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.
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.


