Dead Defender

[MajorHavoc]

Thanks. But I don't understand things like does CLK mean that's where the clock input signal is going to the chip? Or is that a signal coming out of the chip? And what if it has CLK1 and CLK2? What's the difference between CL and CK in the abbreviations. What's Q? And what's Q with a bar over it? All that stuff? Is there a general resource available for folks just starting out?

Once you start down the dark path, forever will it dominate your destiny.

A book:
http://www.amazon.com/PBS-Beginners-Guide-Reading-Schematics/dp/0830676325

A web site:
http://www.learn-c.com/schemat.htm

Pinouts for chips (74xx series and others):
http://ganswijk.home.xs4all.nl/chipdir/index.htm

Schematic icons:
http://library.thinkquest.org/10784/circuit_symbols.html

 

[MajorHavoc]

Thanks. But I don't understand things like does CLK mean that's where the clock input signal is going to the chip? Or is that a signal coming out of the chip? And what if it has CLK1 and CLK2? What's the difference between CL and CK in the abbreviations. What's Q? And what's Q with a bar over it? All that stuff? Is there a general resource available for folks just starting out?

Inputs and outputs are not intuitive. If you figure out an input or output, usually the pins they attach to are the opposite.

CLK1 & 2 are probably different clocks (like 2MHz vs 1MHz).

CK is clock and CL is clear.

Forget what Q is but Q with the bar over it is the OPPOSITE signal from Q.

And / before a signal is active low. Like /EN is enable but active when low, like here:
http://ganswijk.home.xs4all.nl/chipdir/giicm/74245.txt

 

[Arcadenut]

More Helpful Links:

Go to this site and download the Pocket Guide
http://www.onecircuit.com/node/27

If you want the actual Data Sheets for most TTL chips, you can try these sties:

http://www.datasheetcatalog.com/
http://www.datasheetarchive.com/

Site for Finding Chips and other Components to purchase:

http://www.findchips.com/

NTE Cross Reference, good for finding suitable replacements for some obsolete or hard to find chips:

http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search

 

[YellowDog]

Thanks. But I don't understand things like does CLK mean that's where the clock input signal is going to the chip? Or is that a signal coming out of the chip? And what if it has CLK1 and CLK2? What's the difference between CL and CK in the abbreviations. What's Q? And what's Q with a bar over it? All that stuff? Is there a general resource available for folks just starting out?

On most chips CLK or CK is clock input.
CL is clear.
Q is a signal output. !Q (read as not Q, same as Q with a bar over it).

In this case, when Q = 0, !Q = 1 and vice versa.

As for learning about reading schematics, just google 'how to read schematics' and look for a writer that covers things in a style you like.

ken

 

[jehuie]

So from Pin 35 of the CPU go to:

Pin 2 of 7L
Pin 5 of 7J
Pin 9 of 7J
Pin 4 of 6R
Pin 8 of 7P
Pin 12 of 7P

Thanks for all the reading tips guys! I'll start working on my electrical engineering degree here shortly. In the meantime, I used the logic probe and got some non-pulsing chips. I noticed that 7J was socketed and I had a spare so I threw that in there.

Now when I start it up it actually makes a game sound briefly but that's all. Then it just sits there silently with no pic. I ran through it with my probe again and get the following:

Pin 2 of 7L - pulsing
Pin 5 of 7J - pulsing
Pin 9 of 7J - not pulsing
Pin 4 of 6R - not pulsing
Pin 8 of 7P - pulsing
Pin 12 of 7P - pulsing

But I don't really know what that means from a practical standpoint.

 

[Arcadenut]

Thanks for all the reading tips guys! I'll start working on my electrical engineering degree here shortly. In the meantime, I used the logic probe and got some non-pulsing chips. I noticed that 7J was socketed and I had a spare so I threw that in there.

Now when I start it up it actually makes a game sound briefly but that's all. Then it just sits there silently with no pic. I ran through it with my probe again and get the following:

Pin 2 of 7L - pulsing
Pin 5 of 7J - pulsing
Pin 9 of 7J - not pulsing
Pin 4 of 6R - not pulsing
Pin 8 of 7P - pulsing
Pin 12 of 7P - pulsing

But I don't really know what that means from a practical standpoint.

You could just replace 7J and see if that fixes it. It's a small chip

 

[jehuie]

You could just replace 7J and see if that fixes it. It's a small chip

See above....I already replaced it and that's when it started making the startup sound.

 

[Arcadenut]

See above....I already replaced it and that's when it started making the startup sound.

Sorry meant 7L.

 

[jehuie]

Sorry meant 7L.

