Inside the Lell PSR Drum Synthesizer, Part 2 - A Deeeeeeeep Dive!
Channel: Keri Szafir
Date: 2023-08-27

Going through the ins and outs of the Lell PSR rhythm synthesizer a.k.a. drum machine made in the last months of the USSR. After a few days of frustrating work figuring out what was wrong, I got it back up and running. Oh my goodness, this was an awesome relief! You think it's gonna be a babysitting job... nothing farther from truth.

Sharing some insights I gained from reading the info (http://www.dubrovenko.ru/ddssite/dshlelsw.htm, https://ruskeys.forum24.ru/?1-0-0-00000041-000-0-0-1344017700 and https://www.dtech.lv/techarticles_lel_psr.html) and my own reverse-engineering work. Also featuring two little mods I did on the unit.

I may be making another video on Soviet chip markings because they're pretty confusing at first but logical if you know how they're constructed. 

0:00 Intro and Recap
2:55 Info on the Lell PSR
3:39 Panel Design Versions
5:31 Russian User Manual
7:47 Translated and Annotated By Yours Truly
10:20 COP402 Firmware - Lost?
12:10 Notes on the PSR I worked on
14:30 MIDI? What MIDI?! Ranting
16:06 At the Bench... Again!
17:00 VFD Cover Color
17:30 Fixes on the Control Board
18:00 Firmware Storage and Addressing
21:44 The Diagram of Discombobulation! Control Board Layout
23:00 System Architecture
25:50 Memory Subsystem, ROM and RAM
27:45 Battery Backup Issue
29:48 Unimplemented MIDI Functionality
31:40 Buttons
32:50 It Sounds!
33:25 Predefined Rhythm Demonstration
39:05 Putting It Back Together
40:55 How To Screw And Not Get Screwed
44:10 Bottom Board Mods and Audio Out Circuit
47:10 Closing
49:00 Watch Out For Things Getting In The Way!
51:25 Back Panel Connectors and Battery Compartment
53:10 Testing
55:00 Programming a Song
58:20 Firmware Bug?
59:35 Rhythm Programming?
1:00:00 Afterword

Hey @LOOKMUMNOCOMPUTER and @cathode_gay_tube1312 - you're gonna like it! @momtnz and @GLvintageSHOP might be interested too.

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