Uploaded August 2022 | Updated September 2026, 2 weeks ago
Sponsored by pcbway.com
Part of my Atari ST Mandatory Fixes series.
Today I look at the change that can improve stability across all parts of the machine: overhauling the bus pull-up resistor packs.
The 10 kilo-ohm pull-up resistor packs fitted onto the data and address busses of most Atari STs was barely adequate for the task of stabilising the busses back in the mid-80s. Forty years of degrading boards coupled with the desire to add new hardware to these old machines has rendered them woefully so.
Exxos (of the eponymous Exxos Forum) has investigated this in detail and has found the best compromise value for these should be around 2.2kOhm.
The normal technique is to desolder the five resistor packs that cover the two busses and replace them with 8-way bussed 2.2kOhm resistor packs.
In this video I try something different: fitting extra packs, in parallel, underneath the motherboard.
Mandatory Fixes master thread: exxosforum.co.uk/forum/viewtopic.php?f=17&t=1585
This particular fix: exxosforum.co.uk/forum/viewtopic.php?f=17&t=2235#p27504
twitter.com/thetechnoshed
PCBWay offer PCB manufacture, CNC machining, sheet metal fabrication, 3D printing and injection moulding: pcbway.com
Check out their new price reduction on 4 and 6 layer boards here: pcbway.com/blog/News/Big_News_Sale_Promotion_for_Multilayer_PCB_86a5864f.html
0:00 Introduction
1:45 The Mandatory Fixes
2:18 The address and data bus and their pull-ups
8:28 The plan for today
11:43 PCBWay!
12:34 Adding the resistor packs
29:56 Testing
31:18 Shielding on
34:17 Summing up
Sponsored by pcbway.com
Part of my Atari ST Mandatory Fixes series.
Today I look at the change that can improve stability across all parts of the machine: overhauling the bus pull-up resistor packs.
The 10 kilo-ohm pull-up resistor packs fitted onto the data and address busses of most Atari STs was barely adequate for the task of stabilising the busses back in the mid-80s. Forty years of degrading boards coupled with the desire to add new hardware to these old machines has rendered them woefully so.
Exxos (of the eponymous Exxos Forum) has investigated this in detail and has found the best compromise value for these should be around 2.2kOhm.
The normal technique is to desolder the five resistor packs that cover the two busses and replace them with 8-way bussed 2.2kOhm resistor packs.
In this video I try something different: fitting extra packs, in parallel, underneath the motherboard.
Mandatory Fixes master thread: exxosforum.co.uk/forum/viewtopic.php?f=17&t=1585
This particular fix: exxosforum.co.uk/forum/viewtopic.php?f=17&t=2235#p27504
twitter.com/thetechnoshed
PCBWay offer PCB manufacture, CNC machining, sheet metal fabrication, 3D printing and injection moulding: pcbway.com
Check out their new price reduction on 4 and 6 layer boards here: pcbway.com/blog/News/Big_News_Sale_Promotion_for_Multilayer_PCB_86a5864f.html
0:00 Introduction
1:45 The Mandatory Fixes
2:18 The address and data bus and their pull-ups
8:28 The plan for today
11:43 PCBWay!
12:34 Adding the resistor packs
29:56 Testing
31:18 Shielding on
34:17 Summing up
