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**HP 29C CALCULATOR DIAGNOSIS and RESTORATION**

Presented by: Jim Johnson HP Handheld Conference 2013 – Fort Collins, CO September 21-22, 2013

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Synopsis: The HP 29C is one of the last of the Woodstock series of calculators to be developed and introduced by HP in 1977 and was produced for the next 2 years until This was the top of the line Woodstock series calculator (code name “Bonnie”) along with its twin, the HP 19C which had a printer incorporated as part of the calculator. This presentation will follow my diagnosis of the electrical characteristics of the HP 29C and its functionality. We’ll take a look at the schematic, including the power supply section. Then we’ll dive into the output waveforms of the Arithmetic, Control and Timing (ACT) chip. Finally we’ll finish with the restoration of functionality of the HP 29C and the completed unit (S/N: 1811S20315).

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**Agenda Synopsis Calculator acquisition – brief history**

Disassembly, Photos, Identification of Integrated Circuits and Power Supply Schematics Troubleshooting and Diagnosis Functioning HP 29C Calculator Contrast and Compare Past with Present Summary and Conclusions

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A WORD OF *Never* attach the charger of a Woodstock series unit to the calculator without a known good rechargeable battery in place. An AC charger connected to an HP 29C with a bad battery, bad contact or without a battery in place, has a high degree of certainty that the excess voltage will destroy or damage the unit.

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**Setting Expectations What this presentation is:**

A discussion of my passion and interest in vintage HP calculators from a hardware perspective Sharing information learned/not available on the web Troubleshooting methodology for HP Woodstock Series Bringing a vintage, rare HP 29C back to life! A brief contrast and compare of HP 29C versus a modern HP calculator What this presentation is not: Not an in-depth discussion of the operation of the HP 29C Not a critical examination of the routines or ROM firmware used in the HP 29C Not an exhaustive study of the mathematical concepts used to create “Bonnie”. Personal Collection: HP01, HP10bII, HP12C, HP15CLE HP17bII+, HP21, HP25, HP29C, HP30b, HP32E, HP32SII, HP34C, HP35S, HP41CX, HP42S HP45, HP67, HP97, HP200LX, WP34S

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**HP 29C’s sell on eBay for range from $81 - $372. Avg. sell price $202 **

Acquisition of two HP-29C calculators SN: 1811S20315 May 7, eBay SN: 1904S21718 June 28, eBay HP 29C’s sell on eBay for range from $81 - $372. Avg. sell price $202 Listing prices range $ $495. Note: According to the Museum of HP Calculators, the HP 29C sold new in 1977 for $ (USD).

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**Disassembly, Photos, Identification of Integrated Circuits and Power Supply**

To open remove the top 2 Screws under the footpads

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**Disassembly, Photos, Identification of Integrated Circuits and Power Supply**

3 1 2

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**1 Arithmetic Control and Timing (ACT) IC ROM IC’s CMOS Static RAM**

Disassembly, Photos, Identification of Integrated Circuits and Power Supply Arithmetic Control and Timing (ACT) IC, RAM, ROM, POR/Battery Low Comparator Arithmetic Control and Timing (ACT) IC ROM IC’s CMOS Static RAM I.C.’s RAM/ ROM IC 1 POR (Power on Reset), Battery Low Comparator IC SN: 1811S20315

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**2 HP 29C Power Supply PCB 3.3uF, 10v NPN Transistor**

Disassembly, Photos, Identification of Integrated Circuits and Power Supply 3.3uF, 10v NPN Transistor Tank oscillator circuit 330pf cap. & 15uH coil 68Ω 10KΩ 10uF, 16v 6.8uF, 10v 2.2uF, 6v 15uF, 10v 2.2KΩ 22uF, 10v 330pf 100pf diode 2 HP 29C Power Supply PCB (Daughter Board)

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**3 ROM/Anode Driver IC Cathode Driver IC**

Disassembly, Photos, Identification of Integrated Circuits and Power Supply ROM/Anode Driver IC Cathode Driver IC 3

