Орель БК-08 (Orel BK-08): Part 2
17TL&B;DW {too long & boring; didn't watch} ... made an RGBS+audio cable and got both machines to boot - don't know why the red power LED didn't light on the 2nd machine yesterday.
00:00 ... looking at the 2nd machine
02:00 ... checking the schematics
05:25 ... check the 2nd machine's internal PSU
06:03 ... comparing the two internal PSUs (slight differences)
09:10 ... making a 7-pin DIN video + audio cable
booooooooring
24:50 ... cable is ready
27:10 ... testing the 2nd machine (Zilog Z80)
28:45 ... testing the 1st machine (DDR Z80)
Checked the schematics (link below, djvu format) - the internal switching regulator provides +5VDC and +12VDC to the system. The available schematics aren't very good quality - tempted to buy a NOS machine just to scan in higher quality ... {June-2023 ... done! See below}
https://speccy.info/Орель_БК-08
https://djvu.sourceforge.net/
The 2nd machine has a genuine Zilog Z80 and so I suspect both machines are using 2.54mm pin spacing rather than traditional Soviet 2.5mm pin spacing - for the main chips at least. A genuine Zilog Z80 does fit in the same socket as the DDR clone.
The machine with the DDR clone Z80 doesn't boot properly - multi-coloured garbage on the screen ... DRAM issue in ZX Spectrums?
The machine with the genuine Zilog Z80 boots to the welcome screen ... "Бейсик - Система Вер. 2.0" ... "BASIC System Ver. 2.0" ... but doesn't respond to any keyboard interaction.
So some further work to do:
[1] image the ROMs and burn copies,
[2] figure out why the keyboard isn't working (issue with the K155ЛП9/K155LP9 buffers used in place of the usual diodes?),
[3] figure out the DRAM (?) issue.
Video cable pinout (7-pin DIN):
Pin 1 = audio
Pin 2 = synch
Pin 3 = blue
Pin 4 = green
Pin 5 = red
Pin 6 = ground
Pin 7 = +12VDC (not connected in my case)
Documentation & schematics are available here:
{5-June-2023 ... in progress}
https://archive.org/details/orel-bk-08-documentation
Other videos in this series:
https://youtube.com/playlist?list=PL5pwokf56wMJBOEz2L63fmnHyD5Q3ABJH