dead Blasteroids PCB

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So I finally got my eprom burner tonight and spent time verifying roms for my Blasteroids. Currently the board is 99% dead and has been for most of the time. Initially it gave a rom error so I thought I'd verify the rom in question (4C I believe) when my burner arrived. I ended up finding 4 that read as really messed up and was able to erase and re-program them. At first I wondered if I was not using the burner correctly but a large group of eproms on the other side of the board verified fine (comparing these to the MAME set). So like I said the board is still doing what it did before which is mostly nothing. If I put it into test mode and re-boot I can get a few screens of changing color like it should normally do but then that's it. Game mode gives nothing at all. Power as measured across a TTL chips is at 5 volts. At this point I'm guessing maybe processor or checking to see if the clock is even running? Anyone have any thoughts on this?
 
If you get screens of changing colors then I'd think the clock & CPU are running.

Check the enable lines for the ROMs and RAMs to see if they are working.

Do you get activity on the program ROM data and address lines when it's in normal (not test) mode?
 
Thanks for the reply channelmanic. Unfortunately this is what separates the men from the boys in terms of technical knowledge. I can grasp what the purpose/concept of these various data lines are, but I do not understand how to test them. I assume they must be easy to check with a logic probe since it's just activity I'm looking for, correct? I do own and know how to use a probe for checking things...mostly I've used it for clock and watchdog checking. Anyway, if you can point me in the right direction I'd really appreciate it.
 
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Many systems use only one of the EPROM control lines and leave the other one permanently enabled by tying it to ground. I haven't looked at the schematics for this game to see if it's that way too... A logic probe will tell you quickly if that's the case.

There should be activity on the address and data busses. The CE* line and OE* lines will only be active when they are low. If you have one line tied low and the other never goes low then the chips won't be read. Typically on a board you'll see that the first ROM being read will have low pulses on the enable lines. If NONE of the ROMs have low pulses on the enable lines then you have an issue with the address decoding circuits.

Also, the logic probe can show activity but the busses could be in a bad state. I've seen many systems where there are pulses on the busses but they double in pulse speed from the highest address line down to the lowest (and fastest pulses) address line. That could be indicative of bad RAM, ROMs, sockets, or address decoding.

If this is another one of those silly Atari games with the 28C04 or 28C16 EEPROM chips connected to the CPU then it's possible that chip went bad and is tying up the bus. It wouldn't be the first time that has happened.

RJ
 
Thanks again for the reply. I'll have to see if there's a copy of the schematics at arcarc or another site and then I'll do some digging. There are some rom files from the mame set that I couldn't mess with because the burner didn't seem to be able to read them...not sure if there were 28C04s or 28C16s or not.
 
verify you have about +5.1 volts going into game board

sometimes a low +5V will cause those problems you describe

get your multimeter and put black on the GND on the switcher and the red probe on the +5 volts. i think there might be an adjustment pot on the switcher there where you can adjust it. dont be adjusting it without a multimeter as voltage over +5.25 may cause damage
 
Bumping this one with an update. I decided to try poking around with my logic probe to see what I can find. I may have my some progress, but hopefully someone more knowledgeable can be the judge. I probed the chip and operate enable lines on chips 4B, 4C, 6B, and 6C. The game has sometimes shown a rom error for 4C in test mode so that's why I started in that area. I didn't get any reading for the operate enable lines (pin 22) on 4C or 6C which I assumed wasn't good. From looking at the schematic, it looks like all 4 of these chips share that same operate enable line so I'm not certain why 2 show activity and 2 don't. Looking further at the schematic, I checked out pins 4, 5, and 6 of the TTL chip at location 12B....should be controlling the enable line for the 4 chips, correct? Both inputs at 4 and 5 and the output at 6 all read the same according my probe...both the high and low indicator led's were lit. I'm not certain what to make of that. Any thoughts? Hopefully it's some kind of small victory for me hehe. BTW, the schematic can be seen here. Page 5 shows the 4 eproms and how the operate enable line relates to the TTL at 12B.

http://arcarc.xmission.com/PDF_Arcade_Atari_Kee/Blasteroids/Blasteroids_SP-316_1st_Printing.pdf
 
High/low means the line is changing from high to low to high... in other words there is activity on it.

The /CE and /OE lines must be active on the ROM for it to output data. If one or both of them are high then the chip isn't outputting data as it's not being told to.


If the schematic shows all 4 /OE lines being connected together and you don't see activity on 2 of the chips, verify continuity between the 4 ROMs and the chip driving the line. If continuity is there then replace the chip driving the line.

Raymond
 
Found a continuity break between the 4 chips. I fired the game up and no dice. I then started probing to verify all 4 chips had activity on CE and OE. I think during this process was when I only hooked up video and power and didn't bother to hook up anything else. The game now boots up with sound and video! Oddly enough I now have a problem where plugging in the control panel connector at the pcb causes it to not boot. I'm assuming it has to be some kind of stuck switch or something with the spinner controls. :confused:
 
Yep turned out to be a leaf switch that was always closed. Board now boots up with controls hooked up. I'm still 99% sure that jumping those pins was needed. I don't think that button by itself would cause the rom error i had seen before.
 
Yup... Jumpering that trace got the signals to those chips that they needed to work. :)

Congrats on fixing the board!
 
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