At long last, my hard to find replacement LED chips for the HP 9825 display arrived from the UK, courtesy of her majesty the Queen and eBay UK. They are not the original HP military grade glass on ceramic construction, but HDSP-2000LP compatible chips made by Siemens, presumably under license. Th...
2021-09-12 23:33:29 +0000 UTC View Post
This is from our mystery Apollo Uplink Command box. The tape reader is at the bottom left.
2021-09-07 18:16:03 +0000 UTC
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Marcel has given us another mystery box to add up to our Apollo USB link setup. This one appears to have to do with checking the uplink commands functionality. We could not find any documentation on it.
It has a whole bunch of cards plugged in.
2021-09-07 18:08:24 +0000 UTC
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Short raw clip to follow up on my previous post about the HDSP-2000 hybrid on ceramic LED chip. This is what happens if you tie the output of the shift register to its input after having ...
2021-08-30 07:30:56 +0000 UTC View Post
All the LED chips that make the beautiful 32 character display line in my HP 9825 are dead! They died from the 13V overvoltage. These chips, capable of displaying 4 characters, each a matrix of 5x7 dots, were specifically developed for the HP 9825. HP sold them later commercially, under the HDSP-...
2021-08-30 07:23:35 +0000 UTC View Post
At least first light for us! The Apollo transponder turns on after almost 50 years and transmits its beacon 2.28 GHz signal to earth. In return, we send it a rubidium-controlled signal at...
2021-08-30 06:37:20 +0000 UTC View Post
Patron John Lawson recommended this excellent British video. Nice footage of IBM hardware (IBM 7090 computer, 026 card punches, 729 tapes, our cherished IBM 1401 makes an apparition)....
I just got this picture of David Boggs. He was the famed designer of the first ever Ethernet card for the Xerox Alto. That's also a picture of younger him shown on the just restored Digibarn Alto screen! I'm tickled pink that we are also in the photo - we are not worthy...
David came ...
2021-08-16 06:00:04 +0000 UTC View Post
Carl has moved to Florida! But fear not, he has rented a commercial space for his collection on the beach near Cape Canaveral. Now that's retirement for you. So he can restore while he watches the rocket launches. This is actually quite an upgrade from his cramped garage space in California!
<... 2021-08-13 17:15:11 +0000 UTC View Post
We recently got quite a few more mystery boxes from Steve Jurvetson's garage. Steve had bought a large lot, mostly for the flown artifacts in it. But it also came with a pile of somewhat generic ground equipment boxes, and he was unsure whether he was going to keep them in his collection or put t...
2021-08-10 05:14:41 +0000 UTC View Post
View on YouTube: https://youtu.be/m9rETFe7v5M
I blame Ed Thelen ( http://ed-thelen.org/ ) for getting me interested in gyros and spending way too much on ...
2021-08-06 15:01:04 +0000 UTC View Post
This one is for you, HP-80 series lovers . You can now upgrade your HP-85 (and 86 and 87) thanks to Philip's EBTKS add-on board. Foremost, it gives you mass storage emulation: no need to take on the difficult tape drive mechanism restoration, and then having to deal with the finicky and notorious...
2021-08-05 16:01:03 +0000 UTC View Post
I was having great fun with my HP 7475A and giving it a good workout, trying to have it plot schematics and PCB layouts. I had my technique almost perfected (took a lot of trials!) when I prepared for the final video shot of the plot. And of course that's when it failed. It printed in one single ...
2021-08-05 06:04:34 +0000 UTC View Post
Ken and I gave some attention to our neglected HP 9825, which had been displaced by Apollo stuff. The next board to repair is the keyboard. We know the reset is not working, neither the direct signal from the key, nor can the processor read the correct status byte through the custom KDP chip, whi...
2021-08-03 06:40:52 +0000 UTC View Post
I did a quick build of a Tauntek IC Tester. This is designed by subscriber Robert Grieb and was brought to my attention by Josh Dersch who used it to test all the ICs on the Digibarn Alto. More info at:
We are making progress in figuring out the boxes we got from Steve Jurvetson. They are incredibly heavy. About 15 kg each, so 33 lbs. And it's not from the cases that are incredibly light - way lighter than aluminum.
