Dear Lazyweb, any idea why switching from a Pi 3b to a Pi 4b made my MAX7219 start behaving like this? If I switch back, it's <A HREF="https://www.jwz.org/blog/2021/08/more-payphone-shenanigans/">behaves properly</A>. Same CF card, so no software differences. <P><DIV STYLE="text-align: center; width: 100%; max-width: 500px; margin: 0 auto;"><DIV STYLE="display: inline-block; margin: 2px; width: 100%;" STYLE=" margin-bottom: 0.5em"><DIV STYLE="overflow: hidden; position: relative; padding-bottom: 56.25%; display: inline-block; width: 100%;" STYLE="padding-bottom: 56%"><VIDEO STYLE="position: absolute; top: 0; left: 0; border: 0; margin: 0; padding: 0; z-index: 1; width: 100%; height: 100%;" SRC="https://cdn.jwz.org/images/2025/img_4423.mp4" AUTOPLAY LOOP MUTED PLAYSINLINE CONTROLS ALLOW="autoplay; fullscreen" ALLOWFULLSCREEN POSTER="https://cdn.jwz.org/images/2025/img_4423.jpg"></VIDEO></DIV></DIV></DIV> <P><A HREF="https://www.jwz.org/blog/2025/10/tool/">Previously</A>, <A HREF="https://www.jwz.org/blog/2025/10/excluding-a-volume-from-overlayfs/">previously</A>, <A HREF="https://www.jwz.org/blog/2023/04/hard/">previously</A>, <A HREF="https://www.jwz.org/blog/2021/08/more-payphone-shenanigans/">previously</A>.

Dear Lazyweb, any idea why switching from a Pi 3b to a Pi 4b made my MAX7219 start behaving like this? If I switch back, it's behaves properly. Same CF card, so no software differences. Previously, previously, previously, previously.

Dear Lazyweb, any idea why switching from a Pi 3b to a Pi 4b made my MAX7219 start behaving like this? If I switch back, it's <a href="https://www.jwz.org/blog/2021/08/more-payphone-shenanigans/" rel="noopener noreferrer">behaves properly</a>. Same CF card, so no software differences. <p></p> <p><a href="https://www.jwz.org/blog/2025/10/tool/" rel="noopener noreferrer">Previously</a>, <a href="https://www.jwz.org/blog/2025/10/excluding-a-volume-from-overlayfs/" rel="noopener noreferrer">previously</a>, <a href="https://www.jwz.org/blog/2023/04/hard/" rel="noopener noreferrer">previously</a>, <a href="https://www.jwz.org/blog/2021/08/more-payphone-shenanigans/" rel="noopener noreferrer">previously</a>.</p>

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Pi 4 SPI lossage

Pi 4 SPI lossage