Well that means I need to break out my soldering iron. Don't mind doing it....but do you have a good rational for that one in particular?

 

[Arcadenut]

Well that means I need to break out my soldering iron. Don't mind doing it....but do you have a good rational for that one in particular?

It's the last one you haven't replaced?

Before you replace it though, are you getting anything at the CPU now?

 

[jehuie]

It's the last one you haven't replaced?

Before you replace it though, are you getting anything at the CPU now?

Is it common to have multiple 7474's go bad at the same time? Perhaps due to a faulty power supply?

And yes, I am getting a heartbeat at the CPU now! So you still suggest swapping out 7L?

 

[Arcadenut]

Is it common to have multiple 7474's go bad at the same time? Perhaps due to a faulty power supply?

And yes, I am getting a heartbeat at the CPU now! So you still suggest swapping out 7L?

I wouldn't replace it at this time. If you're getting something on pins 34 and 35 of the CPU then you probably fixed the clock issue. Now you have another issue to resolve.

Are the LED's still on solid or do they show a different result now?

Is the RESET on the CPU pulsing or HI/LOW?

If the RESET line is pulsing, you can disable the watch dog by cutting the pad at 5N. This may allow the game to boot further. Once you test that you would want solder it back.

If the RESET line is good, then check the PINS 8 - 31 again to see if there is any activity there. If there is, chances are your CPU is good and you can start checking other things.

 

[jehuie]

I wouldn't replace it at this time. If you're getting something on pins 34 and 35 of the CPU then you probably fixed the clock issue. Now you have another issue to resolve.

Are the LED's still on solid or do they show a different result now?

Is the RESET on the CPU pulsing or HI/LOW?

If the RESET line is pulsing, you can disable the watch dog by cutting the pad at 5N. This may allow the game to boot further. Once you test that you would want solder it back.

If the RESET line is good, then check the PINS 8 - 31 again to see if there is any activity there. If there is, chances are your CPU is good and you can start checking other things.

Ok I'll check those things out when I get back from the stinking scout meeting. So even though some of the pins listed are not pulsing you think the clock is likely ok?

 

[Arcadenut]

Ok I'll check those things out when I get back from the stinking scout meeting. So even though some of the pins listed are not pulsing you think the clock is likely ok?

If you're getting activity at 34 and 35, I would say yes.

 

[YellowDog]

If you haven't downloaded this yet, you really need to. It will walk you through a lot of the common diagnostics with a logic probe.

ken

 

[jehuie]

If you haven't downloaded this yet, you really need to. It will walk you through a lot of the common diagnostics with a logic probe.

ken

Now that looks like my kinda document. Troubleshoot without having to actually know anything! Thanks!

Ok here's the results so far:

- The LED's come on and then all go out after the power-up sound. Pressing reset now causes them to flash and then go back out.

- The RESET line seems to be operating properly and stays hi until I press reset then goes low for a moment before returning to high.

- Pins 8-31 of the CPU seem active

So....I think the CPU is now functioning properly. Thanks guys!

Now to figure out why there's nothing else going on! Let me dig through some of my materials again. This is fun!

 

[Arcadenut]

If you haven't downloaded this yet, you really need to. It will walk you through a lot of the common diagnostics with a logic probe.

ken

Thanks Ken

For some reason I was thinking that was for replacing the caps on the boards, so I never really looked at it

 

[jehuie]

Ok I take it back. Even with the flowchart I'm not smart enough to do this.

I followed it down to page 6 where it says to check "5P Pulsing in CRT". Well pin 6 pulses but incredibly slowly. Not even a pulse really but more of a flicker every 10 or 15 seconds. I'm checking at the chip on the PCB...not sure what it means by "in CRT".

But this sounds wrong...so should I assume something is wrong with the Vertical Count Buffer now?

 

[jehuie]

Here's where I'm stuck:

Not sure what "Lift 5P Isolate" means.

 

[YellowDog]

The document was part of a set, I think there may have been some videotapes that went with it. It really only covers some of the most basic tests. Unfortunately, over time, many other components are starting to fail that are not covered in these sorts of guides.

It also helps to have a working one. There is nothing like being able to plug a working board in and seeing that chip X pulses slowly on pin Y, but on the broken one it is pulsing like a bat outta hell or not pulsing at all.

What I have been seeing is that there is very rarely a single chip failure. Mostly there are multiple chip cascading failures. One chip fails and takes out it's next upline neighbor, who in turn passes the favor along. And sometimes those failures manifest themselves in very strange ways.

Just keep plugging along. As frustrating as it is right now, when you look over and you see the logo pop up on screen, there is no better feeling.... Except sex..... and getting really drunk.

ken