on the back of the system indicating +5V “Standby” voltage is on. This voltage is used by the 555 timer and it could be used to keep power on RAM or RTC circuitry or other new ideas. This voltage along with the +3.3V are available at the top of the backplane to power new circuits. This allows endless ideas going forward.
New backplane up and running!
<image001.jpg>
New backplane up and running!
<image002.jpg>
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Updates:
I will add next front panel to check bus operation.
Partially assembled board pictures attached.
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H8 Front Panel fully operational with new backplane.
Next steps:
Thanks,
Norberto
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H8 Front Panel fully operational with new backplane.
Next steps:
- Complete the Backplane assembly
- Update my H8 to use this backplane and PC Power Supply.
- Do test with DUAL CPU’s.
<image005.jpg>
Thanks,
Norberto
From: se...@googlegroups.com <se...@googlegroups.com> On Behalf Of norberto...@koyado.com
Sent: Saturday, July 10, 2021 3:41 PM
To: se...@googlegroups.com
Subject: RE: [sebhc] Initial H8 Backplane test!
Updates:
- PSON Switch Jumper working great.
- PSU momentary pushbutton latch circuitry working great. I did about 30 cycles and no failures detected. Very solid and stable. Even additional AC cycles to verify that the PSU does not turn on by itself when AC is applied. I love this circuit better than using PSON header.
I will add next front panel to check bus operation.
Partially assembled board pictures attached.
<image001.jpg>
<image002.jpg>
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On current draw, I will need to load the whole backplane and measure it. As it has 9 main slots (not using the auxiliary slots) based on a 1Amp per slot, so it should be around 9 amps. If using my boards, I think perhaps about 5 amps. To be accurate I will need to load the backplane and measured. For now we can speculate about 10Amps or less.
The Dell PSU from Dell Optiplex 390 will work just fine as the power supply is a 265W PSU.
The yellow plastic header is to break the backplane into two independent backplanes. The goal is to run two Z80 systems at the same time on same chassis. You add jumpers on this header to create a single backplane or take out the jumpers and have two independent small backplanes. The first CPU will use the H8 Front Panel as always and the second CPU will run without the Front Panel as the H89 does.
One CPU could run HDOS while the second CPU could run CP/M. The first CPU will have 4 main slots for I/O devices. The second CPU will have 2 main slots. The last slot on the second CPU is labeled “Expansion Card”, so it can be expanded into another H8 backplane if needed.
Hope this helps,
Norberto
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The resistor is insurance that you never need to worry about what is or is not plugged into the bus.
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Here is a link that shows current vrs trace width Also copper weight plays in. . Forgive me if this has been discussed before as I didn’t read all the threads. Short circuit current can be calculated if you know the output impedance of the power supply. Hope this helps.
Pat
https://www.mclpcb.com/blog/pcb-trace-width-vs-current-table/
From: Steven Feinsmith
Sent: Monday, July 12, 2021 5:22 PM
To: se...@googlegroups.com
Subject: Re: [sebhc] Initial H8 Backplane test!
I am glad that you decided to make further tests to ensure the backplane will function correctly with maximum current on traces without risk of burning out. I also suggest you if you happen to have an infrared camera to see the backplane in false color. The infrared camera is blind to any visible light but can see heat. I tend to use FLIR camera attachment with my iPhone to troubleshoot the components even, heat build-up on traces. It is a straightforward method to catch the problem.
Steven
On Mon, Jul 12, 2021 at 1:47 PM norberto.collado koyado.com <norberto...@koyado.com> wrote:
Steven,
You got me thinking over the weekend on the backplane current handling capabilities. So, I decided to buy 10-pcs of 5 OHM, 5W resistors to load the backplane to 10AMP. This allows me to verify that the backplane traces can handle such current as the power traces are different than what HeathKit did.
Also, I will short out pins 48, 49 to pins 0, 1 on the backplane to verify that the backplane traces do not act as a fuse.
Thanks,
Norberto
From: se...@googlegroups.com <se...@googlegroups.com> on behalf of norberto.collado koyado.com <norberto...@koyado.com>
Sent: Saturday, July 10, 2021 10:51 PM
To: se...@googlegroups.com <se...@googlegroups.com>
Subject: Re: [sebhc] Initial H8 Backplane test!
H8 Power Supply is rated at +8VDC @ 10 amps.
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Steven,
I loaded the backplane with 5W/5 OHMs for a total of 10 amps or 50 watts @5Vcc. I left the backplane with this load for an 1hr. The +5Vcc traces were cold to the touch. The ground plane was warn due to heat coming from the 5W resistors. The 5 amps PTC fuses did get hot, but did not trigger. The backplane worked fine under these extreme load conditions. As the ATX PSU can drive 30Amp on the +5Vcc traces, I’m limiting it to 10 amps with the PTC fuse to protect the backplane. Also the +12v can drive 46 amps, it is limited to 1 amp as well as the -12V. As I have two 5 amps paths to the +5V load, I forgot to add a trace to combined them, so I had to solder a piece of wire as shown on the picture below. I fixed that for the production board. I feel happy that flowing 10amps thru the board for an hr. did not damaged any copper traces.
During the testing I also noticed that I need to add two 2-pin header to provide +12V/GND and +5V/GND to drive a +12V or +5V fan for the system if needed.
PTC Fuse specs:
Holding Current:5A
Tripping Current:8.5A
Operating Voltage: 16V
TEMP MEASUREMENTS: Using the home touchless thermometer.
PTC FUSE: 102.6F
+5V TRACE AT P9 – 93 F
+5V TRACE AT FRONT PANEL CONNECTOR: 96.9F
GROUND TRACE: 104.8F
Voltage across all resistors was 5Vcc, so no significant voltage drop observed.
Here is the setup:
Thanks,
Norberto
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Fully assembled and tested H8 backplane. I will defer installation into the H8 chassis until 7/24 as I’m very busy until them.
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