HP LaserJet 1000-series continuously feeds paper.

2024-03-23 22:00:12, In: DIY, Electronics

This happened to my old LaserJet 1005, but will happen to any printer of this line, as this (not to confuse with types starting with P or M, these are totally different printers!) is one of the last decent HP laser printers. The first symptom is that the printer, instead of feeding the paper once, does it twice. It means that you cannot use auto-feeder and have to feed every page separately, but it still works.
Then, it starts to repeat the paper feed cycle three times. Quickly three becomes four, and when it becomes around five, then the printer stops with error. If you try to feed the paper then, it may even work, depending on time passed - you then have to make it try to feed the paper by quickly putting paper back and forth, and when it resets to the "ready to feed" state, you put the paper and it prints.
Or, in extreme cases, it will still repeat the paper feed cycle and, when paper is fed, will pass it thru without printing. But if you wait, you hear a metalic cling from the right side of the...

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Curiosities: Inside a late-80s energy meter

2020-08-02 17:40:34, In: Electronics, Curiosities

And now something totally different, related more to electricity than electronics. These electricity meters were commonly installed since 1990s in many households and were used until early 2010s when they were replaced with digital meters. The principle of operation is quite simple: There are two coils: One energizes because there is mains voltage flowing through it all time. The second coil is put in series with energy receivers, so it energizes when current flows through it. If both are energized, it means that there is both voltage and current, and voltage times current equals power. Action of both coils induces eddy currents in a flat aluminum disc, it rotates and spins the counters, like in a peculiar low-power induction motor with 90-degree phase difference made by two coils.
The curent constantly present in voltage coil draws some energy, but it is not integrated to total power consumption.

A neutral wire is connected through a pass-through, while live is passed through coil. Additionally...

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Mikrosha repair log

2019-11-22 12:35:44, In: Electronics, Retrocomputing

Mikrosha is a Soviet home/educational microcomputer made in LEMZ plant near Moscow. This looks like a quite consistent 8080 system with a CPU, a few 8255s, 8275 as display controller, DMA controller, timer and 32kB of RAM in 2118 clones (in case of failure I will be able to substitute with modified 4164, knowing that it's possible to put modified 4164 as 4116 and 2118s are like 4116s but single-voltage).
Review of the power supply unit shown that the -5V regulating transistor (total current: 50mA, no protection at all, dissipation: really poor) conducts C-E in both sides. That's why as I measured it initially, it gave -11.3V in -5V line. Replaced the transistor with the first 100mA PNP I had in my "desolder box", voltages returned to normal. The power supply unit has separation coil, transformer and linear regulators for...

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A TV Tennis game description

2019-08-24 21:17:37, In: Electronics, DIY

The device, a TV Tennis game, has been made using designs from different sources, especially a description in "Radioamator" and images of the prototype. The general rule is similar to "Odyssey" but the signal mixing is simplified while still giving TV-friendly signals. There are only NPN signal transistors and 74 chips, to be exact one 7474 dual flipflop, 7473 as divider and 7493 as additional divider. Other chips are 7400, in many possible configurations. All other things like delays or integrations are made using discrete components. If someone wants to build a similar unit, prepare for a long tuning and selection of components.
This is a general view of the device. It has a power switch, 1/2 player switch and speed setting. Two controllers consist of X/Y pots, serve and "Lift" buttons which changes deflection...

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Restoring the old PC-XT clone mainboard

2018-10-27 01:42:04, In: Electronics, Retrocomputing

A long time ago I got an XT mainboard. The history of it is known: previous owner got it from someone else, who told that it is damaged and cannot be easily repaired, so it became an interesting exhibit in a bookshelf. It was for last 2 years in my stuff and finally I decided to restore it to the working condition.

The mainboard is a really old one - it has an additional ISA edge connector on the side, all TTL chips from around 1984-85, socketed, but it was not an IBM. The logo, visible on a silkscreen under the processor, resembles a stylish written "S" letter with its center line shaped in an american resistor symbol.
It was a clone, but a clone made with some uncertainity. Not that there are circuit errors, it electrically still is a 5160, but the design itself is... like someone took schematics from the technical manual, looked at original PCB and said "OK, let's try to design it again", and this was the first try, made quickly to verify is everything OK. The mainboard has a piece of breadboard...

