Asteroids Arcade game vector issues?

[RobII]

Hi electronic Guru's!!  I have a sick Asteroids arcade game.  Currently the game plays blind (Game plays but no graphics on the screen).  Before I start tearing into the monitor chassis I want to make sure the PCB is outputting the proper signals.

I have verified the 5vdc to the logic and 36vac to the vector section.

I hooked up a scope and tried to get some good pictures but I'm not sure they will be of any use

Here are the X and Y outputs, I think the Y output is on the bottom.



I also uploaded a short video

https://youtu.be/xghOtT-se40

I am not an electronics engineer but can navigate my way around a PCB.  Any suggestions on where to start would be most appreciated!!

[miguelvp]

Put the Scope on X-Y mode, you should be able to actually see the graphics because that's pretty much vector mode.

[RobII]

Did that.  The last few seconds of the video are what I get in X-Y mode.

Put the Scope on X-Y mode, you should be able to actually see the graphics because that's pretty much vector mode.

[Macbeth]

You should see something like the real thing in X-Y mode, though the blanking intervals are probably showing up and making a mess. Does it use the Z for beam intensity?

You say the Atari CRT has no output at all? Have you checked its getting EHT?

[wreeve]

is the spot save circuit kicking it? I think there is a red led which indicates it's on. It's there to stop the phosphor burn in when the beam isn't moving.

[RobII]

It does use Z for blanking retrace lines but I'm not getting any recognizable game output in XY mode. 

The spot killer LED is on, on the monitor deflection board but that could also mean it's not getting a proper signal from the PCB.  If I turn up the brightness I do see a dot in the center.

Since I'm not getting any kind of game output on the scope, I am leaning towards an issue with the game PCB.

You should see something like the real thing in X-Y mode, though the blanking intervals are probably showing up and making a mess. Does it use the Z for beam intensity?

You say the Atari CRT has no output at all? Have you checked its getting EHT?

[Macbeth]

0.2v per div - I'm guessing 2V per div with x10 probes, that still isn't enough to drive the deflection plates. But there is clearly some "intelligence" in the X/Y signals that would indicate a game field that is working. So the output amplifiers have failed. But it would be exceptional for both amplifiers to fail at the same time (to give a single dot).

Now I have to admit my work used to involve raster scan TV stuff and so a field collapse would be one fault or a line output fault was much more common (and would take everything else down with it as the LOPT generated all the other supplies including field). I'm guessing with a vector screen the X,Y are supplied by the same voltage - so rather than the amplifiers it would be the supply for them that has failed. Something in the low 100's of volts?

[MagicSmoker]

Personally, I'd start checking for the proper voltages on the CRT (filament/heater, grid, screen, 2nd anode [careful - HV!]).

Here's a page on troubleshooting Asteroids: http://arcarc.xmission.com/Tech/Asteroid%20Tech/asteroidsrepair.html

Also, search for "asteroids manual schematic" and the first hit is the operator/service manual.

[RobII]

Let me back things up a bit.  On the Asteroids PCB there are X and Y output test lugs which is what I have the scope connected to.  Currently I have the monitor disconnected at the molex.  I want to concentrate on getting game play output on the scope so I can rule out the PCB definitively.  Once I can get that part working I can start rebuilding the monitor chassis.

[mikerj]

Let me back things up a bit.  On the Asteroids PCB there are X and Y output test lugs which is what I have the scope connected to.  Currently I have the monitor disconnected at the molex.  I want to concentrate on getting game play output on the scope so I can rule out the PCB definitively.  Once I can get that part working I can start rebuilding the monitor chassis.

You'll need to connect the Z output (if your scope has one) to a suitable blanking signal otherwise the output will be a mess.

[RobII]

Agreed it will look like a mess but will have a definite game play which I do not get right now.  Scope does have a z input . All i see on the scope for gameplay is a jumbled mess squished at the left side of the screen as seen in the last few seconds of my video.

[Andy Watson]

All i see on the scope for gameplay is a jumbled mess squished at the left side of the screen

So turn up the gain on the oscilloscope to fill the screen. It looks as if there is some intelligence in those signals - and it looks like it is moving around at typical game playing speed.

[Macbeth]

Yes. Initially the fault was reported as a totally dead screen (or blind screen) but I guess sound, etc ok.

Later it turns out the screen isn't totally dead because a centre dot is reported. So the EHT must be there, but the X/Y plates aren't getting voltage and the Z must be turned off otherwise there would be a very bright dot in the centre burning the CRT.

