Rainbow 100 Troubleshooting Guide
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Fault-finding on the Rainbow 100 (PC100-A) follows DEC's User's Service Guide (EK-P100E-SV-001) and chapter 10 of the Rainbow 100 Technical Manual (EK-PC100-TM-001): the power-up self-test with its screen messages and seven rear-panel LEDs, the extended self-test, the diagnostic diskette, and DEC's symptom table.[1][2] DEC's strategy is to test the suspect unit last, so that the units used to test it have already been shown to work.[2] The same messages and LEDs apply to the PC100-B and Rainbow 100+, which show the message number instead of the bracketed PC100-A wording; their hard disk and other differences are on Rainbow 100+ Troubleshooting Guide.[1]
The system unit contains a mains switching supply and the VR201 monitor a CRT. See CRT Discharge Procedure and DECmate II Power Supply Service.
Nothing on the screen
[edit | edit source]DEC's checks, in order:[1]
- Brightness and contrast controls on the back of the monitor turned down.
- Mains cord unplugged, or no power at the outlet.
- Monitor cable not plugged in.
- Circuit breaker on the back of the system unit tripped.
- Read the LEDs on the back of the system unit (table below).
- Power cable loose at the system module or at the power supply.
- Plugs between the fan assembly and the power supply loose.
- Fan turning slowly and silently: the voltage switch is at 230 V on a 115 V supply.
- Swap in known good parts one at a time: power cord, monitor cable, monitor, language ROM, system module, fan assembly, power supply.
The VR201 is powered from the system unit, through +12 V on pins 7 and 8 of the monitor connector J3, so a dead monitor can also be a system unit fault.[3]
| Problem | Possible causes, most likely first |
|---|---|
| Fan does not run with power on | No mains at the outlet; fan-to-switch connectors not seated; power switch; fan; power supply |
| Fan runs, blank screen | Intensity turned down; video connector not seated; system module; monitor |
| Printer prints garbage or nothing | Printer baud rate in Set-Up does not match the printer |
| Screen shows garbage | Modem baud rate in Set-Up wrong (run individual test 11); language ROM missing, misfitted or faulty |
| Screen flickers or rolls | Power frequency in Set-Up not set to 60 Hz (DEC says 60 Hz in any country) |
| Screen shows everything except what is typed (computer mode) | Keyboard; language ROM |
| Garbage or nothing in terminal mode | Modem baud rate wrong (run individual test 11) |
| Drive will not load programs | Dirty or scratched diskette; diskette not in a Rainbow format; drive cables; RX50 controller; RX50 drive; system module |
Self-test messages and LED codes
[edit | edit source]The self-test runs at power-up and reset. A non-fatal error is shown above the Main System Menu; a fatal error is shown on its own as CONSULT USER'S GUIDE FOR ASSISTANCE followed by the fault.[5] The seven LEDs at the back repeat the code, which helps when the monitor itself has failed.[6] On DEC's layout drawing four of the LEDs are labelled 8088 and three Z80A.[7]
In the table, 1 is an LED lit, 0 an LED off and – either; LEDs are read 1 to 7 from left to right as numbered on the back panel. The bracketed words are what a PC100-A shows; later models show the message number. Codes marked * can appear at any time because their circuits are monitored constantly.[8]
| No. | Message (PC100-A wording) | LEDs 1–7 | DEC's action |
|---|---|---|---|
| 1 | Main Board (video) | 0110101 | Power off and on; if it persists, replace the system module |
| 2 | Main Board (unsolicited interrupt)* | 1111010 | Remove any memory board and retest; then replace the system module |
| 3 | Drive A or B (index) | 0010011 | Try another diskette; check drive cables; then drive, cable, RX50 controller in that order |
| 4 | Drive A or B (motor) | 1100011 | Try other diskettes (a bent one slows the motor); then replace the drive |
| 5 | Drive A or B (seek) | 0100011 | Try another, formatted diskette; check cables; then replace the drive |
| 6 | Drive A or B (read) | 1000011 | As message 3 |
| 7 | Drive A or B (restore) | 0110011 | Check drive cables; then drive, cable, RX50 controller |
| 8 | Drive A or B (step) | 1010011 | As message 7 |
| 9 | System Load Incomplete (system load) | 0000000 | Not a Rainbow system diskette, unreadable or blank; use another copy |
| 10 | Main Board (video, vfr) | 1110101 | Power off and on; then replace the system module |
| 11 | System Load Incomplete (boot load) | 0000000 | As message 9 |
| 12 | Drive A or B (not ready) | 0000011 | No diskette, diskette upside down or door open; then cables; then drive |
