Ceronix 1492 repair logs (and some 1490)

[Chris-socal]

While there are several databases and log sheets for the 1492 and Ceronix 1490 family of CRT boards, there are scenarios where a board has problems not covered, or the suggested fix doesn’t resolve the problem. The Ceronix 1492 manual is one of the most detailed and comprehensive manuals ever written but if you haven’t spent a lot of time around the chassis it can feel intimidating. My goal is to document these scenarios as I come across them and point the future “me” in the right direction and hopefully explain how I got there.

The attached database combines the 3 known tech repair logs, the most famous comes from former member Certech who I thank a million times every year! This list also contains a few scenarios that I have personally come across. This list is also available in the NLG file system and I will update a few times every year.

If you have questions regarding a specific Ceronix board please create a new post in the LCD and CRT Tech support category.

Chris

[Chris-socal]

Model: 1492
Symptom: Board starts and has HV but no image.

The baseline bias control lines at top of raster are not visible (this typically tells us the image is pulled down before gain control)
The RGB pins on neck board are reading normal (70-110v) and change when gain knob on remote board is rotated. This means the color and image amplifier is working.
Installed known-working flyback for testing purposes and to verify problem isn't flyback.
The input pins on CA3234 are reading near zero (should be 5.8-6.4v). This is a symptom, not a cause.
LA7830 pins to ground are not shorted but diode 190 measures some voltage drop in reverse. This diode should be completely shut when measured in reverse. Diode tests fine out of circuit.
Pulled LA7830 and ghost load disappeared. Replaced LA7830. Still no picture.
Checked LA7851 pin readings since it is directly tied to LA7830. Pin 16 is 12v and pin 15 is 2.4v, both are way over driven. Both pins are outputs so the assumption is that when LA7830 fried it took out LA7850. Or the other way around?
Replaced LA 7850, have image now but Horizontal is too narrow.
Verified capacitor 121 isn’t shorted. Move attention to PRA-G board (Horizontal width control). Found trace of pin 18 to LM324 is open. Repaired trace, all good now.

All pin readings I referenced are stated on the circuit diagram in the manual, page 15. No need for me to state expected range on every reading.

Note: On rare occasion a catastrophic event like shorting the bottom of the board will short out the laser imprinted resistors on PRA boards. When investigating problems on circuits that contain PRA boards be sure to visually inspect for burned spots. If a surface resistor does burn out you can solder a 1/4watt across the pins. The schematics for PRA boards is in the back pages of the Ceronix manual.

[Chris-socal]

Model: 1492
Symptom: Resets and/or has retrace lines

Previous tech labeled board as “Resets”.
Found Power supply filter capacitor was loose in solder joint. Also found 3 capacitors with extremely high ESR (286,230,233). Board starts now but has severe retrace lines.
Tested voltage for each color on neck board and green was significantly lower than red or blue when on RGB display. Low voltage translates to over driven color.
Checked transistors in color section and none are shorted or open. There are 3 per color, near each PRA-B board.
Tested continuity of traces on transistors in Green section, all test good.
Replaced PRA-B board for Green, the NE592 SMD burns out on them. It is a color amplifier.
Board has great image now.
Installed standard capacitor kit. Reflowed solder joints.
Connected to PE board and set flyback voltage to 4.6v (pin 8 on 146)