Road Blasters needs saving baaaad

ComputerBooter

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Whats up guys, just purchased this road blasters cab and it basically turns on with garbage all over the screen.

When I have the game PCB plugged in, the scrambled mess is even worse. At this point all I am trying to do is actually get the Atari System 1 board to power on properly. Without the game cartridge in, just garbage shows up on the screen.

I have tested 5v power and that seems good.

I have an oscilloscope (just got it so not to versed on how to use it properly, but am a quick learner!)

The bottom LED on the mainboard lights up, but the top LED does not do anything. I have grounded WDIS after poweron and that changes nothing.

Where in the heck do I go next?!

I have connected the scope to pin 15 of CPU and I see activity, but cannot verify that it is correct since I dont know how to use the scope properly. I have tried to view the reset line (pin 18) but get the same result as pin 15.

Here are a few pics

The second picture is strange because the 2 leads were cut behind the PCB and then fixed like this (but they are actually reversed) (when I swapped them it made the garbage on the screen scroll up continuously so I put it back to how I found it and the scrolling stopped)

Thanks in advance for any help, would love to get this bad boy up and running to share with our customers (we are a local repair/retro shop!)
 

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Also wondering if the power supply is correct. There is a loose wire thats burnt uo on the end.
 

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I just popped out the CPU for giggles and the same screen pops up, so im thinking the CPU is dead for sure, I have a spare 68000C8N64 but it doesnt do anything different with it.

Anyone got any advice?? I just ordered a logic probe so that should be here in a few days.

TIA
 
Here is a picture of what it looks like when the game cart is connected, scrambled Video with yellow lines through it.
 

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I love Road Blasters, but I don't know if I have much to offer. First, check the voltages on the power supply. Then check the voltages on the board. If there is any doubt, change the power supply as they are cheap. Next, look for corrosion on edge connectors. Clean with Deoxit if there is any corrosion or other concerns that there isn't a good connection. Finally, check all seated IC's for corrosion. Carefully remove them and reseat each of them. If non of the above works, I would suggest you send the board out for repair.

Most likely your fire buttons will not work. Look for my post on here on how to repair them.

While not likely causing your immediate issue, I always check each capacitor on the board with a ESR meter while I have it out.
 
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I love Road Blasters, but I don't know if I have much to offer. First, check the voltages on the power supply. Then check the voltages on the board. If there is any doubt, change the power supply as they are cheap. Next, look for corrosion on edge connectors. Clean with Deoxit if there is any corrosion or other concerns that there isn't a good connection. Finally, check all seated IC's for corrosion. Carefully remove them and reseat each of them. If non of the above works, I would suggest you send the board out for repair.


Most likely your fire buttons will not work. Look for my post on here on how to repair them.

While not likely causing your immediate issue, I always check each capacitor on the board with a ESR meter while I have it out.

Thanks for the reply brother, the voltages on power supply and test points are all 5-5.2v
I have removed all the IC's and reseated them.. I am going to try to get my hands on a new CPU because I have a feeling that its bad. I am getting my logic probe tomorrow I believe so i'll start checking with that once I get it. But I am def going to get a new CPU put in this one and test that first.

Ill keep yall updated if anyone is interested!
 
Good luck and I'm interested to see how it works out.

I thought you already swapped the CPU. Was that not a known good one?

The great thing about Road Blasters is the T-shirt promotion during the attract screens.
 
Good luck and I'm interested to see how it works out.

I thought you already swapped the CPU. Was that not a known good one?

The great thing about Road Blasters is the T-shirt promotion during the attract screens.

well the system 1 board has a 68010 in it, and I have a spare 68000, which might just not be compatible?

Today I believe I found a few pins on the cpu that had no continuity to the pins on the bottom of the PCB so I ran some wire but that didnt do anything different.

From all the videos I see it sure looks like I have a CPU problem, especially since the screen stays static and doesnt change when turned on, there might be bad characters on the screen but they aren't doing anything, so the CPU isn't executing code.

I was messing around with my oscilloscope today and was trying to read the signals for the clock and the reset lines on the CPU (Pins 15/18 respectively) and was getting the same waveform on for clock/reset (I even used the schematic and read the reset signal from a chip on the other end of the board and got the same waveform. So not sure if that means the reset (watchdog?) is triggering? Id figure if it was resetting I wouldn't get static garbage on the screen but who knows.

