🇷🇺 Сириус (Sirius) ZX Spectrum Clone: Part 2 (RGB & Tape In) [TCE #0575]
24A bit of a mixed bag - I managed to figure out the RGBS pinout, although I think the video appears a bit dark ... too many resistors? Most of the time I spent going around in circles trying to figure out the TAPE IN ... it looks like I did finally figure out where TAPE IN and TAPE OUT signals are on the board ... but the TAPE IN is a real mess (in my humblest of opinions) ... I can't see how it ever worked.
I had another crack at it tonight and I finally made some progress - couldn't load anything, but at least the machine could see *something*.
No luck with the speaker output either. Some further work required there.
00:00 ... Intro
05:30 ... Figuring out RGB pinout
10:00 ... Testing RGB output
16:00 ... No audio output?
17:30 ... Figuring out cassette pinout
19:15 ... Cassette input (MIC, TO, tape out)
20:40 ... Cassette output (EAR, TI, tape in) ... confusion reigns
34:15 ... Checking tape signals on oscilloscope
42:00 ... Trying to fix the mess - progress made?
45:44 ... Other БМК-based machines to check
48:18 ... Channel thanks & outro
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From Part 1:
This machine was initially a bit of a mystery - well, obviously it's a Sinclair ZX Spectrum clone. It has all Soviet-era parts (dated mostly 1991 & 1992) including a beautiful, ceramic Т34ВМ1 CPU, a Т34РЕ1-020 ROM (containing the Czechoslovak "Didaktik Skalica" firmware) and absolutely no manufacture markings on the case or motherboard.
Thanks to some sleuthing by Martin (via Patreon) who discovered that the machine (case at least) appears to be a "Sirius" from Russia (confirmed also with UCHC, Ukrainian Computing History Community, on Telegram):
https://sblive.narod.ru/ZX-Spectrum/Sirius/Sirius.htm
Thanks to Eugene on UCHC for his insight:
"Actually, this is one of numerous cheap clones that built around latest Soviet ULA replacement. This one, in particular, created by small garage company with a quite shitty soldering and assembling. And board itself seems to be assembled somewhere using automated production line, so seems they have ordered boards somewhere else and then assemble them in case. This can explain why boards in these instances are different."
This Wiki page about the T34 series of chips seems to indicate the Sirius is from Ukraine, but maybe different "Sirius" ... or it's just wrong:
Sirius (Украина)
https://ru.wikipedia.org/wiki/Т34ВМ1_и_Т34ВГ1
It was initially AC powered with a very simple and unsafe looking transformer (assuming 220VAC-to-9VAC), a КЦ410Б bridge rectifier and a КРЕН5А 5V linear regulator. I will replace these with a simple 2.1mm DC socket for direct 5VDC input (i.e. USB charger). On booting it was drawing about 330mA at 5V.
It utilises a Soviet equivalent to a Gate Array or ULA called a БМК (Базового Матричного Кристалла, or Basic Matrix Crystal) ... the КА1515ХМ1-216. I have had very little success with machines that use this chip actually working ... however it does greatly simplify the circuit design!
The only other major chips are the Т34ВМ1 (Soviet Z80 clone, later called the КР1858ВМ1 or КМ1858ВМ1 depending on case type), a Т34РЕ1 (Spectrum ROM), 64KBytes of DRAM using КР565РУ5 and a few other support chips.
The machine only has three ports: 5-pin DIN for joystick, 5-pin DIN for RGBS video & sound output and a 3-pin DIN for cassette input/output. It also has a reset button.
The keyboard is okay ... but when you pull it apart it does appear to be quite cheaply made.
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Music by Karl Casey @ White Bat Audio
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/ @whitebataudio