Ceronix 1793 help please

[Nepa Coin Op]

I have been goofing around with this monitor a few years and now need to get it going, on the bench the unit has no HV, some of what was done so far

All caps replaced
Vert IC replaced
few of the other ics swapped from another 93 chassis
The manual for these things arent the best they more explain how it works not really help you trouble shoot. anyone who can point me in the right direction I would really appreciate it. I am sure im really close on this one at this point from what I remember I think it used to tick it no longer does that so I am either moving forward or backwards. I hear the relay when I power it up just no hiv to the secondary

Thanks guys

[Nepa Coin Op]

only thing i havent changed is the la7851 im going to try that next

[Chris-socal]

I don’t think LM7851 will help get HV.
Did you replace the HOT?
I couldn't find a troubleshooting chart for this monitor like the 1492. There is a resistor and a diode that is known to fry on those without any visible indication.
Check all traces and solder joints very closely. They didn’t use the best foil on these and it can separate at the edge of the solder after years of use.
There is also the possibility that the flyback is dead.

[Richard S]

I'm curious if you were able to fix this chassis.

[Nepa Coin Op]

Since last time I posted I changed the HOT, still no Hv … I noticed hot is not pulsing and the control circuit for the transformer that controls it is not getting power, however the 7812 is good tested out of chassis. That’s as far as I am right now it’s sitting there with the 7812 still out

[Richard S]

Do you have the XX93 service manual? It is a great resource for circuit descriptions and servicing information.
https://www.ceronix.com/dlfiles/manuals/XX93_SVCMAN.pdf

Start with the power supply section.

[Chris-socal]

When you say you aren’t getting HV do you mean B+ or are you talking about the second anode on the tube?
 
Its possible the monitor is going into shut down immediately upon power up. Do you hear anything? Listen closely, do you hear a faint chirping?
Im sure the manual would say where you test B+, you mentioned 7812, are you getting voltage into the 7812? It would probably be 14 or 16v, if there is a schematic in the manual find 7812 and see where it gets its power. Some monitors get their 16v from the flyback. See where this is going?

Editing: I am not an expert but looking at the block diagram there is an important section. See my attached image and highlights, the entire power circuit  is governed by a protective watchdog, if any of those checks are out of tolerance the power circuits will be shut down. All CRTs have them to prevent giving the user an unexpected xray.
It is possible the flyback is bad and causing all of these issues. My suggestion is to check every diode, check all transistors for shorts. If none, you are running out of components. If you are not getting 16v into the 7812 its probably in shut down. You could hook up a meter and see if you get momentary power before it shuts down. You might also try removing the flyback and see if DC voltage comes on.
Just remember to discharge the anode before you pull it. You could technically unsolder the flyback and leave the anode cup attached.

[Chris-socal]

You are very lucky, there is a COT1558 flyback on ebay for $40, you should buy it. Even if it isn’t bad now it will go out some day.

[Nepa Coin Op]

You are very lucky, there is a COT1558 flyback on ebay for $40, you should buy it. Even if it isn’t bad now it will go out some day.

new fly installed still No HI V

[Chris-socal]

But you have B+?

[Jim]

I have three of these on brand new boards, never crossed them over to see what else they could be used for, if nothing else, a ton of electronic parts for someone who repairs chassis??

Jim

[Richard S]

I have three of these on brand new boards, never crossed them over to see what else they could be used for, if nothing else, a ton of electronic parts for someone who repairs chassis??

Jim

Jim,
Which chassis (make/model) are those boards?

[Jim]

these are brand new, people at Ceronix said to convert to 115vac you have to remove two diodes. I am sure they can help if asked.


Jim