First post, by tsalat
Hi everyone,
I hope all of you are doing great!
I got this board a time ago (https://theretroweb.com/motherboards/s/unknown-386sx-ht18) - I am sorry I thought I have a photo on my phone of the board but unfortunately not, the board looks, however, the same as on the link.
Anyway, the board does not show any sign of life from the beginning and therefore I have decided to look around the KB Bios, RTC, and BIOS and de-soldered everything to see if there is any damage caused by the battery - to my surprise there wasn’t any damage or damaged traces. After soldering everything back in sockets the board is behaving the same - just a note, I didn't have the scope at that time so I was not able to look on the signals at that time.
After I got the scope I have checked all the OSC on the board, all good.
The KB Bios and the RTC is outputting on the Crystal I/O, however, no life on the BIOS at all.
I have checked the signal to the CPU on CLK2 and the CPU gets only 16MHz but according to the documentation it should have 2x the CPU frequency and thus 50MHz.
I have found the documentation for the HT18/C (https://theretroweb.com/chip/documentation/ht … 98435658181.pdf) and the input clocks are fine, PROCLOCK output as measured on the CPU only 16MHz. According to the documentation the 16MHz is if the HISPEED pin on HT18/C is low, and it is low indeed.
The CPU is not getting any hot from what I have tried, and now I am not sure about how this should actually work, hence decided to ask 😀.
- Does the CPU should be at the beginning at low SPEED triggering the HT18 to get HISPEED?
- The HISPEED pin seems to be running to the KB Bios - does that make sense?
- Any idea what to try next?
thank you and best regards, Tomas