Tom Verbeure

I find it amazing that this scope was last calibrated in 2023. (Could also be 1923, but I don’t think so. 🙂)

They’re probably more expensive than the $10 I paid for this scope!

SR620 time interval counter with an oscilloscope on top of it. The scope shows a screen with frequency and other data.

Zoomed in on the oscilloscope screen.

The SR620 time interval counter came to market around 1986, just before VGA was a thing. But analog oscilloscopes were everywhere, so it cleverly (ab)uses the XY mode to render images.
It’s unusable on a digital scope, it’s readable on an analog one.

Someone on Mastodon told me that this is probably not an ILO, because the circuit doesn't oscillate by itself when there's no input.

YouTube video by Harvard Natural Sciences Lecture Demonstrations Synchronization of Metronomes

It's a very much like those metronomes that start toggling in phase when they're placed on movable plank.

I would love to see a video with metronomes that toggle at a 1:2 frequency ratio.

www.youtube.com/watch?v=Aaxw...

Each ILO consists of an LC tank with a natural resonance frequency of 10 MHz and a very low Q factor. The input signal periodically inserts a bit of energy into the LC tank and after the while it will phase lock to the input signal.

The 3rd LC tank is a final 10 MHz output filter.

Schematic of the 5 MHz/10 MHz to 10 MHz clock circuit of the HP 5370A. 3 10 MHz LC tanks are marked in red.

The HP 5370A time interval counter accepts an external clock of 5 MHz or 10 MHz to create a 10 MHz reference clock.

The schematic is deceptively simple, but it's really interesting and I needed a Spice simulation to understand the basics: it's a cascade of 2 injection-locked oscillators (ILO).

Next project!
This time I wanted to avoid the situation where I find a Digikey bag in my cave and I have no clue what it was for.
I have a Digikey list for each project. It would be nice if @digikey had the option to automatically copy the list name to the customer reference field.

Digikey bag. The customer reference field says “TDS 220 recap”.

Digikey box arrived with components for 6 different projects.
What I should have done earlier is fill in the “customer reference” field for each component with the project name. Makes it so much easier to sort through the pile.
This baggie has a 450V cap for my TDS 220 recap.

It’s a Yokogawa DL1520L. Only 100Msps, but good enough to debug a 10MHz clock driver and, yes, I love the form factor.

Those are definitely better at powering through a short or 2!
I have a 6632A on the bench, waiting for a recap. Digikey package arrives tomorrow. 😀

In the case of the 5370A, the time measurement functional blocks run at 200 MHz, which was not bad for 1978.

Closeup of a PCB with wires and probes

The patient is reference clock buffer board A8 of the 5370A time interval counter…
It generates 10 MHz out of 5 MHz by using a very low Q factor 10MHz LC tank that syncs to the positive phase of the 5 MHz signal.

2 power supplies. The top one shows -5.2V and 0.4A.

If you ever wondered why old test equipment needs beefy power supplies: 6 puny ECL logic chip running at 10MHz consume 2 W (-5.2 V x 0.4 A) !

Workbench with laptop showing a schematic, an oscilloscope showing a square waveform and a sine wave, and a PCB with probes and wires.

HP 5370A repair: I had the short isolated to down to the components around 2 transistors, or so I thought. Soldered power supply and input wire for easy out of chassis debug. 
The thing works totally fine and creates a beautiful 10MHz ECL signal. Now what???

Reference frequency buffer PCB of an HP5370A. A red arrow points to a burnt capacitor.

The reference frequency buffer PCB plugged into the chassis. There is a red bodge wire.

The HP 5370A displaying a measured frequency of 9,999,999.9925 MHz.

There was (and is!) a short and a burnt capacitor on the clock reference board of my flea market HP 5370A counter.
I was able to bypass the short with a bodge.
After that, it works fine! The only thing not working yet is the circuit that was bypassed: the external reference clock input.

That looks really good!

This is the ancient equivalent of using a digital waveform viewer and debugging a simulation of a CPU that runs a program: by displaying the address as an analog signal, you can immediately detect execution patterns, program jumps etc.

Screenshot with the following text highlighted: "There are also two DACs for displaying the lower eight bits of the addressbus on one axis of an ordinary oscilloscope and the upper eight bits on the other axis to provide a "map" presen- tation that, to someone familiar with it, gives an instant indication of the behavior of the instrument."

The HP 5370A time interval counter was one of the first to use an MC6800 CPU. To make debugging easier, it has a service board that can send the MSB and LSB of the CPU address to 2 DACs, so that programming execution can be tracked on an oscilloscope in X/Y mode.

YouTube video by Cannonbreed Sopranos Beat em' Up

www.youtube.com/watch?v=uhMC...

I tried to make a convincing looking looking sopranos game

Yup! I have adapter cables to SMA on order!

Closeup of xtal and heat sink and the PCB.

The PCB has this 40MHz XTAL with heat sink that’s floating in the air, suspended by some wire and rubber bands. Or maybe it’s not a heat sink but just weight to increase mass and move vibrations to a different frequency range?

A gold and a black cylinder in the synthesizer.

The 5 MHz input is directly connected to that black cylinder. What is that???

BNC-like screw connectors on synthesizer.

Anyone know what type of connectors these are?

Inside of a flea market clock synthesizer.

Connectors of the synthesizer.

One of the flea market treasures is this heavy box that’s marked “Syntheziser”. No company or model name at all, but it must be HP, based on 1820-xxxx components inside.
5MHz in, 10 and 100 MHz out.
After removing around 30 screws, you get to see this. Stunning.

Variac, clock synthesizer, HP 5370A and Fluke 6071A stacked on top of each other in the trunk of my car.

A shiny variac, a high precision HP 5370A time counter, a back-breaking, broken (“it worked 2 months ago!”) Fluke 6071A signal generator and a nondescript 10MHz/100MHz clock synthesizer, all for $80.
‘t Was another successful Silicon Valley electronics flea market, but being there at 6am is rough.

A spicy pillow!

I didn’t measure the output with the switch open. According to the LM317 datasheet formula, increasing the FB resistor reduces the output voltage, but even at infinite resistance, it wouldn’t be 0 volts.

tomverbeure.github.io/2024/04/06/G...

I use it to measure the output of my other test equipment. 😀
But doing so often tricks me into learning how stuff works. See this blog post, which I wrote before I got the SR620.

tomverbeure.github.io/2023/06/16/F...

Front panel PCB on the SR620

Close-up of the switch while still in the metal case

Closeup of the switch on eBay.

Let's see if we can replace the switch? It took a while to get the switch out. (I still don't know how they were able to get it through the metal case hole!)
It's an obsolete ITT Shadow NE15 TE. You can find them for $7.50 on eBay + $5 shipping.
Part ordered, to be continued.