🇺🇦 ПК-01 Львов (PC-01 Lviv): Part 8 (Where Was I?) [TCE #0610]
32Sorry, this one is a bit long - I now have a fourth machine that looks in good shape (ahem) and as it's been a while since I worked on these machines, let's try to get back up to speed and get one working. After this video I might have an idea what might help, although one or more of the ROMs may also be suspect and require de-soldering and re-programming ... a hassle which is why I've not done it yet.
Soundtrack: The Twilight Sad
https://thetwilightsad.bandcamp.com/
00:00 ... Intro
06:30 ... Opening machine no. 4
13:40 ... Examining the motherboard
15:21 ... The Twilight Sad
16:20 ... Damn capacitors
23:40 ... Okay, this is the nicer looking machine (ceramic EPROMs, original KM capacitors)
24:45 ... Power cable shibari
27:30 ... Power on test - NOK
29:05 ... Data bus contention?
32:00 ... Final thoughts
32:40 ... Channel thanks & Outro
Repair notes:
https://github.com/codepainters/lvov
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From Part 7:
I 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
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.
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Music by Karl Casey @ White Bat Audio
https://karlcasey.bandcamp.com/
/ @whitebataudio