| 13 | Keyboard | 1101010 | Keyboard cable at monitor and keyboard; video cable; stuck key; do not press keys during the test; then replace the keyboard |
| 14 | Main Board (nvm data) | 1111011 | Saved Set-Up not read: recall defaults with Shift/D, save with Shift/S, power cycle; then system module |
| 16 | Interrupts Off* | 1110000 | Power cycle; if it appears only under one program, suspect the program |
| 17 | Main Board (video ram) | 1110110 | Power cycle; then replace the system module |
| 18 | Main Board (Z80 crc) | 1111001 | As message 17 |
| 19 | Main Board (ram 0–64K) | –––1101 | As message 17 |
| 20 | Main Board (unsolicited interrupt, Z80)* | 1110001 | As message 17 |
| 21 | Drive Not Ready | 0000000 | Door open, no diskette, upside down, or non-existent drive named; then cables and drive |
| 22 | Remove Card or Diskette | 0110001 | Protective card left in drive, or diskette in A upside down |
| 23 | Non-System Diskette | 0000000 | Load an operating system diskette first |
| 24 | New Memory Size = nnnK | 0000000 | Shown once after memory is added or removed; otherwise check the memory board is seated |
| 25 | Set-Up Defaults Stored | 0000000 | Information only: Set-Up storage was corrected and defaults are in effect |
| 26 | Main Board (ram arbitration) | 1110100 | Power cycle; then replace the system module |
| 27 | Memory Board (ram option) | –––1100 | Fault on the memory option; test or exchange it |
| 28 | RX50 Controller Board | 1110011 | Power cycle; reseat the RX50 controller; then replace it |
| 29 | Main Board (Z80 response)* | 1111000 | Check it is not a VT180 diskette; try another system diskette; reseat ROMs; then system module |
| 30 | Main Board (rom crc, rom 0) | 1111111 | Power cycle; reseat ROMs; then system module |
| 31 | Main Board (rom crc, rom 1) | 1111110 | As message 30 |
| – | Main Board, rom crc, rom 2 | 1110111 | As message 30 |
| 33 | Main Board (contention) | 0000010 | Power cycle; then replace the system module |
| 40 | Main Board (printer port) | 1011010 | As message 33 |
| 50 | Main Board (keyboard port) | 0011010 | As message 33 |
| 60 | Main Board (comm. port) | 0111010 | As message 33 |
Several messages share the code 0000000, so read the screen as well whenever the monitor works.[8] All four keyboard LEDs flash when the keyboard fails its own self-test.[10]
Extended self-test and diagnostic diskette
[edit | edit source]Press S at the Main System Menu to run the extended self-test, with a diskette in drive A (and drive B if it is to be tested). It takes about 90 seconds with 64 KB and about two minutes with 256 KB.[11] The diagnostic diskette boots from any drive. Its main menu offers a drive test, a full computer test (about 24 minutes, needing scratch Rainbow-formatted diskettes) and twelve individual tests including memory, video controller, disk system, the communications, printer and keyboard ports, the video alignment pattern and an external loopback test of about 25 minutes.[12] DEC's loopback plug part numbers are 12-15336-01 for the PC100-A communications connector and 29-24631-00 for the printer connector.[13]
Known faults from repairs
[edit | edit source]Video
[edit | edit source]Rob Jarratt's Rainbow 100A showed LED code 1110110 (message 17, video RAM). Logic analyser traces showed the screen RAM was only being written at its first two addresses; he replaced the TMM2016 static RAM at E122. The machine then stopped at 0110101 (message 1, main board video), which persisted with a monitor connected. Following the attribute data through the line buffer to the DC012 led him to an unreliable 2114 line buffer at E100, and replacing it restored the display.[14] The screen RAM is E121 and E122 and the attribute RAM E123 and E124 on DEC's layout drawing.[7]
Power supply
[edit | edit source]A burning smell with a tripped breaker, a bang at the next switch-on, or a pop when the mains cable is plugged in before the switch is touched, all point to the H7842. Jarratt's two repairs found a destroyed switching transistor with collateral damage to its drive, the start-up regulator, the PWM controller, a comparator and the mains bridge; and, on another machine, a Corcom power entry filter shorted across its input.[15][16][14] The details, output tolerances and capacitor values are on DECmate II Power Supply Service. Once the crowbar has fired on an overvoltage, the supply stays off until it is switched off and on.[17]
RX50 drive
[edit | edit source]Jarratt's RX50 stepped its head at power-up but would not turn the spindle, which only twitched. The spindle was stiff to turn by hand; a cone-lift cover was out of alignment, and taking the covers off and refitting them freed it. The same drive had lost the pins holding one door, which he replaced with similar pins reduced to fit.[14] See also Floppy Drive Repair.
