New PAL-1, Still troubleshooting

[Christopher Bock]

I ordered my PAL-1 kit (and all of the expansion boards) back in May, but I've had troubles sinc that have prevented it from working properly.

When I first put it together it worked. Entered in a counting program and everything. But not long after the displays cut out and I couldn't get them back. I checked all the usual stuff. Voltages, bad solder joints, reseating ICs, etc. Finally I got to the clock. The 1mhz clock signal was just gone. I ordered some new 1mhz oscillators on ebay. Clearly the the one that came with the kit was flakey at best. Those arrived today. I soldered in a new oscillator and bam, it worked again. But after about 10 minutes or so it just stopped again. I was still getting 5v and the regulator didn't feel overly warm, so I wasn't going to blame it yet. And this time I was still getting a 1mhz clock signal.

I found a few discussions in this group and followed them. I couldn't connect to serial. I tested the 74L ICs. The reset was causing the reset pin on the 6502 to switch. Everything seemed in order. Then I remembered that I had a second RIOT chip from my order. I did one final check for shorts and popped in that chip. Bam. Now the machine is working and has yet to shut off after a couple hours of use. 

A bad RIOT and a bad Oscillator in the same project! oof. 

I still can't get a connection with my serial to usb cable. I'm following the setting described in the instructions, but nothing. Any ideas? 

[GN Liu]

Hi Christopher,

[this message was copied from Tindie message] 

Thank you for providing more detailed information about the issue.

 

The oscillator is brand new in the kit, so it's unlikely to be broken. The most likely cause of the failure might be the 6532 chip, as it is a recycled chip that went out of production a long time ago. Although I checked all the major chips, including the 6532, before packaging, the testing process only validates the basic functions of the chip. There may be some hidden issues that I could not detect, such as robustness. I apologize for any inconvenience this has caused. I appreciate that you identified the real problem. From one perspective, the process of troubleshooting can also be part of the experience when working with a vintage computer kit.

 

I will send you a replacement chip and oscillator for free, which will be shipped within 3 days to your order address.

 

I hope you will continue to enjoy playing with the PAL-1 in the future.

 

Best regards,

Liu

[Christopher Bock]

Liu, Thank you so much! I don't think anyone blames you for these vintage chips being flaky. That's pretty much par for the course at this point. Your kits are actually really great! Organized and well packed. And I completely agree that troubleshooting kits like this (or anything scratch built from some else's design) gives way more insight into how these machines function than if it just worked right away. I've spent the last two decades thinking with z80 machines that I built from kits (and one cosmac elf that I wire wrapped from scratch), but I've learned far more in the last couple of months about UARTs and their role in how these CPUs communicate with the world from troubleshooting this kit and a an Altair clone I built (and now trying to get the serial board working).