wiggly asteroids vectors

[virtvic]

I have had 'wiigly' vectors on my Asteroids basically since I first got it and now I have it back again it's really annoying me.

The vectors just aren't straight. As you move your ship around and as the asteroids are flying around they look like they are passing over something dark (if you know what I mean) I'd take a picture, but I don't think you'd be able to see it very clearly.

The AR has had a rebuild kit on it and I have just swapped it with a spare I have - no change.

The deflection board also had a rebuild kit fitted and the 2 large ally caps on the monitor were renewed, as was the Big Blue.

Any ideas what could be wrong?

I just found out tonight that the power connector pins on the lower monitor pcb are dodgy, as I got the monitor working again and when I pushed the machine back to it's place it didn't when I turned it back on

I think its just some reflowing needs doing.

 

[DaveAS]

A picture or video might make it easier to work out whether the digital or analogue part is likely to be at fault.

Can you see anything wrong on the test mode screen? A close shot of a dodgy line would show up a digital fault perfectly.

For instance, do the diagonals look anything like this:

???

The pic is a crude attempt to simulate what you'd get if bit 1 of the digital x-coordinate was stuck. Filtering on the board would make it look a bit smoother.

--
Dave

 

[virtvic]

Ah - yes they do look like that.

Unfortunately, my board plays fine, but gives out the low pitched beep on the final tone and has never actually got to the test grid. I have read that this is possibly a ram problem?

 

[DaveAS]

A low final tone is a failure on RAM P4. The meaning of each is listed in the manual. It probably really is the RAM rather than decoding problem, otherwise you'd expect the game to screw up in a more spectacular fashion. It's worth swapping it out.

To diagnose a possible stuck bit, start at the DAC inputs looking for static data lines. If you find one, refer to the schematics and trace back through each stage to see where the bit is getting 'lost'. It's easier to do this on the test screen because you know all of the bits will be active all of the time. A DAC fault can also look like a stuck bit... better hope not 'cause those are expensive to source.

You'll need a scope or logic analyser. I'm pretty sure I remember you saying you didn't have either in a another post. Can you beg / borrow one from somewhere?

--
Dave

davespicer2011-07-10 00:59:06

 

[virtvic]

I'll swap out the RAM (I may have to solder in a socket first) and see if that sorts it out.

 

[virtvic]

Er, what kind of ram is this and where can I expect to buy some, or do I go hunting thru old knackered boards to find some?

 

[P-Man]

2114, but you need faster stuff for fixing a problem like this, look for -20 or -25, because -30 and -40 -45 are too slow and will result in similar ram beep issues.

As for your wiggles, vectors are not rigid lines as you see displayed in MAME. Depending on many, many factors they can have slight wiggles. If you are sure your signal path from pcb to monitor is perfect and grounds are perfect, then the 'passing over' syndrome is usually down to primary or secondary deflection transistors that are not smooth along their response curve. They are within their specs, but being 30 yars old, they wander a little, causing this 'passing over an invisible hump' syndrome. This anomonly (and i wont say fault) is tough to track down, and unless you are seeign more than a few mm in deviation its more hassle than its worth to try and track down. Take a photo if you can, but i feel you might have unreasonable expectations of what a vector game should look like...

but you do also mention vectors passing over 'dark' areas... how burned is your tube? vectors passing over burned phosphor are not going to be as bright passing over unburned phosphor...

P-Man2011-07-10 11:04:05

 

[virtvic]

A kind hearted member is going to have a look at my board for me.
Without you guys help, I'd still be fiddling with the monitor to try and iron out my vectors - so thank you to you all!

To answer one of P-mans questions - there are no dark spots on the monitor (it is a nigh on brand nos tube) it was just me trying to explain the 'texture' of the vectors. Ta anyway for all the explanations - it's good to hear about a game I adore...

 

[guddler]

I've played this cab on a few occasions, and would always eventually walk away from it so I can understand why Vic wants to get to the bottom of it, it's definitely out of the realms of normal !! Let's start by establishing if it's the PCB or not which will be a 2 minute job to do

 

[guddler]

Ok, I'm not really taking on repairs at the moment but I offered to have a quick look at this as a favour since I had everything set up to just pop it on the bench and have a nose.

I can confirm that there's nothing wrong with the PCB aside from the inability to go into test mode which I'll cover in a mo.

So, game play. Note the small dark area on my tube, bottom left (don't recall that being there before it went in the loft for 3 years!!):

Test mode. Lovely clear straight lines, even over the dark area:

So, I'm assuming it's not likely to be the high voltage PCB so it's either the deflection PCB or the wiring between the PCB and the monitor. Now then, I did anticipate this and asked Vic to stick the deflection PCB in with the game board. Of course, numpty that I am, I always forget about the damned G05-801 monitors that aren't compatible with the 14" versions. Unfortunately then, I've got no way of doing anything further unless I just blindly replace parts, which I'd rather not.

At least now though if I send it back, we can now get a decent photo of the board in test mode on the offending monitor...

We really need that before we can take this one much further unfortunately.

As for the board not going into test mode, as suspected it was just a duff RAM chip at P4. The only one that hadn't previously been socketed and replaced. Typical! The fact that the game would play fully despite this was a new one on me I have to admit but I guess the RAM may have just had a very small bad area (1 bit or so maybe?) and we were just lucky enough that it wasn't getting hit in normal play. I could probably dig out all my notes and stuff, stick the board on my Fluke to find out the exact area or areas of duff memory and come up with a more precise explanation but it's not really worth it. Suffice to say, the 6th tone is for P4 and P4 was indeed faulty

Martin.guddler2011-07-18 22:43:00

 

[virtvic]

Right! - I have now had enough time to drag out a bunch of machines to get to my lovely Asteroids.

It now goes straight into test mode - after I had to reflow some solder on the regulator pcb to get the monitor working again. Thanks to Guddler

for sorting my board out. But, as he suspected - the wiggly lines are not a gameboard specific problem. Here it is in test mode, you can't see how bad the wiggles are, but you CAN see them.

 

[P-Man]

are these moving or static squigles?

 

[DaveAS]

Is the shield missing from the HV cage?

--
Dave

davespicer2011-08-13 11:38:13

 

[virtvic]

They are static wiggles and the cage is present, what do you mean about the shielding?

 

[DanP]

The HV box has a faraday cage on it which acts as a shield to em interference. It's the mesh like cover on the HV box.

Dan

 

[virtvic]

Sorry, yes the mesh cover is present.