1998' Robotron plotter - renovation, part 2 - the prophylactic EPROM 2716 replacement

Time ago was published the article about equipping the old-made (but not used) plotter Robotron REISS K6418 (CM 6415) with Bluetooth COM-port.

The plotter can be used for PCB making, drawing on face panels of cases, etc.

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This plotter was made in DDR, but didn't work even once since 1989, and was kept in its original package. In 2019 he was powered for the first time and works without any problems.

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Some bulged capacitors were on PCBs. All electrolytic capacitors were replaced with new one.

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No other elements of the plotter looks requiring a repair.

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But folks are reminding, that UV EPROMs (here is M2716 type chips) had limited guarantee time for storage of data. In the best consumer versions of UV EPROMs it is 25 years.

Despite the fact the plotter is working fine now, it seems right at least to save UV EPROM's dumps in an archive. With these dumps, it will be possible to reflash native UV EPROMs now placed within the plotter if they will start errors. Or other variants can be used nowadays with stored dumps:

  • the EPROM emulation with some controller, as Arduino, STM or other (with built-in, or external flash-memory);
  • to make a copy of UV EPROM with some PLD;
  • to make a scheme on simple logic chips that transforms "old time" parallel interface in to "modern" serial interface for a flash-memory;
  • the shadow RAM realization;
  • with use of a wormhole generator. But this method will be available a little later;
  • or simply by programming any EPROM (the UV type not important) that can be bought now and has architecture "N by 8 bits". For example it can be used Winbond W27C512, ST M27C512, etc.

In prophylactic purposes, the new programmed Winbond W27C512 was installed in the plotter and works instead native 30-year old M2716 UV EPROMs.

Ok. Step 1 - make dumps the Robotron's native M2716 UV EPROMs bank.

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This components were collected from what were at hands:
Sipeed Longan Nano - RISC-V GD32VF103CBT6 Development Board, haves 32KB SRAM and enough 5V-tolerant ports;
- 28-pin ZIF IC dip-pad;
- prototype printed circuit panel (green colored about having metalized holes).

The GD32VF103CBT6 board was programmed with this sketch (VSCode project with PlatformIO extension, deployed as here ruled) and wired to the ZIF IC dip-pad as commented within the sketch. The 5V power and GND were wired from GD32VF103CBT6 board to the IC dip-pad.

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Once the GD32VF103CBT6 connected to a PC with use an UART-USB adapter, any plotter's EPROM placed in the dip-pad can be read with command 'peek' to GD32VF103CBT6 within SUDT AccessPort utility (any other utility, works with COM-ports, can be used). Serial port settings were 9600,N,8,1.

The EPROM bank of this plotter is formed with five chips M2716 soldered all parallel at one 11-bit address line and at one 8-bit data line. The EPROM chip for read at current time by the plotter's processor is selected with logical low to /OE and /CE pins joined on the PCB for this chip.

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Four chips, looks like with firmware, is high level quality - in ceramic cases and with golden-plated pins, while the fifth chip, looks like for the codepage, has the ordinary consumer quality. Four chips with firmware soldered on PCB, the fifth chip placed in the IC dip-pad.

The attempt to solder out one of the firmware chips had unsuccessful. The vacuum desoldering tool tears off PCB tracks with chip's soldering points. The desoldering wick was unusable too as holes in the PCB are too big (the solder being heated, falls inside these holes, becoming inaccessible for the extraction). Moreover, the PCB was varnish-coated at the factory, so the use of a hot air or a hot plate is also not effective.

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But any firmware chip is possible to read being soldered on the PCB via the dip-pad of the fifth EPROM chip, pointing each one chip for reading with logical low to /OE and /CE pins of them.

Unfortunately, it was necessary to cut the 5V lines to these EPROM chips (but not ground lines) before reading dumps, as when reading, the power comes from the reader, and this power had tried to turn on the plotter's processor.

Each of the plotter's EPROM were readed three times, with checksum verification within HashTab. This is all five dumps:

EPROM marked 1

EPROM marked 2

EPROM marked 3

EPROM marked 4

EPROM marked ANZ

Now the native EPROM bank of the plotter backuped.

Ok. Step 2 - make the prophylactic EPROM bank replacement.

All five chips M2716 type (impossible to purchase long ago) can be replaced with only one Winbond W27C512 (can be bought now). Then the W27C512-based emulator can be connected to the potter's address and data lines via socket (dip-pad) of the native fifth EPROM chip.

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The W27C512-based emulator of M2716 chips was assembled as this simple scheme. The idea is /OE and /CE signals of each native M2716 chip will point to the part of W27C512 memory where the dumped firmware from this M2716 chip flashed, by sending the logical HI signal to one of A11-A15 pins of W27C512.

The W27C512 chip was flashed with this firmware. This file consists of five dumps of native plotter's M2716 EPROMs, stacked all together and placed at these addresses using the program Frhed.

Start address within W27C512, binStart address within W27C512, hexThe dump of which native EPROM chip is flashed from this address in W27C512Switch to the dump by send logical HI to W27C512 pin
000000000000H--
100000000000800H2A11
10000000000001000H3A12
100000000000002000H4A13
1000000000000004000HANZA14
10000000000000008000H1A15

It is possible to flash W27C512 on the self-made programmer who had used it to read native EPROM's dumps, but it is a good idea to make this on a professional device in a service center, as for the flashing operation the precision tacting and voltage need to be realized.

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The W27C512-based emulator was assembled on two small printed circuit panels, which takes into account the place on the plotter's PCB.

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The 24-pin IC 2.54 pitch socket was used in order to connect the emulator to the plotter.

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Then the W27C512-based emulator was placed in the socket (dip-pad) of the native fifth EPROM chip. The plotter is not detect of native EPROM chips, as +5V lines to these chips had bisected since time when dumps were made.

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Then wires from the W27C512-based emulator were connected to /OE and /CE points of each native EPROM chip. As the plotter is a vibration-abused device, some varnish and hot-glue was used to fixation of newly added elements.

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That's all. Now this plotter has the fresh EPROM bank instead native 30-year-old UV EPROMs, in addition to the previously added opportunity to work on Bluetooth.

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