Author Topic: Ceronix 1793 Cuts Out after a few minutes (Read 24716 times)

Justin · « **Reply #20 on:** July 28, 2024, 11:08:38 am »

There are some diodes in a slightly dark spot near the fly back under some mylar caps. The caps seem to be alright and the diode seem to tear fine too.

I was really hoping it was the HOT lol, I have a spare I could've thrown in. Can't be that easy can it lol.

Justin · « **Reply #21 on:** July 28, 2024, 11:32:06 am »

Some more images:

Justin · « **Reply #22 on:** July 29, 2024, 03:38:14 pm »

Cap kit installed. No difference. The dark spot on the board is around the two diodes by the inductors, but they measure ok.

gametech2 · « **Reply #23 on:** July 29, 2024, 04:42:03 pm »

Quote from: Justin on July 29, 2024, 03:38:14 pm

Cap kit installed. No difference. The dark spot on the board is around the two diodes by the inductors, but they measure ok.

Those have been really hot to darken the board like that!
Could be breaking down under load, and dumping ac across the circuits.
just a quick guess.
Could also be those resistors getting really hot.
I can't tell from the picture, but they look like .61 ohms, which is almost a short on an ohm meter.
Did you check them to see if one or both are open? That is in the horizontal out section, and I would suspect the fudge brown colored cap behind the resistors, it may
have gotten so hot that it changes value under a load, this would change the horizontal frequency dramatically.
just my 2cents

Justin · « **Reply #24 on:** July 29, 2024, 04:58:51 pm »

I will take a look at those. Right now I have probed the shutdown and fault detection signals and the monitor is shutting down due to the Fault Detection Circuitry. I am not sure which fault is the cause at the moment thought, I am not sure what else to measure to narrow it down more.

gametech2 · « **Reply #25 on:** July 29, 2024, 05:07:56 pm »

If you have a variac , you can turn it all the way down, slowly bring it back up, listen for the horizontal frequency, see it it sounds crazy high. this might get it to stay on also at around half power, long enough to see what is happening on the screen, and be able to do some voltage tests.
just a thought from way back in the dayz......jb

Justin · « **Reply #26 on:** July 29, 2024, 05:42:18 pm »

I just tweaked the G2 adjustment on the Flyback down, and the monitor has been running a lot longer than it usually does. Does anyone know the proceedure to correctly adjust the G2 pot?

Justin · « **Reply #27 on:** July 29, 2024, 06:02:22 pm »

Ok, this is really weird, at least I think so:

With nothing hooked up to the monitor but power, I get a full blue screen and it dies after about 30 seconds, no HV

With my oscilliscope hooked up to link 019 for fault shutdown and another probe on G2 and GND, the monitor stays on. Fault signal floats around negative a couple mV and 0V. G2 is roughly 220V

Justin · « **Reply #28 on:** July 29, 2024, 07:14:46 pm »

The monitor also refuses to power up in the cabinet. I could also have a power issue in the cabinet I guess. Very weird

Justin · « **Reply #29 on:** July 29, 2024, 09:03:51 pm »

Here is a video I took of it: https://drive.google.com/file/d/1V8uZaiPhC0-fAEqkYV1ndKs3Yny8KjDI/view?usp=drivesdk

The monitor has no video signal yet it has a blue screen and diagonal blue lines. After a little bit it shuts off but I did not unplug it.

Chris-socal · « **Reply #30 on:** July 30, 2024, 06:13:19 am »

I don’t know what the pin arrangement is on the Vertical IC, its the flat one in the middle of the board mounted to a heat sink, 7 or more pins.

With the power off:
In a typical arrangement only one pin would be ground. If you put your meter on diode check, black on ground, touch the red lead to each of the other pins none should short, they should only read like diodes or open. If any others short to ground you need to pull up the data sheet and verify if more than one pin goes to ground.
Im highly suspicious of the vertical IC and/or one of the PRA boards.
You also need to check the 12v power rail. Do you have any mini grabber clips?

