🇺🇦 УМПК-Р (UMPK-R): Part 7 (New Keyboard) [TCE

Thanks to #PCBWAY for their ongoing support! https://www.pcbway.com
The new keyboard I designed arrived and looks pretty good, in my humblest of opinions. It should certainly remove any problems with the 40+ year old lavsan-membrane based original keyboard.

I replaced the remaining three original Soviet-era КР565РУ5Д1 32kbit DRAMs with 4164 64kbit versions, but no obvious improvement. I can get a video signal out but still garbage character output, so I guess the 8275 CRTC is working ...

Now that all the DRAMs are swapped, I will need to get back into troubleshooting ... unfortunately only the monitor ROM is socketed and it's not simple to de-solder and try other chips ... the original Soviet chips are 2.5mm pin pitch and I only have 2.54mm pin pitch IC sockets ... over 20 pins this small difference really adds up.

00:00 ... Intro
03:41 ... Key switches (Cherry MX) & key caps (DSA profile)
07:30 ... First fit
08:15 ... Key caps all fitted
10:10 ... Recovering the СНП58 connector
11:35 ... Testing if the keyboard fits ...
13:38 ... Back to troubleshooting - all DRAMs now 64kbit
16:10 ... Final thoughts for tonight
19:01 ... Channel thanks & outro

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From Part 6:
Maybe it's working ... ? As per ‪@sergijtolmeros‬ & ‪@viktoruzhgorod‬ advice, I added a [RESET] or [СБРОС] button to the motherboard ... this grounds the active-low /RESIN reset input to the 8224 clock generator.

I also removed the A7 wiring to 5V (per Sergij). With the [RESET] button I could now more reliably see garbage on the screen 🥹

I still have a lot of info from Sergij's comments in the Part 5 video to digest if I need to continue troubleshooting.

It looks like I might be getting proper character data but my video converter isn't doing its job ... but I was getting some sort of video output before, so maybe that's a red herring ... ?
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From Part 5:
After some effort I managed to replace the four faulty 32Kbit DRAM chips with 64Kbit. Those four bits on the data bus are no longer stuck high when powered on ... and I do get some sort of video output now, but it's all garbage ... so, some problems still!

Still a faulty DRAM there or something else?

The manual, including my rough English translation, can be found here:
https://github.com/0ddjob/UMPK-R_Comp...
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From Part 4:
I've started translating the operation manual (thanks to Grok & ChatGPT) which has helped me to understand the machine a bit more. I'm thinking that four of the eight DRAM are possibly faulty, pulling those bits on the data bus high permanently. So I'll be looking at replacing those 32kbit КР565РУ5Д1 DRAM chips - well, replace one and see if that changes the data bus behaviour.
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From Part 3:
Just continuing on trying to get a video signal out of the machine, similar to the modern РАДИО-86РК implementation before I continue troubleshooting the rest of the machine (if required).

Sergey's excellent reproduction of the Radio 86RK:
https://github.com/skiselev/radio-86rk
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From Part 1:
Here we have another "serially produced" version of the Soviet-era home brew computer Радио-86РК (Radio-86RK) based on their Intel 8080A equivalent, the КР580ВМ80А (KR580VM80A). This fellow comes from Мукачево (Mukachevo) in the Ukrainian SSR (as far as I can tell). There was a 16KByte version (УМПК-Р16) and this 32KByte version (УМПК-Р32).

It is a pretty simple machine, nicely made if we ignore the membrane keyboard with a dozen space bars. It has a four-pin socket for power in, a 5-pin DIN for cassette, RF-output for TV and a DN4612-style expansion port (СНП?).

As it's an 8080-based machine it requires ±5VDC and +12VDC.

My understanding of the special keys on the JCUKEN keyboard layout (thanks to ‪@Mercury13kiev‬ & ‪@sergijtolmeros‬ for their input!):
[ВК] = Возврат Каретки = carriage return
[ЗБ] = ЗЗабой = backspace
[СС] = Специальные символы = special characters
[ПС] = Перевод Строки = line feed
[СБР] = Сброс = reset
[УС] = Управляющие символы = control characters
[АР2] = Автоматический Режим 2 (automatic mode), or more recently Альтернативный Регистр 2 (alternate register)
[СТР] = Система Трансформации Реальности, or [CTRL]
ВКЛ = Бключить (turn ON)
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  / thecluelessengineer  
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Music by Karl Casey @ White Bat Audio
https://karlcasey.bandcamp.com
   / @whitebataudio