Burgertime no video output--Help!

[Blur2040]

Simply put, I have a Burgertime Machine with a PCB that is in need of repair.

I have tested my monitor with a Neo Geo board, so I know it works.

The game board plays blind, but displays nothing. I've checked and there is voltage on the edge connector where the R, G, B and Sync lines come out.

I have used the game board's schematic to try and trace the RGB lines
back...but I can only go so far...as it all goes back to ICs...and I
have no way of testing those, as I only have a multimeter.

I've tested all resistors that seem to be related to video output, and I've replaced all but one electrolytic capacitors that are on the board that outputs video.

Can anyone think of anything simple that I'm missing...or could
suggest something to try?

Is it possible to switch out boards/roms with a cheaper game that's on
the same hardware? (I'm looking at you, World Tennis).

Failing all else, could anyone suggest someone to repair it? Someone who does good work. I'm normally the type who fixes things himself, but I was expecting a monitor problem, and not a PCB problem.

 

[Xian Xi]

One thing you might wanna try is pushing down on the ICs in case a leg lifted.

 

[Blur2040]

One thing you might wanna try is pushing down on the ICs in case a leg lifted.

Nothing like that going on. Anyone?

 

[channelmaniac]

First check R24 (22 ohm) on the video board. It supplies power to the transistors used to drive the red, green, and blue outputs.

After that you need a logic probe to:

Check IC 1K and 2J - 74LS175 to see if they are good.

If that's not it then check the 74LS06, 00, 04 and 112 chips that are involved in the sync and blanking outputs.

Next check the 74LS174 at 2D. It contrls the latches on 1K and 2J.

Beyond that you need to check all the ICs involved in the address/data latching and read/write control signals for IC 1H and 2H the 7489 SRAM ICs.

I emailed you a copy of the manual with schematic.

RJ

 

[Blur2040]

First check R24 (22 ohm) on the video board. It supplies power to the transistors used to drive the red, green, and blue outputs.

After that you need a logic probe to:

Check IC 1K and 2J - 74LS175 to see if they are good.

If that's not it then check the 74LS06, 00, 04 and 112 chips that are involved in the sync and blanking outputs.

Next check the 74LS174 at 2D. It contrls the latches on 1K and 2J.

Beyond that you need to check all the ICs involved in the address/data latching and read/write control signals for IC 1H and 2H the 7489 SRAM ICs.

I emailed you a copy of the manual with schematic.

RJ

Bing Bing Bing. This is the kind of answer I was looking for. I had found the schematic, but I was lost on how to check the ICs.

My computer sciencey friends suggested that I could test them by hooking them to a battery...and somehow testing them...but it would be time consuming and clumsy. Then again, their practical experience is limited. After reading about logic probes, its seems that one would solve my problem.

Now, I just have to find a logic probe (hopefully locally). I'll double check that resistor tonight...though I'm pretty sure I checked it

Thank you very much, channelmaniac.

 

[channelmaniac]

Great! Glad you found the schematic. Gmail didn't like the 10Mb attachment and puked.

RJ

 

[Blur2040]

Help!

Ok, bumparoo here, hopefully channelmaniac or somebody else can help me out.

I received a logic probe in the mail today...and started screwing with my burgertime game...

Hooked one end up to 5v, one to Ground, started probing at one of those 74LS175s... The one at 1K. I could see what was high, what was low, etc...but well...


Later I came back to it...and accidentally hooked one of the plugs on the probe up to 5v, the other to the master reset line of the 74ls175 at 1k...and now theres a picture up on the screen. Its not perfect (theres some repetition at the top and bottom of the screen while its being played)...but the picture is definitely there.

I'm assuming then the problem is related to this chip...or something near it...but I'm not sure what I've done...whether I need to replace it or whatever.

Also, if somebody could point me in the direction of a tutorial on testing ICs w/ a logic probe, I'd appreciate it. I have the data sheet up...but I just don't quite get how to interpret what exactly the chip is supposed to be doing... I've looked around for help, but maybe I haven't found the right place.

Thanks again,

(Burgertime wooo!!!!)

