I purchased a couple of HP 1340A XYZ Displays which I thought would be useful as troubleshooting aids and as graphical displays of CRT technology (oscilloscope clocks, and the like). Upon receiving them, they both worked, but careful visual inspection showed some potentially serious problems. I will document the repair process here.

Visual inspection of the units revealed the following problems:

• Heat damaged A1R81 (both units)
• Heat damaged A2R13 (both units)
• Loose mounting hardware and corroded wiring on A2Q2 (one unit)

A2Q2 is mounted directly to the case for heatsink purposes. The hardware was loose, therefore the transistor effectively had no heatsink. I suspect that it had been running hot for quite some time because the PVC insulation had degraded releasing hydrogen chloride which immediately formed hydrochloric acid on contact with moisture in the air. This corroded the copper wires. Note that this transistor is part of the +165v regulation circuit, so a failure would most certainly damage other components.

The next part of this series will document the replacement of these components and final voltage checks.

Thanks for reading.

Shaun Merrigan

Electronics Troubleshooting HP 1340A HP1340A Display Repair Shaun Merrigan