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Monday, 20 February 2017

Really? Wow!


How about this then?

I seem to be having a phase of collecting old 'scopes. I kind of love them, especially the old Tektronix devices.

There's a You Tube channel that I subscribe to by W2AEW where he does loads of fab and groovy things in general, but when I saw this, I just had to have one!

Using an Arduino Uno, a very primitive resistor based DAC and a bit of code, we end up with this, here on the scope I just repaired, a 2465:

Just fantastic!

This is the W2AEW actual video itself including the links to the code:

The Arduino and the DAC look like this on my bench:

and here running on an old 465 'scope:

Local conditions.

Wednesday, 8 February 2017

Tek 2465 Teardown


I have a Tektronics 2465 'scope that has some issues with it's timebase:

The sweep A is all out of bonk (that's a technical expression) - in the image above there's a 10MHz signal applied and at a 50ns sweep time per division we should see 5 sinewaves - we see 8 :-(

Sweep B is correct at 20ns however at 20ns we see two complete transitions of the signal.

I've started to take the 'scope to bits and will use this blog entry to document things as I go. Here are the initial shots of the 'scope in bits:

So here you can see both U700 and U900 removed, they are the main hybrid components in the Sweep A and B circuit. I'm going to try the 'scope with these two swapped round as they are the same component but for Sweep A and B:

So, swapping the two hybrid devices U700 and U900 made no difference; I now need to focus initially on this bit of the circuit:

I've also looked in more detail at the exact problem that I have. It seems all sweep speeds EXCEPT 5ns are impacted. I've annotated two points in the diagram above and have taken the voltage measurement at these points at all sweep speeds:

You will also note the consistency in the delta at all sweep speeds above 5ns - this is the same right up to 500ms but I just got bored writing the same thing over and over.

So, why is the voltage at the first test point so dramatically different at 5ns (the only sweep speed working) than all the others. Could it be that the B Sweep hybrid actually does the 5ns sweep on A? The B sweep can never be slower than the A sweep so there is no need for both to implement 5ns - I don't know if this is true or not.

I pulled R724 and in the process the end snapped clean off - but it measured 35.55K (it should be 35.3K) so I dont think that will be the problem. However, I've had to order some bits as this is a very non standard resistor value.

I also had a look at C712 which I have replaced. I also need to check that the +42V line is as it should be.

Once I have the replacement bits I'll update this post with my findings.

Some more pics while I wait for the bits:

Now the bits have arrived I have replaced R724 (made from two resistors in series) plus C712 and BINGO - the fault has gone and the sweep speeds are back on the money. The unit needs calibration now :-(

Final update: I've been through the step-by-step calibration routine. To access the routine you set a jumper on the control board and then press the delta T and V buttons together and whilst holding them down stick a chicken down your trousers (actually you press the slope button). Then you go step by step through the calibration routines and using the other test gear I have hear I seem to now have the 'scope very much on the money.

Local conditions.

Tuesday, 7 February 2017

A Lawful what?


Back in the spring of last year we removed a load of trees from our property and also had some fairly extensive works undertaken in the garden. The net result was that the antennas at the property became much more visible from the road.

Now, one of my neighbors who is particularly grumpy, decided to question the legality of the mast(s) and antenna(s) at the house with our local council.

In accordance with the planning laws, they all should be subject to planning permission. However, theory says that because they have been in place for in excess of four years the council are unable to take enforcement action. Unfortunately, the onus is on me to prove they have been in place for that time.

Thanks to this blog and my obsession with taking photographs, I was able to generate a very comprehensive document containing a load of google dated photographs stored in the cloud showing each of the antennas and masts in place with a photo upload date.

Finally, after a long bureaucratic process, my Lawful Development Certificate has been issued.

So my grumpy neighbor can go stick his complaining!

Local conditions.