Fairchild Channel F Repair - Help Request

[+KylJoy]

Hi,

 

I bought a Fairchild Channel F since I was told that it worked fine. But...

 

SURPRISE!!!

 

It doesn't.

 

So, the primary symptom is that the unit doesn't SEEM to be operating at all other than displaying garbage. The good news? The display of garbage is pretty crisp, clear and colorful. From what I have found online I understand that you should be able to hear the system playing hockey by powering it up, pressing 1 and then pressing 4. I get no BEEPS or BOOPS if I try to start a game. The speaker does output an occasional GLEEP when I power the unit on so it seems to be connected and functioning. The screen most often shows random color and dot patterns like...

 

 

...and has very rarely shown a half-black/half-white screen, a half-green/half-orange screen (or was it another color with green?), or even, once or twice, an all grey screen. Here's the all-green screen:

 

 

I am on a mission to repair this thing, even if I have to socket every chip on the board. Here's what I've done so far:

• replaced all electrolytic capacitors (some were measuring out of spec so I just replaced them all)
• re-flowed all IC solder joints and most of the others (looked ok, but you never know...)
• replaced all four RAM chips (with MK4027N, someone let me know if those are wrong)
• pulled, polished pins and re-seated the 3 large, main, 40 pin chips
• replaced the 12v regulator (7812 was measuring at 11.5, should have been OK but what the hell...)

And, after all of that... NO DISCERNIBLE DIFFERENCE. Well, to be fair, there are nice voltages all over the place and very clean pins on chips now. But it still ain't workin'.

 

The 12v, 5v, and -5v all measure fine at the various ICs and RAM chips. That is, unless someone can tell me if -4.6v is enough of the -5v.

 

Does anyone know where I should look next rather than starting to delve into all of the logic chips? Any suggestions welcome. Could someone sell me or LEND me the three main chips to swap out? I'm talking about these guys:

 

 

Is there a place to buy those? If I go through all of the chips and it turns out to be one or more of those easy-to-swap-out chips I'm going to be sad.

 

Help!

 

KylJoy

[+KylJoy]

No one?

[Middleway]

Looking at the Service Manual (https://archive.org/details/Fairchild_VES_Service_Manual_1976_Fairchild) and comparing your screenshots to theirs, it seems to point to the PSU, which is ROM chip SL31253 (PSU = Program Storage Unit). It sounds like you already ruled out a bad connection by cleaning and re-seating it. The chip itself could be bad, I don't know if there's an easy way to get a replacement other than scavenging one from another Channel F.

[CatPix]

If the Channel F have no BIOS of sort (that is, the processor access the internal ROM games directly or an inserted cart if there is one present) and that the interal ROM games are toasted, you should be able to have a working display with a game cart inserted.

[+KylJoy]

OK... Haven't touched this in a while.

 

Does anyone have a set of ICs (SL31253, SL31291, SL31254) they would lend me to swap out for my originals to see which one is the culprit?

 

Please?

[+KylJoy]

Can I program any of the custom ICs (which ones are ROMs?) with my EPROM burner to test replacements?

[7800fan]

Short answer: no

 

You can only reprogram EPROM and some flash ROM (flash didn't come in general use until around 1990s). Those without any window can't be reprogrammed at all as they are fixed internally and aren't meant to be changed or reprogrammed.

[Spare]

I found this video when I was trying to check an untested Fairchild I bought. I suck at this kind of stuff so I did not do anything with the dead one but maybe it will help you get yours rocking again

https://www.youtube.com/watch?v=Uop2A94W6EA

 

Also, they have ICs for sale on the website, not sure if they have channel F ones

 

http://www.arcadecomponents.com

Edited April 6, 2017 by Spare

[Iwantgames:)]

I have a dead system (broken buttons) that might have parts to help you if you need. I can look for it in my junk room haha.

[+KylJoy]

Wow! Big thanks to Iwantgames:) for a donated Fairchild Chanel F motherboard!!!

 

I was able to salvage an IC (SL31291) and, 'Voila!", The dead have risen! It is functional.

 

Now, three more issues (hopefully small ones)...

 

1. The right controller has a bad cable. Anyone have a spare controller from a junker?

2. I get some video corruption when playing Pac-Man from the multicart. Bad video RAM? Something overheating?

3. Sometimes the screen goes black but the game seems to continue in the background. Ideas? Same issue as #2?

 

UPDATE - Seems I fixed the graphic issues (unless and until they happen again) by replacing the SL31253. All seems well now. Isn't there anywhere to buy these ICs?

 

I still need a controller if someone has one to spare.

 

Thanks a lot for everyone's assistance!!

 

KylJoy

[HoshiChiri]

I'm glad you were able to get your unit working again!

 

I don't know anywhere specific to get a controller- the ones on the model 2 weren't hard wired, so perhaps you can scour ebay for one of those and find a way to attach it? I'm not familiar enough with the wiring to know if that's an option.

[e5frog]

Are you sure the IC:s you have swapped are bad, could be the socket or oxidation on the chip pins.

 

Good work!

[+KylJoy]

Are you sure the IC:s you have swapped are bad, could be the socket or oxidation on the chip pins.

 

Good work!

 

I checked but you have me second guessing myself. I know I swapped the ICs back and forth a couple of times to make sure the problem was following the ICs.

 

I'll verify that the chip pins are not oxidized. I will report back after testing.

 

Thanks!

[+fdr4prez]

Wow! Big thanks to Iwantgames:) for a donated Fairchild Chanel F motherboard!!!

 

I was able to salvage an IC (SL31291) and, 'Voila!", The dead have risen! It is functional.

 

Now, three more issues (hopefully small ones)...

 

1. The right controller has a bad cable. Anyone have a spare controller from a junker?

 

 

I still need a controller if someone has one to spare.

 

Thanks a lot for everyone's assistance!!

 

KylJoy

 

The internal wires in the cable are fairly fragile.

 

If people wind the cable around the controller, then the stress of the cable bending out from the bottom of the controller housing up around the body causes one (or more) of the wires in the cable to break.

 

You can snip the cable just under the housing and retest the wires. If one wire is still NG, then cut it a little shorter and retest.

 

Once you get a good set of wires then you'd have to remove a few inches of cable insulation so the individual wires can be resoldered within the controller.

 

I've not done this process before, so not sure what to do for the strain relief. I'd imagine that it could be removed and reused; even if you have to butterfly it open and glue it in place in the new location on the cable.

[e5frog]

Yes the controller wires are quite thin, not many strands in each wire.
I have fixed a few, it's not that hard to drill (or use a milling bit - very handy) out the old cable insulation from the strain relief, thread wire through it and when done soldering fasten the cable with a small zip tie inside the controller.

It's possible to leave the cables soldered in the controller and make joints in the same position using shrink tube on each of them, it will save a few inches of wire.

This is a Video Command stick but they don't differ that much.

You could make three joints under the base plate plastic (where the stick attaches on the bottom) then three straight after and three a little above them - so you don't have all the jounts in the same place as it will get quite thick.

If not going for that approach I recommend taking a few pictures of the mounting then desolder wires from the controller and strip the wires of the cable to the same length and follow the same path as before. This is the way I usually do it unless the cable is really short already.

It would be possible to buy a plain joystick extension cord from eBay and solder that in, it's however guaranteed not to have the same color order so make sure you measure and solder correctly.