Atari SC1224 General Maintenance

Adjustment points on the Goldstar CA-3 chassis (Atari service manual)

Care, opening and adjustment of the Atari SC1224 colour monitor. The SC1224 was built in three versions by JVC, Goldstar and Samsung under the one model number. Atari's service manuals survive for two of them: the Goldstar set on the CA-3 chassis and the JVC set that Atari calls Version 2. The procedures below are from those manuals; check which version you have before using a designator (see Atari SC1224 Capacitor Replacement Guide#Which version is it?).

Safety

• The anode supply is 22.0 kV on the Version 2 and 23.0 kV nominal on the CA-3. Discharge the CRT before touching anything near the flyback or the anode cap: see CRT Discharge Procedure. The Version 2 manual says to discharge it with a clip lead from the ground frame through a 10 kΩ 2 W resistor to the anode button, and never to check the high voltage by drawing an arc.
• Goldstar's manual requires an isolation transformer between the monitor and the mains before the chassis is serviced. On the Version 2 the 125 V B1 supply is rectified straight from the mains by D1901 to D1904, so the main board is not isolated from the mains.
• Replace any part shaded in the schematic or marked as a safety part in the parts list with the part the manual specifies. Both manuals give this rule for the high-voltage, X-ray protection and mains parts.
• The CRT has integral implosion protection. Avoid knocking or scratching it, and fit only the same type of tube.

Fuses

SC1224 fuses

Version	Ref	Rating
CA-3 (Goldstar)	F901	3.15 A 250 V
Version 2 (JVC)	F1901	4 A 125 V, mains
Version 2 (JVC)	F1902	1 A 125 V, after the mains bridge

A blown fuse has a cause. Check the bridge, the reservoir capacitor and the regulator or switching IC before fitting a new one (see Atari SC1224 Troubleshooting Guide).

Opening the Version 2

1. Unplug the power cord and remove the five screws marked A to take off the rear cabinet.
2. Discharge the CRT.
3. To remove the main board, take out the two screws marked B, the two marked C and the two marked D, remove the bracket if necessary, and disconnect the anode lead and the other wires. Withdraw the board.
4. To remove the bottom cover, take out its five screws (F) after removing the main board.
5. When the set is powered for checks with the board out, keep the CRT earth wire connected between the CRT socket board and the main board. When the CRT socket board is disconnected, coat the CRT socket with silicone.

Atari's CA-3 manual does not give a removal procedure for the Goldstar set.

Degaussing

The CA-3 has an automatic degaussing coil round the tube, which runs for about one second at switch-on. After the monitor has been moved or turned to face another way, leave it switched off for at least ten minutes so the automatic degausser works fully at the next switch-on. If the chassis or cabinet has become magnetised, use an external degaussing coil: move it slowly round the faceplate, sides and front, then withdraw it slowly to about 2 metres before switching it off. The Version 2 also has a degaussing coil (L01) switched by the posistor TH1901.

Adjustments: CA-3 (Goldstar)

Atari's CA-3 manual lists these adjustments. The rear-panel controls are the user's; the others are on the main board and need the back off.

CA-3 adjustments

Adjustment	Control	Setting
Vertical hold	R603 (rear)	A single still picture
Vertical size	R616 (rear)	Picture 150 mm high on the 12-inch tube
Vertical linearity	R635 (rear)	Best on a cross-hatch, within ±7 %; recheck size afterwards
Vertical centre	R626	Picture centred on the screen
Horizontal hold	R716 (rear)	A stable picture
Horizontal position	R710 (rear)	Picture centred on the screen
Horizontal width	Coil L702, with a hexagonal tool	Picture 210 mm wide
Side pincushion	R621	Distortion at minimum, within 1.5 %
Focus	Focus control on the flyback	Sharp scan lines at the 1/4 and 3/4 points of the screen
Sub-brightness	R742	With a white input, contrast at maximum and brightness at minimum, turn R742 until the picture just cuts off
Drive (white balance)	R323 (red), R303 (green), R343 (blue)	With brightness and contrast at maximum, 45 V p-p video at R510 and R511 for red and green; blue set to match green
Cut-off (white balance)	R317 (red), R337 (green), R357 (blue)	Set with a colour analyser on a reverse pattern; the manual's target is x 0.279 to 0.283, y 0.309 to 0.313
Level	R369 (red); R372 (blue level, shown on the chassis figure)	R369 matches the red output to green at minimum contrast; recheck red drive at maximum contrast afterwards
X-ray protection (hold-down)	R725	Factory set: 10.25 V DC at the cathode of D704, then fixed with epoxy

