The Museum of HP Calculators

HP Forum Archive 21

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hp-67 card reader problem.
Message #1 Posted by Marcel Samek on 9 Dec 2013, 2:36 a.m.

I recently picked up a beautiful HP-67 but am having an odd problem with the card reader.

If I write a short program that fits on one track, the card reader reads and writes the card OK. I don't get any errors and the program is read in correctly.

If I write a longer program that needs two tracks to write, the card reader appears to write track 1, then gives me the prompt to turn the card around and appears to write track 2. However, when I go to read the card, it will always give me an "error" when I try reading the first side. If I skip the first side and try reading the second, it will read it without any errors and prompt me to to turn the card around.

Is this some sort of alignment issue where it is blowing away track 1 when it is writing track 2?

      
Re: hp-67 card reader problem.
Message #2 Posted by Paul Berger (Canada) on 9 Dec 2013, 10:18 a.m.,
in response to message #1 by Marcel Samek

Hmmm that is an odd issue. According to the illustrations in the 97 service guide (same card reader hardware) the card reader write 2 tracks near the edges of the card for each side, and it would seem there should be enough space between them to prevent one side from writing over the other. Inside the reader there are two crescent shaped leaf springs that hold the card against on rail to position the card in the reader, if one or both of these where missing I would suppose the card could enter the reader far enough away from the one rail to cause the tracks to overlap, however if that was the case I would be surprised you could even write one side and read it back. If you shine a light into the reader from one side and look in from the other side on the side towards the charger connector you should be able to see two small bumps in the guide rail, these bumps are the leaf springs.

The more I think about this the more it would seem that this is likely a mechanical issue as the same electronics are used to read and write both sides of the card. The fact that it does feed cards without them coming out with a gummy residue on them would suggest that someone has been inside and replace the tire on the drive wheel and perhaps something was not put back together correctly. I would probably start by making sure that mechanically the reader is ok, you will find a couple write up on disassembling the reader in the repair section here, the biggest things to watch out for are the small plastic balls that operate the switches they can be easily lost if you are not careful, and don't adjust the switches unless you really need to, I never have had to in the 7 readers I have rebuilt. The leaf springs that hold the card in place are also very tiny and are not fastened to to reader so they can fall out easily as well when the reader is taken apart.

I looked through the troubleshooting flow charts in 97 service guide but there is nothing that covers your scenario. This manual contains useful information about the electronics of the card reader but is little help with the mechanical assembly.

            
Re: hp-67 card reader problem.
Message #3 Posted by Marcel Samek on 9 Dec 2013, 2:49 p.m.,
in response to message #2 by Paul Berger (Canada)

Thank you for the detailed thoughts. I failed to mention that when I bought it, the seller did say that the drive had been rebuilt to fix the usual gummy problem. So, you may very well be right in your analysis that something when wrong when that work was being done.

When I look through it as suggested, I do see two small bumps. They are right next to each other but do not look centered. How should those bumps be distributed in a properly assembled drive when looking through the side like that?

                  
Re: hp-67 card reader problem.
Message #4 Posted by Paul Berger (Canada) on 9 Dec 2013, 5:00 p.m.,
in response to message #3 by Marcel Samek

The ones I refer to are in the side of the card path, if you look into the input side with the calculator upright, they will in the right guide rail. If you go to http://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/articles.cgi?read=179 nine pictures from the top shows the card reader open and the leaf springs are identified. From the picture you can get an idea how these springs push the card against the guide rail on the read head side, and now that I look at this picture carefully the springs would not be your problem as if they where missing or deformed the card might get offset in the direction of going off the edge rather than overlapping. I was going from memory before, but should have looked at the pictures before I posted. The only other mechanical thing might be the cards not going through smoothly but that would be more likely to be an intermittent issue and not be consistent.

The R/W head does not move, it is factory positioned in the top half of the assembly and glued solidly into place, so I will retract my earlier comment as it does not seem like an alignment issue would be likely.

Are you writing both sides of the card and reading back side one immediately? If so I wonder what would happen if you wrote both sides of the card and then power off and back on to make sure everything is reset before reading the card. I guess it is possible this could be an electronic problem but if it is it would be a pretty strange one, and would be hard to isolate without swapping parts.

                        
Re: hp-67 card reader problem.
Message #5 Posted by Marcel Samek on 9 Dec 2013, 6:43 p.m.,
in response to message #4 by Paul Berger (Canada)

Yes, I have been turning off the calculator between testing writing and reading.

However I have some more data and now suspect that it is a recording issue.

I had forgotten that I had one pre-recorded card - the HP diagnostics - in my possession. That is a two sided card that prompts you to flip it over. I tried several times to read it and execute it and every time it succeeded and ran the diagnostics as expected.

With the diagnostics program loaded from the prerecorded card, I recorded it to a blank card. When I tried to read that one after powering off the calculator, it gave an error. One time, I was able to get it to read without an error, but the program did not execute successfully.

So, I decided that it seems to be a recording problem since reading the prerecorded card seems to work OK.

I had received a pack of cards with the calculator. I thought I would try a different card when I realized that in the pack was an abrasive cleaning card that I had not seen before.

I ran the cleaning card twice through the calculator (I do not know what the manufacturer actually recommends).

I loaded from the prerecorded card, then recorded to the same blank card I had been trying before. And, lo and behold, it read and when I executed it ran the diagnostics as expected.

So, I guess it was a recording issue after all.

So, now my question is this. The abrasive card seems to have improved the situation. I am reluctant to use it often. Is there some other cleaning procedure (deoxit?) that I should use to get everything working as best it can?

Edited: 9 Dec 2013, 7:01 p.m.

                              
Re: hp-67 card reader problem.
Message #6 Posted by Paul Berger (Canada) on 9 Dec 2013, 9:09 p.m.,
in response to message #5 by Marcel Samek

Well the manual for the 67 says " If you suspect that the head is dirty, or if you have trouble reading or recording cards, by all means use the cleaning card; that's what it is for." It also cautions against excessive use of the card as it is abrasive and may lead to shortened head life. I am not familiar with Deoxit however a quick Google search suggests that some of the Deoxit products contain lubricant and that would be really bad. In the 1/2" reel tape days we used 99% isopropyl alcohol, and even earlier on a solution of trichloroethylene and isopropyl however I don't suggest the later trichloroethylene is a very strong solvent, one time partially dissolved the handle of a screwdriver, and it is also fairly toxic. I guess you could put a little pure isopropyl on a card and run it through, but never use rubbing alcohol it contains lubricants and will cause more issues than it will resolve. Also watch out for contaminated cards, any junk on a card will get transferred to the head, the users manual notes you can clean contamination off cards with alcohol (again 99% isopropyl never rubbing alcohol) and a soft cloth. Really severe contamination of the R/W head can only be resolved by disassembling the card reader and cleaning the head with a lint free cloth and alcohol.


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