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Curiosities: Inside a 1970s professional multimeter

2018-08-12 17:32:44, In: Electronics, Curiosities

Mera V640 is a multimeter made by Polish Meratronik plant in 1970s. It is an analog meter, able to measure voltages (1.5mV - 1500V), currents (0.15uA - 1.5A) and resistance. With specialized probes it was possible to measure high frequencies and even temperature. In 1970s Poland started to make international deals, usually with licenses. Some licenses were bought, like from British ICL for their computer designs, German (western) Grundig (tape players), or Japanese Busicom for calculators, but Poland also manufactured their equipment for export. In 1972 the Masteranger 639 multimeter has been made for Conway, a Canadian electronics company, and manufactured purely for export. The design was successful enough that it was also manufactured for British Marconi company as TF 2650. Year later it was also sold in Poland, under V640 name, after some changes in range switch and adding temperature probe.
These times, export and import with eastern block country was very different than typical transaction,...

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Expanding Arduino UNO memory with 32kB static RAM chip

2018-07-04 17:42:04, In: DIY, Electronics

Arduino Uno is a cheap microcontroller platform which can be used in lots of applications. If we prototype our solution using Arduino board, it is possible to dump the Arduino board and use single microcontroller instead which is even cheaper and looks more professional even on an universal solder-in PCB. However, ATMega328 chip used in Uno has a significant drawback - its memory which is only 2kB. If we want to make a small control device it's not a problem, but for some specific applications 2kB may be too small.
For example, since few weeks I have an idea to develop a BASIC computer using AVR chips. Implementation of Tiny BASIC uses some memory and has some code clutter which can be replaced with something more usable by the cost of e.g. moving storage code to external devices. Unfortunately Tiny BASIC leaves a very small memory for user's program and its variables.

So what are options to add RAM into Arduino?
- Use a larger Arduino module. This solution is present in Internet forums all...

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About PC power supply units

2017-11-21 10:26:00, In: Electronics, Curiosities, Other

Recently I acquired a few power supply units for PCs and I decided to share some knowledge about their quality. Because these units were defective I had to open them, fix if possible, and re-solder wires as they were from some e-junk wjere copper is valuable. Testing was simple: Load the power supply unit with an old, damaged IDE hard disk, turn it on, check voltages (they should not be well OK, as one old hard disk is not enough to keep regulated line), then load the unit on 5V line with 12V/21W light bulb and check regulation then. Most passed these tests after capacitor repairs.

Tagan TG380-U01

Let's see the first example: The Tagan TG380-U01. Tagan is known as manufacturer of a good, high-end power supply units, and it looks like they made them really well. The unit is packed with technology, they put large heatsinks and thermal regulator on a separate, small board. Because packing is tight, two fans are pumping air through the unit.

Here is an example how the good power supply unit...

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Re-making a gear for tape memory

2017-09-24 01:47:52, In: DIY, Electronics

A long time ago I acquired a microcomputer-grade tape recorder produced by Polish factory: MK-450. The problem with this device and a few other tape drives (like Mera one for large cassettes) and even consumer-grade decks (MK-250) was a poor quality of its gears prone to breakage. Usually, during seeking or playback, a loud crack is heard and tape is pulled into recorder or forward seeking stops working while motor is still heard. Recently I got a possibility to print something with 3D printer, so I decided to experiment with it. In this post I'll show how to re-produce the existing, physical gear into computer model. To quickly show things, the result is nice:

But... why does it fail?

The plastic used to make these two specific gears (in MK450) is different than polymer used in other gears. It degrades into white, crumbling powder with atmospheric contact and probably...

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Curiosities: Inside a lab-grade power supply from 1970s

2017-08-22 01:17:11, In: Electronics, Curiosities

Some time ago I was looking for an used adjustable power supply unit. Finally I had a possibility to purchase a 300W adjustable (0.1-30V, 10A max) power supply unit for a relatively lower price. The only thing about it was that it was a unit from early 1970s, transformer-based, 25kg of hardware. I finally got it, brought home and decided to restore it.

It is a ZTR-1/71 power suply unit made by Inco in Poland. In 70s and 80s, Inco (Full name: Zaklad Produkcyjny Aparatury Elektronicznej INCO) was known manufacturer of measurement devices, lab equipment and all "special" production e.g. for military, intelligence or security offices (also devices for communication, location of radio stations or radar applications), so I expected quite interesting things inside. It is still possible to get their old catalog on Silesian...

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