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H7864 (BA23 Power Supply) Modern Replacement Now Available

Alegend

Experienced Member
Joined
Jun 13, 2017
Messages
86
Location
Israel
Hi All

After quite a few years in planning and one year in the making, a modern replacement for DEC's H7864-A and H7864-B power supplies for BA23 enclosures is now available.

A replacement for DEC p/n 30-21749-01 (Astec AA12131), it is fondly named H7864-C.

The power supply is based around the following main components:

- A metal shell, 1:1 copy of the original in shape and size. Even the color is right.
- Two TDK/Lambda LS200-L power supplies, these are 200W power supplies - allowing for 5V @ 40A and 12V @16.7A total loads
- A custom PCB, generating the POK and DCOK signals and the fan supply voltage
- All the various connectors and looms needed to make it all work and attach directly to any existing BA23 without modification

The custom PCB has several assembly options:

- Fully digital - a Microchip PIC microcontroller generates the POK and DCOK signals and a fake 50Hz LTC signal
- Fully analog - 50/60Hz line-connected circuitry samples the AC supply and generates the LTC signal, and an analog delay circuit provides the POK and DCOK signals using a 74AC14
- Mixed digital + analog - the PIC microcontroller generates all the signals while following the line 50/60Hz in order to generate the correct timing POK and DCOK signals upon a power failure

All assembly versions support:
- Jumper-selectable fan speed (10V or 12V)
- Jumper-selectable LTC line enable/disable and pull-up option - in case anyone needs it
- On-board LEDs for 12V, 5V, POK and DCOK state indication


The only difference from the original is the remote on/off mechanism. The original would have a switch connected to the remote on/off input for enable/disable functionality. The H7864-C needs a positive voltage to (remotely) disable the supply.
Otherwise the H7864-C exceeds its predecessors in total load capability, and in expected lifetime - much better than a used 30-year-old unit anyway.

Tested and working now in a couple of BA23's for several weeks. No issues at all - as expected.

I would still need someone with a PDP11 verify that the LTC signal performs as expected. But that would mean someone with a PDP11 first needs to buy one.

Finally, some observations I can provide, for those of you who may wish to undertake a similar project for a DEC power supply:

1. It is a lot more work than you think
2. Prepare for some serious and tedious re[verse]-[re]engineering work
3. It is more expensive than you think
By the time you have got yourself a set-up, all the required parts, metalwork, connectors, CAD software, prototype PCBs, crimping tools, soldering equipment, pins and what have you, you would have spent a lot of money.
4. It may well end up being less than perfect. One issue I have is the fan connectors - the old DEC fan connector seems to have its two female sockets closer to its surface than the presumably identical connector you can get today. It means the new connector barely holds to the fan connector.
Some gentle filing is necessary, to shave off enough PVC (or whatever) to make the new connector fit nicely on a fan and hold its position.

I will include several photos of a finished unit, inside and out, in the next post. I will also post the PCB schematics and some oscilloscope snapshots showing tests of the PIC microcontrollers' DCOK and POK response to a power failure (in the mixed analog-digital option). I did these tests in order to verify that the timings are within the required 4ms limit. If you do not run a mission-critical application, you don't really need this option.

Now about purchasing one - yes I can build one for you. Please contact me directly. Currently all existing PCBs are built for digital option - as I think no one really needs anything else.
The H7864-C is a fully functional, commercial-grade product but it is intended for hobbyist use. It will probably pass UL and FCC certification without a problem, but this is something I will leave for when an order for 100 units comes along. Which will never happen.

-Alon.
 
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Test Results and Schematics Attached...

Test Results and Schematics Attached...

60HZEXP3 2017-05-10 09-50-55.jpg50HZEXP1 2017-05-10 09-37-32.jpg50HZ DRY STARTUP 2017-05-10 09-55-45.jpgH7864-C Schematic Sheet 2 of 2.jpgH7864-C Schematic Sheet 1 of 2.jpg
 
After quite a few years in planning and one year in the making, a modern replacement for DEC's H7864-A and H7864-B power supplies for BA23 enclosures is now available.

