Sharp PC-1500 Troubleshooting Guide
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Fault-finding for the Sharp PC-1500. Sharp's service manual gives the supply voltages, the all-reset procedure, the key matrix and the circuit diagrams, and the instruction manual lists the error messages, so most faults can be narrowed down with a multimeter and the documents hosted on Sharp PC-1500 Documentation.[1][2][3] The Sharp PC-1500A has its own guide: Sharp PC-1500A Troubleshooting Guide.
Preliminary checks
[edit | edit source]- Fit four fresh AA dry cells. Sharp says rechargeable cells cannot be used in the PC-1500.[4]
- Remove any memory module and undock the computer from the CE-150, then try again with the bare machine.
- The logic is CMOS. Use an anti-static strap, and do not touch the connector in the module compartment.[5][4]
- A battery change, an all reset or
NEW0clears the memory. Save anything you want to keep to cassette first if the machine still works.[6][2]
Things that are not faults
[edit | edit source]| What you see | Explanation |
|---|---|
| The machine switches itself off | Auto power-off after seven minutes without a key press. Press ON to carry on where it stopped.[7] |
NEW0?: CHECK after fitting cells |
Normal after a battery change. Press CL, type NEW0 and press ENTER.[7][4]
|
| Programs and variables gone after a battery change | A battery change clears them.[6] |
| The battery indicator dot has gone | The cells need replacing.[8] |
CHECK with a number or letter on power-up |
A peripheral is connected and reports a fault; the code identifies the option.[7] |
| The PC-1500 runs although its own cells are flat | A charged CE-150 powers the computer through the 60-pin connector.[9] |
All keys dead, including ON/BREAK
[edit | edit source]Sharp's service manual and instruction manual both say that strong external electrical noise or a sharp impact can leave every key inoperative, including ON/BREAK. The instruction manual adds that docking the computer in the CE-150 with the power on can cause the same hang-up.[2][10][11] The cure is the all reset:[2][10]
- Hold down ON/BREAK.
- With ON/BREAK held, press the ALL RESET switch on the underside for about 15 seconds. Use the tip of a ball-point pen. Sharp says not to use a pencil, whose tip may break off, or anything sharp such as a needle.
- Wait for
NEW0?: CHECKto appear. - Press CL, type
NEW0and press ENTER. - If
NEW0?: CHECKdoes not appear, repeat the procedure.
The all reset clears the program, the data and the reserve area. Sharp says not to use the switch for anything else.[2] If the all reset never brings up the prompt with fresh cells fitted, measure the supply voltages below.
Power supply diagnostics
[edit | edit source]The power supply is a resin-moulded "Hi-MIC" module (Sharp part EHM718L70) holding the stabiliser, temperature compensation and bleeder circuits. The cells reach it through a 1SS98 diode and the adaptor jack through two 1S1588 diodes. Two 10 V 220 µF electrolytic capacitors sit between VGG and ground.[1][12][13]
| Rail | Hi-MIC pin | Specified voltage | Notes |
|---|---|---|---|
| VBAT | 14 | Four AA cells | Input from the cells and the adaptor |
| VGG | 13 | 4.7 V | Feeds the LH5801's BF flip-flop, which keeps its state as long as VGG is present, and the µPD1990AC clock[14][15] |
| VCC | 8 | 4.7 V ±0.02 V | Switched on by the ON key through BF1 and BFO[5] |
| VDISP | 4 | 3.7 V ±0.01 V | LCD drive voltage; the module includes temperature compensation |
| VA, VM, VB | 3, 2, 1 | Not specified | Taps on a resistor divider, decoupled by 0.1 µF capacitors |
| GND | 5 | 0 V |
The service manual's supply line reads "1.5V x 4 = 7V ±0.05V", which does not add up; the instruction manual gives the supply as 6.0 V DC.[1][16]
VGG supplies the LH5801's BF flip-flop, which keeps its state as long as VGG is present, and Sharp uses it for memory back-up. Pressing ON sets BF1 high so that VCC is supplied from BFO.[14][5] So VGG should be present with the machine off, and VCC should appear only when it is switched on.
No display at all
[edit | edit source]- Measure the cells under load. A cell that reads well off-load can still collapse when the machine is switched on.
- Measure VBAT at Hi-MIC pin 14. If it is missing, check the battery terminals in the bottom case and the 1SS98 diode.[12]
- Measure VGG at pin 13. If VGG is low or missing with VBAT present, check the two 220 µF capacitors for a short before suspecting the module.[12]
- Press ON and measure VCC at pin 8. VCC missing with VGG present points at the ON key path (BF1, BFO) or the regulator.[5]
- If VCC is present, measure VDISP at pin 4.
Adaptor works, cells do not (or the reverse)
[edit | edit source]The cells and the adaptor reach the module through separate diodes: one 1SS98 for the cells and two 1S1588 in series for the adaptor.[12] A machine that runs on one source and not the other has a fault in that source's path: the battery terminals and the 1SS98, or the adaptor jack and the 1S1588 pair.
