Author Topic: Ceronix 1793 Cuts Out after a few minutes (Read 24725 times)

Justin · « **Reply #40 on:** July 30, 2024, 01:44:50 pm »

Yes 0.01 ohm or 0 ohm, a dead short. Beeps on continuity mode too. I found pin 11 to be ground on the chip please verify that as well. Let me know what you find. I pulled the chip out of circuit too and the short was gone so if it is not supposed to be grounded, it's not the IC it's something else on the board

Chris-socal · « **Reply #41 on:** July 30, 2024, 01:54:51 pm »

The manual has a very good schematic so it should be easy to trace that leg. If that leg goes to the flyback or another coil it might read shorted but still be ok. I am not at home so I can't browse the schematic right now.
There is another transistor in the Vertical area, you need to test it too. Actually, anything with 3 legs, especially if mounted to a heat sink, needs to be diode tested. I can't think of any that read shorted across any two legs except the HOT will read dead short across the two outside legs. Anything else should read like a diode, open or low continuity. Nothing should be shorted.

Chris

Chris-socal · « **Reply #42 on:** July 30, 2024, 02:02:57 pm »

Modified from original post:

I had a schematic saved here at work. Pin 5 does go to ground, highlighted below the pin. I need to check that at home just to verify they don't have an error where that trace crosses ground. You can easily follow that trace and see if it connects to ground according to this.

I highlighted the trace and a few components that you might want to look at but if that pin goes to ground I'm not sure why it goes to the rest of the vertical linearity components.

Chris

Justin · « **Reply #43 on:** July 30, 2024, 02:17:54 pm »

Ok, I checked all the components in the highlighted portion. I did the cap kit already so no surprise that cap reads fine. 0.13 est and 970uF. Only thing I don't know how to check is the comparator.

I did double check and between pin 5 and ground on the capacitors nearby or on pin 11 is 0.0ohms

jay · « **Reply #44 on:** July 30, 2024, 02:24:09 pm »

My bet is still on one of the high voltage (heat sync mounted) 3 pin transistors... but this is from repairing older tube TVs in the late 80's. Two screws, and some of that white thermal paste. No soldering required. I have seen these both short and open causing the picture collapse or shutdown.

Justin · « **Reply #45 on:** July 30, 2024, 02:37:51 pm »

None of the big transistors/mosfets were shorted. 5 and 11 are still dead shorted with comparator removed too.

Chris-socal · « **Reply #46 on:** July 30, 2024, 02:55:42 pm »

I agree with Jay.

Justin, did you look at the image I sent you?
Pin 11 is Ground and that trace will/should short to ground.
The schematic also shows pin 5 going to the ground trace but the schematic for the IC doesn't show Pin 5 as Ground.
When I say look at the traces to see if Pin 5 really goes to ground, I meant look at it with your eyes. We know the meter reads shorted but can you find where the trace connects to a ground trace? The reason I wanted you to look at this is because it seems strange that pin 5 would connect directly to ground, not through a component like a small cap or resistor...but it might make sense. I Just want to make sure there isn't a solder bridge or something along the way. Until I get home I cannot verify it on my board.
As Jay said, every transistor needs to be checked, especially the big ones. They are most likely to fail because they are working the hardest.
Eventually you will have checked every component on the board and we will be left with Flyback and XRC5184.
Oh, and I still say you need to check the 12v voltage regulator.

Justin · « **Reply #47 on:** July 30, 2024, 04:08:17 pm »

I took another look at the board:

Following the trace for pin5, it goes to the screw for the heatsinks on the LM7838 and then to the negative side of a few capacitors.

All the transistors on the board (even the small ones) are not shorted. I am going to check the neck-board now because I realized I forgot to check those as I was typing this.

I did find a component that felt loose and upon further investigation, the traces were lifting. It was component #159 which is an inrush current limiter. I ohmed it out and it was within spec at 13-16 ohms. I put it back in and added botch wires to follow the route of the traces. Not sure if this would actually cause the issues I'm seeing and I don't want to put the whole thing back together right now just to see that it has the same issue lol. I just want some input first.

Justin · « **Reply #48 on:** July 30, 2024, 07:30:19 pm »

Chris,
Is there any chance you had the ability to grab those readings off your board yet?

Chris-socal · « **Reply #49 on:** July 30, 2024, 08:41:54 pm »

Pin 5 and 11 both connect to ground.
If that trace was broken it would certainly shut down color processing. Look very closely at all pins and traces.

Justin · « **Reply #50 on:** July 30, 2024, 10:28:52 pm »

Progress... I think...

I reflowed all the solder points on the neck board because I saw how many were cracked/ pads were coming up. I had to repair some traces. Now the screen is Red instead of Blue! Idk if this is really progress but it's something different.

Chris-socal · « **Reply #51 on:** July 31, 2024, 06:15:22 am »

All one color can mean the problem is in that color circuit. My original hunch was solder joints if you recall. If you put your finger on the surface mount IC of each color PRA they should all be warm.

Also, I don’t remember you answering if your 12v line checked ok. Third leg of 7812 (#296) is the output.

Chris

Justin · « **Reply #52 on:** July 31, 2024, 08:31:39 am »

My apology I forgot to put it in there, yes 12v rail is spot on at 12.0V

Justin · « **Reply #53 on:** July 31, 2024, 12:16:05 pm »

Ok so I've either fixed it or broke it lol. No more red, no more blue, no more shutdown. Blank screen and when I unplug it, I see the screen flash so I know it was running

jay · « **Reply #54 on:** July 31, 2024, 12:37:43 pm »

So are you putting it back in to see if you get an image ?? or what are your next steps.... to feed it a video signal.

Justin · « **Reply #55 on:** July 31, 2024, 12:51:18 pm »

I'm going to have to put it back in, I don't have what I would need to feed it a video signal unless it's in the cabinet. I'm just going to wait a few minutes to see if it stops downpouring here.

Chris-socal · « **Reply #56 on:** July 31, 2024, 12:56:09 pm »

You will usually have a gray or slightly white screen with no input it may flicker because there is no sync.
Fingers crossed you got it.
But really, on those joints and traces around the PRA boards and the corresponding transistors you need to look close, really close, really really close. I can’t say it enough. Magnifying glass close.
I worked on for nearly a year and finally discovered a trace that was split right at the base of the solder. It was One of those seals where I had tested continuity… but when I pressed on the solder joint it would connect and test fine. I eventually re-tested all traces with a meter and saw that one flicker in and out of continuity.
Depending on which pin or transistor it is, one goes out, all colors go out.

Did you add solder to the yoke pins yet?

Chris-socal · « **Reply #57 on:** July 31, 2024, 01:00:11 pm »

I think that is an SVGA board. Your only option is probably to put it back into the game.
We anxiously await from the sidelines.
The only thing it’s pouring here is traffic and taxes. Lol

Justin · « **Reply #58 on:** July 31, 2024, 02:00:13 pm »

1 of three possibilities I guess.
1. I broke both red and blue and it's just showing green
2. My board is screwed (Game King 3902)
3. More traces to look at

I also hear snapping probably low voltage arcing by only sometimes when it's running.

Justin · « **Reply #59 on:** July 31, 2024, 02:08:39 pm »

Ugh. It's all 3. Looks like I have red and green, but no blue. Can't say I'm surprised looking at the traces for blue. This will NOT be fun.

My board is probably screwed too. It only works when it feels like it. Otherwise it outputs that garbage above.

See the attached pictures.

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Author Topic: Ceronix 1793 Cuts Out after a few minutes (Read 24725 times)