Editing DECstation 3100 Troubleshooting Guide

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[[File:DECstation 2100 3100 rear panel diagram.png|thumb|right|340px|Rear panel of the DECstation 2100/3100. The eight diagnostic lights (13) show the self-test result; the reset button (7) reruns the test (DEC, ''Operator's Guide'', Figure 1-2)]]
Fault-finding on the '''[[DECstation 3100]]''' (and the DECstation 2100, which shares its KN01 system module), from DEC's ''Operator's Guide'' (EK-302AB-OG-002), ''Hardware Installation Guide'' (EK-290AB-IN-002), functional specification and KN01 schematic, with power supply notes from Malte Dehling's repairs.<ref name="og" /><ref name="ig3" /><ref name="fs" /><ref name="sch" /><ref name="dehling" /> DEC's own maintenance guide for the machine (EK-291AA-MG-002) is not online.<ref name="ogb" />

== No power ==
If nothing happens at switch-on, DEC's installation guide checks that all power cords are connected, the outlet is live, and both the monitor and system unit switches are on.<ref name="ig3" /> The system unit selects 100–120 V or 220–240 V by itself; the monitor plugs into the outlet on the back of the system unit and gets its power from there.<ref name="oga" /><ref name="ig1" />

The KN01 takes +5 V, +12 V, −12 V and −9 V through a 14-pin power connector, which also carries a DC OK signal from the supply. The schematic shows DC OK driving an LED on the system module and holding the reset logic until power is good.<ref name="sch" /> The functional specification gives the loads:<ref name="fs3" />

{| class="wikitable styled-table" style="width:70%; text-align:center;"
|+ '''KN01 supply rails (DEC Table 3-1)'''
! Rail !! Tolerance !! Maximum !! Typical
|-
| +5 V || ±5% (4.75–5.25 V) || 15.6 A || 10.0 A
|-
| +12 V || ±5% (11.4–12.6 V) || 0.89 A || 0.07 A
|-
| −12 V || ±5% || 0.11 A || 0.04 A
|-
| −9 V || ±5% || 0.18 A || 0.13 A
|}
<ref name="fs3" />

Dehling reports that the H7821 and H7822 supplies used in this family run well enough on the bench without a load, with the fans turning and the voltages about right, but that the supply's LED does not light until there is some load.<ref name="dehling" /> He found that in most cases these supplies are fixed by cleaning the board with isopropanol and replacing the capacitors listed on [[DECstation 3100 Capacitor Replacement Guide]].<ref name="dehling" />

Warning: the supply rectifies the mains onto high-voltage capacitors; Dehling lists a 220 µF 400 V part and two 470 µF 250 V parts. Unplug the supply and confirm they have discharged before touching the board.<ref name="dehling" />

== Power-up self-test ==
The self-test runs at power-on, when the reset button is pressed, or with <code>test -a</code> at the <code>&gt;&gt;</code> prompt. It counts down subtests 7 to 0 on the screen; on failure it stops and prints FAILURE, and the last number shown is the subtest that failed.<ref name="og7" /> All eight status LEDs light while the reset button is held.<ref name="fs15" />

{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+ '''Subtests (DEC chapter 7 and Table D-1)'''
! Subtest !! Part tested !! What to do
|-
| 7 || Video SIMM (frame buffer module) || Record the number and report it to service
|-
| 6 || VDAC and PCC || Record the number and report it to service
|-
| 5 || DZ serial lines || Record the number and report it to service
|-
| 4 || System module || Record the number and report it to service
|-
| 3 || Keyboard and mouse || With the power off, reseat both cables, then try another mouse and another keyboard
|-
| 2 || Network interface (LANCE) || Check the Ethernet connections, loopback and terminators (below)
|-
| 1 || Disk and SCSI bus || Check the SCSI terminator, cables and connector pins (below)
|-
| 0 || End of test || Passed
|}
<ref name="og7" /><ref name="ogd" />

