Computer Space TV rebuild

cwilkson

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Well, after the CAX performance I've decided to finally go though the TV in my Computer Space. It ran all weekend, but it has sync issues and horizontal...iffiness. Any suggestions before I take it out of the cab? I plan to rip into it tomorrow.

I don't know much about it yet, but it's a GE television using a 16CWP4 picture tube. I picked up new tubes for it today. All except the picture tube (which is fine) and the HV rectifier (1BC2B). Can I use a 1BC2A instead? I found one of those but not the 'B suffix.

This will be my first tube equipment repair. Are there general precautions to take? Also, what's the best way to pull tubes from the chassis? Just wiggle them?

Clearly, I'm a solid state guy. But I'm trying to branch out. :)

How would I find a service manual for it? (after I find the model/chassis #)
That would rule. I need to know what all the coils do, what the supplies should be, etc...

And where can I get a multicap rebuilt? On other monitors I've replaced them with discrete caps. But this one I'd like to keep as original as I can.
 
I don't know much about it yet, but it's a GE television using a 16CWP4 picture tube. I picked up new tubes for it today. All except the picture tube (which is fine) and the HV rectifier (1BC2B). Can I use a 1BC2A instead? I found one of those but not the 'B suffix.
I looked it up in the databook, and it does have identical characteristics. That is the HV rectifier tube, and the B version is probably a revision with better glass - HV rectifiers are known for their ability to produce X-rays. For example, the 6BK4C is just the same tube as the 6BK4B, only with leaded glass.

But, in any event, this tube is not your problem, and won't need to be replaced.

This will be my first tube equipment repair. Are there general precautions to take? Also, what's the best way to pull tubes from the chassis? Just wiggle them?

Yeah, gently wiggle. BE CAREFUL! This is a printed circuit board type chassis. The heat from the tubes will have 'cooked' the board, and it'll be brittle right near the tube sockets. Rock the tubes very gently until they start to loosen, and pull them out. It _is_ possible to rip the tube socket and a little circle of circuit board right out...

How would I find a service manual for it? (after I find the model/chassis #)

You want the Sam's Photofact. Find the chassis number, then go to www.samswebsite.com and type it in. That will tell you which photofact issue/folder it's in. Take that information to your local library - I know mine has all the old Sam's Photofacts. If yours does, you can look at it and photocopy it there.

And where can I get a multicap rebuilt? On other monitors I've replaced them with discrete caps. But this one I'd like to keep as original as I can.

You'll have to do it yourself. On the aluminum ones, cut it with a dremel right along the ridge near the bottom of the can. Then you can clean out the old gunk, and solder new caps to the old terminals. For the common terminal (the can), you will have to be creative, since the can is aluminum and won't take solder.

You have left the solid state world and entered the wonderful world of vacuum tubes. A couple of notes when working on tube stuff:

- There is high voltage in many more places. The plate voltage on those tubes is probably just rectified line voltage.

- This isn't isolated from the line. Despite the fact that it plugs into the wall directly, it's still "hot chassis". Cheap portable sets like this use rectified/voltage doubled line voltage for stuff. The tubes are a series string, like Christmas lights, to add up to 120v. USE AN ISOLATION TRANSFORMER when working on the bench.

- The tubes are some of the most reliable parts in the set. Seriously. You may have a weak one here and there, but they're remarkably reliable parts. And in many cases, a weak tube won't even degrade performance. Oh, and tubes have an infinite shelf life, they don't go bad from age. Shotgunning all the tubes isn't the cure-all.

- This set uses carbon composition resistors. Resistors above 1meg or so in value like to drift upwards. Check them wherever possible. Note that they are probably 1/2 watt parts. You can replace them with standard carbon film resistors.

- This set is new enough to not use paper capacitors. Be glad.

- Most of the capacitors in this set are not going to be electrolytics.

And, there's probably some other stuff I forgot, but post picture of what you've got and what chassis it uses. If you can't find the Photofact at the library, I can check mine.

Welcome, to the wonderful world of vacuum tubes!

-Ian
 
Chassis is a GE SF series. 9SF, 12SF, and 15SF all share the same parts acording to my schematics and parts list that I have.

