No 12V, Midway linear power supply board in Omega Race (1981)

ifkz

ifkz

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No 12V, Midway linear power supply board in Omega Race (1981)

I have owned this particular game for years, it has had a few issues that I can't seem to squish. The coin door lights and marquee lights are inactive. I have given the power supply board new caps and I've fixed several cold solder joints. The fuse tests good, when the machine is on I can meter both sides of the fuse and they test the same. The 12V pot does not adjust any of the voltages. Any common failures? I wish Bob Roberts sold a rebuild kit....
 
I think Bob does sell a rebuild kit, or at least a cap kit, but if you're not getting 12v, first and foremost I'd check the fuses in the power brick again, with the power off. Remove the fuse out of the actual holster and check it, I"ll bet its bad.

If thats a no go, I think the next step would be to check or replace the 2n3055 (or whatever that big can transistor is on the big heat sink. You can get those and prob the 7805 transistor at radio shack.
 
part of my restoration was new fuse holders, and they all tested fine. Nice thought though. I noticed Bob doesn't stock the heat sink mounted transistors, looks like it's down to my local Fry's and some NTE equivalents.
 
All 3 of those transistors are very common and pretty cheap. They should have ntes or originals. I *think* (don't quote me on this) the 2N3055 is a 12v regulator, the 7805 is the 5v regulator and the other should be the -5v which I think is a....7905?

Also...very common on those boards is for the diodes near the black plug to burn up.
 
Looking at the schematics.....the 12VDC circuit is regulated by a 2N2509, 2N3772, and a LM305.

Edward
 
ifkz said:
I have owned this particular game for years, it has had a few issues that I can't seem to squish. The coin door lights and marquee lights are inactive. I have given the power supply board new caps and I've fixed several cold solder joints. The fuse tests good, when the machine is on I can meter both sides of the fuse and they test the same. The 12V pot does not adjust any of the voltages. Any common failures? I wish Bob Roberts sold a rebuild kit....
Click to expand...

LM305s are used as the regulators on those, with the big TO3s as pass transistor drivers....

He probably doesn't do a rebuild kit, as LM305s are $5-10 each if you can find them. (Or just rape them off other midway supplies.)
 
My bad I forgot thats a different MIdway power supply from the one I was thinking off (Sea Wolf/SI style). I gotta stop posting after 1am.
 
IFKZ I am now in the same boat. I found out last night that the PS in my machine does not match the one in the owner's manual. The 2 bottlecap transistors on the heat sink are supposed to be 2n3772's, and the PS should have 3 jumper wires by the CO2 9-pin connector. Mine's missing 2 of the jumpers, and the transistors on mine are 2N5301's :(

I wrote to Bob this AM to see if there is a rebuild kit for this PS. I'll let you know what I hear back if you haven't already done the work on yours.
 
vintagegamer said:
IFKZ I am now in the same boat. I found out last night that the PS in my machine does not match the one in the owner's manual. The 2 bottlecap transistors on the heat sink are supposed to be 2n3772's, and the PS should have 3 jumper wires by the CO2 9-pin connector. Mine's missing 2 of the jumpers, and the transistors on mine are 2N5301's :(

I wrote to Bob this AM to see if there is a rebuild kit for this PS. I'll let you know what I hear back if you haven't already done the work on yours.
Click to expand...


In this application.....2N3772's and 2N5301's are interchangable. Midway used both in their supplies.....whichever they had on hand at the time.

Edward
 
ELutz said:
In this application.....2N3772's and 2N5301's are interchangable. Midway used both in their supplies.....whichever they had on hand at the time.

Edward
Click to expand...

Wow interesting Edward- what about the jumpers, I would think those would need to be set up as on the schematic for the game to work properly, right?
 
vintagegamer said:
Wow interesting Edward- what about the jumpers, I would think those would need to be set up as on the schematic for the game to work properly, right?
Click to expand...