Trimmers
[edit | edit source]Two trimmers sit beside the module: RV 220 kΩ in the VGG regulator's reference chain and RV 250 kΩ in the VDISP chain.[12][17] Sharp's service manual gives the target voltages but no adjustment procedure. Do not turn them unless a measured rail is out of specification and the cells, the capacitors and the joints have been checked first.
Reset faults
[edit | edit source]The power-on reset comes from a TC50H001F Schmitt gate fed through a 50 V 1 µF capacitor from VCC, with a second 50 V 1 µF capacitor on the output network that drives the I/O port, CPU and µPD1990AC reset lines.[18] A machine that powers up into rubbish, or needs the all reset every time, may have a failed reset capacitor. Both are listed in the Sharp PC-1500 Capacitor Replacement Guide.
Keyboard faults
[edit | edit source]The 64 matrix keys are scanned by the I/O port's strobe outputs PA0 to PA7 and read on the processor's inputs IN0 to IN7. ON/BREAK is not in the matrix: it connects VGG to the processor's BF1 input.[12][5]
| PA0 | PA1 | PA2 | PA3 | PA4 | PA5 | PA6 | PA7 | |
|---|---|---|---|---|---|---|---|---|
| IN0 | 2 | . | 1 | ) and > | + | = | INS | 3 |
| IN1 | 5 | − | 4 | L | * | DEL | MODE | 6 |
| IN2 | 8 | OFF | 7 | O | / | P | CL (CA) | 9 |
| IN3 | H | S | J | K | D | F | A | G |
| IN4 | SHIFT | ! | % | & | " | # | DEF | $ |
| IN5 | Y | W | U | I | E | R | Q | T |
| IN6 | N | X | M | ( and < | C | V | Z | B |
| IN7 | ↑ (√) | ⇕ | 0 | ENTER | RCL | ^ | SML | ↓ (π) |
The six function keys under the display are the !, ", #, $, % and & keys in row IN4.[12]
- One dead key: clean the key board contacts and the key rubber.
- A whole row (one IN line) or a whole column (one PA line) dead: trace that line from the key board through the FPC to the main board.
- Several unrelated keys dead or intermittent: suspect the FPC.
Replacing the FPC
[edit | edit source]Sharp's procedure for the flexible printed cable between the key board and the main board:[2]
- Remove the crimp metal that holds the FPC to the main (operation) board, then separate the key board from the main board.
- Peel away the double-sided tape that holds the FPC to the key board.
- Apply the soldering iron to the soldered side and lift the FPC end lightly as the solder melts.
- Tin the FPC and the board pads evenly.
- Fix the new FPC temporarily with double-sided tape.
- Line up the FPC pattern with the board pattern and secure it temporarily, sliding the FPC about 1 mm backwards, then solder it.
Display faults
[edit | edit source]The 7 × 156 dot LCD (Sharp LF8082GE) is driven by four SC882G chips used in pairs, which also hold the display buffer. The panel connects through rubber connectors.[5][13]
| Symptom | Check |
|---|---|
| Blank display, no response to ON | Cells, then the supply voltages above |
| Blank or faint display with the machine responding (it beeps or runs a program) | VDISP at Hi-MIC pin 4 against 3.7 V[1] |
| Missing dots, columns or a band | Lift the LCD, clean the rubber connectors and the contact faces, and reassemble squarely |
| Display garbled after a battery change | Remove the cells, refit them and check for the prompt; if that fails, carry out the all reset[4][2] |
Error messages
[edit | edit source]Most of the PC-1500's numbered errors report BASIC mistakes. The instruction manual's list includes these, which point at cassette, printer or memory problems:[3]
| Code | Meaning |
|---|---|
| 22 | No memory space available to load the program |
| 27 | No optional printer connected and no program for the given label |
| 42 | The cassette file is too large to load |
| 43 | CLOAD? found a file whose format does not match |
| 44 | Checksum error on cassette data |
| 70 | The printer pen has gone, or would go, outside the range −2048 to 2047 |
| 71 | The paper has backed up, or would back up, more than 10.24 cm in TEXT mode |
Repairability
[edit | edit source]The service manual lists every part by Sharp part code, including the LCD, the rubber connectors, the FPC, the key rubber, the key board and the main board as complete units, and the Hi-MIC regulator module.[13] Those part codes were for Sharp service centres; whether any are still obtainable is a matter of finding new old stock or a donor machine. The electrolytic capacitors, diodes and trimmers are ordinary through-hole parts.