I did have a bad tube in mine, when I replaced it, another component started arcing, and I shut it down. Eventually I will get to it. Right now it is my last broken game, so maybe sooner rather than later. I will post in this thread if I find anything.

Thanks for starting this thread, just might be the kick in the butt I needed to get mine going!
 
Keep posting Chris, I to will be working on a CS with no display in the next few weeks. Thanks again for taking me through the inside of your CS at CAX Friday evening. I still can't get over the little resistors in the shape of ships and saucers plunked down on the pcb.
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Mind sharing how much you paid for those tubes and where you got them? I may be buying some soon.
 
Retrohacker,

That's all great information. Thanks! Yeah, tube stuff is cool. I always wanted to build a tube amp. Or maybe a theremin. I have a Philco table top radio from my dad, early 40's model I think, that I wanted to get working when I was in highschool, but never got around to it. I'm finally jumping in with the tv.

Every place I looked online mentions the SF chassis for Computer Space. But mine is a S-3 chassis. I found the schematics in the back of the manual for CS. That might be enough for me, but I'll be hitting the library tomorrow morning to try to get the Photofacts. Sams # 1217-1.

I started to rebuild the can cap from a Motorola XM-501 for my Tank cab. I got as far cleaning the can, and arranging the new components inside (tricky). But I didn't even think about it being aluminum until I was ready to solder it closed. DOH!! I realized it before trying, but just. So out came the caps and into the chassis somewhat haphazardly. Ehh...it works. And nobody sees it but me. What do people use to close them? Epoxy?

For the HV rectifier, I figured I was safe. Being a diode, it probably either works or doesn't. Mine works.

I'm glad you mentioned the ISO xfmr. Months ago when I was considering this, I dug out my xfmr but then it faded from my mind. I might have forgotten it this time. It's hooked up and ready to go. I also would never have thought about the board getting baked by the tubes. Makes perfect sense. Though this thing may not be as bad as a regular use tv. It was parked in a garage since '77, and saw very light usage before then I was told. I've only used probably 3 hours in the last 2 years. (Plus this year's CAX experience.) Still, every bit of precaution is good.

The monitor is out now, ready to go. After I get the docs (hopefully tomorrow) I'll start the rebuild. Good thing too. It died on the table. Horizontal collapse...I watched it happen over a space of about 10 seconds. I don't know if it's from a connection shorting (doubtful) or some marginal thing failing because of the jostling. Or if it really was ready to go due to age. Once I'm prepped, I'll probably go through it component by component, verifying everything. Normally, I wouldn't be that thorough. But this being what it is, I feel it's worth it.
 
Here is a thread someone put together on atariage to document his repair. Maybe not the same as yours, but still good info

http://www.atariage.com/forums/index.php?showtopic=129003&hl=computer+space+monitor
Thanks. Thats a good thread. I've actually played Cassidy's machine before. Looked pretty good. I don't think it's his anymore though. Too bad...I'd have tried to get it if I'd known he was parting with it. Mine's only 1-player.

Getting the tubes and the coils will be my main concern. Everything else I can get, probably locally. I'm really nervous about the horizontal hold coil. The knob slips in and out and the adjust was was really touchy ever since I got it. It may have something to do with the collapse thing. I'll find out soon.
 
Chassis is a GE SF series. 9SF, 12SF, and 15SF all share the same parts acording to my schematics and parts list that I have.

I did have a bad tube in mine, when I replaced it, another component started arcing, and I shut it down. Eventually I will get to it. Right now it is my last broken game, so maybe sooner rather than later. I will post in this thread if I find anything.

Thanks for starting this thread, just might be the kick in the butt I needed to get mine going!
Good luck with yours! As I mentioned above, mine is a S3 chassis. But I do have schematics for it at least. And hopefully tomorrow, fairly good service data.
 
Keep posting Chris, I to will be working on a CS with no display in the next few weeks. Thanks again for taking me through the inside of your CS at CAX Friday evening. I still can't get over the little resistors in the shape of ships and saucers plunked down on the pcb.
icon10.gif


Mind sharing how much you paid for those tubes and where you got them? I may be buying some soon.
I was glad to show it off. It really is cool how they laid out that diode array ROM. I'll post as I make progress. Oh. I think the tubes are available online, including the 1BC2B. But I got mine from Halted (HSC), here in Santa Clara. Very reasonable prices...~$3 per tube I think.
 
