First post on TI resto

Gemfile

@@ -33,3 +33,5 @@ gem "wdm", "~> 0.1.1", :platforms => [:mingw, :x64_mingw, :mswin]
 gem "http_parser.rb", "~> 0.6.0", :platforms => [:jruby]
 
 gem "jekyll-openmoji", "~> 0.1.6"
+
+gem "jekyll-figure", "~> 0.2.0"

Gemfile.lock

@@ -54,6 +54,7 @@ GEM
       webrick (~> 1.7)
     jekyll-feed (0.17.0)
       jekyll (>= 3.7, < 5.0)
+    jekyll-figure (0.2.0)
     jekyll-openmoji (0.1.6)
       html-pipeline (~> 2.14)
       html-pipeline-negarmoji (~> 0.1.6)
@@ -110,6 +111,7 @@ DEPENDENCIES
   http_parser.rb (~> 0.6.0)
   jekyll (~> 4.3.2)
   jekyll-feed (~> 0.12)
+  jekyll-figure (~> 0.2.0)
   jekyll-openmoji (~> 0.1.6)
   minima (~> 2.5)
   tzinfo (>= 1, < 3)

_config.yml

@@ -31,6 +31,7 @@ theme: minima
 plugins:
   - jekyll-feed
   - jekyll-openmoji
+  - jekyll-figure
 
 # Exclude from processing.
 # The following items will not be processed, by default.

_source/_plugins/overline.rb

@@ -0,0 +1,15 @@
+module Jekyll
+  class OverlineFilter
+    def self.apply_overline(content)
+      content.gsub(/~([^~]+)~/, '<span class="overline">\1</span>')
+    end
+  end
+
+  Hooks.register [:documents, :pages], :post_render do |item|
+    if item.output_ext == ".html"
+      item.output = OverlineFilter.apply_overline(item.output)
+    end
+  end
+end
+
+puts "✅ Overline plugin loaded!"

_source/_posts/2025-03-23-ti99-4a-restoration.md

@@ -0,0 +1,93 @@
+---
+layout: post
+title: "Restoring the TI 99/4A"
+date: 2025-03-23 12:00:00 +0200
+comments: true
+categories:
+---
+
+My father purchased that console in 1982. I was 5 at the time, and it was my very first contact with a computer.
+We used it for 5 years, till we got an Amstrad PC1512 in 1987.
+
+It has been non-working for a number of years, and today I'd like to bring it back to a working condition, if only to show my kids
+what the "computer experience" was like back in the twentieth century.
+
+## What do we have in our hands?
+
+The machine is a European (PAL) model (6 pin DIN component video output, which we used with a PHA2037 RVB modulator).
+
+Model PHC004A (silver console), serial R030174 / 44 83 RCI.
+
+When I opened it up, I first noticed that the VDP was missing! My father mentioned a former colleague opening up the machine at
+some point... So I started with getting a replacement 9929 from eBay.
+
+When connecting the machine to a TV and powering up, I get the typical black screen and continuous tone symptom, which is
+consistent with the failure mode I remember from years back when I had last tried to use it.
+
+## First tests
+
+### Visual inspection
+
+The motherboard shows no obvious sign of damage such as corrosion or swollen electrolytics caps.
+
+### Voltages
+
+* the voltages provided by the mains transformer look good
+* the DC voltages at the output of the power supply board look good
+
+### Clock signaks
+
+The four 12V clock signals at the TMS9900 look OKish. They are not super clean, with significant ringing in particular
+in the negative region, but the frequency and the phase relationships look right.
+
+The four TTL clock signals at the TMS9904 also look about right.
+
+{% figure caption:"12V clocks" %}
+![12V clocks](assets/TI-resto/DS1Z_QuickPrint3-12V-clocks.png)
+{% endfigure %}
+{% figure caption:"TTL clocks" %}
+![TTL clocks](assets/TI-resto/DS1Z_QuickPrint4-TTL-clocks.png)
+{% endfigure %}
+
+The VDP clocks look OK:
+{% figure caption:"VDP XTAL2" %}
+![TMS9929 XTAL2 (40)](assets/TI-resto/DS1Z_QuickPrint5-VDP-XTAL2.png)
+{% endfigure %}
+{% figure caption:"VDP XTAL1" %}
+![TMS9929 XTAL1 (39)](assets/TI-resto/DS1Z_QuickPrint6-VDP-XTAL1.png)
+{% endfigure %}
+
+_No CPUCLK on pin 38 as this is an EU console with a VDP9929 VDP: pin 38 is the R-Y video component._
+
+GROMCLK taken on pin 37 the VDP loops OK:
+{% figure caption:"VDP GROMCLK output" %}
+![TMS9929 GROMCLK (37)](assets/TI-resto/DS1Z_QuickPrint7-VDP-GROMCLK.png)
+{% endfigure %}
+
+### CPU signals
+
+* :thumbsup: ~RESET~ seems to be high as expected
+* :thumbsdown: A0 and A1 appear to be rippling at odd voltage levels somewhere between logic 0 and 1
+{% figure caption:"TMS9900 address bus A0" %}
+![TMS9900 A0](assets/TI-resto/DS1Z_QuickPrint9-CPU-A0.png)
+{% endfigure %}
+{% figure caption:"TMS9900 address bus A1" %}
+![TMS9900 A1](assets/TI-resto/DS1Z_QuickPrint10-CPU-A1.png)
+{% endfigure %}
+
+* :thumbsdown: ~MEMEN~ seems to be stuck high, I'd expect it to go down regularly as memory cycles are executed
+{% figure caption:"TMS9900 ~MEMEN~" %}
+![TMS9900 MEMEN](assets/TI-resto/DS1Z_QuickPrint11-CPU-MEMEN.png)
+{% endfigure %}
+
+## Conclusion of first tests
+
+At this stage of investigation, it looks like the CPU is not working as expected.
+
+From there I see three possible next steps:
+* I'm wondering if the clock signals might be too much out of spec to allow correct operation (in which case
+  I'd need to first sort these out)
+* Could a faulty cap in the CPU's vicinity account for the symptom?
+  * I'm disinclined to do a full recap in the dark without a positive indication that that's the problem -- visually the caps look
+    all right, and those from the power supply side appear to be in a good enough state that all voltages look right
+* ~MEMEN~ stuck high and A0/A1 at weird level (or high-Z) make me suspect a nonfunctional TMS9900

_source/assets/main.scss

@@ -0,0 +1,14 @@
+---
+# Custom stylesheet
+---
+
+@import "minima";
+
+.overline {
+    text-decoration: overline;
+}
+
+figcaption {
+    font-style: italic;
+}
+