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Recapped Astro city psu. Then monitor died

VodkaGobalsky

VodkaGobalsky

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Help, I recapped my Astro city psu and plugged it back in again. The machine turned on okay for 5 minutes and then the monitor shut off. It’s not coming back on again. My psu is 400-5261Y. I tested the machine with a second psu I know that works fine and the monitor is not coming on so I definitely think it’s the monitor that has the issue now. I don’t want to risk putting the psu I recapped into my second machine and having it kill that monitor too. Could the recapped psu have caused some sort of power surge that killed my monitor? The red 5V indicator LED is on. Not sure if that matters or not.
 
Your monitor is powered by AC. Your PSU outputs DC. I think you just had bad luck.

Just to double check, is your game playing blind if you turn it on? Can you hear sound effects?
 
Not having much experience with that monitor, I can’t say for sure, however, I thought monitors pulled power directly from AC and not the PSU.

Edit: what Nem said 👆
 
Annoying that it worked fine for 5 minutes and then started blowing things up - oh the joys of vintange hardware. The number of times I've done some quick tests, smiled to myself and thought "jobs done" only to have it crap out on me a few hours or days later....

Astro City monitor boards are normally a Nanyo MS8, but i've seen a lot of folks also have MS9's in there. The MS9 is a better electral design from a safety perspective. If it's easy to find the chassis model number that info might be helpful too.

This is an extreamly weird one because the monitor is not directly powered by the PSU - the PSU takes approximately 100v AC and converts it into +12v, +5v -5v DC. It mainly just passes the 100v AC voltage for the monitor through.

You can find the schematic for the 5261 here, but as noted above I dont think your problem is in the DC section
https://segamadebaddecisions.wordpress.com/category/astro-city/

For this reason I'd start by probing the output voltages on the PSU and see if it is actualy producing +12, +5 and -5 DC as expected, and also that the input voltage (approx 100v AC) matches the output voltage from the PSU for the monitor (100v AC).

Probing what could be mains voltages is reasonably safe, but its still not a day at the beach, the pinout for the 5261 is here
https://wiki.arcadeotaku.com/w/File:400-5261-pinout.JPG

It's the pins labled OTL (100v AC out Live) and OTN (100v AC out Neutral) that are of particular interest.

Also worth checking your grounds at this point - in my part of the world we are 240v mains power, all of the cabs here were fitted with some flavor of transformer when they were imported. Sometimes these are step-down transformers that pass mains earth, sometimes they are proper isolating transformers. Floating earth can cause all sorts of strangeness if the earthing is coming from the metal chassis of the cab

From there I'd look at the fuses in the power supply, there will be a big 4(?) amp one in the AC section, and a smaller 2(?) amp one in the DC section on the 5v line.

Then I'd start checking the buttons on the front - if this PSU is destroying monitors then a stuck degaus/demag button will do that too
 
I checked the DC. The 5V looks okay but I’m not getting anything from the 12V. I’m also not sure if I’m checking the VAC correctly. I’m not seeing 100V. I see 16 and 0.6. I also hear a slight buzz when I turn on the psu versus the other one which makes no noise. The capacitors I replaced didn’t all match exactly with the voltage but the capacitance matched. Some voltages are higher which I was told would be okay. If the VAC is a pass through, would I be able to plug the power plug straight into the monitor power port to test it?
78B11073-187D-4F21-AC3A-8B9D8E9587FB.jpeg
 
As a general rule of thumb the capacitance needs to match, the votlage can be the same or higher. I guess if we were industrial designers the difference between a 16v cap and a 25v cap is 3 cents per unit, 3 cents times a million units adds up. But for hobby use not so much.
Same with resistors, the resistance needs to be the same but the current (wattage) can be the same or higher. Which is handy with resistors because they dont always mark the wattage and the only way to test them is to blow them up. So you kind of have to guess based on size.
There are some exceptions to this that i have read about but never seen IRL, mainly in amps and audio circitury where the voltage/wattage DOES make a difference. But for the kind of work we do I've never seen it

We'll come back to the 12v thing later, as long as it's producing 5v it's alive somewhere so that's a good start

The 100V thing could be because your multimeter is set to DC (straight lines), if you want measure AC you'll need to flick it over to AC (wavy lines) to get sensible readings. The number of times I've thought "thats weird" before remebering to change the current...
Some multimetres are Auto ranging, if that's the case with yours it will manage tyhe AC/DC thing automagically. it will hopefully correctly identify AC on the display when you are probing the AC pins.
But generally if I'm getting unexpected numbers out of my meter it's because I'm testing an AC source with the meter set to DC

The buzz coming from new caps on the PSU is them gently cooking themselves into their new life. Did you change the monster filter cap too? (I think there is a big 470/250 one in there somewhere?) those things can make a hell of a racket for the first few weeks. Incidently if you ever see a power supply with hot glue or silicone glued all over the filter caps it might have been done to stop them buzzing.
 
Yes I changed the large filter cap as well. I was wonder what that glue stuff was. I see now.
 
From the working psu, I’m reading 59V out of OTL and 58 out of OTN. From the recapped one, I’m reading 62V out of OTL and 55 out of OTN. They also match the input VAC.
 
You're measuring it wrong. It's AC, not DC. Red meter lead on live, black on neutral (or vice versa). You should see a full ~120V on both connectors.
 
I put it on AC. The neutral line is in the middle right? Or just ground like chassis casing?
EC344F7B-9C9F-4D33-87FE-10C42C24B0A1.jpeg
 
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OTL is live, OTN is neutral.

Connect a PCB and measure your DC voltages from the jamma edge.
 
The DC voltages seem to be fine. I’m getting all the right voltages besides the -5 seems to be around -2~-3v
 
Okay I’ve measured all the values and decided to try out the psu on my working monitor and the psu is working fine it seems. Maybe I just had bad luck and the monitor decided to die on me. Looks like I’ll just have to take that chassis in and get it looked at and repaired.
 
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