DOH!
10/3/2004 12:10:20 PM
Ok, brain fart time... After replacing a part the (D44H2 on the Heat Sink), I realized that I was working on the Power Supply section of the Jr Pac board rather than the Audio section. DOH!
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10/3/2004 12:14:00 PM
Well, now the Jr. Pac board has a brand new NTE377 on it, even if it didn't need it! Won't hurt anything, and it's a cheap mistake ($2). Guess I should pay more attention :-)
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10/3/2004 12:16:00 PM
So now, we start looking at the correct section of the board, which is the opposite side of the board, I noticed that the LM377N (which crosses to an NTE990) is VERY hot. and the bottom looks a bit burnt.
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10/3/2004 12:18:00 PM
My plan is to find the part tomorrow and replace it. I will put a socket in it's place since I want to avoid burning up that part of the board anymore.
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10/8/2004 12:18:00 PM
Well, I replaced the Audio AMP (LM377N/NTE990) and I'm still getting a Humming noise. Another $5 down the drain :-) Knowing my luck it's going to be something like a dirty edge connector.... Time to start looking at other items.
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10/9/2004 12:26:00 PM
Replaced the cap at C29 (2200uF @16V) with a Radio Shack Part (272-1020) and the Hum is still there. Total in parts so far is about $14.Also cleaned the edge connector and the same results. Back to the drawing board...
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10/10/2004 12:29:00 PM
Replaced all the caps except the two 10KuF @16V, and it still has the Hum... Will be getting the two 10K's from Bob Roberts this week and will replace those. I'm not all that confident that it will help anything, but might as well replace them too.I replaced the cap marked as 330uF @ 16V with a 470uF@35V as that is the closest I could find. It doesn't appear to have any ill effects on the game, so I'll leave it in. Since replacing the cap didn't have any affect on the game, it's safe to assume that the original cap is still good. Since it's an oddball size, I'll hold on to it. The old 470's will get trashed. So that's another $5 down the tubes today in my quest to rid Jr Pac of the Hum. So I'm up to about $20 in parts so far and it's still not fixed. It will probably turn out to be something that I could have fixed for free, or it may turn out that I'll just live with it. I'll keep going for now though. I also noticed something odd, in that the Audio Amp that I replaced was a LM377N while the Jr Pac Schematics show it as an LM378. If anyone knows if these are compatible or not, please let me know. If that part is wrong, that could explain a lot of things!
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10/12/2004 12:31:00 PM
Ok, just for the heck of it, I wanted to see what would happen if I replaced the 330uF with a 220uF rather than the 470uF. What happened? Nothing. The game works just the same with the 220, 330, or 470uF in there. Not sure why they used a 330 there, but it doesn't appear to be critical to the game functioning properly. New 10,000uF caps arrive Thursday.
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3/6/2013 12:32:08 PM
10,000uF caps arrived today. Replaced them, and as expected, nothing changed. I still get the hum. It also sounds like there is static/white noise in the background.So at this point the majority of the Power Supply has been replaced and a portion of the Audio section has been replaced. Without an Oscilloscope at this point, I'm not sure where to go from here. I've posted a message on USENET in hopes that maybe someone can suggest something to try.
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