Omega Race power issues: help sorting through the muck.

vintagegamer

Well-known member

Donor 2024
Joined
Sep 1, 2007
Messages
21,092
Reaction score
2,602
Location
Bear, Delaware
Omega Race power issues: help sorting through the muck.

ELutz has been helping me work my way through my current Omega Race power issues, but I thought that to keep the progress-status contained, I'd start a new thread unique to this machine.

Currently, on power-up, I have the following:

1. linear PS is showing 12V at the 12V cap, but 5V cap is no longer registering 5V (reads 0)
2. the resistor at location R20 showing no voltage when game is on, but shows 163 ohms
3. the big cap at the bottom of the linear PS showing no voltage
4. the 3-pin connector at the bottom of the linear PS showing no voltage
5. upper "Omega Race" marquee lights at top front of game, coin lights are lit, waistline marquee was lighting until I just started messing with the fuses in the power brick. See below.
6. I do not have any game boards hooked up currently in the game.

In the power brick are 5 fuses: 3 mounted on the base of the brick, and 2 over top of the caps (that look like big blues); the 3 mounted on the power brick are a 2A slow blo, and in a 2-fuse holder are 3A slow blo and .5A slow blo. I had checked all 5 of the fuses that were in these locations as of last night (pulled each one out and tested continuity), and all 3 were good. However, as mentioned, there is no power going to the linear PS via the 3-pin connector.

To start fresh, I pulled all 3 fuses and put brand new ones in today. I powered up the machine and saw a brief spark at the 3A fuse location, everything else that was working before is still working, with the exception of the waistline marquee now. If I check voltage across the 3 fuses mounted on the power brick, the only one showing voltage going across it is the .5A fuse, which is registering approx 30V AC. The other 2 show 0.

Is my best bet to start by replacing the single and dual-fuse holders on this game? God I wish a switcher was produced for this thing!!!

(here is where ELutz has been helping to date: http://forums.arcade-museum.com/showthread.php?t=156256)
 
Last edited:
Sounds like one or more of your diodes on the full wave bridge is shorted. Things that I find bad on these power supplies are bad pins on the connectors. Sometimes they get pushed back and don't make good contact. The 2n2905a transistors bad so you can't regulate the voltage, and it drops out under load.
 
Sounds like one or more of your diodes on the full wave bridge is shorted. Things that I find bad on these power supplies are bad pins on the connectors. Sometimes they get pushed back and don't make good contact. The 2n2905a transistors bad so you can't regulate the voltage, and it drops out under load.

But the problem currently is, I'm not even getting voltage from the power brick to the linear PS via that 3-pin connector. So, wouldn't the problem lie with something like the fuse holders on the power brick, or another component on it?

The 12V cap is getting power, and it's enough to drive the upper marquee, coin lights, and black light in the bezel area.
 
But the problem currently is, I'm not even getting voltage from the power brick to the linear PS via that 3-pin connector. So, wouldn't the problem lie with something like the fuse holders on the power brick, or another component on it?

The 12V cap is getting power, and it's enough to drive the upper marquee, coin lights, and black light in the bezel area.

Ok unplug the 3 pin connector. Replace the 2 amp slow blow fuse, and measure the voltage. I'm guessing what is happening, is that when it's plugged in and one of the diodes is shorted, it blows the 2 amp fuse. Thus you don't read power.

If voltage is good, then plug it back in. I'm betting your fuse blows.
 
Ok unplug the 3 pin connector. Replace the 2 amp slow blow fuse, and measure the voltage. I'm guessing what is happening, is that when it's plugged in and one of the diodes is shorted, it blows the 2 amp fuse. Thus you don't read power.

If voltage is good, then plug it back in. I'm betting your fuse blows.

I unplugged the 3-pin connector. I removed the 2A and 3A fuses from the power brick, and checked both of them for continuity and they were fine, so I did not replace them with new ones. I cleaned off of the fuse holders (did not replace yet), put the original 2A and 3A fuses back in place, and powered it up. There is still no reading of any voltage at the 3 pin plug (the one that's disconnected from the linear PS). There is also no voltage reading across the 2A or 3A fuses while the game is powered on.

The only change that I have noted is after this most recent cleanup and check, I now have 8.8V travelling across the 4700 cap which is for the audio. However, in the meantime, I've lost power to my black light now, along with the waistline marquee light. This thing is like a one-armed bandit from Hell.

I also checked the 2 fuses that are enclosed on the power supply (they go into little holders vertically) for continuity, and they check out as OK as well.

Do I need to rebuild something on the power brick? Even if the 2A and 3A fuses were blown, I'd still see a voltage reading across the fuse holders when the game was powered up, right?
 
If I am reading the attached schematic correctly, it's saying that 0V is going via the 3-pin connector to the linear PS board. Can someone help in confirming this?

The only thing I don't get is, if there is no voltage going from that connector to the PS board, then a. why does the connector need to be there at all, and b. why is there a 2A fuse on that line-circuit-whatever?

Thanks!
 

