SR-52 not writing cards

[Kees Bouw]

Status update. The trouble was that when writing cards, the card stopped half way in. This was the case with and without a write protect (or rather: write enable) tab on the card. I thought initially that stopping half way was normal behaviour if you try to write to a card without a tab and that there was something wrong causing this to happen even if there was a tab present. So I opened the calculator to check for anything visually wrong. Everything looked as it should be, but to make sure there were not any reflections I glued some black paper on part of the metal strip that holds the pressure pad. See the attached photo. I also did some testing and found that the card ran completely through when writing. I attributed this to the photo-transistor not being in the correct position. I put the calculator back together again and... now writing cards works fine. Which is great, but the downside is that I still have no idea what was wrong. I really don't think that covering the metal strip solved it, if this could be a problem then TI would have done so in the factory. Anyway, it turns out that stopping half way is NOT normal behaviour when writing a card without tabs. What really happens is that the card runs through but there will be a blinking zero in the display to indicate that writing did not succeed. If I had known that beforehand, I would possibly not have wasted time and energy on finding working tabs.