In praise of dirty calculators-- again.


I bought an SR-52 from TOS. It's pristine... not a mark on it, rubber feet have no wear, and there's no wear near the switch as always develops on this model.

It appears that someone spilled something on this calculator, as all the keys were sticking and some wouldn't even press. I'm guessing that it was put back in its box without the battery, as there's no corrosion whatsoever. And no battery. After a good bath of the case and all the keys, and a new foam sheet behind the keys, it works perfectly. Nice.


This is now really a dirty calculator:

(FYI: 26.5 years in use)



Nice. O.K....Joerg. As you know, my point is that the dirty calculators I've bought have often turned out to be little or even unused, and often clean up nicely. Let's see you clean that one up to look new....<grin>. That one looks well used... not just dirty! Nice photo.

Moral question: once fixed, can I call this calculator mint or even NIB? I guess I could just tell its story... There isn't even a mark on the red plexiglas... it really looks new! The blank magnetic cards were never removed from their package.


"once fixed, can I call this calculator mint or even NIB?"

I guess you could call it one of those but here's a way to make sure. Someone posted the following in about 2000 or 2001 so you might have seen it then. Five or so of the more cynical definitions are mine.

-EBAYese to English DICTIONARY-

Hard to Find = It's the only one I'm auctioning today.

Rare = "It's the only one I'm auctioning this week.

Very Rare = It's the only one I'm auctioning this month.

Unique = It's the only one I'm willing to sell.

Seller Prefers Paypal = I want your money and I want it NOW.

Mint = It looks more-or-less like it did when I bought/inherited/salvaged/found/stole it.

Minty = It's mint (q.v.), except for the funny green sauce I dribbled on it while eating lamb chops the other night.

M.I.B. = Mint In Box, but the item and box got slammed in the tailgate at the flea market.

New in Box (NIB) = I bought this with the sole intent of selling it for many times what I paid for it.

Nice = Looks great - doesn't work.

Complete = Except for the valuable, hard-to-find bits required to make it work.

Not Tested/Sold As-Is = 12VDC? 120VAC? There's a difference?

Like New = Like running over it with a car could really be that bad for it.

With Extras = I didn't feel like auctioning the manual, battery door, and case separately.

Buyer protection on eBay = We have your money. What's your problem?

I'm no expert on this.... = broken

I don't have batteries to test it = broken

I don't know how to test it = broken

It worked last time my dad used it = broken

Reserve Price = Cost of an item in Heaven - the SELLERS Heaven.

No Reserve = none needed in light of the outrageous miniium bid.

Buy It Now = ...for twice what it's worth, or risk paying three times as much to stave off snipers.

Joerg; That's a great idea you have there - wiping the dirt off your hands on a T.I. first, before using an RPN calculator. I'm going to start doing that! ;-)


Thanks for the list!!! I guess it's a moot point. I was playing with the new toy last night and decided I couldn't let it go any time soon anyway. I've bought several SR-52's over the years, and most were severely damaged by age and corrosion. The keyboards seemed especially prone to damage, relative to TI-59's. This one is like having a brand new one in my hands, and every key works perfectly... Even the two I've successfully restored aren't as sweet as this one. It does read cards, but needs the reader re-built due to dents in the drive wheel. (I'll probably break it somehow in the process...)

I noticed that the sticker on the back is different than any other SR-52 I've seen. It's in 3 languages, and the calculator was assembled in Holland rather than U.S.A.

Damn hobby... is collecting. I haven't sold a single calculator yet...


Two questions about my formerly dirty SR-52:

I found this loose piece between the LED board and the main board. See bottom of picture. Does it go somewhere in the calculator?

There is a 10K resistor soldered between two other components. See horizontal resistor in picture (ignore blue wires - it came with those in place of battery contact springs). Is the resistor a factory mod or some hack?



Claus- I'm not really sure. The resistor doesn't appear in my 52's, and I've never seen that other piece before either. I do know that the TI-59's went through lots of different re-designs, and it wasn't unusual for TI to add things- like the resistor shown- to the circuits, so that probably holds true with the SR-52 as well. It looks like that like the loose piece was used to insulate something, perhaps the battery contacts themselves? I guess.


Thanks for checking. This one's date code is 0776DTA. Are yours later or earlier models?



In my SR-52A serial n°032631 (manufactured 11/76), the horizontal resistor is present.

I will try to check the other 52's this week-end and also check the part you found.




Great! Thank you very much.



Now, on my later SR-52s serial 959034 & 960227 manufactured 05/77 and 07/77, NONE
of them have this resistor found on earlier series.

I'll try to post a couple of pics if I can convince my battered camera to turn on.

MfG aus Frankreich.




And now a pic showing a first gen & 2nd gen SR-52 side by side:



Edited: 6 Mar 2010, 5:53 a.m.


That is very informative. Merci.

The one on the left looks just like mine, which was made 4 weeks earlier. The one on the right looks like the picture on the Datamath site.



As I understand you have an SR-52 rev 1, I'll be glad to send you any part you need for this model.

Just let me know at E t i e n n e . v i c t o r i a @ f r e e . f r

I wish you success with this beautiful machine.



Dear all, if it can be of any help, I'm attaching a picture of my two SR-52s

This one has S/N : 942058 (top label) and LTA4176 (bottom label)

I use it for spares, and it was not working since it has arrived.

The second one has S/N 014131 (top label) and 4775DTA (bottom label)

Frankly speaking, there has been a time when both were on the table open up, and I mayhave swapped the bottom covers.

