Bubbles - dead with no error code

joeycuda

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I hope someone can point me in the direction to get it working. I bought a Bubbles project, complete with all original boards in it, but dead.

First thing was, the p/s didn't have all of the voltages. I did the Bob kit (except for the heat sink transistor and 2 ICs) on it and replaced the 4 headers on the p/s, and replaced the corresponding IDC with molex housings and trifurcon crimp pins. Still (LED 2 I think?) out, so I replaced the big BR, adding a heatsink, then replaced that heat sink mounted T03 transistor and the 2 replacement ICs. Noticed that the connector from the big heat sink was BURNED, so I replaced that connector as well.

All voltages check out. Well, at the p/s, it's 4.95 volts, -5 and 12 are about bang on.

At the ROM and RAM board, I measure about 4.93 volts.

Still dead with no action on the error display on the ROM board. I removed the ROM board and can see where someone touched up the solder joints. The boards though are very clean.

What should I check next? I hoped it was a p/s and connector issue entirely, but not this time..

Thanks for reading through this and for any advice...
 
Start with a logic probe or oscilloscope...

Check the clock signals first. Next check the reset signal and see what it is doing. If stuck low or stuck high (should be low momentarily then go high on power up) check that.

After that, check the address/data busses and the program ROMs.

RJ
 
Check the model numbers on the boards. Bubbles is a special case and the Bubbles ROM board (5771-10177-00) will only work with the Bubbles MPU boards (5770-10179-00).

There is another thread (link) recently that had a similar issue.

If they both check out, check pin 37 on the CPU chip with a logic probe. This is the RESET line. It should show HI. If it is pulsing, that is the watchdog circuit resetting the CPU chip because something is stopping the CPU from addressing a specific address to reset the dog.

ken
 
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