Attachments

  • or3-pin.jpg
    or3-pin.jpg
    92.9 KB · Views: 14
And if I'm reading THIS attachment right, there should be no voltage going via the 3A fuse that's in the power brick. That means that the 2A fuse and the 3A fuse, which are both currently reading 0V when the game is turned on, are working as they should be, right? Again, I don't know why you'd have a fuse for a circuit with no voltage going through it but hey, I'll leave that kind of stuff up to the electrical engineers to explain :D

So if my conclusions are correct about these 2 fuses, then in theory, my transformer brick is OK. It doesn't explain though why my 5V cap on the linear PS isn't reading 5V (it's reading 0). I'm guessing that means I need to rebuild the linear PS, right?
 

Attachments

  • or3Afuse.jpg
    or3Afuse.jpg
    88.1 KB · Views: 5
After thinking a little more on this, it looks like tonight's task will be to check the 9 pin connection going to the linear PS from the filter assy, to see if any of the pins are not making contact with the linear PS. I will also be checking voltages coming from the filter assy to make sure they are where they are supposed to be....

Hopefully all of these thinking out loud posts are helping someone other than just me! :D
 

Attachments

  • filter_to_linearps.jpg
    filter_to_linearps.jpg
    92.7 KB · Views: 4
Think I may have found some new evidence tonight as to why my OR is having power issues.. First off, the colors of the 9-pin harness going to the linear PS do not match those on the schematic. I didn't really have a concern about that, so long as the voltages of the wires were correct. Well, they aren't...

On the schematic, it gives the following values by pin: 1- GND, 2- 8V common, 3- 8V common, 4- 8V unreg., 5- 12V common, 6-15V unreg., 7-5V common, 8- 8V unreg., and 9- 12V common.

I'm not sure of how the pin order is supposed to be, but no matter what way you look at the values I have, they still don't match the ones above. Mine are as follows (I will do the pins in the order of 1 is top left, 2 is first one down from that, 3 is bottom of that column, etc): 1- GND, 2- 9.1V, 3- 0 (and has no wire going into it at all), 4- 9.1V, 5- 0V, 6- 0V, 7- 0V, 8- 15.3V, and 9- 0V. That's wayyyyyyy different from the schematic IMO!

So, that's telling me that even though the overall power brick reads "O.R. CT" on the tag (yes I know it's a cocktail brick when my machine is a UR), I think the filter assy is from "something completely different" (enter your Monty Python jokes here).

I guess that at this point I'm open to suggestions as to what my next steps should be.

Oh, on a brighter note (pun intended), I replaced the .5A fuse in the power brick and got my black light and waistline marquee light back on. WHEW!
 
Last edited:
This just keeps getting crazier and crazier LOL- the part number listed on the schematic for the OR filter assy is A945-00002-0000. It is a 9-wire filter assy. In my parts bin I just happened to have a filter assy from a Midway Kick that I parted out some time back.. The part number for it is A945-0000-0000. All of the voltages and wire colors match those of the one for OR, with one exception: the #1 pin is for a wire which is used as a ground on the OR filter assy (G-Y in color). The Kick filter assy does not have this one wire at all in the harness. Everything else is exactly the same! Can I use this one and somehow create a #1 ground wire for it like the OR would have? Man this is wak'd... (I've attached the Kick Man schematic showing the pinouts)
 

Attachments

  • kick_filterassy.jpg
    kick_filterassy.jpg
    86.7 KB · Views: 4
Wow no feedback. Aren't I the unpopular one LOL. Do I need to start writing poems about other KLOVers? :D :D :D
 
There is still no reading of any voltage at the 3 pin plug (the one that's disconnected from the linear PS). There is also no voltage reading across the 2A or 3A fuses while the game is powered on.

There should be voltage on that plug if you have 120 going into the transformer. If you don't then the transformer is bad. You can't measure voltage across a fuse. It's a dead short, it would be like putting your meter leads together, and expecting a reading other than 0

The only change that I have noted is after this most recent cleanup and check, I now have 8.8V travelling across the 4700 cap which is for the audio. However, in the meantime, I've lost power to my black light now, along with the waistline marquee light. This thing is like a one-armed bandit from Hell.

If you have 8.8V on the 4700uF cap, you have voltage coming in on the 3 wire plug. However your bridge rectifier is not fully rectifying the voltage you should have about 9.45Vac going into the bridge coming from the 3 pin.

I also checked the 2 fuses that are enclosed on the power supply (they go into little holders vertically) for continuity, and they check out as OK as well.

The 8, and 10A fuses on the filter, are for the 12,and 5V regulated power, and have no bearing on the unregulated 12V

Do I need to rebuild something on the power brick? Even if the 2A and 3A fuses were blown, I'd still see a voltage reading across the fuse holders when the game was powered up, right?

You would only see voltage across the fuses if the fuse was blown, if the fuse is good you will not get a voltage reading, as it's the same as touching both leads together, and trying to measure voltage anywhere, your leads are now shorted, and no voltage is passing through the meter.


If I am reading the attached schematic correctly, it's saying that 0V is going via the 3-pin connector to the linear PS board. Can someone help in confirming this?

