HP 3335A Synthesizer/Level Generator: Unlock issue, soldering issue?

The recently fixed 3335A, it still has some issue with the reference input. From time to time, or when touching the BNC cable connecting the 10 MHz OCXO output with the reference input, the *UNLOCK* light comes on.

First I thought it has to do with the low cost and cheaply made BNC cables, but even with very good BNC connectors, the issue persists. So, let’s open the thing up another time. I don’t like partially fixed instruments – even though this error could probably be solved by just not touching the cable….

Fortunately, the BNC connector has a long cable internally, and can be disassembled without destroying the crimping.
Checking it, the center wire has no connection. Looking at it in magnification, it seems that only ever the very tip has been in touch with solder, but inside of the golden BNC center connector, there is no solder. So it is clearly a HP manufacturing issue, someone didn’t solder it quite right.

After soldering it again, with plenty of solder, and removing the excess, all is working well! Finally!

4 thoughts on “HP 3335A Synthesizer/Level Generator: Unlock issue, soldering issue?”

  1. Now that is a nice challenge. I have encountered this kind of “bug” myself in the past, they can be quite confusing because you tend to think “this cannot be the problem”. Aka “Das gibt’s doch nicht?!”.

  2. That’s quite disappointing for HP. Surprising no one found it until you did. I recently took apart an HP5071A. (bad tube) I found one of socket-ted IC had only 13 pins properly seated. Last pin was bent and clear out of the actual socket.

    1. Probably it made a little bit of a connection at the tip of the center conductor where there is a trace of solder. Then it disconnected after some use. In other instrument I found bits of solder shorting a trace, but luckily in a place with no big effect.

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