The action column of DEC's appendix table does not line up with chapter 7: it gives the SCSI procedure for subtest 4 and "contact your Digital service representative" for subtest 1. The table above follows chapter 7, which matches the part tested.<ref name="og7" /><ref name="ogd" />

=== LED codes ===
Without a working monitor, read the red LEDs on the back panel, viewed from behind (1 = lit):<ref name="ogd" />
{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+ '''LED self-test codes (DEC Table D-2)'''
! LEDs !! Hex !! Part tested
|-
| 0111 1111 || 7F || System module
|-
| 1011 1111 || BF || Disk
|-
| 1101 1111 || DF || Keyboard
|-
| 1110 1111 || EF || Memory
|-
| 1111 0111 || F7 || Mouse
|-
| 1111 1111 || FF || Set at power-up or reset
|}
<ref name="ogd" />
All lights staying on means the test never got past reset. The schematic and specification show the reset logic held by the supply's DC OK line as well as the button, so check the supply rails first.<ref name="sch" /><ref name="fs15" />

=== Subtest 2: Ethernet ===
Caution from DEC: switch the system unit off before checking or connecting any cable.<ref name="og7" />
* Not on a network: fit the ThickWire loopback connector (its light should glow green) and a ThinWire T-connector with a terminator on each side, then rerun the test.
* On ThickWire: check the cable connector and its slide latch. The green light between the connector and the Ethernet button must be lit; if it is not, press the Ethernet button with a ballpoint pen. DEC warns against using a pencil, because the graphite can damage the unit.
* On ThinWire: check the T-connector and its terminator or onward cable, then check the ThinWire light the same way.
<ref name="og7" />

=== Subtest 1: SCSI ===
With no external drives, the SCSI connector must carry its terminator; check the terminator and connector pins. With external drives, check every cable, that the last box has a terminator in its spare connector, and that the cables between boxes are DEC's 18-inch ones.<ref name="og7" /> Do not give any drive SCSI ID 7, which the console display shows empty; assigning a device to it can make the system malfunction.<ref name="og3" />

== Memory ==
The KN01 takes 4 to 24 MB in 4 MB banks, each of two MS01 modules. The configuration display at the console shows the memory found; compare it with what is fitted.<ref name="fs1" /><ref name="og3" /> Handle the modules as little as possible: DEC rates the sockets for 25 insertions and recommends no more than five.<ref name="fs1" />

== Clock and console settings ==
The MC146818 clock and its 50 bytes of RAM keep their contents through power-off from a battery that the KN01 charges while running. DEC specifies at least 100 hours from a full charge, so a machine left unplugged for a few days loses the time.<ref name="fs6" /> The schematic shows the battery on a two-pin connector, charged from +5 V through a diode and 180 Ω resistor; with the battery missing, the clock still runs from +5 V while the machine is on.<ref name="sch" />

== Common problems ==
DEC's table of common problems, summarised:<ref name="og7t" />
{| class="wikitable styled-table" style="width:100%; text-align:left;"
|+ '''Solutions to common hardware problems (from DEC Table 7-1)'''
! Problem !! DEC's steps
|-
| Blank screen || Press a key (screen saver); turn up brightness and contrast; check the system unit and monitor are on; with the power off, check the monitor-system unit power cable, the power cord and the video cable
|-
| Distorted or unstable display || With the power off, check the video cable at both ends
|-
| Colour distorted || Move electromechanical devices and magnets away; press the monitor's degauss button for 5 seconds, and again after 10 minutes if needed
|-
| Red or blue missing || With the power off, check the video cable connectors
|-
| Screen freezes || On a network, wait a few minutes, then press reset; otherwise press reset
|-
| Typing does nothing || Press Hold Screen (F1); check the keyboard cable; try another keyboard
|-
| No cursor, or cursor does not follow the mouse || Check the mouse cable; clean the mouse; try another mouse
|-
| Diskette error || Use a high-density diskette; check write protection; try another diskette
|-
| External drive error || Check power, cables, the 18-inch inter-box cables and the terminator on the last box
|-
| Tape drive red light blinking rapidly || Press the load/unload button four times; then turn the drive off and on, once only
|-
| Printer or communications device error || Check power, cable and the device's baud rate
|}
<ref name="og7t" />

