AC transformer help

YODAinMN

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I'm getting a Midway MK2 cab back in order and wet to Menard's today to replace the marquee bulb. Installed it and, flash-- gone. Took another working bulb to be sure and the same thing happened.
I checked the AC at the connector at the light assembly and it's reading 137.5 Volts. Checked it at the switcher and at a open connector at the transformer block with the same result. What could be causing the voltage to be stepping up from 120V?
I don't want to screw up the monitor so I unplugged everything. I checked voltagess on the switcher and everything on the DC output side is correct, just having some over-voltage issues on the AC. Outlet in the house is normal additionally. The bottom of the Txsformer has the AC line filter coming in. What would be the correct pinouts to trace back to the original 120v? thanks!
 
Is this a flourescent tube bulb? If it is then the problem is more likely your ballast, not the higher AC power. Take a resistance measurement across the two wires that come out of the ballast, the reading should be around 25 ohms.
 
So the 137V shouldn't be a problem elsewhere like to the monitor and switcher? I just want to cover my bases here. I'll get a read on the ballast now and report back!
 
So the 137V shouldn't be a problem elsewhere like to the monitor and switcher? I just want to cover my bases here. I'll get a read on the ballast now and report back!


The 137vac is likely a non-loaded condition and will drop off when the load(s) are applied. This should be the same voltage reading you see coming out of the iso.
 
The 137V was at the connector on the florescent connector with the game powered up. Checked the schematic on the transformer pinout and all that looks correct as well as the jumpers on the opposite side of the transformer connector for 120V. Now, I'm really starting to scratch my head on this.. Are you sure the load is supposed to drop on the AC side, It wasn't doing that at all with the game running?
 
I just don't want to eff up the switcher and the monitor on this beast...
 
It is not unusual for the iso to output a slightly higher voltage. The loads, if the iso is powering everything, will be the monitor, the marquee, and the switcher. The monitor is the largest load by far. I understand the concern about trashing the other components, and the iso may be messed up, but I doubt it is. Do you have another iso you can throw in there for now?


What did the ballast read?
 
Have not tested the ballast, going to do that now-- I guess the switcher can handle the extra voltage. I have no other Midway iso transformer assembly to drop in to test-- wish I did. Or maybe someone else could test theirs and see if the reading are similar to what I'm getting? I rechecked and double-check the pinouts again too and everything looks correct compared to the schematic.
 
The input for that transformer may be configured for 110v. If you are putting 120v into it, that would be about a 10% increase in input voltage. Add that 10% increase to the output 120v + 10% = ~ 137 volts.

Might want to check the schematics for the transformer and see if there are different input settings for the AC.
 
If the tube blew out right away then you have a shorted ballast plain & simple. Replace the ballast, tube, and starter. The tube and starter were destroyed by the bad ballast.
 
Thanks Ken,

I'll give that a try on the bad ballast.

On the AC configuration, it is the same as was set from the factory for 120V. I checked the wiring harness as well as the harness on the jumper. Yes, you can change the settings to 110, 120, 135v, etc. etc. I wanted to be sure of this.
Fortunately for me, the manual that I ordered for it came in the mail this afternoon. Maybe I'm just being too anal. I'll give the ballast a switch tomorrow and see what happens after I plug everything back in and re-check it under load.
 
Thanks Ken,

I'll give that a try on the bad ballast.

On the AC configuration, it is the same as was set from the factory for 120V. I checked the wiring harness as well as the harness on the jumper. Yes, you can change the settings to 110, 120, 135v, etc. etc. I wanted to be sure of this.
Fortunately for me, the manual that I ordered for it came in the mail this afternoon. Maybe I'm just being too anal. I'll give the ballast a switch tomorrow and see what happens after I plug everything back in and re-check it under load.

Well, if you want to drop the voltage a little......change the transformer to the 135V setting.

Edward
 
Or possibly replace the batteries in your meter. Low batteries mean improper voltage readings...
 
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