RS 424-169 Diode - Transistor Checker - Tester: For soldered parts inspection

[Kiriakos GR]

This is one of hidden treasures of electrical engineering of 90s  
RS 424-169 Diode - Transistor Checker

Product description:
The RS diode/transistor checker has been designed to serve as a very versatile instrument for checking the condition of semiconductor devices whilst still in circuit.
The two test probes are connected across the junction to be checked and two LED (one at its probe)  instantly show its state.
1) Junction is open circuit  (both LED Off)
2) Short circuit     (both LED flashing at High-brightness)
3) Faulty junctions (both LED flashing at Low-brightness)
4) Polarity of a good junction. (single LED will be On).
Suitable for checking N.P.N. & P.N.P. transistors, diodes and Zener diodes.


Product design details:
This is actually a Pulse wave generator which delivers feedback at LED indicators at a rate of approximately three times per second.
IC: TC4011B Quad 2 Input NAND Gate
ODM this is named as NEUTRAL-Brand, unfortunately this might be fake news made by RS components so to hide it true origin.

 
Product testing by a multimeter:

Prior owning an Oscilloscope, I did  manage to confirm by a fast multimeter at ( June 08, 2011) that (what I had since 1996) this is a square signal generator at  14.87Hz  60% duty cycle   +4.181 / - 4.175 V   

Prior saying Good Bye at the year 2019, I did decided to confirm it by the best way this time. 
First screenshot this is with nothing connected to it.
Second screenshot this is when a BY225 diode this is under test, and this represents the output under load.

In conclusion: 
Personally I love this tester, it is not the best all-in-one tester but it helped me thousands of times since 1996 up to 2019. 
Once I did manage to damage it IC (that is the hart of the circuit)  because the circuit that I was testing was powered-on by mistake.
The Toshiba IC were replaced, luckily for me by one 100% genuine made by PHILIPS of the same era.

While such a product did not show again in the market after be discontinued by RS, the electronic design this now lives inside of Keysight U1272A multimeter, at diode test function when Auto secondary function this gets activated by pressing the orange button.
Keysight reduced the square wave frequency to 1.8Hz and possibly they did that so the measuring circuit of the multimeter to be able to calculate and deliver accurately measured diode junction voltage.
This is the same concept as when we speak of Oscilloscope dead time, this Dead-Time it is required for signal processing and delivery of a measurement that we can trust!