Hi Well it happened Sunday. Right in the middle of copying some disk on my Poly 8813, it died. I tried to reboot but nothing seemed to work. I tried all the obvious things like swapping the RAM addresses around on the main RAM boards and swapping RAM chips around on the CPU board before I realized that I was going to have to trace it out. The Poly's have a built in machine video front panel monitor. With all the boot ROMs loaded, it wouldn't come up but if I removed one of the ROMs, I was able to get the monitor working. I did some quick checks of the floppy controller card and that seemed to work. Placing the ROMs in the extra socket, I wrote a simple checksum. Again, not problem found. They all matched my copies that I'd filed away( One should always have backup of machine ROMs ). I guess now, I was forced to look at the symptoms and use that to track down the issues. Something I should have done from the start but I kept expecting something simple. I noted that the processor was clearing the video and starting the floppy but not doing the steps to track zero. When the ROM was removed, all seemed to work OK so the basic processor operation was OK. It was something in the process of getting the floppy read. I reentered the monitor and was able to write some simple code to verify that, yes, the controller could step both in and out. Still, this was were it seemed to be hanging. A while back, I'd made a listing of the code so I figured I'd look through that. Following the code, I could see the video clearing and then the setting up of the disk access. I could see where the drive was selected and then there was a wait for delay. Bingo, the timer interrupt was not happening. Now I had something to trace down. Following the interrupt ended me on a daughter card that was tacked onto the CPU card ( I didn't have the schematic for the daughter card but it only had 3 chips ). A little more looking and I found a miss behaving 74LS75. I found a spare on one of my scrap boards and replaced it. After about 4 hours, I was back in operation. Why is it that the latching and flopping ttl parts seem to have such a high failure rate? Dwight