How to check if clock circuit operating

Zinfer

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can someone tell me how to check if the clock circuit is working on a Gravitar/Space Duel?
 
Use a logic probe or an oscilloscope and check for activity in the circuit.
 
You can also hold the RESET low. (I can't remember if those board have a dedicated reset button.) If the screen freezes or behaves differently, chances are good the clock circuit is operating. Operating how well? .. that's another matter. :)
 
Ok, well I don't know which IC's compose 'the Circuit'. Which pins specifically should I be probing with the LP? Where should I be attaching the oscope probe to find the clock signal?
 
You don't want to probe the crystal itself though... you need to probe after it's been buffered, since the probe will affect the crystal. I believe both Space Duel and Gravitar have tabs labeled for the clocks... from a quick look at the schems of Gravitar, you should have one labeled 12MHz, 6MHz, and Φ0 (1.5MHz)... and if you don't see those tabs, you can check pin 5 of chip E4, and that'll be the 12MHz input. The other frequencies (6, 3, and 1.5 MHz) are generated by E4 (counter) on pins 3, 2, and 6 respectively.

DogP
 
Thanks Dog for helping the lamen out there. :) I did take the logic probe down through the line of IC's from the two tantolem capacitors and was getting alot of high and low rapid alternations. I thought I could stop that by jumpering from GRD to HALT, but it kept right on alternating. I'll try the oscope tomorrow when it's a little lighter out and check those tabs and IC pins.
So basically, let me get this straight. I'm looking for a straight dead - nothing happening flatline where there should be a clock signal. Right? Otherwise if I get the clock waveform then everything is running fine on the clock circuit?
This keeps coming down more and more to the AVG. I wish I had one of those. I'll see what Clay's up to.
 
Yeah, I'd check the 12MHz first, since the others are generated from that. If it's flat, then you've got no clock. Note that some logic probes are only good up to ~10MHz, so if you get funny readings, check the 6MHz, and if that's good, you know your 12MHz is good.

DogP
 
I picked up this Logic Probe in particular because of a video I watched with Colin Kraft repairing a Berzerk. Radio Shack logic probe. Works a hell of a lot better than something I earlier found on Ebay where I found out after winning the auction that the guy makes his own logic probes. ugh! Ended up utilizing it as a dart against a wall. If you don't have reliable tools, then your diagnostics are unreliable. I love a tool I can rely on to be accurate and easy to use.
Ease of use however doesn't come with the territory on Oscilloscopes. I really need to teach myself more on those. I love the one I have, but I seriously need to use it as more than just a cheap X-Y monitor.
This space duel is really kicking my rear end. At this rate, Chad will be finished with my Asteroids issue long before I get this fixed.
But I think I'm down to the Clock or the AVG. I'd have been done with it weeks ago if the problem turns out to be the AVG.
 
Checking the clock circuit, at the 12Mhz tap and the lights were both lit steady but the tone was lower than the 6Mhz tap. With the 6Mhz both lights lit steady and higher tone. Pin 5 is hi on E4. Pins 2 & 3 are Hi and 6 is low. None of them pulsate. No heartbeat there.
I also noticed that K4 pins 2, 3, 4 have nothing hi or low. No signal at all there. So maybe that's an issue. As I move up the line M4 is behaving the same as K4 with pins 2,3 and 4 having nothing. I am using a +5v tap and ground for my probe. I believe pin 1 is lower most left, so I'm measuring from bottom left to right on the ic.

You don't want to probe the crystal itself though... you need to probe after it's been buffered, since the probe will affect the crystal. I believe both Space Duel and Gravitar have tabs labeled for the clocks... from a quick look at the schems of Gravitar, you should have one labeled 12MHz, 6MHz, and Φ0 (1.5MHz)... and if you don't see those tabs, you can check pin 5 of chip E4, and that'll be the 12MHz input. The other frequencies (6, 3, and 1.5 MHz) are generated by E4 (counter) on pins 3, 2, and 6 respectively.

DogP
 
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