Completing Opt 004 on the 5342A

Continuing from Part 1. 

I got all the required components and based on the schematics and board layout in the service manual, I simply installed all of them. I was trying to make it look as original as I could, so I even used proper push on pins for the additional connection of wires (though I did not have gold plated ones, bummer), and in general, used parts that fitted well to the footprints on the board. 

This was quite simple. A handful of components to the A2 display board and a couple of wires from the backplane to the board. An hour later I had the finished board.

The new components are on the right. The DAC80-CCD-V chip is evident. There are the four TTL ICs next to the DAC to the left. Some resistors and trimmers on the upper right and the SMB connector for the output just below the DAC. The empty socket is for the connecting cable to the mainboard.

That is all for the display board.

Three wires are needed from the backplane to provide power (+- 15V) to the DAC and to provide the LDA signal for the CPU access. 

Also required a run of coax cable from the SMB socket to the BNC connector on the backside of the instrument (upmost BNC on the picture).

All components were installed, the wires connected and secured. Then I hooked up a multimeter to the DAC out, gave some signal to the 5342A to count and hit the DAC button. I got a voltage out which was about right. Promising start, so I did the adjustment procedure described in the service manual. Basically the offset and the gain pots had to be adjusted to get zero and 9.99V out for 000 and 999 counts at the specified digits. 

The video shows the somewhat useless demonstration of selecting the drifting Hz digits for DAC source. The voltage is accurate and sometimes it can be seen that the digits are probably entered sequentially into the DAC, the Fluke 87 is fast enough to do a measurement between the update of the most and least significant digit.

It is also good to know that the DAC will convert any digits to voltage, so if the unit is equipped with Opt 002 for RF level measurement, one can hit AMPL for the dBm display and then do a SHIFT-DAC-9 and the DAC output will provide the dBm level, though without the sign for negative values. But still, this could be useful

So to summarize, it is possible to retrofit Opt 004 to the HP 5342A counter. There is only one special part required, the DAC, but even that can be sourced easily. All other parts are common and readily available.