We bring to life the canonical DEC VT100
Previously, there was a translation about restoring another terminal - LA30 . Italic my comments
VT100, in a sense, is the industry standard among terminals. The set of commands supported by this terminal was borrowed by anyone else. In the lineup of terminals from DEC, the VT100 was first released with a freestanding keyboard. The heart of the device is the Intel 8080 microprocessor. A similar case was found in the VT103 terminal, to which were added two TU58 tape drives and a small backplane with a QBUS bus. In addition, VT125 was also released, which, in fact, differs from the VT100 only by the presence of an additional fee to support the ReGIS instructions implementing simple computer graphics.
')
We decided to first test the power supply, because the terminal last turned on many years ago, I connected a continuously adjustable transformer ( variac / variac ) to the 110V AC input ( I'm not sure why this was done ), and also shunted a small primary transformer through which is provided a bias voltage of + 12V for the control circuit. I then applied the bias voltage with a small laboratory power supply. After connecting the test load to the + 5V output, the incoming alternating current began to grow slowly. The key element quietly switched, and the power supply unit gave the nominal voltage according to the specification. The damping circuit power resistor (R27) produced a faint odor, but since everything else was in order, I decided to connect the power supply unit back to the terminal. The R27 resistor in the power supply unit was rated at 1 kOhm, although, judging by the scheme below, it would have to be 500 ohms.
Having installed the PSU in the terminal, I launched the system. After some time, a dim and unfocused cursor appeared on the screen, and the smell from the resistor only intensified. Since there was no focus, I missed all the potentiometers on the monitor board with a Deoxit D5 contact cleaner.
However, the next launch attempt was not as successful as the first one. Almost immediately, smoke came from the line transformer. A bad sign ... Today, it is difficult to get a lower-case transformer, but I was lucky - a fellow collector from the United States kept several pieces and sent me one of his stocks. On the top left of the photo - my broken original, on the right - a new replacement.
How can we check the performance of the line transformer and not burn the transistor of the horizontal output stage? Let's "call" him! We drive the signal in the form of a meander through a small capacitor (3.3nF, for example) connected in parallel to the primary winding of the transformer. The signal can be taken, for example, from an oscilloscope calibration pin. A serviceable line transformer must attenuate both on the positive and negative fronts of the meander. If there is at least one short-circuited coil in the coil, then the dial will show it. A shorted coil can be simulated by simply wrapping a ferrite transformer core with a wire.
On top of the oscillogram of the working line transformer, and the bottom of the transformer with a shorted loop. Such an element needs to be changed!
The board is connected to a horizontal transformer and to the neck of a CRT. Unfortunately, the old burned-out transformer provoked damage to the transistor of the horizontal output stage - there was a short circuit between the base and the emitter. The BU407D transistor (Q414 in the diagram) was replaced with a BU406D with a slightly larger maximum allowable voltage. The short circuit of the transistor caused knocking out a small two-amp fuse.
As a precaution, I checked all capacitors with an immitance meter. One of the measurements showed a slight understatement, but, all the same, the value fit into a 20 percent tolerance.
Replacing the transistor of the horizontal output stage, the fuse and the line transformer, I decided to carefully check the operation of the monitor without the risk of breaking any component. Therefore, I connected the laboratory power supply unit to the horizontal section of the board. I was able to do this by disconnecting the 1-ohm power resistor R478. I started the terminal and smoothly increased the voltage supplied by the laboratory power supply. At about 5V, the screen showed a weak and narrow picture. When applying 10V and adjusting the height, horizontal linearity and brightness through the appropriate potentiometers, I got a fairly good image. The current strength of the laboratory power supply remained at an acceptable level and I did not feel any strange smells (well, besides the power resistor in the power supply).
The terminal is controlled by a processor board, on which are located: intel 8080 (the processor itself is located under the AVO board, Advanced Video Option, pictured below), several memory chips, firmware on four ROMs, a character generator's ROM, and two logical matrixes on TTL designed for video processing -out In addition to these components, of course, there are many standard TTL chips.
On our board there is also an optional AVO (Advanced Video Option) board with 4 sockets for ROM chips, which could overlap ROM data from the main board. The pin connector on top was designed for the VT125 terminal, and allowed the special module to intercept RS-232 signals before they were processed by the VT100 main board. This module recognized the special ReGIS commands that were used to draw graphics.
Instructions for the user is very helpful in setting up, because it is quite difficult to remember which option in the menu is responsible for what. During the repair, of course, need a service manual and a set of schemes .
