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Based around a Motorola 6800 microprocessor, with 14 KBytes of firmware in ROM.
A lot of functionality packed into a small desktop form factor,
including the ability to interface to external I/O devices.
Servicing these units is awkward as the main boards are folded tightly over each other.
Extension connectors can be constructed to permit operation and access with the boards unfolded.
The 9815 'exploded' into it's constituent modules. Power supply, tape drive interface and printer on the board in the case bottom; 6821 PIA, 6800 CPU and memory on the large board on the left; display and other device interfaces on the board on the right, mounted over the keyboard. The I/O interface attached to the right side is 'Option 2' and hence may not be present in all units. |
Shown is how some service adapters can be used to connect the two main logic boards for operation while the boards are unfolded for access. The adapters were constructed by cutting the fingers from discarded ISA-Bus boards and associated edge connectors. Physically the two logic boards could simply be screwed together in unfolded form. Unfortunately, HP left 4 fingers off the contacts on the normally-unused side of the CPU board, making the adapters necessary to provide continuity for all the circuits. |
| 1529A01234 | |
| 1976 (ICs stamped with 7609) | |
| Manuals, dust cover, several tapes, plotter, 98130A and 98135A interfaces & cables. | |
| 09 Nov 2001 | |
| UBC SERF. | |
| Functional except for gooey rubber on tape drive wheel. | |
| Functional except tape drive (15 Feb 2007). |
| Nov 2001 | |
| Cleaned. |
| 30 Jan 2002 | |
| Tape drive does not work due to gooey rubber on drive wheel. | |
| Motor and drive wheel replaced with units from a HP9825. |
| 30 Jan 2002 | |
| Test/Utility tape messed up from gooey drive wheel. | |
| Drive band replaced with band from another cartridge. |
| 30 Mar 2002 | |
| Decayed padding cleaned out of printer. Original 4 peg bumpers still OK. |
| 15 Feb 2007 | |
| Some keys (8,9,CLEAR,CLx..) do not work. | |
| Boards separated to access keyboard, keyboard tests OK. Presumed to be connector contacts, reassembled, functional. |
| 18 Feb 2007 | |
| Tape drive wheel melted while reading Utility Routines tape. | |
| Not repaired. |
| 26 Feb 2009 | |
| Some keys (9,CLEAR,CLx,RD..) do not work. | |
| Problem of 15 Feb 2007 returned. Same procedure, OK. Schematic made of keyboard matrix, problem keys appear to be on two columns of the matrix. |
| 07 Mar 2009 | |
| Keys not working again. Problem has progressed to include more keys (f,f-1,A,F,K,B,G,L..). Also seems to correlate with temperature. Problem shows up when ambient temperature is low, disappears after unit is on for some minutes or room temperature rises. | |
| Problem keys correspond to 4 columns on the sense side of the matrix (not-2 address). If the problem were the scan counter or 2 bit, bad keypresses would show up in other columns, so problem must be in the 1-of-8 decoder. U269 (74LS151) replaced. Functional initially, failure again next morning when temperature is lower. |
| Mar 2009 | |
| 680 uF electrolytic capacitor on V+15 supply observed to have been installed with the incorrect polarity (manufacturing error). (Not corrected at this time.) |
| 23 Mar 2009 | |
| Keyboard problem again. | |
| A,B service connectors constructed so calculator can be operated with the boards unfolded. 2 & 4 outputs from U257 observed to be odd. 2 output has two levels depending on 4 output, 4 output goes up a bit with 2 output. U257 removed and tested in isolation. Open-circuit 4 output only goes low for brief spike on negative edge of 2 when operated at low Vcc (~4.6V). U257 replaced. 2 output is clean, 4 still pulls a tad higher with 2, opposite of other outputs. |
| 25 Mar 2009 | |
| 5V supply is low (~4.6V) on the display/devices board. Most of the drop occurs across the wire connections from the power supply board to the CPU board. | |
| GND and 5V connections of P connector scraped lightly. Supply on display/devices board is now above 4.8V. Should have done this before replacing ICs. Idiot. |
| 9872A Plotter: 1742A01137 | |
| 1977 (transistors stamped with 7739) | |
| Manuals, dust cover, box. | |
| 09 Nov 2001 | |
| UBC SERF. | |
| Not tested. Electrostatic hold-down sheet on platen is partially loose. | |
| Functional (17 Feb 2007). |
| 15 Feb 2007 | |
| Dusted out. |
| 15 Feb 2007 | |
| Flaky response from front-panel switches. | |
| Front panel switch assembly removed for cleaning. Switches cleaned with paper strip inserted between switch body and PCB, and contact cleaner. Improved. |
| 17 Feb 2007 | |
| Y-axis movement is good, however X-axis movement shudders or oscillates at right-side stop. Slow movement buttons result in similar oscillation-in-place, fast movement works but is very noisy and rough. | |
| Guess that the problem is one of the two amplifiers for the X-axis motor. Output driver Q6 has open BE junction. | |
| Q6 replaced with 2N6055. X-axis movement now good. |
| 17 Feb 2007 | |
| Electrostatic hold-down sheet on platen is partially loose. | |
| Re-stuck with double-sided tape. Could still do with improvement. |
| 19 Feb 2007 | |
| Successfully operated under control of HP-9815. |
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Hewlett-Packard 9815A
Calculators | Integrated Circuits | Displays | Simulations EEC |
bhilpert |
