🇷🇺 Микроша (Mikrosha): Part 2 (Power On - NOK) [TCE #0623]
30Sorry, a bit of a long-winded one with no payoff at the end - the machine isn't working at the moment.
I removed all the key caps and gave them a wash. The underlying key switches look a bit dodgy ... might look at creating some sort of converter boards so I can use Cherry MX key switches.
The power supply seems to be working okay - I had to replace the fuse holder as the original Soviet 500mA slow blow fuse is smaller (15x4mm) than the M205 (20x5mm) fuses I can source. But that was pretty simple and the power supply seemed to be working quite fine.
The Микроша itself seems to be quite dead - there was a clock signal being generated by the 8224 (КР580ГФ24) but I didn't see any activity on the 8080 (КР580ВМ80А) or the DRAMs (КР565РУ6). No chips looked particularly hot so no obvious shorted-IC that could be causing the problem.
There's a lot of bodge work ... cut tracks, bodge wires, re-soldering work ... so no idea what has been done nor why - it's one of the bodgiest 86RK clones I've come across. Could the issue be as simple as a shorted address or data line ... ?
00:00 ... Intro
05:45 ... Keyboard & motherboard close up
06:59 ... Key switches (replacement?)
11:40 ... First peek underneath the motherboard (yikes!)
16:40 ... Replacement fuse
20:10 ... Replacement fuse holder
26:33 ... Power supply test - OK!
30:55 ... Video pinout
32:02 ... Making the video cable
36:00 ... Power on test - NOK
39:51 ... Checking 8224 clock generator on oscilloscope - OK
43:18 ... Discussing next steps
47:30 ... Channel outro & thanks
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From Part 1:
This just arrived from Belarus today - this Микроша (Mikrosha) was based on the home brew Радио-86РК (Radio-86RK) design and built in the Russian SFSR. This particular example was built in 1988 and cost (цена) 500 Soviet Roubles ... about US$120 (1988). This might seem cheap but consider that this equated to about two months salary.
As it's based on the 86RK it uses the Intel 8080 family of chips (well, the Soviet equivalents). This means that it also requires a tri-voltage power supply: ±5VDC and +12VDC. It does have one but the fuse has blown so I'll need to replace it before attempting to power on the power supply.
It apparently has some differences to the pure 86RK ... for example, the 8253 PIT used for sound. One other major difference to the other 86RKs I've worked on ... this appears to have baseband video output, rather than RF modulated ... yay!
Once I get a replacement fuse and check the pin out of everything from the documentation, I'll be able to try powering it up.
https://github.com/alemorf/retro_computers/tree/master/Microsha
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