|Re: HP 9815A repair|
Message #3 Posted by frankabc on 23 Aug 2007, 3:55 p.m.,
in response to message #2 by Tony Duell
Thank you, Tom,
Our misbehavin' HP 9815A does a few interesting things.
Run Mode: First, when you key in 2, 2.00 enters automatically. When you try to key in 25, you cannot, because it will display 2.00, and then 5.00. Though the enter key DOES work, and can be used, it is not necessary to hit enter to do arithmetic. So you can now key 2, 5, +, and the result, 7, appears on the display. Normal RPN would be 2, ENTER, 5, +, display 7.
Auto Start mode: When you flip the power-on switch, the 9815A will attempt to load a program from a DC100A tape cartridge. This seems to be working. Unfortunately our tapes are 20 years old, and we fear that they might not have readable programs any longer. The priter prints "file not found" or, on more encouraging attempts, "Checksum error". But we cannot tell if the tapes are good, or not, because we do not know it the computer is good, or not. The cartridge drive itself seems to be working.
Program mode: One cannot simply enter the program mode with the switch. If I go through the following mindless steps, I can enter the program mode, every time.
Switch in run mode
turn power on
then switch to program mode.
Once in the program mode, the display reads 0000 on the left, and 0136 on the right. There should be 432 programmable steps, minimum, not 136. Furthermore, our machine has the 001 memory and 002 I/O options. The 001 option should increase memory to 2008 steps. Again, not 136. On good days, I can program a few steps. For example, I can key in steps to recall numbers stored in A -> J registers, multiply, end, etc. But when I switch back to run, she does not run.
The printer prints "memory overflow", on almost every interraction. I have attempted to clear the memory by the protocol in the manual, and sometimes I can clear it. I have pressed the list button, and the printer prints the memory steps and contents, usually to 136 steps, but on one occasion, out to 216 steps. On that 216 day I was able to reallocate the 80 store registers to programmable registers by the protocol in the manual. Note that 80 + 136 = 216. I only have gotten 216 programmable steps once, and have never again been able to repeat it.
I also have wondered why the priter prints "memory overflow" even after only turning power on in run mode. Isn't the memory supposed to clear when power is turned off, and then back on? Well, I decided to press list, immediately after turning the power on. The print out informed me that memory really was already full of all sorts of stuff.
That is about as far as we have gotten.
In answer to your questions. I have an electrical engineering friend who is going through the machine. Don used to repair electronics for our Biochem Department. We have a digital volt meter, and that is about it. Don has a logic probe at home. We have all of the manuals, including the service manual. We have found the Utilities and Test Cartridge Tape (09815-10004), but we are not sure if it is still readable. It yielded "no file found" when inserted into the tape drive. It would be nice to obtain a known-to-be-good copy of the Utilities and Test Tape from someone. We also cannot locate the 9815A Test ROM Assembly plug-in (98140-66501). It would be very beneficial for us to find these two troubleshooting aids.
We are wondering if Digital Signature Analysis is possible with the 9815A. It looks like HP was developing Signature analysis around 1980.
We also are wondering where your web site is with the schematics of the HP 9815A.
We greatly appreciate any assistance and suggestions that you may offer.
Thank you, Frank Simpson