🇺🇦 Міко-Спектрум (Miko-Spectrum): Part 2 (Troubleshooting Begins) [TCE #0482]
31Let's see if this machine actually works (TL; DW ... no, it doesn't seem to).
{TL; DW ... too long; didn't watch}
It strangely uses Soviet РГ (RG) type connectors instead of DIN for the power and RGB output, which is why I didn't get far in Part 1 (TCE #0414). But let's bypass these for now to see if it works.
It uses a Soviet Z80 clone, the КР1858ВМ1, which has a 2.5mm pin pitch.
BUT ... @charlesdorval394 has creared a Soviet-2-Imperialist converter board ... something I've been meaning to do for some time.
If I do have to replace the Z80 then I'll try one of these out:
https://github.com/deskwizard/Breakout_PCBs/tree/master/Boards/40Pins_Wide
The video output connector has more connections than required for plain RGBS + ground, so I assume it includes sound at least ... just complicates trying to figure out the pin-out.
So ...
As it has an RF modulator output, let's just try the baseband composite video signal.
I noticed that three decoupling capacitors (I assume) have been removed by someone after a few Roubles worth of scrap, so I replaced them with axial 100nF capacitors.
I had to adjust the voltage in to between 6.5V and 7.5V to get anything to function, apart from the oscillator. Not sure what is going on there.
But it seems to be working intermittently. When I think I'm getting a video signal, it stops.
I'm not too happy with the input voltage ... I'm wondering whether this is causing the instability. I'm tempted to install a 5V regulator and then just blast it with 9V, knowing that a nice 5V will be supplied, rather than just increasing the input voltage to account for a loss somewhere ... ?
From Part 1:
Yet another Sinclair ZX Spectrum clone from independent Ukraine, this time built in Ternopil (Тернопіль) by a joint venture company called "Miko" (as far as I can tell). The latest date I can find on the chips is 1994.
The box calls it a "Домашній Комп'ютер", or "home computer", and allows you to program in БЕЙСИК (BASIC).
This appears to be a more cheaply produced computer - the plastic feels cheap and the keyboard is simply made. It also utilises the Soviet version of the Zilog Z80, the КР1858ВМ1 (KR1858VM1), rather than a genuine Z80.
Normally a DIN socket would be used for video and power but they have opted to use Soviet-specific РГ (RG) type connectors for some reason, not available in the West. But my colleagues in Ukraine might be able to source them for me, which would allow me to keep the original ports and create new cables.