Posts: 149
Threads: 22
Joined: Feb 2009
Hi Reinhard,
Take a look at the pictures of the 9815 and 9820 (or 9821) here on the HP museum. The 9815 and 9821 are very different machines. The 9821 is much larger than a 9815, and it would be hard to mistake one for the other. The 9820 and 9821 have three ROM sockets on the left side of the top of the machine directly behind the keyboard. Directly below them on the keyboard is three sets of keys. Each set has two columns of keys. When a ROM is plugged in, it's functions are automaticly assigned to the set of keys below it. The 9815s don't have any ROM sockets. The 9815S, 9815 option 1, 9820 and 9821 all have sockets in the back of the machine for I/O interfaces. (The 9815x and 982x machines have different intefaces.) I have no idea how you ended up with a machine that has both labels. BTW, A 9821 is a 9820 with a tape drive instead of mag card reader.
You can use ordinary thermal paper in the printer. If you can find a supply of old DC-100 tapes they'll work fine in your machine. Or you can buy the HP brand tapes but frankly the HP tapes aren't very good. They have a tendency to shed the medie. When they do, the clear tape material is exposed and the End-Of-Tape sensor detects it and reports it as an Unexpected End of Tape error. ALL of those type of tapes were made by 3M company but for some reason the HP marked ones seem to be the worst of any of the brands that I've tried. I've also used old DEC tapes in these tape drives. All the different brands work fine but you have to INITIALIZE the non-HP tapes in the machine before you can use them. But before you try a tape in the drive, check the drive wheel. You'll probably find that it's gotten soft and gooy. That's a common problem with this type of tape drive. The HP-85s have the same problem and it's rare to find one that still has a good drive wheel.
I have both of these machine so let me know if you have any more questions.
Joe
Posts: 572
Threads: 49
Joined: Jan 2005
If you meant 9815A on the front and 9815S inside, then yes - I have calculators marked like that too. I also have 9815As with options that make them equivalent to the 9815S.
This is also one of my favorite designs.