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REPAIR HP 3764A DIGITAL
TRANSMISSION ANALYSER
August 2020

The first 3764A (#1) was bought in 2010 and had several assemblies missing so was not repairable. This was an early 3764A S/N 2322 circa 1983 at the start of production and is identified by the (missing) internal printer.

The second 3764A (#2) is complete and is S/N 3228 circa 1992 near the end of production. This has Option 007 instead of the printer.

The foam insert in the fan cover had disintergrated and spread itself all over the inside. The HP 3764A requires a complete strip down to assembly level to clean-up and inspect.

The complete 16 Plug-In Assemblies
An extra A23 Assembly for Option 007 behind the front panel
A21, A22 & A23 Assemblies and coax cables behind the front panel
A24 Power Supply Assembly behind the rear panel
DANGER: exposed mains voltages on pcb!

Rear Connector Panel and cables behind the rear panel
The end result, stripped down to Chassis
There are quite a few differences between the original #1 assemblies and the later #2 ones. The Service Manual is for up to S/N 2615 and does not reflect all the changes. I will search for later Manual updates although probably unlikely to find anything. Please Contact Me if you can help.

September 2020

The only obvious damage on the 16 plug-in assemblies was an unusual 3 leg axial electrolytic capacitor on A2 Power Supply.

Replaced with a conventional 2 leg electrolytic capacitor.

Powered-up very slowly to 230Vac with just the Power Supply Assemblies fitted: A0, A2 and A24. The fan is running ok and all 4 red LEDs are on. Voltage rails are: -5V on A0; +12V -15V +15V +5V on A2. The 15V rails are both low so fault finding required.

This is a surprisingly complex power supply design which HP seemed partial to designing! Annoyingly there are several closed loops between the 3 PCB's which makes isolating the fault difficult, plus it would help if I had the correct circuits!
IMHO a poor design and must have been challenging for production and test.

A15 Processor
There is a 3.6V 100mA/h battery on A15 Processor which has discharged to 1.2V so will need recharging or maybe replacing.

Held up by needing to find a working power supply A0 and A2 Assemblies to compare measurements.