Which power supply do you have? You stated yours was different from the one called for in the manual. The manual calls for a 90413.

And what voltages are you getting?...or missing?

Edward
 
I am pretty sure mine is the A082 90413 D000 (don't have it in frt of me at the moment, but I matched it to the schematic last night and everything matched up with the exception of the bottlecap transistors and the jumpers by CO2 9-pin connector - I also remember seeing the D000 on the back of the board). Below is what I posted about voltages last night:



So tonight, I put a fresh fuse in the PS, disconnect the main PCB, and start all over again. I have the wiring diagrams in front of me, and for the life of me I just can't put together what's on the paper to what I have in the machine. It finally hits me that I can now test voltages across caps (something I didn't know how to do at the beginning of the year), so I start checking the caps on the PS... The big 4700MF (MF, appropriately named...) is reading a big fat ZERO.. I'm like "WHAT???!!" The other 2 caps read 12V and 5V. So, I'm thinking OK cool, I made some progress. I swap in the other PS that I have, and check the voltages on the same three caps... The 2 small ones read ZERO, and the big one reads.... .3V!! I'm like ah OK, maybe it's been the PS's all along! So I pull them both out of the game, and while looking at them I figure that since I'd noticed earlier in the day that there was a diagram of the PS in the owner's manual, I'll match them up to be 100 percent that I have the right PS... after all, it looks the same as the one in the pic, so it should be the same, right? (this is where things start going downhill)

Upon matching the pic of the PS up to what I have, not only do I notice right away that the bottlecap transistors are different (the ones in the manual show 2N 3772's, the ones on my boards are 2N 5301s.....), I also notice that on the pic in the manual, there are 3 jumpers shown near the top of the PS (at bottom when it's mounted in place in the game)- my 2 PS's only had 1 jumper... Immediately a 4-letter word beginning with the letter F came out of my face, and no it wasn't "fuse".... So, I'll either have to find the right PS already built correctly for this game, or I'll have to sacrifice one of these boards and rebuild it specifically for the game from a kit (I'll probably do the latter).
Click to expand...
 
Last edited:
vintagegamer said:
I am pretty sure mine is the A082 90413 D000 (don't have it in frt of me at the moment, but I matched it to the schematic last night and everything matched up with the exception of the bottlecap transistors and the jumpers by CO2 9-pin connector - I also remember seeing the D000 on the back of the board). Below is what I posted about voltages last night:
Click to expand...

The big 4700MF cap is for audio. Check for voltage across R20. If nothing there, you've got a blown fuse or a broken connection.

The other power supply board.....with no voltage on any caps.....well, at minimum, you've got three issues with it.

Have you checked all the associated connectors for "green" gunk from potential battery corrosion? That shit gets everywhere.....and seems to like imbedding itself into connector pins.

Edward
 
ELutz said:
The big 4700MF cap is for audio. Check for voltage across R20. If nothing there, you've got a blown fuse or a broken connection.
Edward
Click to expand...

I will definitely check that tonight, but I'm not seeing where R20 is on the schematic. Can you tell me where it's at?

ELutz said:
Have you checked all the associated connectors for "green" gunk from potential battery corrosion? That shit gets everywhere.....and seems to like imbedding itself into connector pins.
Click to expand...

I thought I'd checked everything but I'm sure I could have missed something.


I also just noticed the note on the schematic that says "for Omega Race, omit jumpers 1 and 3". And here I thought I'd found something :(

Thanks for your help!
 
I've given up on my 12V for now. I will say after replacing the three heatsink components, my video is very close to being stable (before, it had a mild bloom to it after it heated up).
 
ELutz said:
Voltage and ohms are two different things. What's the DC voltage across that resistor.

Edward
Click to expand...

darn i was hoping you'd made a typo, bc i checked dc volts first and it read 0, so i figured you'd meant to say ohms instead. So, w zero volts i guess it's time for a rebuild?
 
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