Oh yeah. Here it is out of the cabinet, just after dying. Ready and waiting for me to start tearing into it! It's still hooked to the cab except for the speaker which a replace because the leads were too short to reach the cab.

For anyone following this thread, with a mind to repair their CS tv, I'll mention the isolation transformer again. The bottom is just visible on the table, behind the right wing of the tv case.

I almost forgot to use it, and I don't want other people to forget.
 

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Retrohacker,
Every place I looked online mentions the SF chassis for Computer Space. But mine is a S-3 chassis. I found the schematics in the back of the manual for CS. That might be enough for me, but I'll be hitting the library tomorrow morning to try to get the Photofacts. Sams # 1217-1.
If for some reason your library doesn't have it, I can check mine.

I started to rebuild the can cap from a Motorola XM-501 for my Tank cab. I got as far cleaning the can, and arranging the new components inside (tricky). But I didn't even think about it being aluminum until I was ready to solder it closed. DOH!! I realized it before trying, but just. So out came the caps and into the chassis somewhat haphazardly. Ehh...it works. And nobody sees it but me. What do people use to close them? Epoxy?
Hot glue.

I'm glad you mentioned the ISO xfmr. Months ago when I was considering this, I dug out my xfmr but then it faded from my mind. I might have forgotten it this time.
You would be suprised how much tube stuff is hot chassis. Most table radios and inexpensive TV sets are. The higher end console sets have power transformers, but not the small stuff.

The monitor is out now, ready to go. After I get the docs (hopefully tomorrow) I'll start the rebuild. Good thing too. It died on the table. Horizontal collapse...I watched it happen over a space of about 10 seconds. I don't know if it's from a connection shorting (doubtful) or some marginal thing failing because of the jostling.
Could be all sorts of things. Cold solder joints are pretty common in this sort of set. The old "whack the TV" sort of problem. Tubes generate a fair amount of heat - another thing to watch out for, you CAN burn your fingers pretty easily if you go to pull a hot tube out. Go over the areas around the tubes for cold/bad joints. Also, dirty tube sockets/tube pins can cause problems. Carefully wiggle all the tubes while the set is on and see if there is any effect.

Coils are going to be the only difficult parts to find. Tubes are easy, believe it or not.

-Ian
 
If for some reason your library doesn't have it, I can check mine.
Got it. 20 pages of service goodness. Mmm....
Hot glue.
Yeah. Just as ugly as epoxy. I might wander to an antique radio forum. They have to have nice pretty ways of rebuilding those cans.

You would be suprised how much tube stuff is hot chassis. Most table radios and inexpensive TV sets are. The higher end console sets have power transformers, but not the small stuff.
Makes sense. Transformers are expensive. Especially considering how/what they're made of. Old, mechanical, power stuff --> big, heavy, expensive. Maybe I'm just bitter because the one replacement xfmr I found for Tank was $300.

Could be all sorts of things. Cold solder joints are pretty common in this sort of set. The old "whack the TV" sort of problem. Tubes generate a fair amount of heat - another thing to watch out for, you CAN burn your fingers pretty easily if you go to pull a hot tube out. Go over the areas around the tubes for cold/bad joints. Also, dirty tube sockets/tube pins can cause problems. Carefully wiggle all the tubes while the set is on and see if there is any effect.
Definitely a loose connection on the sync seperator tube. I'll probably replace the socket. I *think* I can find one. Funny thing: today when I powered on, the tv was working. So...nothing blown up (yet). Just a loose connection somewhere. I tilted it to look for mounting screws before turning it on. I guess something moved back into place.
Coils are going to be the only difficult parts to find. Tubes are easy, believe it or not.
Yeah, even before finding the tubes, I was most worried about coils. They always seem to be custom.