The CA-3 has no high-voltage adjustment. The 115 V supply sets the high voltage, which the manual says must measure below 24.0 kV at zero beam current and must not exceed 24.5 kV at either extreme of the brightness control. Let the monitor run for at least fifteen minutes before touching convergence.

Adjustments: Version 2 (JVC)

Warm the monitor and the instruments up for at least 30 minutes. Atari's equipment list is an RGB signal generator with analogue output at 1.0 V, an oscilloscope, a voltmeter, a screwdriver and a hexagon core wrench.

Version 2 adjustments

Order	Adjustment	Control	Setting
1	HB voltage	HB ADJ R1570	120 V on the HB line
2	Horizontal hold	H HOLD R1506 with H FREQ switch SW1501	Set H POSITION R1516 to mid-travel, switch SW1501 out, turn R1506 until the picture almost holds, return SW1501 to centre
3	Horizontal width	Coil L1522	Picture 216 mm wide
4	Vertical hold	V HOLD R1432	Picture vertically stable
5	Vertical height, linearity, position	R1408, R1406, R1429	160 mm high, equal top and bottom spacing on a cross-hatch, centred
6	Black level	Y BIAS R1006	With black input and BRIGHT and SUB BRIGHT at mid-travel, 6.0 V DC at TP-G2
7	Bright pulse	SUB BRIGHT R1015	With black input and BRIGHT R1019 at centre, no pulse at TP-G2
8	Cut-off	R1025, R1028, R1031 and the SCREEN control	105 V at TP-47R, G and B; then with SERVICE switch SW1401 at S, set SCREEN until a faint line shows and bring the other two colours up to match with their cut-off controls; return SW1401 to N
9	Drive	B DRIVE R1304, then R1104 and R1204	With CONTRAST R1013 at maximum and white input, 30 V p-p black-to-white at TP-47B; then red and green drive for a white raster
10	Focus	FOCUS control	Centre and edges equally sharp with the contrast set so the characters just saturate

All settings are from Atari's service adjustments. Purity and convergence are needed only after a tube or yoke change or when colour shading appears. Atari's procedure demagnetises the tube, sets purity with the purity magnets and the yoke position, sets static convergence with the 4-pole and 6-pole magnets on a cross-hatch, and corrects the corners with the yoke and rubber wedges.

Safety checks after a repair

Atari's Version 2 manual requires a leakage check after any repair. Plug the monitor straight into the mains without an isolation transformer, and measure from each exposed metal part to a good earth through a 1500 Ω 10 W resistor with a 0.15 µF capacitor across it. The AC voltage across the resistor must not exceed 0.35 V, which corresponds to 0.5 mA; repeat with the plug reversed. The manual also asks for the B1 setting to be checked after any chassis repair.

Capacitors

Electrolytic capacitors on both versions are now around forty years old. Owners report leaking power-board capacitors on Goldstar sets. Full lists for both versions are on Atari SC1224 Capacitor Replacement Guide.

Related pages

• Atari SC1224
• Atari SC1224 Troubleshooting Guide
• Atari SC1224 Capacitor Replacement Guide
• Atari SC1224 Documentation
• CRT Discharge Procedure
• Recommended Tools