DEC VT100
VT100, in a sense, is the industry standard among terminals. The set of commands supported by this terminal was borrowed by anyone else. In the lineup of terminals from DEC, the VT100 was first released with a freestanding keyboard. The heart of the device is the Intel 8080 microprocessor. A similar case was found in the VT103 terminal, to which were added two TU58 tape drives and a small backplane with a QBUS bus. In addition, VT125 was also released, which, in fact, differs from the VT100 only by the presence of an additional fee to support the ReGIS instructions implementing simple computer graphics.
')
Launch
We decided to first test the power supply, because the terminal last turned on many years ago, I connected a continuously adjustable transformer ( variac / variac ) to the 110V AC input ( I'm not sure why this was done ), and also shunted a small primary transformer through which is provided a bias voltage of + 12V for the control circuit. I then applied the bias voltage with a small laboratory power supply. After connecting the test load to the + 5V output, the incoming alternating current began to grow slowly. The key element quietly switched, and the power supply unit gave the nominal voltage according to the specification. The damping circuit power resistor (R27) produced a faint odor, but since everything else was in order, I decided to connect the power supply unit back to the terminal. The R27 resistor in the power supply unit was rated at 1 kOhm, although, judging by the scheme below, it would have to be 500 ohms.
Having installed the PSU in the terminal, I launched the system. After some time, a dim and unfocused cursor appeared on the screen, and the smell from the resistor only intensified. Since there was no focus, I missed all the potentiometers on the monitor board with a Deoxit D5 contact cleaner.
However, the next launch attempt was not as successful as the first one. Almost immediately, smoke came from the line transformer. A bad sign ... Today, it is difficult to get a lower-case transformer, but I was lucky - a fellow collector from the United States kept several pieces and sent me one of his stocks. On the top left of the photo - my broken original, on the right - a new replacement.
Transformer Ping
How can we check the performance of the line transformer and not burn the transistor of the horizontal output stage? Let's "call" him! We drive the signal in the form of a meander through a small capacitor (3.3nF, for example) connected in parallel to the primary winding of the transformer. The signal can be taken, for example, from an oscilloscope calibration pin. A serviceable line transformer must attenuate both on the positive and negative fronts of the meander. If there is at least one short-circuited coil in the coil, then the dial will show it. A shorted coil can be simulated by simply wrapping a ferrite transformer core with a wire.
On top of the oscillogram of the working line transformer, and the bottom of the transformer with a shorted loop. Such an element needs to be changed!
Screen board
The board is connected to a horizontal transformer and to the neck of a CRT. Unfortunately, the old burned-out transformer provoked damage to the transistor of the horizontal output stage - there was a short circuit between the base and the emitter. The BU407D transistor (Q414 in the diagram) was replaced with a BU406D with a slightly larger maximum allowable voltage. The short circuit of the transistor caused knocking out a small two-amp fuse.
As a precaution, I checked all capacitors with an immitance meter. One of the measurements showed a slight understatement, but, all the same, the value fit into a 20 percent tolerance.
Replacing the transistor of the horizontal output stage, the fuse and the line transformer, I decided to carefully check the operation of the monitor without the risk of breaking any component. Therefore, I connected the laboratory power supply unit to the horizontal section of the board. I was able to do this by disconnecting the 1-ohm power resistor R478. I started the terminal and smoothly increased the voltage supplied by the laboratory power supply. At about 5V, the screen showed a weak and narrow picture. When applying 10V and adjusting the height, horizontal linearity and brightness through the appropriate potentiometers, I got a fairly good image. The current strength of the laboratory power supply remained at an acceptable level and I did not feel any strange smells (well, besides the power resistor in the power supply).
Terminal control board
The terminal is controlled by a processor board, on which are located: intel 8080 (the processor itself is located under the AVO board, Advanced Video Option, pictured below), several memory chips, firmware on four ROMs, a character generator's ROM, and two logical matrixes on TTL designed for video processing -out In addition to these components, of course, there are many standard TTL chips.
On our board there is also an optional AVO (Advanced Video Option) board with 4 sockets for ROM chips, which could overlap ROM data from the main board. The pin connector on top was designed for the VT125 terminal, and allowed the special module to intercept RS-232 signals before they were processed by the VT100 main board. This module recognized the special ReGIS commands that were used to draw graphics.
Documentation
Instructions for the user is very helpful in setting up, because it is quite difficult to remember which option in the menu is responsible for what. During the repair, of course, need a service manual and a set of schemes .
Source: https://habr.com/ru/post/390971/
All Articles