Both have the battery contacts broken, has anyone ever replaced them and with what ?(BTW, I have the same problem on a couple of TI59).

Also, the card reader works (I mean the card goes through without problems) but not logically.

What could I try in order to fully restore it ?

Thanks for help everybody, Alberto


It appears that your case backs are not swapped. The lower picture is of the older 52, judging by the date codes on the ICs (YYWW on the ICs, WWYY on the case).

My 52 came with wires soldered onto the broken contacts (see photo in top post above). I removed them and soldered on two coil springs from the battery compartment of a broken toy. I'll post a picture later.


Thank you very much, I think your is a brilliant idea, I'm also interested in getting back to work the card reader, from both the SR52 and my TI59s. As for HP's I have understood that other than the gummy wheels, some capacitors should also be replaced. Have you ever did it ? Thank you very much for help, Alberto


My 52 came with wires soldered onto the broken contacts. I removed them and soldered on two coil springs from the battery compartment of a broken toy.

I just tried it with my PC-100A and it works!


Good evening Alberto !

Thank you for the pictures and information!

Unfortunately, I cannot help you on the electronic repair of the SR-52 card reader as I only repaired it mechanically (basically the card reader wheel):


My card reader then read & wrote cards during 3 years and then refused to write them.

Having no service manual and not much time to investigate, I gave up trying for now.

I wish you the best in your restoration!



ciao Victoria,

thank you very much for help, and congratulations for your
website, it's very nice and helpful.

You should only update the old link
to the new link

I'll do some tests on my card reader and I'll let you
know. take care and thank you very much again


Thank you Alberto!

I'll update the links this week-end.

My "site" is more a compilation of various repair procedures I have used and my knowledge of website construction/maintenance is near zero :-)

I just save my Aperture images in my Mac's (site) folder and sync it.

Thanks again and have a nice day.



Hi Alberto!

I have corrected the bad link on the "site" and also updated the email button.

Have also added a couple of (ugly as usual) pictures on the Topcat printer reed switch replacement procedure.

As I work also this week-end, I will try to comment the pictures next week.

Cheers to all!



Yay! It works!

Another of this 52's problems was that an exponent digit would not light up. I experimented and found that the digit driver had failed. The SN97311 IC has 7 drivers and one of them tested open. I wired an NPN transistor and a 2K resistor across it and now the digit lights up. It's not perfect - an 8 is a little dimmer than a 1 - but it's better than pressing [2nd] [log] to see what the digit should be!


Wow... I'm impressed. My abilities to restore these devices stops at the level of mechanical engineering (contacts, card reader, batteries, wiring, etc.) and basic chip exchanges. Nice job. Let me know if you'd like some TI-59 and SR-52 "guts"... I have parts I don't think I'll ever use.


Thanks. I'm pleased it works. I suppose the best repair would be to replace the driver chip but I could find no data on the web, let alone any parts. I don't know how the SN97311 differs from the SN27882 used in other TIs.

Your offer of spare parts is very kind. I just replaced those blue wires with two battery contact coil springs from a broken toy. I should have asked here first for the right parts!


I don't think I'd consider the original contacts to be "the right parts." They were so flimsy and prone to corrosion. Most of the "parts" boards I have are missing the contacts!


Hi, all,
I'm new to calculator collecting. I've accumulated some over the years: my original TI-59; an HP-41C with card reader and printer; a TI-58 with PC-100A; my wife's HP-45; a TI-55; an HP-33e; an SR-40. Recently I've added more from eBay: an SR-56 like I had in '77; a TI-57; a Sperry like my first calculator ever; an MBA; an SR-52.

Many thanks to Joerg and Viktor and the MoHPC for their fine sites in helping me to restore these machines.

I used eBay because I don't know where else to look. Any suggestions?

On topic: The SR-52 keyboard was filthy and the poor photo on eBay did not show that. Some keys were gummed up badly. Disassembly and thorough cleaning restored it. The gumminess seemed to come from the faceplate glue leaking out. Some traces of glue are evident UNDER the brown factory coating! I thought the -52s had high quality. Anyway the keys work well now with no bounce, as with the -56. Can't say that for the later TIs - lots of keybounce there.

Edited: 27 Feb 2010, 8:34 a.m.


The key bounce of later machines is unavoidable. The plastic construction with welded wires simply sucks. That's sad truth.


Interesting. I'd wondered if the sticky and stuck keys was from glue from the face plate. The sticky substance took quite a soaking in "goo-gone" and scrubbing with a toothbrush to remove from the keys. There was no sign of any other substance inside the calculator. Your observation confirms what I'd only suspected!


Same here. Inside was clean. Even the foam sheet was reusable.

You got yours at TOS? What is TOS? Are there other places better than eBay?


I've personally never found a calculator anywhere else but on eBay. I've looked at garage sales and at thrift stores, but the thrift store people tell me that the people who work there usually have pre-arranged deals to sell donated calculators to people they know, so they never reach the sales floor. I don't have time to check out estate sales, unfortunately.


I guess I could just tell its story...
A good deal on TAS often is about items not well pictured. So, let some pictures sell your calculator.

Edit: I forgot something:

can I call this calculator [...] NIB?

I would expect an untouched item in this case, e.g. a sealed box.

Edited: 15 Feb 2010, 6:51 a.m.



How much do you ask for it?

I would Buy-It-Now or do you want to trade it for an RPN calculator?




Hi Jo"rg,

I've sent you an email.



I have sent you a New-IN-Box National Semiconductor NS-900.

You'll love the manual: 15 keys explained in tiny characters.



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