Since you have video for a few minutes I am not suspicious of a diode. Im not saying it isn’t a diode but that monitor exhibits problems in the video circuit. The Vertical IC is a common fail point that causes shutdown.

One component at a time. Don’t get discouraged.

Chris

Chris-socal · « **Reply #31 on:** July 30, 2024, 06:34:27 am »

Sorry guys, when I logged on this AM I only saw Justins post with the video, I didn’t see your other dialogue. I didn’t mean to derail your discussion.

Justin, what are you powering this with on your workbench? Is it isolated?

Chris

Justin · « **Reply #32 on:** July 30, 2024, 06:45:39 am »

Yes, the monitor chassis has a XFR-75W isolation transformer.

I do not have a signal generator. With no signal should the screen be blue or black? My screen comes up blue with no signal, could this be indicative of a bad blue PRA? Would that cause shutdown?

When I connect my oscilloscope to G2 on the neck board to measure, it causes the screen to go from blue to black. I am not sure what this means as the oscilloscope should not add any load to the pins, just measure.

Chris-socal · « **Reply #33 on:** July 30, 2024, 07:18:38 am »

Actually, it’s interesting you say that. On a 1492 anyway, if a blue PRA goes out you get all blue sometimes, kind of opposite of what you expect. But that doesn’t mean its the blue PRA. When any of the color boards has a problem it messes with all the video. There are transistors for each color also. You can check all those with diode checker.

Sorry I don’t know what scope will do.

Could be the power PRA also.
But you really need to check the vertical IC.

Chris

gametech2 · « **Reply #34 on:** July 30, 2024, 08:50:45 am »

Quote from: Justin on July 29, 2024, 07:14:46 pm

The monitor also refuses to power up in the cabinet. I could also have a power issue in the cabinet I guess. Very weird

Hey guys, here is a link to a service manual for this monitor:

https://www.ceronix.com/lcd-specs-manuals-schematics/

SCROLL DOWN TO {CRT Manuals}, YOU CAN DOWNLOAD THE 1492 SERVICE-MANUAL HERE!!!

LOOK FOR THIS:

Models1492 and 2092 SERVICE MANUAL

Does anyone have a list of the caps that come in a recap kit? I hate buying a kit just to get the list, I have cabinets full of new capacitors and resistors from a few years ago
back when I was repairing a few ham radios ( yes, I am a licensed Ham! ) It's no fun at 67 trying to look up all the caps on this schema!!

Thanx..........jb

Chris-socal · « **Reply #35 on:** July 30, 2024, 09:24:19 am »

Yes and Yes. Very good manual, great reading when you can't sleep.

If you need some pointers on how the board is laid out I have a video on Youtube where I babble about the general concept. Let's keep the 1492 to your thread. I can help you with a 1492, no problem. I will venture to say "easy" but sometimes they aren't. LOL

Chris

Justin · « **Reply #36 on:** July 30, 2024, 10:11:48 am »

Pin 5 on the Vertical Deflection IC LA7838 is a dead short to ground. Ground being pin 11 on the IC. The datasheet shows something to do with vertical size control switch. it also references 50/60 HZ on this pin?

Justin · « **Reply #37 on:** July 30, 2024, 10:44:14 am »

Seems to be directly attached by the trace. The ic is checking out ok.

Is this glob of solder on the back of a PRA normal?

Justin · « **Reply #38 on:** July 30, 2024, 11:02:23 am »

I am also measuring ~14k Ohms on the Thermistor 180. Does anyone know what the acceptable range of resistance is for operation?

Chris-socal · « **Reply #39 on:** July 30, 2024, 11:35:48 am »

That solder blob is a jumper. I don't know which PRA is on a 1793 but that probably sets the Horizontal Width if it's in the Horizontal area. Or amplification. It's fine, not the cause of your problem.

Pin 5 should not be shorted to ground. I can check my 1793 when I get home but that doesn't seem right and it certainly would answer for the lack of image and eventual shut down. When you say shorted, you mean it reads 0 ohms?

Chris

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Author Topic: Ceronix 1793 Cuts Out after a few minutes (Read 24716 times)