Logic Probe Experts Help (Super off road)

ArcadEd

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Yes, I am still tackling this super off road issue. I want my game back running and there seems to be a large collection of people out there with dead track pack boards.

I have 2 ICs on my board currently that I have a question about.

Page 32 of the manual. http://www.crazykong.com/manuals/SuperOffRoad.man.pdf

U9 (PAL20L10 http://www.datasheetcatalog.org/data.../497022_DS.pdf)
U10 (LS374 http://www.datasheetcatalog.org/data.../74ALS373N.pdf)

Hitting these two ICs with my probe I get no reading from pins 4,5,6 on the PAL
and no reading on Pins 3,4,7.8 (all data inputs) on the 374.

I have continuity to the Z80 CPU. I followed the schematics (above page 32) and checked the pins.

So I don't know if there should always be a reading there, or only when a game or demo mode starts up. Since this board just sits at a scrambled screen. I thought there should be some reading on the Data Inputs on the 374 since there is a reading on the corresponding outputs.

Please help. Thanks.

Ed
 
If your board just sits at a static screen then the game is most likely not running, ie. the CPU is not executing code for whatever reason. If that is the case you will see a great deal of blank and inactive pins.

Make sure the ROMs containing the maincpu code are good, then concentrate your efforts around the main CPU, I'm not familiar with this board but I think it uses a Z80. Probe around the CPU and the work RAM and make sure their vital signals are good like clock, CS, WR, reset high, etc.
 
Z80 I have swapped with good one and just measured. The only pins that are dead on the Main Cpu are all of the Address Bus pins and all of the Data Bus pins.

I checked the RAM, MS6264 http://www.datasheetarchive.com/MS6264L-10PC-datasheet.html

I am getting Hi on Both Enables, Write Enable and Output Enable. According to the truth table this should not happen.

There are 2 Ram chips next to each other, they both act the same way. Could both RAM chips be bad? There are a few more down the board that probe good.

Ed
 
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I have pulled all the roms, dumped and tested in both MAME and compared each one to a working set. Everything checks out.

There is also a 80186 CPU, I swapped that out with a known good one (from another Super Off Road board) and no change.

THanks for the help.
 
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if there should always be a reading there, or only when

as ive been learning, knowing what there should be when and where is the tough part

one thing might be to buy a working board, build a second test rig so you can see what there should be, where and when
 
Yeah, I have a second board that is working, but since this one doesn't even seem to boot up, most of the settings are not the same anyway, at least that is what I am finding.

I know my Z80 CPU is good, I just don't know why nothing is moving on the Data or Address buses.

Ed
 
I know my Z80 CPU is good, I just don't know why nothing is moving on the Data or Address buses.

Theres more to a Z80 than the address and data buses, the address bus is controlled by the Z80 so as it is doing nothing it looks like the Z80 isn't even trying to run.

Here's where you go next.

1) Check that the clock pin (pin 6) is active, if the CPU has no clock it will never do anything.
2) Check the /RESET pin, this should be high, if it is low then the CPU has the handbrake on. If it is stable low then the Z80 should be running if it has a clock signal. If it is pulsing then the boards watchdog system is trying to bring it up, usually means there is a bus error or bad RAM/ROM or addressing logic somewhere.

3) Check the /HALT pin, this also should be high, if it is low then potentially there is a bus error.
 
First z80 U1/U1 (Slave CPU)
OK, Clock is reading Hi/Low on my probe (which means Square Wave?). I am not sure what that means.

Reset is showing LOW

Halt is showing HIGH

----------------------------
On the Second Z80 (Master CPU) U67/U99b

Clock is the same

Reset is High

Halt is Low

Looks like the CPU I wasn't paying as much attention too is the master CPU.




This may be a really dumb question, but. There is a 5v test point on the board. I turn the board on and measure it, it's at 5.21 (recommended for this game). I keep the meter on it and it goes to 5.22, 5.23, 5.24. Leave the meter off a few seconds and check again, 5.27, 5.28. I was wondering why some of my chips were getting so hot. It got up to 5.44 before I shut it off. I can't believe that is normal. What could be causing that?
 
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I would ignore the slave CPU until the master is going.