There is clearly without a shadow of a doubt gameplay coming from the board - which has to go to the CRT amplifiers. I mean none of that stuff is random noise. If the CRT was displaying similar mess to the 'scope then yes go back and check the game board, but that's not the fault, so why bother checking it further? Clearly its the video amplifiers, and as it's unusual for both to fail at once it must be the amplifier supply that has failed.

[RobII]

I guess i need to clarify my reasoning. I am checking the output from the game pcb with the scope and unable to get any kind of video output. What i am getting on the scope screen was the same mess I was getting on the game monitor (well very close to it).

I was checking voltages for the game pcb op amps, the TL081's are showing good supply voltages + and -15 but the two TL082's are showing a good -15 on the negative supply and -5 for the positive (should be 15 according to the datasheet). I also checked votages to the DAC's a solid -15 but a +15 when the datasheet for them states a supply of only +5.  I dont have the Asteroids repair to verify what the voltages should be.

[tec5c]

Could you take some photos of the cabinet, inside and out?

[Macbeth]

I give up 

[bitslice]

There are a few forums which deal specifically in arcade/console machine repair, you might like to check them out.

[MagicSmoker]

...Clearly its the video amplifiers, and as it's unusual for both to fail at once it must be the amplifier supply that has failed.

This is why I said check the grid voltages on the CRT against the values reported in the service manuals... It also wouldn't hurt to check the deflection yoke current waveforms.

[RobII]

Sorry to have wasted everyones time.  I'm not understanding the logic of checking the CRT voltages when I want to get the game to output properly on my scope first which I have not been able to do. 

The guys that helped me fix my scope were awesome so I thought I'd start a thread about my game. 

Thanks again for everyones help.  Moving on.

[MagicSmoker]

Sorry to have wasted everyones time.  I'm not understanding the logic of checking the CRT voltages when I want to get the game to output properly on my scope first which I have not been able to do. ...

Err, ok... So the goal is not to fix the game, it's to turn your scope into a monitor for said game? 

[RobII]

That is the ultimate goal but I want to verify FIRST that the PCB is outputting the proper signals to the scope.  No need tearing into the monitor chassis and replacing parts if it's not the issue.  Sorry if I didn't make it clear enough.  I honestly didn't think what I was asking was that confusing. 

Step one, is game PCB outputting proper vector info to scope > Yes, issue is the monitor chassis > No, issue is with the game PCB.

Err, ok... So the goal is not to fix the game, it's to turn your scope into a monitor for said game? 

[Macbeth]

Exactly. It appears he starts off saying no output on the CRT at all, so leads us down the garden path. Then states only a centre dot is visible with the brightness turned up, leading us down another twist. Clear evidence of proper game field coming from the board. Now he just wants to display it on his scope all along and isn't interested in the CRT, just wants to see it on the 'scope.

Either a fucking troll or an idiot who couldn't just ask "how can I get asteroids to display on my 'scope in X/Y mode?" and has to invent a non working CRT for it instead... and then give a back handed thanks for the help given. 

[TerraHertz]

Probably either the positive or negative supply rail to the output XY amplifiers on the game board has failed.
So there is signal, but it's all in one quadrant. Hence the scope XY display up in one corner.
Also resulting in the display unit screen protection circuit cutting in, to protect the phosphor from burns.

Btw, it isn't just phosphor burns that result from a fully on electron beam sitting in one spot. It will actually drill a hole into the glass. I've seen this happen. Used to service console video games long, long ago.
It's a bad idea to even try to see the beam (turning it up, etc) if the drive signals are suspect.


I think I *might* have Atari Asteroids schematics, for both the game board and XY monitor. Will have a look sometime today. Aren't they on the net already? The game board schematic is one huge map-sized folded-up sheet, so would be a pain to scan and stitch.


Edit: Hmm... can't find the Asteroids schematic, though I think it's just mis-filed, since I'm certain I do have the XY-monitor manual, and maybe the Asteroids schematics are with that.
But I did find an Atari Battlezone schematic (similar XY-system.) It's two big map-size sheets, both sides. Probably the Asteroids schematic is 2 sheets too.
Also found some crappy photocopies of "ASTEROIDS SELF-TEST and Diagnostics." 5 pages.
Will keep looking for the correct schematic a bit more.

[Andy Watson]

Edit: Hmm... can't find the Asteroids schematic, though I think it's just mis-filed,

For those playing along at home:
http://www.mikesarcade.com/arcade/manuals.html
Have we established whether the scope traces were taken with X10 probes? Even with X10 probes, the signal levels appear to be less than the schematic would suggest.

[miguelvp]

Relevant videos: