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TheSolderMonger

Explosive Fairchild Channel F problems

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Hello again AtariAge! I've got another project needing your assistance!

 

I recently acquired a Fairchild Channel F from a game fest in Austin and when I tested it, the game came up with some glitching but quickly vanished, with the TV losing signal. I saw a capacitor was leaking and replaced it with with a capacitor of the same capacitance, voltage and direction, and when I powered on the system, the TV made buzzing noises and the 25V 1000uf Capacitor I replaced is suddenly hot to the touch and then blew! Now I don't know if the voltages are off from the actual brick adapter or the internal switch bank caps are bad.

 

 

 

Has anyone with a channel F had this issue?

 

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I have reason to believe that the larger 2200 uf capacitor is bad, I measured both it and the blown cap, with the 2200 uf measuring at 9V while the 1000 uf (blown) is measuring 19V. Perhaps a bad 2200 uf cap caused the smaller one to overcharge and therefore blow. I'll have to wait until the replacement 1000 uf caps come in before I try again.

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Update: Soldering a new 1000 uf and 2200 uf capacitor doesn't seem to be solving the problem. The 1000 uf cap in particular heats up extremely fast and I have to constantly shut the system off before the cap blows.

With that, I have a new theory: The original owner had replaced the cap in the wrong orientation, causing it to blow and then giving up before selling it. With that, I ask that someone with the Channel F System 2 attach a picture of the switchbank area, where the 2 capacitors are, with the directional bands on the caps visible. I myself will attach a picture of my board and see if it matches with other machines.

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Update: I fixed some broken solder joints on the switchboard area, but the capacitor blew AGAIN! Funnily enough, the sound works, I hear the pong sounds coming from the system, but when the cap blows it goes away? So either the capacitor is in the wrong orientation or my Channel F's PSU brick is shot. I really need you fellow channel F owners' help. I don't know what the voltages are for the Red White and other Red lines, though when I measured them Earlier they all measured about 10 volts.

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yeah it looks like he inverted both caps, the arrow points this way so I'll point the new arrows the same way

That'll ruin your day

post-5598-0-59216100-1533522004_thumb.jpg

Edited by masschamber

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yeah it looks like he inverted both caps, the arrow points this way so I'll point the new arrows the same way

That'll ruin your day

 

I thank you so much, however this problem (see attachment) still seems to persist after re-aligning the capacitors and powering the system on for a few seconds with or without a cart installed. When I power the system on the game shows up with a bit of garbage but then the picture goes to this line and then the TV loses signal.

post-65010-0-68191300-1533525186_thumb.jpg

Edited by TheSolderMonger

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dead minimum it probably burnt out a regulator

 

Can you upload a picture of where the regulators are?

 

That other smaller cap below the 2200uF jobber looks bulged and is likely bad.

I replaced that capacitor later after the picture was taken, it was no good.

Edited by TheSolderMonger

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Replaced the voltage regulators and the problem still persists.

Can you provide a picture of the regulators at the back to make sure that these regs weren't put in the wrong way.

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Update: The issue at hand seems to be caused by a thermal problem, however the 1976 service manual screenshot 104 seems to match with my earlier uploaded picture of the white line, which points to a faulty PSU. I'm inclined to believe that the PSU is normal, and that the regulators may be in the wrong spot, as the UA7812 regulator is hot to the touch after the TV loses signal. Prior to the signal cutoff, with the regulator cold, the system works just fine until the regulator heats up, and likely causes a drop in the 12 Volt line? (Again, I'm not sure if the regulators are even in the right spot.)

 

I would greatly appreciate if masschamber could upload a pic of the regulator setup, because if the person who last serviced the machine put the capacitors backward, then I am likely to assume the regulators were also put in incorrectly.

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I can't get at the board without removing the rf shield and since it is wrapped around the eject button I don't want to break it, could you upload a picture of your mother board and the power switch daughter board?

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I can't get at the board without removing the rf shield and since it is wrapped around the eject button I don't want to break it, could you upload a picture of your mother board and the power switch daughter board?

 

Sure thing, attached below is the daughter board and the regulator arrangement. The regulator on the left is a UA7812 and the one on the right is a UA7805.

post-65010-0-58545300-1533783781_thumb.jpg

post-65010-0-67875100-1533783796_thumb.jpg

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I don't know anything about the system but the regulators look like they are in the correct way round to me as the metal heatsink tabs are against the metal case so that the heat can be dissipated through conduction.

 

As the regulators appear to be the correct (not back to front) way around there are generally 3 reasons (which apply to any systems) as to why it may be getting very hot...

1) It is Damaged - replace it.

2) Something is drawing a lot of current, you could try the finger test if you do not mind getting burnt, or but a can of freezer spray, spray the board then power on, those parts that are drawing lots of current & getting hot will defrost the quickest.

3) Although the regulators are in the correct way as in not back to front, they may not be the correct way round in regard to which is on the left and right. Can you tell if the main power in is going to both of them or just one/

If it just goes to one then I would expect that to be the 12V regulator the output of which then supplies the 5V regulator (less power dissipation than running directly of the higher primary supply voltage of 19V, i.e. 19V down to 5V @ 1A = 14W = thermal shutdown, 12V down to 5V @ 1A = 8W = operational). Also if the 12V regulator is supplying the 5V regulator and they have been switch round when replaced the 12V rail would only be at 5V maximum.

 

If you have a multimeter to measure the regulators input and output voltages might reveal something.

Edited by Stephen Moss

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I measured the Input/output voltages and with that, the UA7812C regulator is regulating 23.3 volts down to 12.19 while the UA7805C is regulating 11.63 volts down to 5.03 volts. What I may do is to use a small heatsink over the regulator, and if the heat dissipation keeps the system on and working then the problem lies in the regulator or at least narrows down the power path to the regulator.

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Update: Applying thermal compound and a small heatsink did nothing to improve the picture. I still smell electrolytic fluid coming from the daughter board, even after cleaning a good portion of the leakage. Now I need to soak the daughter board in alcohol and see if it changes color, if it does, then there was electrolytic fluid possible conducting power where it should not be going.

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Yet another update, there was some residual electrolytic fluid on the daughter board, and there was a capacitor on the main logic board that had 1 leg unsoldered, and with that the problem still persists, though I may disassemble the switches themselves as a couple of them don't make clicking noises, perhaps stuck buttons cause glitching with conflicting instructions?

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When I setup my channel F on my CRT instead of the flatscreen, I saw that the signal persists, but this is what the problem causes the picture to do. Could this have something to do with the RF circuitry? Or would this have to do with power and/or thermals?

post-65010-0-41211800-1533841850_thumb.jpg

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I would check out the output over your power supply, it should be 18v and if 22 is reaching the regulator it might be high

I did measure 10 volts from all 3 pins from the PSU brick to the daughter board. Can you measure your PSU output voltage from the brick?

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