Here's the results of today's efforts. Getting the CRT neck socket loose was tedious. Wiggle, wiggle...is it moving?....wiggle...it's not moving...wiggle...grrr...wiggle...maybe it is...what's that powder?...more dirt I guess...wiggle...wiggle....wiggle...finally!! Uh-oh. The plastic disintegrated. Damn. Need a new socket. Removing the yoke was much easier. (after I removed the dirt from the neck)

So I got the sevice docs and pulled the chassis/tuner out (+2) and found the CRT socket needs to be replaced (-1). Also, there's a plastic spacer ring on the CRT pins that's all cracked (-1). Is that something that's easy to replace? If not, is it absolutely necessary?

I feel like I wasted a day, but deep down I know I'm moving forward.
 

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Pretty sure this guy doesn't work. It's the video IF amp. Is that even needed here? Probably. I guess I'll find out in the coming days. So how do I remove it? Just start grabbing metal pieces and yanking? What about the pins and bottom of the envelope? Should I just remove the socket and start over?

BTW...I didn't do this. It was loose when I got to it.

It looks like most of the sockets have at least one pin receptacle with corrosion. Looks like I'll be replacing those too. Man this thing is a mess. It's a wonder it was still working.
 

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Pretty sure this guy doesn't work. It's the video IF amp. Is that even needed here? Probably. I guess I'll find out in the coming days. So how do I remove it? Just start grabbing metal pieces and yanking? What about the pins and bottom of the envelope? Should I just remove the socket and start over?
Eek! Yeah, dunno about this particular chassis, but you probably need that. If anything, for the filament series string. If one filament burns out, the rest in the string go out too. You don't need the RF sections, but you do need the video amplifiers working. And those Compactron type tubes are two or more tube in one. This particular tube is a dual pentode. Probably both used for the RF signal though. Check your schematic for the filament string wiring diagram.

To remove it, yeah, just start grabbing things and pulling. You can also get a screwdriver through the holes in the metal collar and try to get under the tube base. You also might be able to desolder the metal collar.


It looks like most of the sockets have at least one pin receptacle with corrosion. Looks like I'll be replacing those too. Man this thing is a mess. It's a wonder it was still working.

I wouldn't worry about replacing the sockets, really. Just clean 'em up. There's no plating, on those, and replacing the sockets is going to be a big job. These aren't IC's, these are tubes. Just clean off the corrosion and clean the tube pins. As long as the socket still grabs the pin, it'll work just fine.

-Ian
 
I got the busted tube out. I made my own crowbar from a 16 common nail, shaped with a file and bent to fit through the holes in the shield. (it's tight with all those boxed coils standing around!) I was able to get it under one side of the tube. And using needle nosed pliers, I was able to pull some of the metal pieces out and get hold of one of the pins on the other side of the base. There were some tense moments, but it finally came out. Glass and mica(?) shards were removed with a shop vac.

For the corroded pins/sockets I used an old toothbrush, dry, to scrub things. It's not perfect, but much better than it was. And it eliminates the possibility of destroying the PCB while trying to remove a socket. One of the old tubes (23Z9) was weak so I replaced it. And the busted 11BQ11. That helped with the display jitters/sync issues. About 3 hours of fiddling with the yoke placement and the centering rings and it looks pretty good. It's still keystoned, smaller at the top, but only noticable with the checkerboard test pattern on. It's "good enough" for actual game play.

Objects are larger near the left/right edges than in the center of the screen. Really obvious when the saucers fly horizontally across the screen. Is there a horizontal linearity adjustment someplace or do I have to live with it? Vertically, it's pretty good.

One remaining issue that I have to address for sure. The entire display sometimes shakes (very minor but repeating) and occasionally drops out for a split second. Think of a zoom feature. It's like I turn off the TV and turn it back on before the display completely dies away. I tried to capture some video, but the problem doesn't show up in the vid. Even the drop out which is very obvious in reality. Any ideas what might cause this? It was there before I started the repair and was one of the reasons for doing it. It's kind of what I've heard called "bloom" but on a much faster time scale.
 
One remaining issue that I have to address for sure. The entire display sometimes shakes (very minor but repeating) and occasionally drops out for a split second. Think of a zoom feature. It's like I turn off the TV and turn it back on before the display completely dies away. I tried to capture some video, but the problem doesn't show up in the vid. Even the drop out which is very obvious in reality. Any ideas what might cause this? It was there before I started the repair and was one of the reasons for doing it. It's kind of what I've heard called "bloom" but on a much faster time scale.

