🇸🇰 SMEP PP 01: Part 3 (First Power On - NOK) [TCE #0463]
36TL;DW (too long; didn't watch) ... it currently doesn't display any video at all, not even a black screen. Some tantalums failed initially (surprise) and were replaced but the lack of video remains.
As @lilbill6089 suggested I replaced the two capacitors that looked to be serving as X-class safety with a proper X-class safety capacitor ... the same as used in the Tesla PMD 10 power supply.
I also gave the EPROM board and RAM board a wash.
Before dismantling the keyboard I decided to give it a quick power on test to see if it was actually working on not.
I had to make up a new RGB cable as the pinout didn't match any existing ones I'd made:
Pin 1 = green
Pin 2 = ground
Pin 3 = blue
Pin 4 = synch
Pin 5 = red
On the first power on nothing happened - no video output at all and the power supply LED was not lit, indicating perhaps a short on one or more the four power rails.
I disconnected the keyboard to start isolating the issue. On the next power on I heard a pop and saw a little bit of smoke ... as expected, at least one tantalum had died ... on the EPROM board.
Removing the EPROM board and the power supply LED lit.
So I replaced the four tantalums: three 47µF with electrolytics and one 2.2µF with another tantalum.
This time the machine powered on - the power supply LED was lit and I could get two of the [INT] LEDs on the keyboard to light.
But still no video output. I checked the video signals quickly and saw no activity.
So, lots more troubleshooting ahead.
An excellent set of re-drawn schematics can be found here:
https://www.sapi.cz/klony_sm5040/pp01.php
From Part 1:
SMEP = Systém Malých Elektronických Počítačov (Small Electronic Computer System), and
PP 01 = Personálny Počítač (Personal Computer).
It was developed at the Computing Technology Research Institute (Výskumnom Ústave Výpočtovej Techniky = VÚVT) in Žilina and manufactured at the Computing Technology Plant (Závodoch Výpočtovej Techniky = ZVT) in Banská Bystrica (now in independent Slovakia).
A good source of information & emulator:
https://pp01.borik.net/index.php