Related pages
[edit | edit source]- Sharp PC-1500
- Sharp PC-1500 General Maintenance
- Sharp PC-1500 Capacitor Replacement Guide
- Sharp PC-1500 Documentation
- Sharp PC-1500A Troubleshooting Guide
- Battery Explosion, Capacitor or Corrosion Damage
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 Sharp, Service Manual, Model PC-1500 & Option, "6) Power supply circuit", printed page 18 (PDF page 20): single resin-moulded IC with stabiliser, temperature compensation and bleeder circuits; supply voltage "1.5V x 4 = 7V ±0.05V"; VGG 4.7 V; VCC 4.7 V ±0.02 V; VDISP 3.7 V ±0.01 V at 25 °C.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Sharp, Service Manual, Model PC-1500 & Option, section 5 "Servicing", printed pages 19 to 20 (PDF pages 21 to 22): measures against an irregular condition (ALL RESET with ON held for about 15 seconds, then NEW0); FPC removal and replacement.
- ↑ 3.0 3.1 3.2 Sharp, PC-1500 instruction manual, appendix E "PC-1500 error code list", printed pages 145 to 149 (PDF pages 147 to 151).
- ↑ 4.0 4.1 4.2 4.3 Sharp, PC-1500 instruction manual, appendix B "Battery replacement for the PC-1500" (PDF pages 144 to 145): rechargeable cells cannot be used; remove and refit the cells if the prompt does not appear; module compartment static warning.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 Sharp, PC-1500 Technical Reference Manual, section 4-2-1, printed pages 88 to 89 (PDF pages 93 to 94): BF1 goes high when ON is pressed so that VCC is supplied from BFO; IN0 to IN7 inputs; PA0 to PA7 key strobes; display chips; CMOS parts. File:Sharp PC-1500 Technical Reference Manual.pdf.
- ↑ 6.0 6.1 Sharp, PC-1500 instruction manual, chapter II, "I. Variables" (PDF page 26): variables are retained until, among other things, the batteries are changed.
- ↑ 7.0 7.1 7.2 Sharp Corporation, Service Manual, Model PC-1500 & Option, February 1982, section 1, printed pages 1 to 2 (PDF pages 3 to 4): "NEW0?: CHECK" after battery replacement and the NEW0 command; a check message such as "CHECK 6" when a connected peripheral fails; auto power-off after seven minutes. File:Sharp PC-1500 Service Manual.pdf.
- ↑ Sharp, PC-1500 instruction manual, chapter I, "K. Battery function indication" (PDF page 16).
- ↑ Sharp, PC-1500 Technical Reference Manual, section 4-1-3 "Power supplies", printed page 87 (PDF page 91): a charged CE-150 supplies the PC-1500.
- ↑ 10.0 10.1 Sharp, PC-1500 instruction manual, "Trouble-shooting" (PDF page 4): noise or impact can make all keys including ON inoperative; ALL RESET for about 15 seconds with ON held; use a ball-point pen.
- ↑ Sharp, PC-1500 instruction manual, "Connecting the computer to the interface" (PDF page 103): if the computer is on when connected to the CE-150 it may hang up with all keys inoperative.
- ↑ 12.0 12.1 12.2 12.3 12.4 12.5 12.6 12.7 12.8 Sharp, Service Manual, Model PC-1500 & Option, section 6 "PC-1500 key & power supply circuit", printed page 21 (PDF page 23): 1SS98 and 1S1588 × 2 diodes, Hi-MIC module pins, 10 V 220 µF × 2, trimmers RV 220 kΩ and RV 250 kΩ, thermistor, key matrix PA0 to PA7 × IN0 to IN7, BREAK/ON on BF1 from VGG.
- ↑ 13.0 13.1 13.2 Sharp, Service Manual, Model PC-1500 & Option, section 11 "Parts list & guide" and exploded view (PDF pages 32 to 34).
- ↑ 14.0 14.1 Sharp, PC-1500 Technical Reference Manual, section 2-3-5 "BF flipflop", printed page 22 (PDF page 26): the CPU has two supplies, VCC and VGG; the BF flip-flop is driven by VGG and keeps its state as long as VGG is supplied, even if VCC is off; it can be used for a memory back-up system.
- ↑ Sharp, Service Manual, Model PC-1500 & Option, section 4, "5) Timer/counter circuit", printed pages 17 to 18 (PDF pages 19 to 20): µPD1990AC pin 14 VDD connected to VGG (4.7 V).
- ↑ Sharp, PC-1500 instruction manual, "PC-1500 specifications" (PDF page 5): power supply 6.0 V DC. File:Sharp PC-1500 Instruction Manual.pdf.
- ↑ Sharp, Service Manual, Model PC-1500 & Option, section 8 "PC-1500 main P.W.B.", printed page 23 (PDF pages 26 to 27): positions of the trimmers, the module and the capacitors.
- ↑ Sharp, Service Manual, Model PC-1500 & Option, section 9 "PC-1500 main circuit diagram", printed page 24 (PDF page 28): reset circuit with TC50H001F and two 50 V 1 µF capacitors.