Test Equipment Anonymous

Another item from the DDRC boot sale, this is the usual Farnell 30V 2A power supply in an unusual IEEE488 equipped form. I like the Farnell PSUs and it was £5 and have a use for another programmable supply so I bought it. When I got home I discovered that the internet had never heard of this PSU, so perhaps it wasn't very popular. This also meant that the documentation for the GPIB interface would not be easy to find so after establishing that it worked in local mode I removed the lid to see if I could dump an EPROM and find the commands.
Here is what I saw… The big chip is a Philips GPIB bus interface. On the other side of an opto-isolated bridge there are two Analog Devices 3.5 digit solid state potentiometers, one for current and one for voltage. The datasheet was available and I quickly spotted that the most significant digit was hardwired to zero, meaning that each potentiometer had three BCD digits, which would likely mean six latches. The six 4042s are quad D-types, each with a separate clock fed by some logic contraption that includes a 4017 counter and a big 1 of 16 decoder chip. I connected up the bus and fed it some letters and numbers, numbers were advancing the 4017 count and alphabetical characters seemed to be firing its reset line. I started to draw a schematic but there were so many wires and it seemed that given certain assumptions I'd be able to figure out what to feed it. I worked out which characters performed each operation by monitoring the 1 of 16 decoder and the 4017.
Vddd programs voltage
Iddd programs current where ddd is 000 to 999, with 999 representing the maximum voltage and current of 30V and 2A.
P resets the state machine without appearing to have another function
C or S switches on the output to the programmed voltage
B or R switches off the output
Both the on and off switching is fake, it just changes the voltage setting to zero as far as I can tell. There's a separate manual switch for isolating the output on the front panel.
Noise level seems very good. I've tested it at full current. In terms of programmability, "000" or 0V measured 17mV and 999 measures 30.088V and current was similarly fine, so it seems the only thing I really need to do is find this power supply four replacement plastic feet that aren't broken.

I've never seen Farnell equipment on this side of the pond but it turns out they do own Newark Electronics.

Farnell started as a components seller in the UK in the late 30s. They branched into manufacturing in the 50s. They made PSUs, audio signal generators, function generators and the odd oscilloscope. My impression of their products is that the PSUs were well thought of. The signal generators were mid market. I don't believe they produced things like ultra-low distortion sig gens. They sold their manufacturing operation in 1995 to concentrate on distribution. They bought Premier, a US based components distributor, in 1996. Premier bought Newark in 1968.

In 2016, Avnet, a US distributor bought Premier Farnell. The Newark and Farnell brands are still used. A convoluted story of acquisitions and sales.

I wonder if the missing components provide a V & I measurement capability?
The Farnell switch mode chassis mount power supplies are excellent apart form the odd RIFA failure. A long time age I donated three used 5V (50A IIRC) ones to a local amateur radio repeater. They were used in series and adjusted to provide 13.8V. As well as running the repeater thy float charged the bac-up batteries. I recently heard that they had been replaced as part of a total repeper upgrade after more than 15 years of flawless service oerating 24/7. I still have stash of various models, more than I'll ever use probably...

Robert.

Robert wrote: ↑Tue Jun 17, 2025 7:03 am I wonder if the missing components provide a V & I measurement capability?

Seems very likely, the command decoding arrangement looks the same, I didn't try playing "guess the ADC" but I did search the web for a Farnell supply that had V & I measurement to see if I could work out which model or models the board was also used in. Unfortunately I didn't find any, but it'd be a fun project to add that capability so I might search a bit harder at some point.

That's a very unusual Farnell power supply; never knew they made a programmable version. In the 80s and 90s, Farnell LT30 supplies were ubiquitous in teaching and at the BBC. Wireless World was full of adverts for them from the 70s onwards. As mentioned, they also made quite reasonable signal generators as well, dependable stuff that was student-proof but definitely not super performance.

EC8010 wrote: ↑Tue Oct 07, 2025 7:29 am That's a very unusual Farnell power supply; never knew they made a programmable version. In the 80s and 90s, Farnell LT30 supplies were ubiquitous in teaching and at the BBC. Wireless World was full of adverts for them from the 70s onwards. As mentioned, they also made quite reasonable signal generators as well, dependable stuff that was student-proof but definitely not super performance.

I read that in context to a problem I had. I had a Farnell power supply that was a good oscillator and a Farnell signal generator that was a good power supply but didn't oscillate