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mojoatomic

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mojoatomic last won the day on March 2 2017

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  1. On both 6 & 4 switch systems, ripple current plays a very large roll in picture quality and longevity of components. Especially on the 2 input caps, which are .22uf on the 6 switch and .1uf on the 4 switch units. Sometimes seen in pairs, sometimes not, based on the rev level of the board - we'll get to that :-) Further, electrolytic caps degrade from spec after about 10 years - weather they're in service or not. Electrolytic caps have a shelf life, and that big fat 2200uf filter cap can cause some nasty issues with your picture for sure. That little .47uf cap will put a snowstorm and bright spots on the screen as well. Recently, I've seen MANY folks converting to composite on these systems, with mixed results. Not all AV kits are created equally and some are better than others, but simply shotgunning one of these kits into a 2600 is unlikely to solve the underlying issues the unit has. It's a garbage in, garbage out principal. Simply changing from RF to composite won't do you much good if your still amplifying line noise and ripple by pushing a signal through failed caps. Besides that, a properly adjusted 2600 with a good RF cable can be crystal clear. I'm more of a purist, but that's just me. The same principal and outcome will hold true for RF or composite. There's another issue, and it relates to the filter or "snubber caps" as they're sometimes referred to. Here's the real deal - they're sacrificial. They're purpose is to take the hit and protect the voltage regulator, 2200uf filter cap and the 9v unregulated reference downstream (on the 4 switch models). As they take hits over the years, they break down and ripple current begins to bleed through - breaking down the 7805 5v voltage regulator. On a final note, Atari was cheap, but unpredictable. They cut corners in some places (removing components) and adding strange ones (aluminum shielding on the 4 switch switches during service and later factory installed). One of the price cutting measures they took was to remove a blanking resistor from all 4 switch models up to version 16 on the boards. This resistor had existed as an 680ohm part strung between pins 6 & 9 of the TIA chip and added those eye popping colors we love so much. In 1982, Atari released a service bulletin "Tech Tip 4" that gave service guys the option of adding this resistor back as an optional billable part during service. In practice, we just added it anyway because the cost was negligible and we were in there anyway, and it makes a HUGE improvement to the picture quality on 4 switch units. The tech tip specified an 820ohm resistor was to be used, soldered between pins 6 & 9 of the TIA on the underside of the board. The last high failure point is the power jack - they should have used Switchcraft jacks, they were making them at the time, but they cost a bit more. Here's how to fix all of it. On the Heavy sixer Switchboard: Replace C103 & C104 with a .22uf 100v or better mylar cap - regardless of what you find there. Replace C106 with a 2200uf 16v or higher electrolytic cap Replace A101 with a 7805 Voltage Regulator Replace C105 with a 4.7uf 35v or higher electrolytic cap Mainboard: Replace C201 with a 4.7uf 35v or higher electrolytic cap Replace J201 with a Switchcraft jack On the Light Sixer Switchboard: Replace C103 with a .22uf 100v or better mylar cap - regardless of what you find there. Replace C106 with a 2200uf 16v or higher electrolytic cap Replace A101 with a 7805 Voltage Regulator Replace C105 with a 4.7uf 35v or higher electrolytic cap Mainboard: Replace C201 with a 4.7uf 35v or higher electrolytic cap Replace J201 with the Switchcraft jack 4 switch units - both woody and Vader variants rev 1-16 Replace C241 & 242 with a .1uf 100v or better mylar cap - regardless of what you find there. Versions 8's will almost always have ceramic disk... replace them with mylar. Replace C243 with a 2200uf 16v or higher electrolytic cap Replace A203 with a 7805 Voltage Regulator Replace C201 & C214 with a 4.7uf 35v or higher electrolytic cap Replace J201 with a Switchcraft jack IF you have a 4 switch unit AND your board revision level is LESS THAN version 16, install the 820ohm resistor between pins 6 & 9 of the TIA chip on the SOLDER SIDE of the circuit board. Other things to do while your in there... On 6 switch units: reflow solder on the cables connecting the swithboard and motherboard. The flex and move every time the unit is moved. All units: Have a look at all of solder points on the 3 big IC's (CPU, TIA & RIOT) and reflow the joints if you need to. Pro tip - almost ALL TIA chips need a reflow - cold or cracked joints here will give you a very ratty picture, even if the unit is functioning. Flow new solder on the connector for the RF unit. (3 or 5 pin) Reflow ALL pins on the joystick ports and switches. Disassemble and clean or use contact cleaner on all switches. There were 2 types of switches used for channel select and difficulty - one is easy to take apart and clean... the other you're better off just replacing it. Unless you have a need to - I.E. no sound... STAY AWAY from the 2 polystyrene sound caps @ C206 & C207 - they are devilishly hard to solder without damaging them if you don't know your you're doing, and unless you use temp control on your iron and a clipable heat sink on the upper leads of the caps. In order of failure - RIOT, TIA and then CPU - just speaking from my experience here, YMMV Image below shows where to solder the 820ohm resistor on 4 switch boards. I've posted SOME of this recently elsewhere, but I hope some folks here can make use of it -
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