Data General Dasher Terminal Tester P/N 005-010-675-02 S/N AA1627/z2007
This looks like it can connect to both Current Loop and EIA terminal interfaces, send just about any format of serial character, send a single character or a line of characters, and display the bits of the received character.
We don't have any documentation on this tester, but it should not be too difficult to figure out how it works.
Since the Current Loop and EIA terminal interface is not unique to Data General we should be able to use this device to test any kind of terminal or serial port.
Two of the big chips on the PCB are a FIFO and a UART. It looks like it can fill the FIFO with a character pattern and then send it out the UART.
We disassembled the tester so we could see what was inside. It has a single PCB containing all of the electronics. Many of the 14-pin ICs had DG part numbers on them, so we will need to find a cross reference to industry part numbers.
An Alpha Power model 2BBMP power supply was installed under the PCB. Google doesn't find anything on this power supply. We disconnected the power supply from the PCB, connected it to an AC source through a Variac, and slowly increased the input voltage over about an hour. This process will reform the electrolytic capacitors that haven't been used in many years. If you just turn it on it is very likely that you will permanently damage the capacitors. We adjusted the power supply voltages to +5, +12V, and -12V, and it seems to regulate well.
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The label on the cover of the terminal tester.