Edit: Bonus Question: If anybody can recommend an electronic supply store in the Columbus OH area, I'd appreciate it. I'd like to get this taken care of this weekend. I know theres a few of you in this general region.

 

[channelmaniac]

Hmmm...

What you need to do is get the pinouts and function list (truth tables) of the 74xx chips from the various datasheets to understand what is happening.

Basically the way that particular chip works is the data coming in on the D pins is latched to the output pin Q and inversly out the output pin Q* as the clock pin transitions low to high.

If you have data in on that chip and no data out you have to check the clock to see if it's there and good. If it is stuck low or high then you have to back track that signal to the source and check it to see if it's there. If it is there then you have a broken trace. If it's not then that chip is either bad or its input is missing and you have to back track further.

Next you check the reset line to make sure it is high. If it is stuck low you have to back track like mentioned in the paragraph above.

Welcome to the world of using a logic probe to troubleshoot.

You can find various 74xx logic datasheets at http://www.datasheetcatalog.com

The 74LS175 can be found at: http://www.datasheetcatalog.com/datasheets_pdf/7/4/L/S/74LS175.shtml

Enjoy!

RJ

 

[Blur2040]

Ok, well, I think the clock is alright....

The problem seems to be with the master reset. Its stuck low on both of the 175s (Pin 1)...so I traced that back to the 174 at D2...and that signal seems to come off pins 7 and thirteen...

But I can't seem to trace the signal back (using the schematic) any further than D2. The way I understand it is that it doesn't seem to go back any further than D2, but I'm sure I'll be smacked in the face with superior knowledge on this one.

http://www.arcadedocs.com/vidmanuals/B/BurgerTime.pdf

There is the Burgertime manual/schematic for anybody that might help. The relevant page is 76.

I'm thinking it is the 174 at D2, so I ordered one...and by that, I mean three, but well...somebody prove me wrong.

 

[channelmaniac]

Well....

Pin 6 is the blanking pin... Pin 7 is the output on that 174 chip for blanking which is feeding the reset pin on the 175 at the output of the video.

If pin 6 on the 174 is stuck low... doh! Check it with the logic probe and trace it back if needed.

RJ

 

[Blur2040]

Hmm...leave it to me to glaze over the spot on the schematic that says pin 6 goes to blank...or rather assuming blank means...uh...blank in the literal sense.

But that stupidity aside (and a little bit more reading/learning about how my probe works, I've determined that there is in fact a signal on pin 6 on the 174 at 2D and no signal on Pin 7, which suggests that it is the 74174 at 2D...and I'm good to go.

So, (as long as I haven't missed anything) thank you very much, channelmaniac.
If theres anything at all I can ever do for you, don't hesitate to ask.

 

[channelmaniac]

Is there a clock signal on the 74LS174, pin 9? Is the clear/reset line (pin 1) stuck low? If there isn't a clock signal or if pin 1 is stuck low then you have to backtrack further in the circuit.

You aren't quite done until you check and verify those pins.

Once you get it running you can thank me. Until then we may still have some troubleshooting to do!

RJ

 

[Blur2040]

Well, I replaced the chip in question...and...yay! Everything came up and I can play Burgertime to my heart's content.

Everything is clear...(aside from some hardcore Burgertime burn in...

...but theres one problem.

When I drop a Burger piece in the second column in from the right, theres some glitching as they drop. Beneath the falling part, theres some white vertical lines. They're only there when the piece is dropping, and nothing happens to any characters when they cross that area.

I've also run through the graphics tests and I don't see any glitching when those run through.

I'll admit that I nicked (knocked the coating off, but didn't see a break in the copper) a trace, but that doesn't SEEM like it would be related.

Seems like it would be the sort of thing that would suggest a ROM chip problem...something like that...but I'd think that if that was the problem, the lines would occur any time something fell.

So...I'm happy, but I figure why not go for perfection? Any ideas?

 

[channelmaniac]

Tap the ROMs gently when playing... see if the board goes bonkers. You may have a bad socket.

Oh, and congrats on getting it running! See? Logic probes aren't that hard to use!

RJ