Atari Avalanche PCB Dead need help fixing

dyno

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Just picked up a 1978 Atari Avalanche which is not working, the monitor fires up but I am not getting anything from the game board. There is +5 vdc getting to the board but nothing shows on the monitor and when you try to coin it up nothing happens and no sound. I usually work on monitors so the game pcb is something I don't usual work on, so where should I start? Since it is a old game it will be hard to find a replacement PCB so I have to fix this one. Please help. I have looked at the pcb and there are no obvious signs of damage, traces all look good. There is a 4ohm 10 watt wire wound resistor on the board that gets smoking hot for what reason I don't know.
 
Does Avalanche have a microprocessor, or is it just a huge number of random logic chips?

First thing to check is if your clock is running. Do you have schematics for it?
 
It does have a 6502 microprocessor, I also have the schematics. I think the clock is working becuase I have a probe that you can check if there is a pulse signal coming from the legs on the chips and they seem to being giving of a signal.
 
Does this sound right? The 4ohm 10watt power resistor is getting smoking hot, doesn't that usually mean there is a short somewhere in that circuit causing it to get hotter than it should be?
 
Possibly. If the +5V is steady and the resistor is too hot to touch then it's likely you've got a short on the card. Are any other components too hot to touch?
 
No just at that resistor, everything else seems okay. When you say card do you mean the game board?

Yes game board. Try probing C5 pins 5 and 6. That's the watchdog circuit. If it's pulsing then you definitely have a problem on the board.

As for the resistor, it is a power resistor, so maybe it's supposed to be that hot.
 
The first things I do when troubleshooting a dead board are:

1. Look top & bottom for physically damaged traces. Repair them.
2. Look for other signs of physical damage: corrosion on pins and sockets, broken capacitors, etc...
3. Pull the ROMs/EPROMs and compare checksums against ROMIDENT or MAME information.
4. Check for clock and make sure reset is going from low to high on startup but not continuously flipping high/low.
5. Check for dead lines on the address or data bus. May be bad address/data buffers or latches. Could also be chips handling inputs from the sticks/buttons had gone bad.
6. Test the CE*/OE* lines on the ROMs. If they aren't toggling the ROMs are being read. Replace the CPU first then check address decoding next. Could also be address/data buffers/latches connected to the CPU too.
7. Test the CE*/OE*/RW lines on the RAMs. If they aren't toggling then check the CPU, the address decoding circuit, and any address/data buffers/latches in between.

Once that stuff is up you should be able to see some activity. If not, at least you have a big portion of the board working and can concentrate on other things after that like video processing/output.

If you aren't sure what a buffer or latch is, look at 74LS367, 74LS244, and 74LS245 chips. Those are common ones found on game boards.

RJ
 
Just picked up a 1978 Atari Avalanche which is not working, the monitor fires up but I am not getting anything from the game board. There is +5 vdc getting to the board but nothing shows on the monitor and when you try to coin it up nothing happens and no sound. I usually work on monitors so the game pcb is something I don't usual work on, so where should I start? Since it is a old game it will be hard to find a replacement PCB so I have to fix this one. Please help. I have looked at the pcb and there are no obvious signs of damage, traces all look good. There is a 4ohm 10 watt wire wound resistor on the board that gets smoking hot for what reason I don't know.

I've fixed a couple of these in the past...

The 10W resistor always gets hot... it's just a poor design.
 
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