2021-07-28 07:47:47 +0000 UTC
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Couldn't resist to share with you the story of one of my viewers, Graham N., and what happened to the plot he made on his trusty HP 7475A:
"Really enjoyed your last video about the 7475A plotter. It reminded me of a time in the early 1980’s when I was working for a project ... 2021-07-25 06:27:17 +0000 UTC View Post
A couple pictures of the Apollo S-Band transponder and power amplifier we picked up at Steve Jurvetson's in the last video.
The transponder:
2021-07-24 01:11:38 +0000 UTC
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A few days ago, we (Carl, Ken, Mike and I) went to visit famed space investor and collector Steve Jurvetson, primarily to return his mechanical Soyuz space clock along with the little clock driver I made for it as a gift. We were treated to a brief tour of his amazing collection.
Steve was ...
2021-06-16 08:39:06 +0000 UTC View Post
I had a nice Zoom conference with Bob, the one and only "Mr. Fancy Pants". From the picture, one would expect a flashy personality, but he is in fact a straight talking and serious engineer, even a bit stern. He could rattle off the HP number of every instrument in the rack he is sitting in front...
2021-06-08 07:24:58 +0000 UTC View Post
The topmost Skoal board has now been repaired. Our 9825T now runs on all cylinders, with all of its 64k or RAM and all of its ROM on the Ebenezer board underneath. All set and done, the Skoal board had 4 bad chips: three TTL and again the Intel DRAM controller, so pretty similar to the Ebenezer t...
2021-06-08 06:50:44 +0000 UTC View Post
It's time we return the Soyuz Clock to it's famous owner, Steve Jurvetson. But I wanted to return it with a little present, a clock driver so he can use and demonstrate his clock without the pile of HP equipment I had used.
I made the clock drivers two ways: one the software way with ...
2021-06-06 21:08:01 +0000 UTC View Post
Probably the most rewarding moments of these restorations is when we actually get to meet design engineers of the superlative hardware we are working on. I still have goose bumps from meeting the original Apollo Guidance Computer engineers and the inventors of the Xerox Alto.
Thanks t...
2021-06-02 19:03:57 +0000 UTC View Post
You might remember the episodes on the Digibarn Alto ( https://youtube.com/playlist?list=PL-_93BVApb59ameMVQhOAzeRcCpS6PCiG ). In the picture below from the 2017 video, owner Bruce D...
2021-05-31 02:49:07 +0000 UTC View Post
After our last repair session of the HP 9825, Ken Shirriff went home with our failed Intel 3242 DRAM controller. He has since decapped the chip and is tweeting about his findings as he discovers things. You can follow him on Twitter at 2021-05-19 16:09:59 +0000 UTC View Post
Yay! Our HP 9825 is back! At least in its "B" guise. We finally got the RAM working on the A24 board, and it booted right up.
The Logisim simulation of the refresh noodle logic led me to suspect the Intel 3242 helper chip rather than the refresh logic itself.
2021-05-15 23:16:37 +0000 UTC
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I was eager to try to get my stuck ROM bit back. I donned my Fancy HP Repair Pants and it seems to have helped.
Not having found any obvious short with the HP 547A probe, I decided to try to isolate the ROM 0 from the other chips and see if our bit would reappear. Was the bit still alive in...
2021-05-01 05:21:04 +0000 UTC View Post
My fried HP 9825 restoration is proving to be quite challenging. We know that we lost a bit in our boot ROM while we were debugging the RAM refresh. But since the data bit line is shared between half of the ROM chips, a RAM chip, and a buffer chip, we don't know if the ROM actually lost its bit, ...
2021-04-27 20:51:27 +0000 UTC View Post
I hauled back an original HP rack from LA during my latest trip, from Ed Blacksmith. I bought it specifically to hold my HP test instruments from the 1960s. This is meant to be the second rack of an HP 9500A Automated Test System, like this one in the 1968 Catalog:
2021-03-07 03:38:56 +0000 UTC
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My HP 6824A power amp just failed while I was filming the latest video. I had spent the last few days wiring up all the external connections of the mechanical Soyuz clock, mainly to my box of Apollo switches and indicators.
2021-03-02 00:20:17 +0000 UTC
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