Shaun Merrigan's Information Pages


Category: Troubleshooting


Racal 9478: Widespread Electrolytic Capacitor Failure

Posted by Shaun Merrigan in Electronics, Restoration, Troubleshooting. Comments Off on Racal 9478: Widespread Electrolytic Capacitor Failure

25th May

The Racal Dana Model 9478 Frequency Distribution System has an internal precision, oven-controlled crystal oscillator, or it can be phase locked to an external signal derived from a GPSDO or other master oscillator.  The system will automatically lock to an external signal above 100 mV, and with a standard frequency of 1, 5 or 10 MHz.  “In Lock” indication is provided.

I recently repaired two Racal 9478 units. What I found was widespread electrolytic capacitor failure such as I had never encountered before. A summary of the issues found in both units follows:

Virtually all electrolytic capacitors in both units (nearly 90 in all) had failed, showing either very low capacitance and/or very high ESR. Interestingly enough none showed short circuit failure.All the failed electrolytic capacitors were made by Philips in late 1980’s The -15v regulator was originally bolted … Read More »


HP 1340A Display Repair -2

Posted by Shaun Merrigan in Electronics, Oscilloscopes, Test Equipment, Troubleshooting. Comments Off on HP 1340A Display Repair -2

29th December

HP 1340A Display Repair


HP 1340A Display Repair – 1

28th December

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.

HP 1340A Overview

HP 1340A Overview

HP 1340A Overview

HP 1340A Overview

HP 1340A Overview

HP 1340A Rear Panel, High Serial Number

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)

Heat Damaged Components

LVPS A2Q2 Damage

Heat Damaged Components

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 … Read More »