Missile Command Voltage Drops

kryptronic

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I've got a Missile Command which is having power issues. Intermittently, dark/shaded diagonal bands cycle on the display, and an up-and-down low hum comes through the speakers matching in rhythm with the display. This doesn't occur all the time, and usually only happens for about 10 minutes after powering on the machine after it's been off for a couple of days. Sometimes it starts fine then the problem appears after a minute. Sometimes a power cycle fixes it. Sometimes a power off, wait a minute, then power on fixes it. Sometimes it runs for days without an issue.

I was able to catch the issue once with the DMM hooked up, but only tested DC on the game board. DC at the game board is a steady 5.05V until it isn't. I saw it drop down to 4.75V. When it hit around 4.80V is when this issue kicked in. So what I'm seeing, it seems, is being caused by a voltage drop, and the culprit should be either the ARII or the power brick.

The ARII is marked as an -02 version modded to be an -03. I've only tested the ARII when the machine wasn't acting up. All the voltages were good, however AC ripple on the 10.3V DC test point was at 0.1-0.4V AC unloaded, and 0.8-1.6V AC loaded. I Replaced the 2N3055 on the ARII because the one on there was date stamped 82, and it's good policy to change it. Plus it can fix a voltage drop. I think the new 2N3055 made the problem more intermittent (less frequent), but can't say for sure.

Due to the measured AC ripple, this is now pointing to an issue with the Big Blue capacitor, which I was all set to replace today. I have a new Big Blue in hand - a 27,000uf 25V capacitor. I pulled the MC power brick, which is the Type B Power Supply Assembly A007197-01. The manual calls for a 26,000uf 15V capacitor for that power supply. Oddly, the capacitor installed in the power supply (which was installed by the previous owner) was a 26,000uf 30V version.

QUESTION: Knowing that the manual calls for a 26,000uf 15V capacitor for my power supply, would the 27,000uf 25V capacitor that I have on hand here work? I don't know enough about this stuff to know whether or not you can use a higher numbers for either or both voltage and capacitance. Can somebody school me on this, please?

Also, I just wanted to add that this machine has it's original G07 with significant MC burn, and I've never trashed a chassis.
 
Also, I just wanted to add that this machine has it's original G07 with significant MC burn, and I've never trashed a chassis.
🤣 I think this forum has MC question trauma at this point…

I know you can use a higher voltage than the original rating. I don't believe you can substitute a higher capacitance but I would defer to the experts here on that. That's only about a 4% variance from the spec'd unit but I don't know how significant that is. My guess is the advice will be "get the right replacement."

Best of luck!
 
Clean and inspect all connections.

Especially the fuse block and tabs.
yep, the 20A fuse quick disconnect will undoubtedly be crispy brown on the right side. sometimes the fuse holder itself will be burned up. I encourage taking the metal power block out and inspecting the bridge rectifier wiring inside also, I've had several location games over the years where these weren't good.

remove the plastic edge connector from the game board, inspect the edge contacts. if any are burned up or flaking off, that's a problem too. and breakdown in the aforementioned connections will lead to increased heat and do damage.
 
Clean and inspect all connections.

Especially the fuse block and tabs.

yep, the 20A fuse quick disconnect will undoubtedly be crispy brown on the right side. sometimes the fuse holder itself will be burned up. I encourage taking the metal power block out and inspecting the bridge rectifier wiring inside also, I've had several location games over the years where these weren't good.

remove the plastic edge connector from the game board, inspect the edge contacts. if any are burned up or flaking off, that's a problem too. and breakdown in the aforementioned connections will lead to increased heat and do damage.

Thank you both. I did clean the edge connector and all molex connections already, but forgot to mention that.

This this the type B Missile Commend power brick, so it doesn't have a fuse block or bridge rectifier. It"s different than a regular raster Atari brick.

Is the Big Blue I have OK to use?
 
That big blue is ok to use. For caps, you want the voltage rating to be equal or higher. And you want the capacitance to be roughly the same. (How different it can be depends on the circuit it's in. But for this case, 1000uF difference won't matter.)

Also, before you do that I would replace the pot on the AR (or hit it with DeOxit and work it back and forth a few times). Those can cause stability issues. Or, if you have any other AR, you can try that as well in the cab. (Any AR-II will work, you just won't be able to plug in the speaker connector, but that's ok. Just plug in the two other connectors for the 10.3V input and 5V output. Connect nothing to the right side of the AR.)

This is one of those problems where you want to narrow it down as much as you can before replacing parts.
 
Right on. Thank you. I'll clean that pot on the ARII, and am going to put in the new big blue sometime this week. I'll post back.
 
Do one at a time. If the pot fixes it, then there's no need to replace the big blue.

It's hard to tell from your big blue measurements if it's bad or not. Also, your 'loaded' measurements were higher than unloaded, which is odd.