Monitor
[edit | edit source]A VR201 with a shimmering picture, and a background that brightened before the text did, had bulging or high-ESR electrolytics; Jarratt replaced six, listed on Rainbow 100 Capacitor Replacement Guide. The shimmer faded after a few minutes' running, and the monitor occasionally blanked until power-cycled.[14] In another VR201, posted on the VCF forum, the vertical hold failed and the picture tripled before the screen went black; another member said his had needed a recap in 2013.[18]
Related pages
[edit | edit source]- Rainbow 100
- Rainbow 100 General Maintenance
- Rainbow 100 Capacitor Replacement Guide
- Rainbow 100+ Troubleshooting Guide
- Rainbow 100 Documentation
- DECmate II Power Supply Service
References
[edit | edit source]- ↑ 1.0 1.1 1.2 Digital Equipment Corporation, User's Service Guide (Rainbow), EK-P100E-SV-001, April 1985, pp. 87 to 88, appendix A (File:Rainbow User's Service Guide (EK-P100E-SV-001).pdf). Incorrect response: no display.
- ↑ 2.0 2.1 DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, pp. 10-1 to 10-2. Field replaceable units and fault detection strategy.
- ↑ DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, p. 3-22, Table 3-6. +12 V on J3 pins 7 and 8 to monitor and keyboard.
- ↑ DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, pp. 10-7 to 10-8, Table 10-2, Troubleshooting Guide.
- ↑ DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, p. 10-2, Figures 10-1 and 10-2. Non-fatal and fatal error displays.
- ↑ DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, p. 1-6, Figure 1-5. The seven error LEDs.
- ↑ 7.0 7.1 DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, p. 4-4, Figure 4-2, System Module Physical Layout.
- ↑ 8.0 8.1 8.2 DEC, User's Service Guide, EK-P100E-SV-001, pp. 96 to 98, Table A-1, Internal Diagnostic Test Messages, with light display.
- ↑ DEC, User's Service Guide, EK-P100E-SV-001, pp. 88 to 95. Corrective action for each self-test message.
- ↑ Digital Equipment Corporation, Rainbow 100 Technical Manual, EK-PC100-TM-001, May 1984, p. 1-5 (File:Rainbow 100 Technical Manual (EK-PC100-TM-001).pdf). Keyboard LEDs flash on a failed keyboard self-test.
- ↑ DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, p. 10-3, section 10.2.2. Extended self-tests.
- ↑ DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, pp. 10-4 to 10-6, Figures 10-3 and 10-4, Table 10-1. Diagnostic diskette menus and test times.
- ↑ DEC, User's Service Guide, EK-P100E-SV-001, p. 123, Table B-1. Loopback plugs.
- ↑ 14.0 14.1 14.2 14.3 Rob Jarratt, "Rainbow 100A Restoration", Rob's Old Computers, 29 July 2025, robs-old-computers.com. Video RAM and line buffer faults, RX50 spindle and door, power entry module, VR201 capacitors.
- ↑ Rob Jarratt, "DEC Rainbow H7842 Power Supply Failure", Rob's Old Computers, 20 November 2022, robs-old-computers.com.
- ↑ Rob Jarratt, "Rainbow H7842 Finally Fixed", Rob's Old Computers, 29 June 2023, robs-old-computers.com.
- ↑ DEC, Rainbow 100 Technical Manual, EK-PC100-TM-001, pp. 7-6 to 7-9. Crowbar and overvoltage protection.
- ↑ "Fixing a dead VR-201", Vintage Computer Federation forum, thread started 12 April 2023, forum.vcfed.org. Community repair reports.