ПК-01 Львов (PC-01 Lviv): Part 7 - ROM Troubleshooting started
26I got feedback on the Lviv forums that it could be a ROM issue, in that the BASIC wasn't booting.
http://pc01.lviv.ua/forum/viewtopic.php?f=2&t=489
Unfortunately only one of the machines has all the ROMs socketed, and this is the one that was stripped for a few roubles of previous metals. The other two machines only have the C000 ROM socketed (why?).
Also, of the three machines, two uses plastic DIPs for the ROMs and one uses nice ceramic ones. The ROMs are КР573РФ5 (KR573RF5) types, equivalent to a Western 2716, holding 2Kbytes each for a total of 16Kbytes of ROM.
Each ROM has address lines A0 to A10, with a КР1533ИД7 (74LS138 3-to-8 decoder) using A11 to A13 to select the eight ROMs.
When I put the logic analyser (Saleae Logic Pro 16) on this chip (D9 on the schematic) it appeared the O5 was not working, remaining active low all the time. This is the enable line for ROM D15.
I removed the suspect part and replaced it with a 74LS138 - no boot screen this time, just garbage. Checking the analyser again I could see O5 was now working, but it looked like the CPU was just stepping through addresses, like it can't find any executable code (just NOPs) in the ROMs to execute ... ?
Quick summary: The PC-01 Lviv is a Soviet Ukrainian machine built around the КР580ВМ80А (KR580VM80A, the Soviet clone of the Intel 8080). There was also, briefly, the PC-02 Kyiv ... I have one sample that is under repair.