On 4/2/2022 5:12 PM, Rob Jarratt via cctalk wrote:
Using tack soldered wires, I have traced back and I *think* I have found something. There could be a fault in E52 (sheet K6, p157 of the PDF). While K6 BUS DCLO L is +5V, I am measuring K6 BUF DCLO H at an average 1.64V with 50us spikes at 2.08V. According to a NatSemi datasheet for the DS8641 (http://pdf.datasheetcatalog.com/datasheet/nationalsemiconductor/DS005806.PD F) the logical 0 output should be 0.4V max and the logical 1 output should be 2.4V min. I also measured K6 BUF DCLO L to be always low, suggesting it thinks the K6 BUF DCLO H is a logical 1. This seems to suggest that E52 may be faulty. Trace here: https://rjarratt.files.wordpress.com/2022/04/e52-dclo-signal.jpg. Regards Rob
Also, consider having a look at whatever E52 is driving - something may be pulling at it's output - a bad chip, a short somewhere in what it drives, etc. That looks to be E53 pin 13, and wherever else that signal might go. And also look at K5 BUS DCLO L, pin 15 of E52, just in case.
JRJ