I'm not 100% sure on this board but on the Galaga boards the other 2 CPUs won't come out of reset until the master CPU boots up. I would expect something similar here.

The Z80 will show no activity on the address/data busses while in reset. They will also show no activity on the address/data busses or show random crap on the busses if not reset properly.

Use your logic probe and check the reset line on the main CPU. It should start out momentarily low then flip to high and stay high. If it's not then check the reset circuitry. I've seen this happen on boards where the cap in the reset circuit was physically broken off the board.
 
Thanks,
You can see my post above, the Main CPU Reset is on High.

Should I check to make sure it starts low when the boards is powered and then switches to high?


And wow, your website has a wealth of information. Gonna be reading up on stuff there :)
 
I have nothing to add, but this is an interesting thread! I hope you get your board fixed, I have an untested one that may need some fixing. :p
 
OK, so the when I turn power on the Reset line of the Main CPU is low for just an instance. Basically flashes green and goes to red (high)
 
OK... That sounds normal. You can always momentarily short the reset pin to ground to see if it comes up. If it does then the reset pulse isn't long enough on start up.

Next check to see if the /CE or /OE lines on the program ROMs are working. If they are NOT then the CPU isn't coming up for some reason. It could be a buffer or latch on the address or data lines... or something doing address decoding... or something handling interrupts or read/write signals.

If the /CE and/or /OE lines are working on the program ROMs then check the CPU RAMs to see if the enable lines for them are working and if there's activity on the R/W line.

RJ
 
OK, I shorted the reset to ground and nothing happened.

There are a TON of ROMS on this board (top and bottom board). Is there a way to determine the "Program" roms, or are they all program roms?

The /CE should not read HIGH correct?
 
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Nothing to add either....But I am following this thread closely ArcadED! I have 4 Super Offroad Boards that are FUBARed that I need to get going.....Keeping my fingers crossed you make some progress....
 
Ok, on the bottom board I have 3 nmc27c256q-200

U93, U94, U95
CE is pin 20, low on all three.

Then I have 5 27128. These have a Chip Enable /E, Output Enable /G and Program /P

U3b -
/E - High
/G - High
/P - High

U67 -
/E - Low
/G - Low
/P - High

U69
/E - High
/G - Low
/P - High

U90
/E - High
/G - Low
/P - High

U92
/E - High
/G - Low
/P - High


Also a question. The bottom board has 4 TMS 4464-10L These are RAM. The 4 on the board got so hot, I actually burned my finger on one. The socket underneath looks slightly melted. NOW, I took the same 4 chips off my other board. They are not the same number, but close V53C464P10L. Now with those chips in, they never get hot. ?????? No change on screen btw.

Thanks
 
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It's normal for chips to get very warm, but NOT normal for them to remove skin from fingers or cause blisters. ;)

Those chip enable lines should NOT be stuck low unless they are tied to ground. It's common for one to be tied to ground and the other to be used to single-handedly control the IC chip. However, that other one should not be stuck low. It should be flipping between low & high as the ROM is being read. If it's stuck low then you have a problem.

Do you have an EPROM programmer? If so, read the ROMs in and use a program such as ROMIdent to identify them. If one can't be identified then use the 32bit checksum output of ROMIdent to search via Google to see if it's known to MAME. If you find one that is bad (doesn't match any checksum) then replace it.

If you find that several don't match then make sure you don't just have a different revision of a game that isn't in MAME. If you ever run across one like that, save all the ROM images then try the version in MAME as you still may have a bad ROM.

To identify what each ROM does you go to http://maws.mameworld.info/maws and search for the game. Once you find it scroll all the way to the bottom and find the link for the game in Caesar. Caesar will list what each ROM is for (GFX = graphics, CPU = program ROM, etc...)

If you don't have an EPROM programmer and eraser then you need to get them.

RJ
 
RJ,
Yes I do have a programmer and I have dumped them all and they are all good.

I even dumped every rom into a folder and replaced all of the ones in mame and ran the game, ran fine.

I have also checked them with RomIdent and with a Hex program that compares files.

CAESAR lists U67b as region USER1. Not sure what that means. http://caesar.logiqx.com/php/emulator_game.php?id=mame&game=offroadt

Where does that leave me? Possible bad socket?
 
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