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The strange case of the 2600 that wouldn't power on properly


CrossBow

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This one was quite tricky and I'm still not 100% convinced this was the full cause. However, grab a snack and a drink cause here we go...

An older 2600 heavy sixer was sent for just a refurbishment and no upgrades. Basically just replacing out the components that come in a standard console5 refurb kit. But I immediately knew someone was off about this console before I even opened it up due the bulging I could see in the front facia switch section near the left side of the cartridge port?

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Upon opening it up I also found that whomever was inside this previously (and I know someone was), had also applied some very sticky foil tape around the RF modulator housing? I think this was done to improve the picture output as this H6 does have pretty poor RF output compared to most I've worked on.

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I actually removed this foil tape completely. Took the RF modulator from off the switch board and disassembled it. I then removed and applied new solder to all components on the RF board as much of the solder was looking pretty old and I could see what looked like old joints with some possible hairline cracks starting to form. This along with the refurb kit has improved the RF output a little but not as much as I've seen in the past. I suspect the RF modulator itself has some other issue going on but as it is the 3pin version, they aren't that common for replacements. Also the tuning coil in these appears to be locked in place as this one just didn't want to move and I didn't want to chance cracking the core trying to force it. So it is stuck in the position it was given from the factory around the channel 3 area. Some of my TVs did have issues locking onto this console's signal but of course the CRT downstairs had no problem with it.

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So what about the power issue that this Blog is titled for? Well, after doing all of this, the console still had a strange issue where sometimes when powered on, I would just get a blinking screen of snow and black...snow....black...snow...black. Something I hadn't seen before. Since you always ASAP electronics issues I first checked the input power which was given me a steady 13.2v on the input side. This would drop to about 12.4v when the console was powered on which, is to be expected for the additional load once the rest of the circuit is active. 

It was when I checked my voltages on the new voltage regulator that was also installed that I found something very odd! I was getting a 12.3v reading on the input pin of the VR which, again is quite normal, but what wasn't normal was that the output pin of the VR was showing 11v ?! It was then, using my meter that I found that somewhere the input and output pins of the VR were shorted. How this console worked in the past is beyond me because 11v off the output pin of the VR would also be getting sent to the mainboard in the metal housing and that can't be good! In looking at the old schemes for these boards the only spot I could see that might cause this was taken up by this rather large guy here:

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That is a 2w Allen Bradley style resistor. According to band colors, this is a 68Ω 5% resistor. I took it out of circuit and sure enough the short I was getting between the input and output pins of the VR went away. But the resistor was reading 71 - 72Ω which is within the 5% tolerance spec. But taking a chance I powered on the system without it and it came right up and appeared to be working just fine. I then left the system running moon patrol for about 8 hours yesterday to make sure everything was good. And it was fine. 

My understanding is that this resistor was added to reduce the current on the input going into the VR so it wouldn't get crazy hot. But the VR was replaced and I drilled a hole into the heatsink so I could use a screw and nut to secure the heatsink to the VR vs the clips that were used on these originally along with new thermal paste. That 8hour session of moon patrol did get the heatsink warm but not enough to burn as I could keep my fingers around it without it getting too hot for me to touch. So perhaps the older VRs couldn't dissipate the heat as well and this is why these large resistors are only present on the very early model H6 units. It might even be the first one I've seen that has one as most of the others I've worked on I don't recall seeing it present. 

Anyway, I'm going to power on and test this system again today to be sure it is still working properly but hopefully it is good to go, and ready to go back to its owner.

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Edited by CrossBow
Missing words and spelling issues that properly convey the context.

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