Atari SC1435 General Maintenance

Adjusting components on the SC1435 main and CRT panels (service manual)

Safety notes and the electrical adjustments for the Atari SC1435 14-inch colour monitor, from its Philips-format service manual.

Safety

• The anode supply is 25 kV. Discharge the CRT before handling the chassis: see CRT Discharge Procedure.
• The power supply primary is at mains potential. The diagram marks it "hot ground" and the board layout marks the area "life part".
• The manual's cautions: restore the set to its original state and use parts identical to those specified; replace parts marked with the warning triangle with identical parts; avoid high-voltage flash-over, which damages ICs and transistors; take care when measuring in the high-tension section and on the picture tube; never change parts with the set switched on; wear safety goggles when replacing the picture tube.

Fuse and degaussing

The mains fuse 1401 is a T2A (time-lag, 2 A) on the 220-240 V model and a T3A on the 110-120 V model. The degaussing coil 5404 is switched by the PTC thermistor 3404 on the main panel.

Adjustments

Apply a video signal, usually a cross-hatch pattern, for each adjustment. The paragraph numbers are the manual's, and the location drawing above keys each preset to its paragraph.

SC1435 electrical adjustments

Para.	Adjustment	Control	Method
1.1	+128 V supply	Preset 3414	Volume (3295), brightness (3662) and contrast (3658) at minimum; 3414 at mid-travel; voltmeter on the junction of 3520 and diode 6453; switch on and set 128 V DC
1.2	Horizontal synchronisation	3257	Short capacitor 2270 (on pin 5 of IC 7270), set 3257 so the picture stands straight, remove the short
1.3.1	East-west correction	3537	Vertical lines at the left and right edges as straight as possible
1.3.2	Picture width	3534	14 blocks of the pattern 260 mm wide
1.3.3	Horizontal centring	3264	Picture centred
1.3.4	Vertical centring	3583	Picture centred
1.3.5	Picture height	3550	10 blocks 186 mm high
1.3.6	Vertical linearity	3573	Best linearity; repeat 1.3.5 and 1.3.6 if needed
1.4	VG2, cut-off and white balance	VG2 (bottom knob on the line output transformer), cut-off 3107, 3117, 3127, drive 3671, 3680	Brightness at a quarter, contrast at minimum, presets at mid-travel, VG2 at minimum; with each colour in turn, set the CRT cathode pins 8, 6 and 11 to 100 V with 3107, 3117 and 3127; on a white frame raise VG2 until the first colour shows, then bring the other two to the same light output; finally set 3671 and 3680 so the background colour is the same at minimum and maximum brightness
1.5	Focus	Top knob on the line output transformer	White pattern; sharpest at two-thirds of the way from the centre to the corners
1.6	Audio balance	3298	177 mV rms at 1 kHz into both audio inputs, volume at mid-travel, the two loudspeakers replaced by 16 Ω resistors; set 3298 for equal output

Set the +128 V supply first; it is paragraph 1.1 in the manual's sequence. The manual names the measuring point as the junction of 3520 and 6453, then as 3524/6453 in the next line; the location drawing labels the point beside 3520 "MP 128V".

Capacitors

The full electrolytic list is on Atari SC1435 Capacitor Replacement Guide. An owner who recapped an SC1435 reported a sharper picture afterwards.

Related pages

• Atari SC1435
• Atari SC1435 Capacitor Replacement Guide
• Atari SC1435 Documentation
• CRT Discharge Procedure
• Recommended Tools