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**Power-on Reset, low battery**

HP 29C Schematic ACT Cathode Driver & Keypad Driver RAM HP 29C Calculator Hewlett-Packard Page 1 of 1 Created: 2013 August 12 12-digit LED Display Based on S/N: 1811S20315 drawn by: JAJ – 2013 August 12 Anode Driver / ROM RAM/ROM 1 2 3 4 8 7 6 5 Vgg Φ 2 Φ 1 ISA Vss Sync Data 16 15 14 13 12 11 10 9 Vram NC POR +6.7 vdc +6.0 vdc 22 21 20 19 18 17 -12.0 vdc RCD SYNC DATA Power-on Reset, low battery 330pf 150uH OSC + 2.2uf To pin 3 on POR A3 A4 A5 A6 A2 A7 +2.4 vdc Vbat 2KΩ STR + 47uf 33Ω o o Blue (g) shift Gold (f) GTO SST GSB STO X Y R ↓ RCL ∑+ CHS ENTER↑ EEX CLX _ + X . ÷ R/S To pin 3 on ACT Segment “a” Segment “f” Segment “b” Segment “c” Vdisp Segment “d” Segment “h” Segment “e” Segment “g” B1 B4 B3 B8 B6 B5 B7 K9 K10 K11 K12 K3 and B8 K2 and B7 K1 and B5 K6 and B3 K5 and B4 K4 and B6 K8 K7 and B1 a b c d e f g h

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**Troubleshooting and Diagnosis**

Acquired 1st HP29C. After examining the pc board for damage, put in charged battery pack and observed 12 zeroes lighting up on display. No keypad button presses would change the display. Suspected one of the IC’s was bad. Measured current of mA. Much higher current than HP25 and measured HP29C supply voltages. The supply voltages measured lower than normal. Unsoldered all RAM/ROM IC’s and applied power observing only one zero lit up in display (far RH digit in display). Suspect Anode/ROM IC. Acquired 2nd HP29C (s/n: 1904S21718) which had no display when powered on. Power supply voltages measured good and the supply current measured good around 200mA. I swapped the Cathode Driver and Anode/ROM Driver from s/n: 1811S20315 into s/n: 1904S21718 (2nd HP29C). No display in second HP29C. Used good HP25 to measure signals on ACT: oscillator, data, Isa, sync, ɸ1 and ɸ2. I measured same signals from s/n: 1811S20315 and found ɸ2 amplitude was low at 9vpp. Suspected the ACT in 1st HP29C may be damaged. Installed low profile IC sockets in HP29C s/n: 1811S Removed ACT from 2nd HP29C and installed into 1st HP29C.

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**Troubleshooting and Diagnosis Is the Power Supply Functional?**

Vss = +6.0vdc Vdisp = +4.37vdc Vram = +6.5vdc Tank oscillator circuit Vbatt-IN= +2.4vdc (switched) Vgg = -12.0vdc

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**Troubleshooting and Diagnosis Is the ACT Functional?**

Arithmetic Control & Timing IC (ACT) Oscillator Pins 13 & 14 ɸ1 and ɸ2 Pins 16 & 17 Ref. Pin# 1

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**Functioning HP-29C Calculator (SN: 1811S20315)**

Installed original IC’s from s/n: 1811S20315 with ACT from 2nd HP29C and turned on power switch. Single zero lit up in LH location on display. Plugged in RAM IC’s and turned on HP29C. Display showed “error”. CLX key cleared the display to “0.00” showing in LH location. EUREKA! Calculator seemed to be functional! Continued to test functions on HP29C and tested programming examples in HP29C Applications Book. All functions worked perfectly!

