Model 61 TRI_STATE RS-232 EIA Breakout Panel by International Data Sciences USA circa 1970's-80's

[inotarobot]

Model 61 TRI_STATE RS232 EIA Breakout Panel by International Data Sciences USA circa 1970's-80's

I FINALLY got one on the 7th June 2026. Cost me Aus$20.00 I could NOT get my wallet out of my pocket any quicker.

It was on a Brick a Brac seller stall, at a one a month Sunday Community market in this County Town I live in.
This semi regular seller had not been to our market since October 2025.
He has never had electronic, and this was his only electronics object, apart from a AC Mains Powered Switchboard mounted Mechanical Time clock.

Was an utter surprise as I've never seen any stall with old electronics in the +10 I have been going to this market,

Came with book and 2 small cards. No marks of any form in the book.



Really does not look like its ever been used.

Had the 5 genuine jumper leads still inside.



Back in the day I built a similar item on some breadboard. That did the job, but I often wished I had a genuine one.

I am 75 on the 14th June so this is a really great self bought Birthday present for me.

I look forward to testing it in due course

Battery terminal are in mint condition, no marks not corrosion.


Annoyingly the seller had written number 20 on front cover in what I was concerned was a permanent black marker. Fortunately not, and IPA removed it without damaging the plastic surface of the case. Photo above was taken prior to me using ISO on the Number 20. Now that number is 100% gone.

 

[inotarobot]

yes you guessed it. I decided to unscrew cover. So here are 2 pics of whats inside.

What I find slightly strange is there is no switch for the Power to turn off the batteries when not in use. Manual makes no mention of this point.

I assume one simply unplugs the batteries when it not being used. OR it has a SMART circuit consumes no power when its not connected into an active RS232 Circuit, but is activated when connected to live RS232 cables etc

Also I tried brand New VARTA Brand Longlife AA batteries and it appears they are slightly larger than the AA available when this was made. both in diameter , length and diameter of the positive terminal.

They are a tight fit end to end and side to side.

 

[inotarobot]

and for those curious here are a couple of pics of the remaining electronic/electrical bits that seller had for sale.

No I did NOT buy any.

 

[inotarobot]

""What I find slightly strange is there is no switch for the Power to turn off the batteries when not in use. Manual makes no mention of this point.

I assume one simply unplugs the batteries when it not being used. OR it has a SMART circuit consumes no power when its not connected into an active RS232 Circuit, but is activated when connected to live RS232 cables etc""

I wrote the above comment latish last night after a long day and 2 strong pain killers for arthritis in the thumb joint of my Dominant right hand. About 4am after a 'mother nature call', I picked up manual as I hopped back into bed, as it was bugging me that lack of power switch comment I had made earlier in this thread. I was sure it was just me having a 'Dumb old male' moment.

Yep there in the Manual was the simple circuit for 1 signal line, repeated for all 13 Led's.

Thankfully I don't live in a Brick house as a 'pile of them hit me' looking at that basic circuit.

When the unit is not connected to a circuit there is NO signal to 'drive' the Base of the Transistor. Therefore no current flows though it to power the Led.

Manual mentions Battery Life at 40hrs, which I assume to mean 'operational' hours

I just did a check on BitSavers but did not see manual mentioned. So I will in due course scan the one I have and submit it.

 

[pbirkel]

When the unit is not connected to a circuit there is NO signal to 'drive' the Base of the Transistor. Therefore no current flows though it to power the Led.

Well there will be thermally-induced C-E leakage currents in both transistors in the low uA range (well below the LED threshold) That will still add up over time and deplete the batteries. Of course the batteries will self-discharge ("shelf life") as well.