On another note, looking forward to seeing the T-Shirt attract screen haha! I actually read about it in the service manual so I was aware of the mail-in but didn't know it had an actual screen advertising it, haha thats cool.
 
So the reset line on the CPU is stuck low, so I got the schematics and measured all the signals near the reset circuitry, but need some help. Hopefully this picture makes sense.

LS197
Pins:
1 - High
2 - LOW
3 - LOW
4 - LOW
5 - LOW
6 - LOW
7 -
8 -HIGH (Vblank)
9 - LOW
10 -
11 -HIGH
12 - LOW (SYSRES should be high?)
13 - LOW

The picture I drew has arrows pointing up and down for the measurements I got with the probe (HIGH/LOW)
 

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Just noticed something, the IC at location 4a in the reset circuit is a NOT gate and the input at pin 9 is oscillating high/low, and the output is also oscillating high/low... I am going to try tracing back maybe the capacitor at c159 is bad?

I would assume that the input/output of the gate should not be oscillating?


TIA for helping this newb
 
I have almost the same problem on a Marble Madness. the only reason I didn't post about it was cause I knew I would get the same reaction you are. (which has been a commonplace fixture for me my entire 11 years here)

I have an extra set of boards coming in, I'm hoping just swapping the CPU board will get it. I have a lot of other projects going this week, otherwise I'd tinker like you are.

are you just running the board outside the cab feeding power into the test points?
 
I have almost the same problem on a Marble Madness. the only reason I didn't post about it was cause I knew I would get the same reaction you are. (which has been a commonplace fixture for me my entire 11 years here)

I have an extra set of boards coming in, I'm hoping just swapping the CPU board will get it. I have a lot of other projects going this week, otherwise I'd tinker like you are.

are you just running the board outside the cab feeding power into the test points?

No I have the board turned a bit inside the cab, not comfortable pulling the PSU out yet, its weird and looks like its using some of the old PSU and some of the new switching PSU... might even be part of the problem I dunno. Just need a push in the right direction...

First thing is first and I need to figure out why the reset is stuck low. I have been trying to figure it out, but obviously have much more to learn.

As far as I can tell the 74ls14 that supplies the reset signal (high) is messed up and is outputting an oscillating signal and I don't think its sposed to do that. I can pull a 74ls04 and try that but it might need the 74ls14.
 
our game had a separate issue where the sound would just quit. if you go in test mode, then sound test, it would reset the sound CPU (6502) manually and it would work again for awhile. it would also show the error "Sound CPU ROM 1 error" which the manual only states is a failure of the 6502 ... which wasn't the case.

it's kind of infuriating knowing $700 was dropped on this kit and the board fails within a month of the arcade being open. there's also like no information on fixing these.
 
So the reset circuit in the schematic says it has 10.3v coming in, but the only power I have going into the board seems to be 5v.

As I said earlier the original PSU is still in the cab, along with a switching power supply, looks like parts of both are being used?!

Do I need this 10.3v line? or does the reset circuitry work fine with 5v? I see the 5v comes in through R106 and has to do with the Q line input to the ls197.

So should I be getting 10.3 volts here?
 
I think I have some schematics for the original ps. If im not mistaken the reset signal is generated on the original power supply. I'll look when I have a free min or 2.
 
I think I have some schematics for the original ps. If im not mistaken the reset signal is generated on the original power supply. I'll look when I have a free min or 2.

Thank you bro!

I have looked at the schematic and you are right the 10.3v unregulated comes from the audio III PCB the orange line (4)

I am confused though, the reset circuitry starts off with this 10.3v and then it runs through Q12 transistor correct?

Why does the reset need 10.3v when it only uses a 5v high pulse?

Attached are the pics of the Audio III PCB 10.3v reset signal
also the pic of the reset circuitry I drew from the schematic.

Appreciate the help!
 

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When I bridge pins 11+12 on the ls197 that outputs the HIGH SYSRES signal to the CPU the whole board shuts down. I assume this means their is a problem after the CPU?
 
yippeeee got somewhere, I bridged pins 1+8 on IC at location C10 which supplies the high sysreset signal to the CPU, and I got no cartridge on the screen!

gunna try with the game cart plugged in and see what I get
 
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