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**Contrast and Compare Past with Present**

HP 29C 98 program steps (with fully merged keycodes) 30 storage registers. (16 were directly or indirectly addressable and the rest were only indirectly addressable.) 3 levels of subroutines and 10 labels 4 level stack (X, Y, Z, T) Indirect storage, recall, branching and subroutine calls Execution speed ~ 3,000 instructions/sec. Continuous memory Rechargeable batteries 928 program steps in RAM 107 global general purpose registers 112 global user flags 6014 program steps in flash memory 30 byte alpha register 16 local flags and 144 local registers 6 (min) levels of subroutines 8 level stack 34 digit decimal accuracy Continuous memory CR2032 (2x) disposable batteries WP 34S Math +,-,x, ÷, 1/x, √x, x2 LOG x, 10x, LN x, ex, yx, pi %, INT, ABS Trig (SIN, COS, TAN) Modes (degrees, radians, grads) Statistical Mean, std. deviation (2 variables) Summation of n, x, x2 Summation of n, x, x2, y Summation of n, x, x2, y, xy Summation of n, x, x2, y, y2, xy Polar/rectangular conversion Dec. hrs./hrs.min.sec. conversion Math +,-,x, ÷, 1/x, √x, x2 LOG x, 10x, LN x, ex, yx, pi %, INT, ABS Trig (SIN, COS, TAN) Hyberbolic Trig. (SINH, COSH, TANH) Modes (degrees, radians, grads, fractional) Conversions and Constants 88 conversions available 50 fundamental constants Pre-programmed Functions HP-42S function set (solver, integration, matrix operations, curve fitting, etc.) HP-16C function set (Logical operators, floating pt. decimal math) HP-21S probability function set (Distributions, linear regression, Chi-squared, etc.) +Euler’s Beta and Riemann’s Zeta functions, Bernoulli and Fibonacci numbers, +Lambert’s W, the error function, and the Chebyshev, Hermite, Laguerre, and Legendre orthogonal polynomials + many statistical distributions and their inverses: Poisson, Binomial, Geometric, Cauchy-Lorentz, Exponential, Logistic, Weibull, Lognormal, and Gaussian, + programmable sums and products, first and second derivatives, solving quadratic equations for real and complex roots, + testing for primality, + integer computing in fifteen bases from binary to hexadecimal, + extended date and time operations and a stopwatch3 based on a real-time clock, + financial operations such as mean rate of return and margin calculations

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**Summary and Conclusions**

The goal of this paper was to share HP29C information with the HHC 2013 audience as well as other HP calculator enthusiasts. Diagnosis of the HP29C begins with examination of the overall condition of the calculator, disassembling, cleaning and using a known good power source. Measure the four power supply voltages in the power supply section. Once the power supply voltages are verified good, then you can move on to check the oscillator, ɸ1 and ɸ2 signals. If integrated circuits are damaged, either from battery corrosion or from excess applied voltage, the only alternative is to find a “donor calculator”. If ACT IC is damaged; same applies in that you’ll need to find another ACT. Finally, the restoration of these fine pieces of history is satisfying and rewarding and keeps part of Hewlett-Packard history alive for future generations.

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Acknowledgements Tony Duell (UK) – Information on MoHPC site and exchange in 2012. Jacques Laporte – HP Calculator Forum (www.jacques-laporte.org/forum) exchange and the very excellent paper “The ‘Woodstock’ generation”. Museum of HP Calculators – (http://hpmuseum.org) Geoff Quickfall (Canada) – exchange regarding HP calculators, particularly the HP19C. Dave Colver (UK) – exchange regarding HP29C schematics. Randy Sloyer – (www.fixthatcalc.com) exchange in 2012. Eric Smith – and posts on MoHPC. Katie Wasserman – exchange regarding HP29C.

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Thank you! © All rights reserved regarding the information contained in this presentation . If you have any questions you may contact Jim Johnson.

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APPENDIX

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Additional photos Single level HP 29C Power Supply Integrated into Main PC Board SN: 1904S21718

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Socketed HP 29C PC Board

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Additional Waveforms ɸ2 Pin# 16 ɸ1 Pin# 17 Isa Pin# 10 Data Pin# 11

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**HP 25 Calculator Waveforms**

ɸ1 & ɸ2 Isa & ɸ1 Sync & ɸ2 Data & ɸ1 Data & ɸ2 Display

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