QA in the reset circuit was bad causing that the reset line went high at the same time as the 5v was applied to the board. This fault was a bit tricky to find, it’s not so easy to measure the short delay of the reset, but after some thinking I realized that the watch dog didn’t reset the CPU as it should and by measuring from the watch dog circuit through the reset circuit I found the faulty transistor. The strange thing is that it measures OK, but after changing it the CPU booted again. I also tried out the CPU board from the second Coney while repairing the Star trip CPU. I wrote earlier that it looked like brand new, but this turned out to be not true. It has had an acid damage but someone had cleaned it up good. When I first tried it it didn’t give any flashes at all, but there was traffic at the address and data bus and this indicates faulty ROM’s. After rebuilding it for EPROM it booted as it should.
måndag 23 juli 2012
Star trip delivered
I have finally delivered the Star trip. It was ready to go a month ago, but when powering it up a last time before delivery the CPU was completely dead. I hate when things like that happens, but it was at least good that it happened while the game was still in the workshop.
QA in the reset circuit was bad causing that the reset line went high at the same time as the 5v was applied to the board. This fault was a bit tricky to find, it’s not so easy to measure the short delay of the reset, but after some thinking I realized that the watch dog didn’t reset the CPU as it should and by measuring from the watch dog circuit through the reset circuit I found the faulty transistor. The strange thing is that it measures OK, but after changing it the CPU booted again. I also tried out the CPU board from the second Coney while repairing the Star trip CPU. I wrote earlier that it looked like brand new, but this turned out to be not true. It has had an acid damage but someone had cleaned it up good. When I first tried it it didn’t give any flashes at all, but there was traffic at the address and data bus and this indicates faulty ROM’s. After rebuilding it for EPROM it booted as it should.
QA in the reset circuit was bad causing that the reset line went high at the same time as the 5v was applied to the board. This fault was a bit tricky to find, it’s not so easy to measure the short delay of the reset, but after some thinking I realized that the watch dog didn’t reset the CPU as it should and by measuring from the watch dog circuit through the reset circuit I found the faulty transistor. The strange thing is that it measures OK, but after changing it the CPU booted again. I also tried out the CPU board from the second Coney while repairing the Star trip CPU. I wrote earlier that it looked like brand new, but this turned out to be not true. It has had an acid damage but someone had cleaned it up good. When I first tried it it didn’t give any flashes at all, but there was traffic at the address and data bus and this indicates faulty ROM’s. After rebuilding it for EPROM it booted as it should.
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