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7800 Mode Good, 2600 Not


gilsaluki
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Total my 2600 mode (for all intents and purposes) stopped working on my 7800. Sometimes I can get it to display by pushing the power sw. on and off a few times. Sometimes the display is black, sometimes scrambled, sometimes nothing in 2600 mode. Wondering if a flakey Power Sw. could cause such an anomaly. I did clean the cart slot. Once I turned the 2600 color pot (lower pot) a tad and the 2600 mode worked for a while (loading a series of 2600 carts). Put it all back together, then it went back to not working with 2600 carts. Any thoughts, previous experiences?

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  • 2 weeks later...

No replies. Well. I changed out the two 220 Caps and the 2200 (large cap) and replaced the on/off switch. I noticed that the LED would flash on and off when first powered on. Then the LED would eventually stay lite after a few tries. This was still leading to a power issue. At first there was a hiss sound that died off. Then after a few tries, I got video for both 7800 and 2600 games, great picture on my CRT. I put the board back together ( few minutes passing); DARN! Same symptoms. I read a few posts about similar lack of vid and sound. One poster asked the person having the issue if he was using a OEM or equiv. PSU. I was not using OEM. I got the 7800 minus the power jack. I soldered a 3.5MM jack and used a El Cheapo PSU from The Bay. It worked for months. I tested a known good 7800 PSU (the output was about 12VDC. The El Cheapo, 9VDC. So, I put the 3.5mm female jack onto the known good PSU; Wha LA! Fires up first time, every time now. Lesson learned, there was just not enough juice to power the 7800. Fixed.

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That's very good to know you got your problem fixed but something still doesn't quite make sense. The 7800 doesn't use a standard 3.5mm connector. It has a unusual rectangular 2-pin connector and a ridiculously thin cord to the power brick. The stock PSU is 9V DC 1A. That "known good" PSU may in fact be putting out too much voltage. The "el cheapo" is putting out exactly the spec voltage. It may not have the amperage necessary.

On the other hand, if your 7800 has been modded to use a 3.5mm connector, it's possible that mod has a bad or marginal connection internally, which is why the higher voltage is providing enough current to run the system with 7800 games.

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I suspect he was testing the power supplies without a load on them. In which case they would read higher than they would with a load. Regardless, the 7800 uses an unregulated power supply, it has an internally voltage regulator that spits out a nice clean 5v for the 7800 to use.

There is also no mention of the amp readings which is an important piece of the puzzle. Too low amperage will cause the 7800 to misbehave as well.

 

Gilsaluki, it is cool that you figured it out!

 

Mitch

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The Cheap-o PSU was 9VDC, 1000mA (or 1Amp). It worked for several months, then would not work without several power ups and power downs. I believe the caps needed repeated charging cycles. The Cheap-o voltage measured right at 9VDC (no load). Two of my real 7800 PS read 12VDC (no load). So, I deduced that the 9VDC is required under loaded conditions. The cheap-o PSU turned on the LED, but would not power the video or audio. With Cheap-o, once I got it powered up and down repeatedly, it worked well. If I turned it off, put in a new game, then turned it right back on...no problem. But, if I turned it off and left if off for several minutes (10 mins or so), then no go.

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