Rainbow 100 General Maintenance

Rainbow 100 with VR201 monitor and LK201 keyboard (David Alcubierre, CC BY-SA 2.0)

Care, routine checks and module handling for the Rainbow 100 (model PC100-A), based on DEC's Rainbow 100 Technical Manual (EK-PC100-TM-001) and User's Service Guide (EK-P100E-SV-001). DEC's own maintenance approach was to replace whole field replaceable units: the system module, RX50 controller, ROMs, diskette drive, power supply, fan bracket, monitor, monitor module and keyboard. The system unit contains a mains switching supply and the VR201 monitor contains a CRT. Read CRT Discharge Procedure before opening the monitor.

For the PC100-B and Rainbow 100+, see Rainbow 100+ General Maintenance, which covers the H7842-D supply, the DC fan and the RD51 hard disk.

Site and environment

Rainbow 100 environment (DEC section 1.4.1)

Condition	Operating	Not operating
Temperature	15–32 °C (59–90 °F)	−34 to 60 °C
Relative humidity	20–80%, maximum wet bulb 25 °C, minimum dew point 2 °C	5–95%, non-condensing
Altitude	2440 m (8,000 ft)	9144 m (30,000 ft)

The maximum operating temperature falls by 1.8 °C for every 1000 m above sea level. DEC also notes that RX50 diskettes may lose data in a magnetic field of 50 oersteds or more.

Power and the voltage switch

The H7842-A supply has a slide switch below the mains connector for 115 V or 230 V, and a 4 A circuit breaker on the back. DEC's warnings for the two wrong settings:

• 230 V applied with the switch at 115 V: internal components are damaged.
• 115 V applied with the switch at 230 V: the fan runs slowly and the computer does not work. DEC's service guide gives a slowly turning, silent fan as the sign of this mistake.

Check the switch on any machine of unknown history before plugging it in. When fitting a replacement supply, DEC says to check its switch with a ball-point pen before closing the unit.

The supply's output specification, its circuit and its capacitors are on DECmate II Power Supply Service; the DECmate II uses the same H7842-A.

Opening the system unit

1. Remove any diskettes, switch off and unplug the mains cord and all cables. Take the unit out of the floor stand if it has one.
2. Pull the two cover release tabs toward you and out until they lock, and lift the cover off.
3. Unplug the 13-pin power cable from the power supply first, then from the system module.
4. Unplug the diskette drive signal cables from the system module with their pull tabs. Leave the ground clips on the chassis lugs.
5. Loosen the four screws on the rear panel a turn at a time with a coin, and slide the system module out of the back.

The RX50 controller, memory board, extended communications board and colour/graphics board mount on standoffs on the system module. Press the tops of the standoffs outward to release a board, and press each corner home when refitting.

ROMs

DEC says to replace ROMs 0 and 1 as a pair so that both carry the same firmware version. If the board has QIKEJECT sockets, push the chip sideways with a small screwdriver to release it; prising it upward breaks the socket. Rob Jarratt found that a QIKEJECT socket on his Rainbow 100A would not relock once the ROM had been taken out, and replaced it with an ordinary socket. Pull the language ROM straight up by both ends, never from one end.

Diskette drive and power supply

Before removing the RX50 drive or moving the machine, park the head carriage: switch on, wait for the keyboard beep, switch off, then fit the carriage restraint card in drive A (and drive C if fitted) and close the doors. The drive slides forward once its front latch is pressed down with a pencil.

To remove the power supply, unplug its system module cable, both RX50 cables and ground clips, slide the drives part way out, then unplug the fan and switch plugs by squeezing their lock tabs. Press down on the supply, release its latch, tilt it up and lift it out without catching the flat cables. Jarratt reports that the RX50 cable runs past a sharp corner of the supply and is easily crushed.

Monitor

Warning: DEC states that the VR201 holds a charge of over 12,000 V even with the power off. The high-voltage parts are the anode and anode wire, the flyback transformer and the connector on the CRT neck.

DEC's discharge method: clip the discharge tool or a test probe to the monitor's wire frame first, then slide the tip under the anode cap's rubber boot and hold it there for a full 3 seconds. Do not scratch the CRT glass, which weakens it. To open the monitor, lay it face down on a protected surface with the tilt foot fully extended, prise out the screw cap at the back, remove the screw and slide the cover off.

Adjustments

Make adjustments with the screen at 80 columns and a dark background, using the video alignment pattern (a screen of Es) from the diagnostic diskette.

VR201 controls (DEC section 11.2.3)

Control	Label	Setting
Brightness, contrast	Rear panel	Raise brightness until the raster appears, then back off until it just disappears; set contrast for comfortable viewing
Vertical hold	VH	Stop any rolling
Horizontal hold	HH	Stop any tearing
Focus	FOC	Sharpest lines at the corners and centre
Horizontal centring	PH	Pattern centred side to side
Width	Width coil	Comfortable viewing; recheck horizontal hold afterwards
Vertical linearity	VL	Es the same height at top, centre and bottom
Height	H	Comfortable viewing; recheck vertical hold afterwards

Vertical centring, rotation and pincushion cannot be adjusted. DEC's limits are a pattern about 4 mm below centre and no more than 3 mm of slant or bow; outside those, DEC replaced the monitor. With the colour/graphics option the centring and linearity checks are made with DEC's video alignment template, 29-24371.

Jarratt removed the "cataracts" from a VR201 whose bonding layer between the safety glass and the tube had decayed: he softened the adhesive with a hair dryer (the glass reached about 65–70 °C), lifted the glass away, peeled off the old layer and refitted the glass on thin self-adhesive rubber spacers.

Capacitors

The system module and RX50 controller have only a few electrolytics; the H7842 supply and the VR201 monitor have most of them. Values are on Rainbow 100 Capacitor Replacement Guide.

Routine checks

1. Check the voltage switch and push in the circuit breaker if it has tripped.
2. Look over the H7842 for bulging or leaking capacitors before the first power-up of a stored machine. Jarratt did this, and checked the output ripple, before powering his 100A.
3. Switch on and watch the screen and the seven LEDs on the back panel. Any message or LED code is listed on Rainbow 100 Troubleshooting Guide.
4. Press S at the Main System Menu to run the extended self-test, with a diskette in drive A. It takes about 90 seconds with 64 KB of memory and about two minutes with 256 KB.
5. Run the diagnostic diskette's "Test computer" selection, which takes about 24 minutes and needs scratch Rainbow-formatted diskettes.

Related pages

• Rainbow 100
• Rainbow 100 Troubleshooting Guide
• Rainbow 100 Capacitor Replacement Guide
• Rainbow 100 Documentation
• DECmate II Power Supply Service
• CRT Discharge Procedure
• Floppy Drive Repair