A replacement for DEC p/n 30-21749-01 (Astec AA12131), it is fondly named H7864-C.

[...]

Otherwise the H7864-C exceeds its predecessors in total load capability, and in expected lifetime - much better than a used 30-year-old unit anyway.
Nice!

A suggestion - when you send these, include the DEC FCO documentation on the two required changes to the BA23 wiring harness (so people can verify they have the "good" one). Or (if you have the connectors) include a new harness with each supply (it isn't that complex - just 2 of the connectors at a 90-degree angle with the pins wired straight-through). The original harness and the first "fix" were prone to catching on fire. With a higher output current available, this could probably also happen here. See my post from 30 years ago! titled "Burned up over BA23 fire" on DECUServe.

For anyone running old DEC hardware (even if not BA23-based), there is a lot of good info in the linked article above (shameless plug :cool:).
 
Some years later... did this ever become available for purchase? And if so, what are the parts that are available? Can I purchase just the sheet metal parts? I've been using a 600W ATX supply with a custom circuit board that manages the power cycling and signals, but it would be nice to put something that looks more original into the BA23 chassis... Thanks, Jon.
 
Some years later... did this ever become available for purchase? And if so, what are the parts that are available? Can I purchase just the sheet metal parts? I've been using a 600W ATX supply with a custom circuit board that manages the power cycling and signals, but it would be nice to put something that looks more original into the BA23 chassis... Thanks, Jon.
HI Jon, yes I have a couple of assembled units that you can buy. I don't have any loose parts though. PM me for details.
On any occasion just a metal shell is not of much use, the space is too tight to fit any ATX power supply, and then there's a ton of work sourcing parts, fitting, crimping and assembling.

I have placed all my production files on github, so anyone is more than welcome to build a "H7864-C" on their own...

-Alon.
 
HI Jon, yes I have a couple of assembled units that you can buy. I don't have any loose parts though. PM me for details.
On any occasion just a metal shell is not of much use, the space is too tight to fit any ATX power supply, and then there's a ton of work sourcing parts, fitting, crimping and assembling.

I have placed all my production files on github, so anyone is more than welcome to build a "H7864-C" on their own...

-Alon.
Hi Alon,

This this time I'm working on refurbishing an (ancient) H7864 by replacing the safety capacitors. I will keep you in mind if I eventually run out of enthusiasm for this particular project!

Thanks, Jon.
 
just wanted to pop my head in since it slipped my mind, been running one of these in my BA23 11/83 since february of this year or so without issue, LTC works as expected and 11M+ and 2.11BSD both boot and run happily. a lot of time and effort was very clearly put into these, thank you Alon!
 
just wanted to pop my head in since it slipped my mind, been running one of these in my BA23 11/83 since february of this year or so without issue, LTC works as expected and 11M+ and 2.11BSD both boot and run happily. a lot of time and effort was very clearly put into these, thank you Alon!
Thanks nice to hear that! Good to learn the LTC is working OK, there's no reason it shouldn't as it is just a clock, but you never know for sure until you check it in a real PDP11.

-Alon.
 
Hi Alon,
I'm interested for 2 or 3 pieces of the H7864-C Powersupply. I've a small dec museum with 11/93 11/73 microvaxes an more with ba23 enclosure.

Do you have still available units. I'm from germany and a retired engineer.

regards
Michael
 
Bah. My account is apparently still too new to do PMs. I'm definitely interested in one of these, since I purchased mostly gutted BA23 case without the fans or the PSU.

Is there another way of contacting you, perchance, other than the vcfed forums?
 
Bah. My account is apparently still too new to do PMs. I'm definitely interested in one of these, since I purchased mostly gutted BA23 case without the fans or the PSU.

Is there another way of contacting you, perchance, other than the vcfed forums?
Yes, me too. My PSU is kaput so interested in looking at modern alternatives. Although the build details are on Github my preference would be to get one 'off the shelf' if possible please.
 
I worked with @Alegend on this one, and while $1k was a bit expensive, it was worth it. I now have one in my BA23 chassis and it works like a dream. Well done, and thank you!
 
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