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After fixing the failed extruder thermistor on my Monoprice Select Mini 3D Printer, it didn’t surprise me at all when the heated bed thermistor also failed. Read on to see how I replaced it.
Jul 242016
Monoprice Select Mini Thermistor Replacement, Pt. 2
Machine Shop
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Jul 102016
I replaced the broken thermocouple in my MP Select Mini 3D Printer this weekend, and it’s back up and running again! Here’s how I did it.
Jul 042016
I’ve measured the resistance vs. temperature of the thermistor in my MP Select Mini 3D printer. It looks like the thermistors that I speculatively ordered don’t have the exact same temperature curve, but they may be close enough to use my printer with a manual adjustment of the temperature set points to compensate for sensor error.
Jul 042016
On June 15, I saw this cryptic tweet from Elecia White. Being out of the loop, I asked what the new toy was, and was directed to Brian Benchoff’s review on Hackaday of the new Monoprice Select Mini 3D Printer. It’s an exciting new 3D printer with a very attractive price point, and I had to have one! Read on for my not-so-smooth initial experience…
Data General Nova 3 Backplane
Computer Room
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Jun 112016
I’m spending some time working on my Data General Nova 3 again, after a long hiatus. Here are some pictures of the backplane.
Mar 142016
I’ve been looking for a good way to transfer images of the hard drives on my VAX-11/730 over to my modern computers for archival and other fun. My previous attempt to bring up TCP/IP networking on the VAX was not successful, so I tried a different approach this weekend. And it worked! Well, mostly.
Now before digging into the details, let’s describe the computer in question. The VAX-11/730 was small by VAX-11 standards, but it’s still a great big beast of a machine that takes up a lot of room in my little house. It also sucks lots of power and gives off a whole lot of heat, but luckily it was a cool and breezy weekend so I could open up windows to keep the room from getting too hot. My VAX-11/730 has 3M of RAM if I recall correctly. It has a 120 megabyte model R80 fixed hard drive, and a 10 megabyte model RL02 removable-back hard drive. It also has a 1600 BPI 9-track magtape drive, model TU80. The R80 drive came with hobbyist-licensed OpenVMS 7.3 on it, with a node name of PIKE and a node ID of 1.730. The previous hobbyist owner apparently had it clustered with another VMS machine named KIRK.
Dec 202015
Back in 2009, I posted about a demilitarized KY-38 NESTOR voice encryption device. Since then, I’ve procured another one. Like the first one, it has been demilitarized (that is, rendered inoperable and unclassified) by removal of key internal components, removal of the original dataplate, and (for some reason I don’t understand) removal of the battery box. But unlike the first one, this one came with a 28″ cable to plug it into the AN/PRC-77 radio, and a matching transit case! There was even an old trouble ticket lost under the padding, though it was for a different unit based on the serial number.
IBM System/32 at the Local Electronics Recycler
Computer Room
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Nov 092015
A couple of days ago, I learned that there’s an IBM System/32 up for sale at an electronics recycler in Corona, California. This is very close to my home, and I happen to have a bit of free time right now between jobs, so I figured I should go look at it. Even though I’m quite tempted by this beautiful beast, I really shouldn’t spend the money or floor space on it at this time. But, being local, maybe I can help it find its way to its new home, just as another collector helped me acquire my VAX-11/730?
The seller says they got it about six months ago, and it was used for payroll at some small company. He says that the folks that he got it from claimed that it still works, but he hasn’t tried powering it up… which is good, because it probably needs lots of cleaning, careful examination of the power supplies, and other such attention to make sure that the magic smoke stays inside.
It’s a bit dirty, but it looks complete aside from a missing paper rack on the back side. This one has the keyswitch option, which replaces the power toggle switch next to they keyboard with a tubular lock.
Cheap HDMI Converter with Apple //c
Computer Room
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Jun 012015
Retro Computing Roundtable episode 100 began with a discussion of the problems often encountered when trying to connect an 8-bit computer from the 1980s to a modern display such as a typical 16:9 1080p TV or monitor with HDMI input. Open Apple #43 also included some discussion of the out-of-spec video output from the Apple II series, and the resulting problems that can cause with many digital displays.