No, what you are looking at is two separate secondary transformers, one is 3.15VAC, the other is 6.3VAC. The 0 you see is the low side, the schematic shows that both of these transformers are tied together, thus giving you about a 9VAC transformer.

And if I'm reading THIS attachment right, there should be no voltage going via the 3A fuse that's in the power brick. That means that the 2A fuse and the 3A fuse, which are both currently reading 0V when the game is turned on, are working as they should be, right? Again, I don't know why you'd have a fuse for a circuit with no voltage going through it but hey, I'll leave that kind of stuff up to the electrical engineers to explain :D

So if my conclusions are correct about these 2 fuses, then in theory, my transformer brick is OK. It doesn't explain though why my 5V cap on the linear PS isn't reading 5V (it's reading 0). I'm guessing that means I need to rebuild the linear PS, right?

The 3A fuse is for the incoming 120V. If it's bad nothing works. Also if the power switch is bad nothing works, if the interlock is not made nothing works.
Again, you cannot measure voltage across a fuse, you would need to remove the fuse. Because you are just measuring a dead short with a good fuse. You will not see anything.


After thinking a little more on this, it looks like tonight's task will be to check the 9 pin connection going to the linear PS from the filter assy, to see if any of the pins are not making contact with the linear PS. I will also be checking voltages coming from the filter assy to make sure they are where they are supposed to be....

Hopefully all of these thinking out loud posts are helping someone other than just me! :D

Yes if you have bad connectors on the 9 pin it will cause problems.

Think I may have found some new evidence tonight as to why my OR is having power issues.. First off, the colors of the 9-pin harness going to the linear PS do not match those on the schematic. I didn't really have a concern about that, so long as the voltages of the wires were correct. Well, they aren't...

The Pin out is
TOP
789
456
123
Bottom

1 GND Blue/White
2 8V Comm Orange
3 8V Comm Orange
4 8V Unreg Black
5 12V Comm White
6 15V Unreg Brown/Orange
7 5V Comm Orange
8 8V Unreg Black
9 12V Comm White

Replace the 2N2905A transistors (make sure they are A) on your linear supply
 
Last edited:
If you have 8.8V on the 4700uF cap, you have voltage coming in on the 3 wire plug. However your bridge rectifier is not fully rectifying the voltage you should have about 9.45Vac going into the bridge coming from the 3 pin.

Hmm, interesting- because when I have the connector unhooked and I put the leads in the 2 connector openings, I'm getting a 0 reading. But I think you have more hours logged on this stuff than me so I will take your word for it. :D

No, what you are looking at is two separate secondary transformers, one is 3.15VAC, the other is 6.3VAC. The 0 you see is the low side, the schematic shows that both of these transformers are tied together, thus giving you about a 9VAC transformer.

Thank you for clarifying that.

The Pin out is
TOP
789
456
123
Bottom

1 GND Blue/White
2 8V Comm Orange
3 8V Comm Orange
4 8V Unreg Black
5 12V Comm White
6 15V Unreg Brown/Orange
7 5V Comm Orange
8 8V Unreg Black
9 12V Comm White

Thanks for your reply Talon- I'm curious to know where you're getting the above wire colors, as the one that's on the schematic that I attached say it's from an OR upright (which is what I have), and as you can see the colors are totally different. I'll have to look tonight at the colors on the current filter assy, but they are definitely closer to what you posted than what's on the schematic. Only thing is, I only have 8 wires, not 9.

Replace the 2N2905A transistors (make sure they are A) on your linear supply

I will check these out and report back.
 
Last edited:
I'm getting the colors from my UR OR

OK, and just to confirm, your connector that goes into the linear PS has 9 wires in the connector? I'm trying to understand how I'm missing 1. I have the filter assy out of the game, will try to snap a pic of it tonight.
 
I've attached a rough drawing of how my connector matches to your wire order on yours. I'm guessing part of my problem is I was using the upper left wire (#7 according to your info) as my ground to test with. Now that I know what is supposed to be the ground (wire #1), and I know that I don't have that wire, I'm going to have to figure out what other ground to use to do my testing.
 

Attachments

  • Photo275.jpg
    Photo275.jpg
    70.5 KB · Views: 10
You voltages you've written look correct.
Comm is short for common, or Return, AKA Ground

Pin #1 is earth ground
Pin #7 is 5V return, or Sense line on the linear, it corresponds to the 8V ground.
 
You voltages you've written look correct.
Comm is short for common, or Return, AKA Ground

Pin #1 is earth ground
Pin #7 is 5V return, or Sense line on the linear, it corresponds to the 8V ground.

Well that's good news then! So if the filter assy is working as it should be, and everything appears to be getting voltage as it should be on the linear PS except the 5V cap and the resistor at location R20, does this mean then that it's probably the pesky power transistors you mentioned earlier needing replacement?

If this hasn't been a Midway power flow crash course for me, I don't know what would be!
 
Well techincally it could also be the LM305AH (Voltage regulator), Or the TIP31, or the 2N3772. But I've found more often than not, it's just the 2N2905A
 
Back
Top Bottom