What does loaded mean? (i.e., loaded with the AR, or with the game board plugged in?)

Also, what type of DMM do you have?
 
Do one at a time. If the pot fixes it, then there's no need to replace the big blue.

It's hard to tell from your big blue measurements if it's bad or not. Also, your 'loaded' measurements were higher than unloaded, which is odd.

What does loaded mean? (i.e., loaded with the AR, or with the game board plugged in?)

Also, what type of DMM do you have?

When measuring the 10.3V DC on the ARII, I tested it as "loaded" by having the MC PCB hooked up and the game running, and "unloaded" without the PCB hooked up. Perhaps that wasn't right, but that made sense to me. I'm still learning.

I had the brick out and the big blue pulled last night before I realized it was a different spec capacitor. I was thinking I might save save a step by replacing the big blue now as the brick is out. But I can put the big blue that was in it back in, and can just clean the pot on the AR and see what's up. Unless you come back to me and say that AC ripple is actually bad the way I measured it.

My DMM is a Fluke 15B+, which I trust.
 
In that case 0.8-1.6 *volts* of AC ripple is too high. The big blue might be bad.

If you have any other working Atari game, you could do the same ripple measurement on it. Just to get a benchmark, and confirm what a 'normal' measurement looks like on your DMM.

Type B bricks look different, but don't work radically differently from the later version bricks. So generally speaking, their measurements should be similar.
 
I'll do some testing and cleaning. I've got a couple of machines I can use as benchmarks to confirm my readings. I should have thought to do that before.
 
The cap is fine to use as a replacement.
 
Alright. I think it may be fixed, but due to the intermittent nature of the problem, I'll have to wait and see. It looks really good right now, though. AC ripple is where it should be now. I ended up with a spare hour this afternoon at work, so I jumped on it.

- I am certain my initial AC ripple measurements on the 10.3V DC test point were done correctly, and saw 0.1-0.4V AC unloaded, and 0.8-1.6V AC loaded. I did the same exact test procedure this afternoon on my Centipede and read 0.140V AC unloaded, and 0.030V AC loaded on that machine, which are expected/normal results.

- I did another deoxit treatment on all the molex connectors on the power brick, ARII and their respective harness connections. The edge connector was gone over thoroughly a few weeks ago (deoxit and fiberglass pen treatment) so that was definitely good already. I also put deoxit on the pot on the ARII and turned that several times today. Proper cleaning done.

- I put in the new big blue capacitor rated at 27,000uf 25V. I appreciate you guys confirming that would go in without causing an issue. It looks like this is the standard size capacitor that places like APAR and Arcadeshop are selling now as big blue replacements.

I dialed in the ARII so it was sending 5.05V DC to the game board (verified at the PCB). I then tested AC ripple on the 10.3V DC test point on the ARII and saw 0.177V AC unloaded, and 0.031V AC loaded. So that looks the way it should now. As an added bonus, all the hum that used to come through the speakers is totally gone. It was a little louder than most of the Atari machines I have and I have been wanting to dig into it. But that is gone and solved now, too.

The only other thing that I have to add is that the previous owner told me he had replaced the big blue prior to selling me the machine. Everyone says these rarely go bad, and I was really trying not to make an unnecessary change by replacing a good part. I put off replacing it, and instead cleaned everything and replaced the 2N3055 and the issue persisted. The failed big blue in there was a 26,000uf 30V unit marked "Sprague Powerlytic (R) 360X 81L31L". I can't say for sure, but I am guessing it's a cheap replacement unit, and if the machine had it's original big blue it probably would have never developed an issue. Just a thought.

Thanks to @andrewb, @ccie38296 @mecha and @ArcadeTechGW for the help. You guys are awesome.
 
A bad 2N3055 would not give you excessive AC ripple.

A bad filter cap will.

If it was a "vintage" cap, it could do that. What is the date code on the cap?
 
If it was a "vintage" cap, it could do that. What is the date code on the cap?

The cap I pulled is marked '11', so I'm guessing 2011. It was newer and shouldn't have failed, but was likely a low quality replacement.

I had the machine running most of the night last night without any issues. Now I can chase my high score without worrying about having to power down halfway through a game. It's time to put up some points.
 
The cap I pulled is marked '11', so I'm guessing 2011. It was newer and shouldn't have failed, but was likely a low quality replacement.

I had the machine running most of the night last night without any issues. Now I can chase my high score without worrying about having to power down halfway through a game. It's time to put up some points.
Well done.

TTL logic doesn't do well with AC Ripple. It runs at 1 - 5 volts, so a high ripple makes the 0's and 1's look like gibberish.
 
Posting a follow up here... I replaced the big blue in Missile Command almost a month ago. Since then, the machine has been fired up and played several times a week, and is usually on for a couple of hours at a time. I haven't had any problems with the machine since, so I'm considering it fixed. Thanks again to everyone for your help.
 
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