With that in mind, I decided to try buying an inexpensive composite video to HDMI converter to experiment with. I got it for $19 from Amazon. I’ve heard reports that results vary a lot depending on the particular converter used, the particular version of that converter (i.e., its innards might get a complete re-design without any outward indication… part of the game one plays when buying these super-cheap imported devices), and the particular video source. Thus, my results here may or may not reflect the results you would get.
HP 8560E Spectrum Analyzer
Radio Room
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Feb 222015
I just bought a really nice HP 8560E spectrum analyzer from eBay seller testcalinstruments. It has been refurbished and calibrated, and I’m really happy with it! I encountered another user over at the EEVBlog Forum who is also considering buying an 8560E series rig from testcalinstruments, and he asked me to share some pictures of my new 8560E.
Nov 302014
Another collector asked me for pictures of the cards in my Tandy Model 6000’s card cage in order to help identify all of them. So, here they are!
Nov 292014
Well, that didn’t take long. As mentioned in my previous post, I’ve just created a Python package providing support for Mini-Circuits brand portable test equipment. Well, more accurately, it just provides support for my model PWR-SEN-4GHS USB-interfaced RF power sensor (and probably the other sensors in that product line), since that’s the only piece of Mini-Circuits test gear that I have.
pyhidapi: A Python Binding for the hidapi USB HID Support Library
Computer Room
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Nov 292014
I’ve just released a Python binding for the hidapi library:
This allows the hidapi library, which allows cross-platform access to USB and Bluetooth Human Interface Device (HID) class devices, to be easily used in Python scripts.
Oct 302014
Another IBM System/23 Datamaster collector just sent me these scanned maintenance manuals. I haven’t had a chance to take a close look to them yet, but I can already see they’re going to be very helpful because at least one of them includes PINOUTS! They’ve also been sent over to Bitsavers for archival. Enjoy!
Oct 122014
I became interested in retrocomputing about a year ago, and since then my web site’s focus has drifted from mostly military surplus equipment to more general technical content. It no longer makes sense to call my site "Mark’s Green Pages (Mark J. Blair’s Blog of Mostly Military Stuff)" so I have renamed my site to "Mark’s Tech Journal (Mark J. Blair’s Blog of Technical Stuff)".
Sep 112014
Here are some pictures of the circuit card drawer and plug-in cards of my System/23 Datamaster. I took them in order to compare my machine vs. a couple machines owned by another nearby collector. I apologize for the less than ideal lighting and focus.
Aug 252014
This Kaypro II computer has led a hard life, but it’s on the road to recovery now. A previous owner has modified it quite a bit, but some of the modifications are hack-jobs. I’ll probably need some help identifying some of the upgrades to determine whether I want to keep them or back them out, but there are a few changes that are definitely coming out.
Word Processing was Expensive in 1980!
Computer Room
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Aug 212014
In a recent eBay purchase that I made, the seller included a 1980 brochure advertising word processing capabilities of the TRS-80 Model I computer system. The advertised system prices ranged from $2,046.95 for a cassette-based system with a dot matrix printer, to $5492.95 for a system with two 80k floppy drives and a daisy wheel printer. Computers sure have gotten a lot cheaper since then!
Aug 132014
I just became the proud new owner of an IBM System/23 Datamaster computer system yesterday. This 8085-based computer is an immediate predecessor to the IBM PC. It has BASIC in ROM, and two 8" floppy disk drives. I don’t have any disks or documentation for it yet, and I would like to get my hands on some of that.
Here are a couple of quick pictures that I took for Big Blue Week over on the RetroBattlstations subreddit.
Jul 292014
Well, I’m finally the proud new owner of a TRS-80 Model 1 system! I just bought it on eBay for the princely sum of $380.85 including shipping. Yes, I’m geeky enough to take pleasure in the presence of "8085" in that amount.
Here are the eBay listing pictures, used with permission from the seller. I’m looking forward to seeing it in person, because I haven’t touched one since around 1979 or so, and back then I didn’t know anything about computers. My first computer experience came with a TRS-80 Color Computer a year or two later, and I never got any experience with the Z-80 TRS-80s until I became interested in retrocomputing less than a year ago.