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Old 17th May 2020, 5:25 pm   #1
garry71
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Default RS diode/transistor checker

Does anyone have the above tester, stock no 424-169?

My dad's given me his old one(looks brand new), and I'm not sure it's working properly.
One of the LEDs is on all the time, but looking at the test notes on the rear of the unit I get the impression that both LEDs should be off by default.

The one mention I can find of it on google also gives me the same impression.
The battery seems ok at 9.09v

Can anyone shed any light on this for me, please?

Thanks a lot.
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Old 17th May 2020, 5:55 pm   #2
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Default Re: RS diode/transistor checker

As far as I can see from here:-

https://www.eevblog.com/forum/review...stock-424-169/

- the voltage between the probes switches back and forth quickly between approx +4v and -4V, and if a current flows the LED on the probe which is negative at the time lights up.

(...Seems odd they chose to indicate -ve with a red LED ??)

So, as you say, if the probes aren't connected the LEDs should remain off.

Cheers

edit: Just checked an old catalogue - it cost £34.50+VAT in 1988 !!

Last edited by Trigon.; 17th May 2020 at 6:07 pm.
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Old 17th May 2020, 6:14 pm   #3
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Default Re: RS diode/transistor checker

Thanks for looking it up.

I'll trace the circuit out and see if I can see what's what. It's 31 years old, so maybe the electrolytics had gone bad.

Cheers
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Old 17th May 2020, 6:19 pm   #4
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Default Re: RS diode/transistor checker

Quote:
Originally Posted by Trigon. View Post

edit: Just checked an old catalogue - it cost £34.50+VAT in 1988 !!
That's a bit steep. My old man worked at Rover cars at the time, I suspect it fell into his bag when he retired
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Old 17th May 2020, 6:49 pm   #5
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Default Re: RS diode/transistor checker

There's a blast from the past,I bought one many moons ago when business was good. I found it very useful at the time for doing go nogo tests on newly assembled boards. The only problems I ever had were with the rather fragile audio type cables and the probes used to fall apart. This always seemed to happen during a rush job. This jogged my memory so I made a brief search and found it, still in its original plastic bag, switched it on and shorted the probes. The LED's flash so it looks hopeful. I have not used it for many years. Peter.
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Old 17th May 2020, 6:53 pm   #6
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Default Re: RS diode/transistor checker

I have one, the LEDs flicker alternatively if the probes are touched together, on a diode or good transistor junction only one LED should flicker. We used to use these in my first job, the normal fault was the probe wiring breaking, I cured that on mine by building the LEDs into the case and fitting a pair of plain multimeter type probes. Your problem sounds more like someone's connected it to a circuit still powered up.

They are very useful for quick go / no-go testing. I have other units that can measure HFE etc, but this is my go to tester.
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Old 17th May 2020, 8:27 pm   #7
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Default Re: RS diode/transistor checker

I found what's wrong with it. One of the legs on the chip bent over instead of going through the board. Can't believe it got through QC at the factory.

I'm not taking the whole chip out, I'll just solder a wire from the errant leg over to where it's supposed to connect to.
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Old 17th May 2020, 8:51 pm   #8
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Default Re: RS diode/transistor checker

Then you'll find there was no track to that pin anyway

(Perhaps)
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Old 17th May 2020, 9:25 pm   #9
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Default Re: RS diode/transistor checker

Seems to be working ok now.

Cheers all.
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Old 17th May 2020, 9:42 pm   #10
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Default Re: RS diode/transistor checker

I have one as well along with the Continuity tester, very useful bits of kit.

Andrew
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Old 18th May 2020, 12:19 am   #11
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Default Re: RS diode/transistor checker

Interesting that 'Off' was on different sides of the switch between the two testers.
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Old 19th May 2020, 6:23 pm   #12
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Default Re: RS diode/transistor checker

Not much in there Terry except some top quality batteries, a CA741CE, one of those little plastic dome transistors marked I102 or 1102 and some passives.

Andrew
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Old 21st May 2020, 3:15 pm   #13
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Default Re: RS diode/transistor checker

Interesting how the continuity tester has a more sensible probe arrangement. Attached is a picture of my modified transistor tester.
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Old 21st May 2020, 3:27 pm   #14
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Default Re: RS diode/transistor checker

That's a better idea, those probe bodies you get with it are really fragile.

Andrew
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Old 26th May 2022, 8:49 pm   #15
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Default Re: RS diode/transistor checker

Reopened as requested

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Old 26th May 2022, 10:17 pm   #16
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Default Re: RS diode/transistor checker

A bit of a postscript to this thread: I've been using the RS 424-169 tester for the best part of 35 years and it's never let me down. However a few weeks ago I had a BC107 transistor which was behaving oddly in circuit, but tested ok out of circuit with this tester. I then dug out my Heathkit transistor tester and this told me Hfe was low and there was emitter to collector leakage! So the RS tester is good for total failures, but can be misleading on a more subtle failure.
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Old 27th May 2022, 2:40 am   #17
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Default Re: RS diode/transistor checker

There were quite a few of those hand held testers about before the test everything ones appeared.
I have a slightly more modern Farnell hand held LED tester in my workshop.
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Old 27th May 2022, 12:56 pm   #18
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Default Re: RS diode/transistor checker

Hi Andrew/Gary (and anyone else who has one of these)
I have one of these but it is missing all its transistors. I have been after getting it working for years. Please could you kindly take a photo of the circuit board, and let me know what/ which transistors go where, and hopefully I can get mine working. I probably won’t be able to get exact replacements, but I don’t suppose they are anything exotic.

Many thanks.
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Old 27th May 2022, 3:43 pm   #19
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Default Re: RS diode/transistor checker

Hi Tim,

Will do this evening. Just to be sure, which one did you want the photo of, the transistor checker?

Andrew
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Old 27th May 2022, 4:40 pm   #20
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Default Re: RS diode/transistor checker

Yes, the transistor checker please Andrew.
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