Электроника МС 0511 (Elektronika MS 0511): Quick Update 3-Dec-2022
14Still no progress ... still the same issue ... at least I've not broken it more, I guess.
The video RAM is supposed to be three banks of 32KB ... I've now checked two banks (64KB in total) and no improvement.
I found that pins 2 (data in) and 3 (write enable) were some how shorted on the last DRAM (DS8) I socketed, so have replaced that socket and am back to square 1.
I replaced the final DRAM (DS6) in the block of eight and no change.
There are two inverting buffers on the address lines ... D11 and D12 ... these are КР531ЛН1 (KR531LN1 == 74LS04). I socketed these and replaced with 74HCT04 ... still no difference.
The 192KB of RAM is arranged physically in two rows of 12, from the left side of the board:
D11 DS13 DS15 DS17 DS19 DS21 DS23 DS25 DS27 DS5 DS7 DS9 DS11
D12 DS14 DS16 DS18 DS20 DS22 DS24 DS26 DS28 DS6 DS8 DS10 DS12
I have replaced DS5 to DS12.
There could still be a DRAM causing the issue ... ?
If it's the ULA-type chip (К1515ХМ1-136) then I'm pretty stuck unless some supply outside of Russia magically appears ...