== Related pages ==
* [[DECstation 3100]]
* [[DECstation 3100 General Maintenance]]
* [[DECstation 3100 Capacitor Replacement Guide]]
* [[DECstation 3100 Documentation]]
* [[DECstation 5000 Troubleshooting Guide]]

== References ==
<references>
<ref name="og">Digital Equipment Corporation, ''DECstation 2100/3100 Operator's Guide'', EK-302AB-OG-002, September 1989 ([[:File:DECstation 2100 3100 Operator's Guide (EK-302AB-OG-002).pdf]]).</ref>
<ref name="og3">DEC, EK-302AB-OG-002, pp. 3-6 to 3-7. Configuration display: memory, SCSI units, unit 7 to be left empty.</ref>
<ref name="og7">DEC, EK-302AB-OG-002, pp. 7-2 to 7-9. Running the self-test, subtest failures, Ethernet and SCSI checks.</ref>
<ref name="og7t">DEC, EK-302AB-OG-002, pp. 7-10 to 7-16, Table 7-1, "Solutions to Common Hardware Problems".</ref>
<ref name="oga">DEC, EK-302AB-OG-002, p. A-2, Table A-3. Input voltage, auto-adjusting.</ref>
<ref name="ogb">DEC, EK-302AB-OG-002, p. B-3, Table B-4. Maintenance guide EK-291AA-MG-002.</ref>
<ref name="ogd">DEC, EK-302AB-OG-002, pp. D-2 to D-3, Tables D-1 and D-2. Monitor and LED self-test codes.</ref>
<ref name="ig1">Digital Equipment Corporation, ''DECstation 2100/3100 Hardware Installation Guide'', EK-290AB-IN-002, September 1989, p. 1-3 ([[:File:DECstation 2100 3100 Hardware Installation Guide (EK-290AB-IN-002).pdf]]). Monitor powered through the system unit.</ref>
<ref name="ig3">DEC, EK-290AB-IN-002, p. 3-6. If the system fails to turn on.</ref>
<ref name="fs">Digital Equipment Corporation, ''DECstation 3100 Desktop Workstation Functional Specification'', revision 1.3, 28 August 1990 ([[:File:DECstation 3100 Desktop Workstation Functional Specification (Rev 1.3, 1990).pdf]]).</ref>
<ref name="fs1">DEC, ''DECstation 3100 Functional Specification'', section 1, p. 1. Memory banks and connector insertion rating.</ref>
<ref name="fs3">DEC, ''DECstation 3100 Functional Specification'', section 3, p. 2, Table 3-1.</ref>
<ref name="fs6">DEC, ''DECstation 3100 Functional Specification'', section 6.7, p. 60. Clock battery.</ref>
<ref name="fs15">DEC, ''DECstation 3100 Functional Specification'', section 6.15, p. 76. Reset switch; all eight status LEDs lit during reset.</ref>
<ref name="sch">Digital Equipment Corporation, KN01 system module schematic, drawing 54-19463-01, October 1988, sheet 12, "Real-Time Clock" ([[:File:DECstation 3100 KN01 System Module Schematic (54-19463-01, Oct 1988).pdf]]). Power supply connector rails, DC OK, battery connector and charging circuit, reset switch.</ref>
<ref name="dehling">Malte Dehling, "DIGITAL VAXstation 3100 PSU Repair", GitHub repository README, May 2022, [https://github.com/mdehling/vs3100-psu-repair github.com/mdehling/vs3100-psu-repair]. Community repair notes on the H7821-00 and H7822-00.</ref>
</references>

[[Category:Digital Equipment Corporation]]
[[Category:Troubleshooting Guides]]