I had already for some time a HP8672A synthesizer running from 2 until 18 GHz

After owning this for several years I wanted to do some measurements with this unit but at start up the display only showed 0000000 and it did not respond to inputs, the instrument was no longer working

A bit confused what was going on I did leave it for some time before I started to try and repair this unit.

On internet I found manuals of the unit and even better I found the operating and service manual.
I started with the troubleshooting manual and measured the power supply voltages, these seemed OK but the 5,2 Volt was a bit low, just out of spec's but in the beginning this did not bother me.

I kept on searching without result until I again realised that the 5,2 Volt power supply was just out of spec and I measured it again and it gave me a reason to check this part of the power supply. I measured the rectified voltage of the 5,2 Volt power supply and found it also too low, but this did not ring a bel yet.

After some further searching I measured the rectified DC voltage over the buffer capacitor and found quite a large ripple on that voltage. I decided to check the capacitor and found that it was broken.
I had to order a replacement capacitor and after it arrived I mounted it.

This proved to be right the synthesizer started up and was working again.