Check the high voltage rectifier tube and the high voltage regulator (if this set even has one). If the tube starts to arc over internally, it'll do this. It also won't show up as bad on a tube tester.

If you watch the tubes while the display freaks out, you will probably see a flash or arc inside.

What's the tube lineup in this set, anyway?

-Ian
 
I thought about HV arcing. But I'm always in the wrong place when it happens. It's really fast. I can't seem to catch it as it drops out. I did look while the display is jittering (it comes and goes), but the changes are small. If there is arcing, it may be too faint to see in that case. The HV rectifier is a 1BC2B. The horizontal output tube is a 33GY7A. A pentode for the flyback driver and a diode for the damper. I'm not sure how that works....gotta do some reading on tube stuff. I don't see any regulators there.

The schematic is available here, page 33: http://www.cityofberwyn.com/manuals/ComputerSpace.pdf
And the tube callout is on page 32. My voltages at the supply are different, BTW. They do match the Photofacts numbers though.

Is it standard for the letter suffix on tubes to designate a revision? I know you mentioned that for the 1BC2A vs. 1BC2B. Do you think that I could safely substitute the -A for my -B version, for testing purposes? I can get one of those today.

I need to get some sleep...I'll check in again later.
 
I would start with the HV rectifier. That substitution will be fine - the specs are exactly the same electrically, according to the databook. Probably just some minor change, like leaded glass or something in the -B version.

I've seen intermittent blooming caused by HV rectifiers (usually the good ol' 1B3GT in older sets), so it's a very logical place to start. And, HV rectifier tubes are also one of those tubes that doesn't test conveniently in a tube tester - i.e, it'll weed out the real duds, but no way of testing it under proper voltage, so an intermittent tube won't show up.

Swap the rectifier, and let it run for a while and see if your problem comes back.

-Ian
 
Turns out the 1BC2A box had a 1BC2 in it. :mad: I tried it briefly (allowing about 10 minutes to warm up). No change, so I put the 1BC2B back in. I cleaned things up and put the TV back in the cab. Got the display aligned after like 2-3 hours of messing with the yoke/rings. I still have some upside down keystoning. The left side slants in at the top, but it's tolerable. I don't notice it during game play unless I'm in hyperspace/extended play. I plan to turn off that feature.

That shake/dropout thing bugs me. It's not as frequent as it was, but it bugs me. So I took the 4-section can cap out today and replaced it with 4 discrete electrolytics. Very minimal change on the supply voltages. Something has to be arcing. But I can't hear it, and there's too much tube glow to see it even with the lights off.

I saw some really weird on the B+ rail. This is really beyond my experience. First, here's a picture of the +365 BOOST supply, coming off the flyback xfmr. Does this look ok? Seems like a lot of ripple to me. (70V p-p) But I've never looked at BOOST with a scope before, only a DMM.

Watching the scope, I can see B+ and BOOST jerking...I assume that's when the dropout happens. But I can't look at the scope and the screen at the same time. It's too quick.
 

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Ok, here's some pics of B+. It's sitting around 125V with 2V of ripple. But the waveform has this very strange cyclic uhh..."thing" going on. First some pics, then some (crappy) video so you get the idea of how it's changing in time. In the scope shots, pink is the main supply, coming straight off the rectifier. Yellow is B+. It's taken from "pink" via an R-C filter. Blue is a saved B+ waveform so I can see how it changes over time.

Is this normal???

I can't upload the video. :mad: :mad: Here it is:
http://www.flickr.com/photos/30920478@N07/3794511980/

The main thing that is killing me now is hum. The vsync frequency is nearly the same as the power mains, so the beat frequency is very low. Drives me crazy! The higher the supply voltage, the narrower the picture. There's a bar that's 1-2 scanlines high. That's minor. And there's a band that's a large percentage of the vertical. And it shrinks the display by about an inch where the score is. Any suggestions on the best way to fix this? Bigger caps, less current draw, I know. But I need help with specific suggestions. Things that won't kill the TV. This all assumes that my horizontal section is behaving normally. I can't answer that myself.
 

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